Do a pressure test on the cooling system.. Also to check the thermostat feel the upper and lower hoses, they should be a similar temperature...

What kind of radiator are you running? Clogged radiator tubes could also do exactly what you're describing. You could also get a block tester, which sniffs for exhaust gas in the coolant.

 

interesting this only happened on my last lap? so is that an indication of anything? no overheating at any other time

 

stock cooling. car has 125k

 

block testing tonight!

 

OEM on my Evo 8 is a black wire. However, connected firewall to manifold as in picture.

 

maybe it just took the time it did to blow out the coolant to a point where it began to overheat.....

what were the outside air temps when you were running?

hopefully the t-stat decided not to open & caused your engine to get hot. swapping out a t-stat is easy to do, especially if you were going to the track again.

 

The full overflow after coming off of the track sounds like my cart when I had a barely-blown HG. Basically like Barney described earlier; the HG would only leak under boost, so doing compression tests etc returned totally normal results. When the head came off, my shop showed me the block and you could see what path the compression gases were able to take to get to the cooling system.

That said, easier and much cheaper to test a thermostat than to go straight to a HG swap. I would start with testing the thermostat.

 

it was like 85/86 degrees with like 20% humidity

 

block tested... the liquid stayed blue!

 

New Tstat coming next week. so i'll be testing it as soon as i get it & the gasket

 

If the problem persists and you are still on stock head bolts, I'm thinking you might try the one at a time ARP stud replacements. It might work and if it doesn't you still have the hardware for later.

 

Ok late to the party here but for others who might find this thread.


Not on an Evo but I had similar issues. Every 300 miles or so would loose enough water for heaters to blow cold. No signs of white smoke etc etc or water in oil.


What I done to prove was pressure test the coolant system by using a bike pump. Took the system to 1.3 bar and looked at pressure gauge on pump. First couple of times found minor leaks over an 8 hour period. When I finally was leak free, left for a week and pulled the plugs. Found about 5 drops of coolant on the top of one of the pistons. Now proceed to do the same test with valves closed on suspect cylinder. If no leak then you can go for exhaust closed/ inlet open to find where your crack is (either inlet or exhaust jacket). If it still appears with both valves closed then you have tracking from coolant jacket to combustion chamber.


For me I was lucky (hopefully) found two of the ARPs where not tightened to spec (standard spec) and the rest not to spec for MLS gasket. So far so good not had re-occurance. Hope this helps someone else. How did the OP get on what was the fix?

 

block tester didn't show my failed head gasket- the fluid also stayed blue. there were not gasses in the coolant present when I was testing it. otherwise, the symptoms were identical. it eventually go worse to where a very long drive on the freeway would pressurize the system and push coolant out of the overflow.

 

I tried sniff test as well, didnt show anything both chemical and via hydrocarbon sniffer used for emission testing. Water had to be going somewhere

 

I ended up taking it to a local evo shop. They did a cylinder leak down test, everything looked good according to them. The tech that did it said that my head studs were stretching. They were replaced with ARP head studs, haven't had issues since.