Over heating under boost.

[Richard Clark]

Ok, so the Evo recently started over heating under boost, it will show that its over heating on the gauge, if i get out of boost within 10-20 seconds it will be back to normal.  If it starts to over heat and I slow down and stop, pop the hood I can touch everything and nothing feels normal and not overly hot.  I can actually feel the coolant in the res and its still cool.

So here is what I am thinking, When under boost the head is lifting and alowing exhaust to enter the cooling system and when this bit hits the coolant temp sensor the gauge sky rockets.  

I am not going through any coolant.  My turbo is burning oil but this shouldnt be contributing to this.  

Compression is 175 across.

Whats your take on this?

[Remi Raymond]

You could be pushing exhaust into your coolant without loosing compression maybe?

Get a proper coolant system test - the type that will test the coolant for chemicals from the exhaust.

[Jason Harwood]

Thermostat.

Coolant systems are closed. If the thermostat is not opening fully, it may cause part of the system to stay cold.

ALSO - The overflow is so rarely used, it probably didnt need to use it.
If you turn the heater on in the car and boost it, does it heat up?

Could be bad flow.

[Ryan Singh]

Mine's doing the exact same thing...my guess was thermostat too. Was gonna flush cooland and possibly replace thermo today.
The heater on high makes it normal tho.

[Kristopher]

Ensure you have no exhaust leaks around the turbo or downpipe. It's super common to see those leaks heat the sensors when under load if there's exhaust escaping behind your rad.

Not sure if this would be a definitive answer, but I'd be inclined to check the HG by popping the WG actuator off and climbing a hill. Without boost you shouldn't be lifting the head without noticing any other problems (oil/coolant). If you still get hot under that load and no exh leaks the thermostat is easy to change and probably the culprit.

[Ryan Singh]

Thanks Kris...sorry for thread jackin' Rich, but they're both similar issues so I figured why not. lol

So I replaced the thermostat and did the coolant, was fine for a while (30 min of driving) but now it's running hot again. Not under any load even, just sitting at a light it gets close to red.
Gonna replace the rad cap next...hopefully it's not the water pump dying.  

One thing I didn't do was disconnect the neg terminal before doing it. Would I really have to reset before doing it? You think if I reset, the issue will settle itself?
Because right now, it's running based on how the old thermostat was functioning...right? Or.....

[Richard Clark]

Thanks for the replies guys, it does have exhaust leaks, and I will be taking care of that, it is off the rd now so theres a shitload of work im going to be doing to it.

[Kristopher]

Singhman, make sure your rad fan is working. I have a feeling it's not coming on or the sensor controlling it is bunk.
to check it try your a/c

[Kimyee Lai]

If you are overheating under boost and from what you're describing, there's a potential your head's lifting, at least enough to allow exhaust gas into the coolant at a point where perhaps the headgasket is slightly compromised.  It will show up in your coolant though...I believe there's a test you can do to see if your coolant has been exposed to exhaust gas.

[Ryan Singh]

Thanks Kris, the fan is working though...thought of that but no good. The AC thing is weird tho...for the past few years, whenever I turn it on...the rpm's drop to like 200-300 to the point of stalling. 

Anyone know of the test Kimyee's talking about? I guess I could just google it...but that would be too easy!

[Paul Pigar]

Mine's doing the exact same thing...my guess was thermostat too. Was gonna flush cooland and possibly replace thermo today.
The heater on high makes it normal tho.

my 2g was overheating too so i replace the thermostat and still overheats and it turned out to be the cap....make sure u test your cap too if it holds pressure.

[Ryan Singh]

Yessir! Replacing it tonight...if Lordco's got one and is still open on the way home.

[Paul Pigar]

Yessir! Replacing it tonight...if Lordco's got one and is still open on the way home.

I got mine from metrotown lordco, they open till 9pm i think

[Kristopher]

Good catch, Paul. I completely forgot about that.

A trick some of us with tons o' boosts do is to use the 2g cap. If memory serves it's a higher pressure so lowers raises the boiling point.

[edit: lower chance of overheating]

[John Hartman]

higher pressures raise the boiling point  the point of pressurized cooling systems 

Kris, your take on no boost testing and chemical testing (others too) are great.  Its what I would do at work for a customers car.

if the fan(s) are coming on, the water is pressurizing and moving around properly(I suspect it may not be) I would look at a partially blocked rad.  If its cold in one area, that can do it.

But you need to know if the water pump is fully pumping as it can do what you are describing if its not moving the water away from the engine and into the rad fast enough.