Over heating when the cap is on but not when off.

[Jorm]

Hi,

So took a trip with the KE35 SR (3K-D engine), then 5h into the drive it started to over heat. I filled water but then it overheat more or less after 1km. So checking for  gas coming but none, only see the water streaming so thermostat must be working, the car didn't overheat when the cap was off so I left it off and drove with no issues. Question is why this is happening ...

Jorm

[rebuilder86]

most people here in the philippines drive around with no cap and swear by it, but the system requires pressure to keep the boiling point up.

when u say it overheats, is that according to the gauge, or according to steam pouring out of the overflow??

if ur just saying its not overheating because theres no steam, thats because its just evaporating and not building pressure.

if its really behaving better in terms of heat transfer and litteraly keeping cooler with no pressure then thats just impossible and id say conditions changed between ur cap on and cap off scenarios.

Edited January 26, 2018 by rebuilder86

[Big G]

It sounds like the symptoms of a blown head gasket between exhaust and water. With the cap on the water circuit gets pressurised with the exhaust gas entering it the only way it can escape is by forcing the water out of the system through the overflow tank. With the cap off the gas is able to escape through the open radiator. I have had this happen on 3 different engines over the years.

[Banjo]

I totally agree with Big G. Take out all four spark plugs & compare colour, and you will probably find one is very clean & white. That will confirm, its time for the head to come off.   Cheers Banjo

[Jorm]

Y

5 hours ago, Banjo said:

I totally agree with Big G. Take out all four spark plugs & compare colour, and you will probably find one is very clean & white. That will confirm, its time for the head to come off.   Cheers Banjo

Yea that was my thought too gas escaping out when the cap is not on, but then on the other hand  don't see bubbles but will check spark plug tomorrow. When I mean not overheating I mean literally I can stick my finger in the radiator and yes warm but not overly hot so cooling system is obviously working and is cooling the coolant so to say. Gauge is not working at the moment got a new temp sensor I will mount tomorrow. 

Jorm

[rebuilder86]

mm mk. i recon the cooling system is performing just as well, but as there is no way for preasure to build up its escaping.

like i said, here, in gridlocked cities in the philippines, where all the public buses are just crawling through traffic, never going fast, they just don't run a thermostat or a radiator cap and it seems to go quite well for them. i don't understand it, but I'm sure theres a reason for it, beyond a radiator cap being unaffordable that is haha.

[altezzaclub]

The reason is....  its the Philipines!

The gas from a head gasket only pushes out water if the motor is cold and has a thermostat. That's because the gas can't get to the top of the rad through the t'stat and as the pressure builds it blows coolant out past the rad cap until the heat opens the t'stat. Then the gas goes up past the t'stat and out the rad cap.

So you only see water pissing out everywhere when it is cold and you have the rad filled to overflowing.

Once hot you struggle to see gas bubbles unless it is really full with coolant, they only need it 10mm low to escape unnoticed.

So running a leaky head gasket with a thermostat is not as good as a leaking gasket with no t'stat.   The other symptom is harder starting or three cyls for a moment in the morning from water going back into a cyl as it cools at night and making the plug wet. It usually clears after a few seconds and then its fine for the rest of the day.

A motor idling around town shouldn't get to 100deg, so it shouldn't need pressurising, same a cruising at 100kph. Lots of throttle at slow speed going up hills it what gives it a hard time, crawling around mountains in a jeep....

For fun, go watch youtube for day one of the Monte Carlo at night, the world's top drivers going 20kph..

 

and this one-     check out the red-hot discs. Some fronts only, some all 4, some none at all...

 

 

check out which cars have all 4 discs glowing red not, which have fronts only and which have none.

[rebuilder86]

So altezza, are u saying when cold, the gas flows in the "contra direction" so to speak, backwards through the system which pushes the coolant back and up the radiator and out the pressure relief valve, but once warmed up, the gas makes its way in the std forwards direction, with the flow of coolant to the rad cap and gets ejected as gas/steam.

am i hearing u right??

That makes sense, and i think i agree with that.

Id allways genetally thought head gasket issues and associated performance symptoms were worse once warmed up for a few reasons.

1. More heat means more pressure in cooling system so more water gets sucked into combustion chamber on intake stroke.

2. head pushes away from the block more when hot, and any inherrent warping is made worse when hot.

3. once hot, choke or ecu leans mixture out and and moisture has more of an effect on combustion (this could be completely wrong, but its just a theory of mine)

4. once hot, the extra pressures on top of std heat in the cooling system combine to form a seriously large pressure in the cooling system, (std heat expansion,  plus combustion gasses).

il never forget driving my shit ford econovan back from kalbarri to perth full of about 10 fully grown men, having overheating problems all the way there, lota of stops on the way back and then bang, off pops the lower hose in the middle of nowhere haha. stranded for the night.

[rebuilder86]

duplicate post, sorry.

Edited January 28, 2018 by rebuilder86

[altezzaclub]

Yep, the gas just pushes the water in front of it out of the way until it gets to the rad cap.  Like this-

The problem definately gets worse when hot, and one factor you didn't list was how much throttle is used. Giving it a good boot raises the chamber pressure a lot and as you say, the heat makes metal expand and gaskets leak more. Not having a  cap on tight means it won't over-pressurise the system and blow a hose.

[rebuilder86]

yeh i see.

i was just listing why i thought it is worse when hot and warmed up.

i always wonder how that seal up stuff, (little copper particles) manages to work so well, against that pressure coming from the combustion chamber. Ive used it in the past to get me by and it basically completely fixed my head issues haha. warped metal, no problem. fill cooling system with... METAL. just can't get my head around how it manages to fill those voids when the gases would be constantly trying to dislodge it back into the coolant.

saying that, the time it saved me, coolant wasnt really being ejected, it was being sucked in and burnt. 

thats a good topic for discussion, in another thread, how do some HG failures go one way and some the other way.