Viterbo

Lower Temperature Thermostat

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A long time ago I bought a 5K assembled head that had some work done to it and was ready to be installed (face machined, all cleaned, etc). It had a brand new thermostat installed also so I just dropped it in.

First time the engine ran the temperature went past the usual maximum point before cooling (signal of thermostat opening). Took the thermostat out and found it was an 88ºC one while I've been running an 82ºC one.

Later someone told me he found a 70 something degree one but wasn't able to provide me a part number.

 

Today I've done a bit of research. Started with my 88ºC part number (Gates TH14088G1) and was able to find several vehicles where it fits (Ford, MG, lots of Toyotas, etc). When I looked for the Daihatsu Charade G100 GTi there was a 78ºC thermostat (Gates TH29478G1) on the list along with the Gates 88ºC one.

But there's a small problem, the sizes are very different and that's where I need your opinion:

 

Gates TH14088G1

thumb.jpg.beb9319a954d07926ecad4158fb812cb.jpg

 

Gates TH29478G1

5a806b08a4958_thumb(1).jpg.a54b17ef1a6e57a489c04eab3ee5dc24.jpg

 

 

Both of them fit the Daihatsu, so is it safe to say they'll fit our Ks?

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What are you trying to achieve?

What's wrong with the thermostat that was designed for your  engine. 

 

 

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I just need it to open a bit sooner. When punishing the engine the temp goes a bit hotter than normal operation and I want to keep it safe.

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That's not how a thermostat works. The thermostat aims to regulate the temperature of the cooling system to the temperature stamped on it. 

First step is to put your thermostat in a pot of boiling water to prove it works. You should see it open relatively quickly once you dump it in the water. 

If you are having overheating issues when "pushing the engine" its not the thermostat. 

If the thermostat is working as it should it will be fully open when you are overheating. and if you are overheating with a working thermostat then your options for overheating are clogged radiator, dodgy water pump or head gasket. 

Removing or modifying a thermostat is not the solution to overheating problems. 

 

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That's exactly what I need, regulate the temperature of the cooling system to a colder temperature. I will run a very modified 5K with a Nissan Primera radiator but need to control the temps to a step colder just to keep it safe. I'm not running into any issues, I just want a lower temp thermostat to play safe. Factory thermostats weren't designed to modified engines pushed way harder than the vehicles were created for. If I noticed a difference from a 88ºC one to a 82ºC, that 78ºC might be exactly what I look for.

I just need to know if it fits, considering what I exposed on the 1st post.

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I don't you're getting Dave's point.

Factory thermostats were designed to run within the optimal temperature range of the engine. If you want to 'push' said engine past what you deem normal operation and create more heat, this isn't a problem for the thermostat, it's a problem for the radiator.

Think about in terms of a thermostat is a heat pump. You want your room at a comfortable 20°. What's going to get there quicker more effectively? The heat pump in the big lounge room or the one in the closet!?

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I get what you're trying to say, and believe me I'm always thankful to anyone who takes some of their time to explain me something.

Let's imagine I live in the hottest place on earth, I don't have any radiator selling point in a range of thousands of kms, but I have access to that specific 78°C thermostat. Will it fit?

Hahaha it's really just a yes or no topic 

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Yes it might fit.

But if the radiator isn't up to the task all that is going to happen is the thermostat will fully open a little earlier and still overheat.

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When it comes to sizing, what is also important, which i only discovered recently, is that the little foot that protrudes out of the thermostat also needs to be the same diameter as oem and it needs to protrude the same distance in order to block off the passage way behind the thermostat. your drawings above don't have these dimensions. 

You know engines run more efficiently the hotter they are?

 

 

 

 

 

Edited by ke70dave

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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)

DSC00459small.thumb.jpg.8fd16743ef2368b180b09db1b779b74b.jpg

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.

5a811105338c5_DaihatsuApplause.JPG.f9c68aa833a55528f2f3a7295b92736b.JPG

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

 

 

 

 

 

Edited by Banjo
  • Upvote 1

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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.

image.png.3500d78b7c6ec2397c14c514cf746de7.png

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  

Edited by Banjo

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This is kinda opposite of what you experience banjo. Your coolant temp graph showed it took quite a while for yours to get up to these temps, so why is Viterbos getting up there so quickly, before the thermostat can react.
Viterbo, id go a new 82 degree one and possible get a high flow one. high flow is probably more what your after. 
Tridon sell them.
TT2040-180 - THERMOSTAT (HIGH FLOW)
They flow more at all oopening ranges, meaninging the change in cooling effect is faster, but also allows the engine to cool better if the thermostat is maxed out, while still providing enough restriction to prevent air cavitation at the water pump.

What your were probably told about was the 71 degree one from here...
http://toyheadauto.com/PerformancePages/4K_AND_5K_High_Performance_Engine_Parts.html#4K_Heavy_Duty_Water_Pump_

$63

Which is actually this.
https://www.rhdjapan.com/kameari-low-temperature-thermostat-carina-celica-starlet-sprinter-corolla.html
$91

I have ordered one of these for my jeepey but damn its expensive haha. I&#39;m doing it not becuase of an overheating issue, but because I&#39;m tryign to run my engine cooler as its going to be slightly turbod. If i was worried it was going to get hotter than the thermostat could handle, I would have jsut gone and got the tridon high flow one from supershit.
 

Edited by rebuilder86

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There we go Viterbo !  Now we know what it is all about.

From the ToyHead website Jeremy has linked above.

Quote

Born from racing technology!
71 Degrees Celsius Low Temp Stainless Thermostat

What is the optimum temperature to get the most power from the engine? 

Different parts of the engine are at various coolant temperatures. For example, the temp gauge is reading at 80 degrees Celsius but at the back of the motor, it is between 85 and 90 degrees Celsius, which means it is detonating.  The perfect temperature for optimum performance is the temperature right before detonation, measured at the cylinder.  However, in order to achieve this temperature, it is absolutely necessary to have good cooling efficiency and a low temperature thermostat. The thermostat opens the valve at 71 degrees Celsius and allows the coolant to flow earlier to prevent overheating and bring out the maximum performance from the motor.

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

Edited by Banjo

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I already knew about that ToyheadAuto thermostat but was looking for a cheap option as I was told there was a Hilux or Dyna or something that had a lower temp one that fit K engines.

I've been running a Payen paper headgasket on my 5K with above 12bar of compression pressure in each cylinder for almost 2 years with lots of punishment and still goes great! 

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On 2/12/2018 at 2:51 PM, Banjo said:

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. 

FWD A-series engines (4AGE, 4AFE, 7AFE etc) have the thermostat on the bottom radiator hose to control the reentry of coolant from the radiator back in to the engine.

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