Banjo

Hi Keith, I tend to agree with you about the need for a cowling. I did a bit of research, & basically the cowling has two functions. 1. To direct air flow 2. To prevent cavitating & looping of the air at the tips of the blades. " The most efficient movement of air occurs when a fan has a cowling. A cowling prevents the looping and forces the air forward, moving much more air for the same power." However, although some could argue that with an enclosed space under the bonnet, all air will pass over the engine, & through the engine bay & exit down under the rear of the car, whilst ever it is moving forward, when the car is stationary at lights, in traffic, there is no forward movement, so maybe the air needs direction more onto the engine itself. Debatable ? The argument against a cowling, is as you say . 90% of the time the fan is not required at all. The best way to decide this is for me to try it out, once I have fitted the thermo electic fan & radiator. I can then take measurements & see what effect removing the cowling has. I will definitely make the weigh & volume checks you suggested when swapping over the radiators. Cheers Banjo

Why would you want an oil filter with anti siphoning valve, when your 4K filter is installed vertically. Siphoning valves are only required when oil in the filter can run out, because the filter is installed either horizontally, or inverted. Cheers Banjo

Interesting thoughts Jeremy. It occurred to me that the real issue is that the cooled coolant from the lower radiator hose enters the water pump, & therefore the block, at the front of the engine. The heated coolant, exits the top of the head at the front of the engine. Best results must be when the coolant enters the engine at one end, & exits at the other. That way you get consistent & uniform flow through the whole engine, however, it does create a temperature gradient along the length of the head, with the rear still being hotter than the front. This assumes that all the water jacket holes in the head gasket between block & head are opened. An even better way, would for coolant to enter the block at the centre of the engine, & exit from both ends of the head. Bit impractical in our case. However, the first scenario, is possible. Leave the water pump where it is, but remove the thermostat enclosure from the front of the head, & replace with a blanking piece. Weld a larger spout to the plate on the back of the head, & direct coolant back to the top of the radiator, via a thermostat. Only trouble is there is not a lot of room between the back of the head & the fire wall. There are some car engines that are designed that way. Anyway, to things current. I've been driving around today, without a fan at all, & with no fan cowling. The results are quite different, & I did get the coolant temperature up over the 90 deg C mark. The average ambient temperature was around 26 deg C. I left home at 10:20am, from a cold engine start, and you can see it took about 10 minutes for coolant to reach 70-80 deg C. The next 10 minutes to 10:40am, was on open road @ 80 klm/hr without traffic, & you can see how stable the temps were. From thereon in, you can count every set of traffic lights I stopped at, once I hit town, with no fan to draw air through the radiator to cool it. Just before 11:10am, I stopped at the P.O. for 4-5 mins, and you can see head coolants, front & rear rise sharply, with the heat sink effect, but the lower hose coolant temperature actually dropping. The interesting part is that it there is only about 1.3 deg C, between coolant temperature entering the engine, & the coolant exiting the rear of the head. In fact, just looking at the graph, in places it looks like they are on top of each other. This is a bit of a puzzle. The other one, is why does the temperature at the bottom of the radiator drop so suddenly, as soon as the engine stops. Hot water rising ?? You can really see why you need a thermo electric fan in city stop start driving, only switched on, when needed. The sensors used under the thermostat & in the lower radiator hose are identical, and were calibrated together, in the same data logger, in boiling water. Graphs of the temperatures of both probes, when the car has been stationary over night, where engine & coolant are the same as ambient temperature, also show both temp sensors reading exactly the same. I might see if I can't "replumb" the return coolant line to the underside of the thermostat, rather than back to the inlet of the water pump, which is where it currently is. That may display a different coolant operating characteristic. Might pop the radiator out at the weekend, & see how easy or difficult, it is going to be to fit the Echo radiator with integral thermo electric fan. Cheers Banjo

No ! No ! No ! I've been trying to "wean" myself of that stuff for years, & it's got me no where. Does it make a good coolant ? ha ha ! Cheers Banjo

Hi Keith, Just about to pull the fan & radiator cowling off, & take a run into town in about 90 mins. & see what changes that makes. Another cool day today, which is pretty unusual for SE Queensland, at this time of the year. I love data logging, as it shows you dynamically what is happening, especially when you measure & record several variables at once, that each have an effect on each other. Sometimes it throws up things, which are quite the reverse to what you imagine is going on. It's always eye opening. They say, "What Gets Measured, gets Managed", & there's another one that says "Without Data, it is Just a Matter of Opinion". It's a great way of quickly solving issues, instead of the "trial & error" method. I'll throw up the graph without the fan, & cowling, when I get back. We will get this issue sorted, I'm sure, but my idea is to change one thing at a time, so you can quantify the results. Cheers Banjo

I had a bit of trouble doing this rear head coolant temperature measurement. I was hoping to insert a temperature sensor in the water jacket itself, in the rear of the head, so that the sensor was screwed into the head itself, just like the one fitted below the thermostat. There are no screw plugs at the rear on my 4K-U head, but it does have the small plate on the rear of the head, for the heater inlet connection, into which I could have fitted a ferrule, & screwed the sensor into it. I was reluctant to remove this plate, as the threads in the head are not blind, & the bolts become rusted, & invariable snap off, trying to undo them; especially the lower RHS one. There is also only a couple of inches to work between the head & firewall, so any issue, would have resulted in the head coming off, which I wanted to avoid. I decided to buy an inline hose adaptor to take the sensor (gold bit). I found a suitable bit of hose, with two appropriate bends in it, at SCA, which was designed for a VR Commodore 3.8L V6 Water Valve to Heater Inlet (P/N CH1779). The pictures below, indicate how I mounted it all, with the sensor as close as possible to the point where the coolant exited the rear of the head, on it’s way back to the water pump inlet, as it’s a heater return line. Got any air out of the system, by running it for 10 minutes, with the radiator cap off, & it was ready to go. A week ago here in outer SW Brisbane, it was in the high 30s, but last night, couldn’t have been more different, with air temperature in the low 20s, probably 15 deg C, below what it had been 7 days previously. So my daughter needs picking up at the bus stop about 15 minutes drive away. I drive to the bus stop, wait less than 10 minutes for her to arrive, & straight back home again. The coolant temperature measurements are shown on the graph below. Unfortunately, the night was so cool, the ram effect of the ambient air, wouldn’t allow the thermostat to open. From previous tests, I’ve done, I know this thermostat opens at approximately 88 deg C, as it should. In this case, the temperature never reached that temperature. However, the rear head coolant temperature, was actually cooler than the coolant just under the thermostat, at the front of the engine, by just a few degrees, which is a great result, as I know previously, I had measured head surface temps up to 10 deg C greater at the rear. Some of this could be because the sensor was not in the head proper, & quite likely, the fact the water was moving over the rear sensor, as it doesn’t return to the top of the radiator, on the inlet side of the thermostat. So a few more tests are required. Firstly, I’ll take the plastic fan off, and run without it. If that does not help increase the coolant temperature, then maybe a piece of cardboard over the front of the radiator, will assist. I may also plumb the heater return line into a spare stop plug in the thermostat housing, just below the thermostat, so coolant exiting the head from both ends, goes to the same point. Not all Rollas have the plate on the back of the head with the heater inlet port. If you have a 3K big port head, you are out of luck, & it may take a bit of machining to remove the “bung” & make a suitable plate. If you have the plate without the heater connection, it does provide a situation, where you could fit an outlet facing to the dizzy side of the engine. If you have ever had that plate off, at the back of the head, you can see why this overheating problem occurs so easily, with low flows. The passages in the water jacket are quite small, & with low flow & “gunk” buildup, it’s easy to see that you could have a head with minimal flow at the rear. If this mod works as well, as it appears it will, it might also be a good idea, to either buy a head gasket with no water jacket feeders between block & head "blocked off". Alternatively, as most head gaskets now block the front feeder holes off, to direct all coolant to the rear of the head, maybe these could be drilled out, in the head gasket. So I’ll do some more tests, & see whether I can’t generate some more heat into this coolant, & see what transpires. Cheers Banjo

Please post some pictures of the actual damaged area, & I'm sure there are those experienced on this forum, which will offer their thoughts. Cheers Banjo

It appears there were quite a few different types of dizzy for the 3Y, with both points & electronic. http://brianlawson59.blogspot.com.au/2012/03/distributors.html The ones for South Africa, were apparently different, & that is where Sipho is located. As Sipho has replaced the condensor, we have to assume it is a points type, which were fitted mainly to the 3Y engines, according to this blog at the above link. Maybe Sipho, your issue is with the rotor or the spring & carbon rubbing point in the top of the dizzy cap. Would need a bit more info, to solve this one. At least if it is points, it is the cheapest & easiest to fix. Cheers Banjo

There we go Viterbo ! Now we know what it is all about. From the ToyHead website Jeremy has linked above. They are saying, what we all know, that the back of the head coolant temperature can be up to +10 deg C above coolant at the front of the head. Therefore, cylinder no: 4 detonates because of the higher temperature, so they use the low temperature thermostat, to lower the overall coolant temperature so no: 4 cylinder doesn't detonate. That's why valves, head gaskets & rings & pistons fail on no: 4 cylinder. The constant detonation, from the excessive temperature. However, whilst cylinder no: 4 may not now be detonating, with the low temp thermostat, the other front 3 cylinders are lower than what they should be, for best combustion & best efficiency. The better way to solve the problem is to increase the flow through the back of the head, so that the temperatures of coolant around all four combustion chamber is with 1-2 deg of each other. The experiment I am currently implementing, should prove that theory, by exiting coolant out the back of the head to the radiator or water pump, external to the engine's coolant galleries. Then you can run a standard 82 or 88 deg C thermostat. I should have the experiment finished, with graphs, in the next few days. Cheers Banjo

I had a think last night, about what Viterbo is requesting. One of the problems with thermostats is that the solid wax has to be heated, by conduction through the metal structure, before it turns into a liquid & then expands, forcing the valve to open. This does not happen instantly, as anyone who has put a thermostat in a pot of cold water, heated it up on the stove & watched the opening, will know. It is relatively slow. This has a dampening effect, which is good, once the valve is opened. If the valve was very fast in its reaction time, whilst regulating the temperature, then the thermostat valve would be in a constant state of motion, & wear out quickly. What I think Viterbo is wanting, is a quicker opening initially, so there is no lag in opening, & therefore overshoot of coolant operating temperature. He believes that using a thermostat with a lower temperature opening characteristic, will be like a early warning, anticipation system. This is probably the case, but the result is that the operating temperature of the coolant must then be somewhere below that crack opening temperature, which puts it down in the mid 70s deg C mark. Appears some thermostat manufacturers, including Gates, have addressed this need. So specific engine conditions which will create extra heat load on the coolant system, are anticipated, & the heating of the wax in the expansion chamber is accelerated with a inbuilt heating element. Once that high loading condition disappears, the wax goes back providing the "damped" response to controlling coolant temperature. Interesting ! Cheers Banjo

Can I wade in on this one ? The thermostats for the K series engines are all 52mm diameter, across the top, where they fit into the "thermostat housing/water outlet". However, there are several different lengths, or depth, dependent on manufacture. I have one on the desk here, exactly the same as your first pic, with 25mm, below the "mounting" point. I have another that is only 20mm in this dimension. When the thermostat is mounted, there is heaps of room below the thermostat. (see pic below with 25mm thermostat inserted) This allows approx 18mm for the back of the thermostat to move down, when fully opened. That is more than enough, as the thermostat valve movement from fully closed, to fully opened is about 10-12mm at most. Your second pic of the Gates thermostat with the 35mm dimension, had me puzzled. Why would they design a thermostat with a temperature below 80 deg. In this case 78 deg C. The answer was fascinating. I discovered that that thermostat was used on early 90s Daihatsu Applause 1600cc engines. When I Googled Daihatsu thermostats, the often question was, I can't find my thermostat. It appears it is at the back of the engine, not the front, up high, & controls the cooled coolant, rather than hot water to the top of the radiator, as in the K series. "On the Daihatsu Applause 16 valve engine the thermostat is NOT located under the alloy housing that attaches the top radiator hose to the head. It is located at the back of the engine block, at the opposite end of the engine, just above where the alternator is situated. Three 10mm bolts hold the thermostat housing to the block. The bottom radiator hose is attached to the housing. All you need to do is disconnect the water temp sensor wire, undo the three bolts & push it toward the alternator. Remove the thermostat from the block replacing it with a new one. A rubber gasket fits around the outside of the thermostat & I used a little silicone on the gasket to hold the thermostat while you re-install the housing. Don't forget to reconnect the temp sender wire & fill with coolant." Obviously cooled coolant after it passes out of the radiator could well be 10 deg C lower than operating temperature. So if the 35mm thermostat is 10mm longer/deeper, than the 25mm one, then it protrudes further down into the chamber below the thermostat. So instead of 18mm of travel, that only leaves 8mm, with this thermostat. It might be borderline, as I don't know what the travel is the Daihatsu thermostat. Apparently, this is where it is fitted< & you can see the special housing is quite deep. But like Dave & Si, I see little need for lowering the thermostat opening temperature. Engines, are designed to operate generally at temperatures between 80 - 95 deg C. The thermostat is designed to do two things. 1. Get the coolant temperature up to operating temperature, just as quickly as possible, from a cold start, as this is the period where most wear occurs in an engine. 2. To control the coolant temperature in a band of say 4-5 deg C. So a 82 deg C stat, might open @ 82, & close @ 78 deg C. Even if you are in the desert, where the ambient & coolant temperature are 40 deg C, at a cold start, that is only half the temperature that the engine needs to be at. In outback Australia, where it is very hot, I know there are lots of people who remove the thermostat all together. There is no evidence, to my knowledge, that removing the thermostat, will increase coolant flow. The reason they remove them, is purely that water supplies are poor, and thermostats reliability is poor, & they don't want a siezed motor. Many motoring organisations, years ago, recommended replacing your thermostat yearly. However, in these days of modern high tech coolants, & more reliable themostats, there is no need for that. I don't think you are providing additional safety, by lowering the coolant temperature. If you are going to generate more heat, as a result of modified or operating conditions, of the engine, and it overheats, then you simply need a larger or more efficient radiator. The usual first step is to go from a 2 core to 3 core, as that requires no "bigger" radiator mods. Cheers Banjo

That is incredible Jeremy ! I figure that guy is standing at the door looking in, because he can't get any further into the building. The sign next to him says NO PARKING, I believe; so I guess, that if you park too long outside, they just dissemble your car, or truck, & take the bits inside. So what happens, if you say you want that gearbox I've arrowed ? I suppose we'll never know, as it is a little bit big & "heavy duty" for a Rolla conversion. (come back in a month ?) Amazing ! I guess you are asking how much extra HP you are going to achieve, with the increased CR, by fitting the correct head. You will have to measure & calculate cylinder & head combustion areas accurately, before & after, to work that out. I think its a case of suck it & see, but it will be an improvement over the very low CR you currently have. Enjoy your trip back to Perth ! Have you got a "shopping list" of things you need to take back ? P.S. For heavens sake, do not cut & weld push rods ! A recipe for a disasaster. Cheers Banjo

Hi Bill, Good one ! Doesn't hurt to have a new water pump. The seals go dry, if the engine not been used for years, & could leak like a sieve, once you fill her up at the end, which would be a bit disheartening. Plenty of alternator brackets hanging around here, so no issue, if you need one of those, shipped with the pulley. There is another bracket on the opposite side of the motor, for the A/C compressor, if fitted. Trouble is, very few Rollas here in Aussie, were fitted with A/C, so they are very hard to find & get hold off. Cheers Banjo

Hi Michael, Welcome aboad ! Most KE3X grills will fit on a KE5X models. The only one you may have a slight modification to do, is if the KE5X you are fitting the kE3X grill to, previous had square headlights. However, my belief is that the extra brackets etc. for the grill with square headlights, can easily be removed, & the gear & mounting points for round head lights were retained. The harder conversion is the other way around, fitting square head lights & associated grill to a kE30, which, to my knowledge, were never offered with square headlights option. I did this conversion a few years ago, & it was possible, by "finicky" ! Cheers Banjo

Wow, that's a bummer ! Did you rebuild the 4K yourself, or did someone do it for you ? What was involved in the rebuild ? Was it bored or honed ? Was there new pistons or rings ? New big end and/or main bearings ? Crankshaft reground ? New crankshaft oils seals back &/or front ? Was the head rebuilt also ? Was the camshaft, & camshaft sprocket removed ? If you tell us what was done to it, it will narrow down where the issue may lie. With all four (4) spark plugs out, with the dizzy out, with the fan belt off, gearbox in neutral, the engine should spin freely on the starter motor, or be relatively easy to turn over using a socket & ratchet on the crankshaft pulley retaining nut. If it won't turn, easily, then don't try to force it, as you run the risk of damaging something. Strange. Normally an engine assembler spins the crankshaft by hand, then adds pistons & conrods, one at a time, spinning it at each addition. Finally camshaft & sprocket & chain. when they are happy, everything is free to spin, then, & only then, does the sump get replaced & sealed. Any chance of you recording the attempt to turn it over, with audio,so we can hear the clunk ? Cheers Banjo

Hi Jeremy, Yes, it is cable operated, but is just a 2 port valve (ON/OFF). However, it is not on the engine side of the firewall. It's under the dashboard, close to the heater coil. You could just keep the old one open permanently, & add this suggested one, in the engine bay. Below are pics of the heater coolant return path to the inlet side of the water pump. Cheers Banjo

Here is another possible "simple to implement" option, to get more coolant flow through the back of the head's water jacket. https://www.ebay.co.uk/itm/16mm-5-8-Heater-Control-Valve-Pull-to-Bypass-Kit-Car-Classic-Car-Taxi-TX2-/192279138616 It would involve simply replacing the existing mechanical heater water ON/OFF valve, with just two (2) ports, to a four (4) port heater FULL bypass valve. When the heater is "ON", the hot coolant would pass through the heater as normal. When the heater is "OFF", the hot coolant would bypass the cabin heater, & return to the inlet side of the water pump, via the existing return coolant line. Consequently, coolant would flow out the back of the head, at all times the engine was running, whether the heater was ON or OFF. The only issue with our Rollas, is that the area where the existing "ON/OFF" valve is located, is a bit tight, so the new 4 port valve may have to be located adjacent somewhere close, & a few 16mm I.D. hose connections made. The area between the back of the head & the firewall, is also tight, but at least, there is only one hose connection there. Here is a cheaper plastic one, that is cable operated & comes in two (2) models. 25-1018 Pull to Open, & 25-1019 Pull to Close. They work like this . . . Only trouble is I have been unable to find a local source here in Australia or S.E. Asia on-line. From what I can see, they are only available on line in the UK & USA. Give us a yell, if you know where I can source one locally. P.S. In researching this, I found out why they are so available in the northern "colder" hemisphere. Apparently, in many older European cars, the coolant flows through the cabin heater coil all the time. The heat is controlled not by regulating the water flow at all, but by the air flap, in the heater box. When the heater box air flap sponge rubber seals deteriorate, hot air leaks into the cabin, when the flap is closed, & in July (their only warm month) it gets too hot inside the car, so these valves have become popular as a mod on older cars, to stop the water flow altogether, when heating is not required. Modern European cars apparently, sometimes have the heater on constantly, & it is turned off, when the A/C unit is switched on. A bit different to our conditions, here in Australia. Cheers Banjo

Love it ! So this little air bubble bleeder valve has to be pointing high, (as you would expect), therefore is should never be described as a "Jiggalo".

In my research on things coolant, in K series engines, I've always presumed all K series engines had coolant bypass circuits, from the base of the thermostat housing to the 16mm spout on the inlet of the water pump. The Toyota Yellow Bible depicts it that way. All the 3K & 4K after market, replacement water pumps on the net, are depicted with a 16mm spout off the water pump inlet, to connect a bypass coolant circuit to. However, around my garage, are a few old genuine Toyota K series water pumps, that have no 16mm spout off the water pump inlet, so I can only presume that maybe some early 3K engines in KE10 & KE15 models, didn't have a coolant bypass circuit. Has anyone got an original Rolla, without a bypass circuit ? I even have a new aftermarket K series water pump, that has the 16mm spout on the water pump inlet, but is blanked off inside. Presumably, this is so it can be used in either application. If you need it for a bypass application, you just drill out the blank aluminium casting. Cheers Banjo

Well, sometimes you can be lucky ! I picked up an Echo radiator & fan complete, this afternoon, here in Brisbane, which I found on Gumtree. The older retired mechanic, had had it in his garage wrapped up for 10 years. Came off an Echo, written off, which he bought for other bits, he needed to repair another Echo. The Echo it came off, had 18K+ klms on it. It's like new. Bargain $ 35.00 ! As you can see, there is not much between them, size wise. The Echo one looks a bit bigger, but some of that illusion, is a piece of plastic on the RHS (looking from the front) that can be cut off. Inlets are on the same side at the top, but outlets on opposite sides, at the bottom. Outlets & are a fraction smaller in dia. (28mm vs 30mm) I'll see how easy it is to attach the fan assembly to the KE radiator, but really, it might be just as easy, to swap the whole radiator & fan complete. What do you think. Probably easier to make a decision, once I remove the KE radiator out, & see how it all fits. Cheers Banjo

Here is the thermostat housing I had all the time, that is perfect for this experiment. That hole there is blanked off, & unused. It is quite large, & it should be easy to drill & file out the back of the hole & break into the thermostat area. there is plenty of "meat" around the hole, to thread it to any size hose fitting I choose. Alternatively, if I want to, or need to run the coolant return line on the opposite side of the engine, then there is a large spout already to be used, but this is designed for the radiator bypass, so I'll probably retain that function. There are two (2) temp sensor points on the thermostat housing, & if I use a cover spout with the threaded hole in the top, I get another measuring point, effectively at the top of the radiator. Happy days ! Cheers Banjo

Hi Bill, Managed to get hold of this elusive pulley late yesterday, but it was too dark to take some pics last night, when I got home. Here are a few shots of the pulley, some along side the standard, & most common conical one, here in Australia. Picture no: 4 clearly shows they are both have the same O.D. Picture no: 3 shows how this pulley is "shallower" than the standard conical one, by about 8mm. The remaining pics show that the centre mounting/alignment hole is much bigger, than our standard 16mm one, but at 32mm, is greater than the 24mm on the mounting boss you have there on your 4K engine. The four (4) off 6mm bolt holes, are spaced 40mm apart, unlike the conical one, where they are only 31mm apart. The pressed on mounting boss on your water pump, is different, in that it has a shoulder on it, to centre the pulley, where the standard conical one, just uses the 16mm dia. water pump shaft. The boss is just pressed on, so I guess it wouldn't be too hard to align the centre of the belt groove, with the crankshaft & alternator pulleys, if needed, by repositioning it, as your shaft appears to have plenty of length. So I'm not sure whether you can use either of the pulleys I have here. Maybe, you can just buy another new aftermarket 4K water pump, on line, as they don't seem to be too expensive, & see what size mounting boss it comes with. Let me know, if I can assist any further. Cheers Banjo

Hi Jeremy, The top piece with the hose outlet spout is the thermostat cover to me. The thermostat sits entirely down inside the lower section, so that to me, that is the thermostat housing, because it houses the thermostat. The first picture is not back to front. It's a guy here in Australia, with a 4K in a KE25, who fitted a Nissan SR20 aluminium radiator, which has it's inlet & outlet spouts reversed to the standard 4K radiator arrangement, so required the top spout to be reversed. You can look at his build here, on Performance Forums. http://www.performanceforums.com/forums/showthread.php?67299806-KE25-corolla-without-powers Cheers Banjo

And to think this thread started out about "Oil Pump Failures". Here are a couple of close up pics I found on the net. There are quite a few different arrangements of the thermostat housing on K series engines fitted to various Corollas, Starlets, Hi Ace Vans etc. However, I think I have found a perfect one, right under my nose, fitted to a 5K engine I have on a test bed, out in the yard. I'll take some pics, (when it stops raining) and post here, & see what you think. P.S. I like that 3rd pic one, with the two large access points on the RHS of the housing. Anyone got one of those ? Cheers Banjo

Been thinking about this overnight, & have another thought. The heater coolant return line, is connected to the input side of the water pump, which is feeding "cooled" coolant from the radiator. It struck me then, that the heater return coolant, never passes through the radiator. It bypasses it completely, except for when it gets mixed inside the engine. This makes perfect sense, when you think about it. Remember the heater coolant, only flows when you have the heater on. You only have the heater on, because it is cold inside & outside the vehicle. If it is cold outside, then this is not a situation, where your coolant will ever get excessively hot. The cabin air passing through the heater box coil, is also extracting heat from the engine coolant. Certainly this is not a time you would want, or need, to cool the coolant any more, by passing the heater return coolant, through the radiator, & cooling it even more. In cold weather, the issue is to keep the engine coolant temperature up to the idea engine operating temperature. That's why trucks put covers over their radiators, in deep winter regions. So, when the heater is "Off", & we take hot coolant out of the back of the head, we certainly do not want to return it to the water pump inlet, & bypass the radiator altogether. So basically, I would leave the heater coolant circuit completely alone. At the point where the coolant comes out of the back of the head, I would put a "T" joint, before the heater coolant tap, & feed this coolant through another tap, and then return the coolant to a point directly under the thermostat, so that this returned water, would always pass through the radiator. The two water valves on the back of the head, would never be opened together. When one is "A" is open, "B" is closed. When "B" is open, "A" is closed. This would hopefully, achieve the result we want, without too much complication. Maybe the mechanical valves could be "tethered"" together, so they worked in tandem, but opposed. Alternatively, an electric valve/s, but they are expensive. Have a think through this logic, & see if you can find any holes in it. Like a said, the proof is in the pudding. So I need to find a thermostat housing, which has a spare space, or hole where we can attach the return coolant hose-line from the back of the head. There are a number of different thermostat housings on K series motors. I know I've got a few in the shed, & I'll try & round them up tonight. If anyone could post some pics of any thermostat housings you have, that would be great, & we'll find one that suits this purpose best. Cheers Banjo