yes i am running the aem

 

You might want to check your coolant values than. AEM updated them for the s2000 AEM forums check on page 2

ps..but if both your fans are kicking on than the coolant values might not need to be updated

 

ok, thanks for the idea but yes both of the fans are coming on.

 

Also, make sure you bleed the coolant properly. S2000's are really sensitive wtih bleeding of the coolant.

Fill your radiator in the morning when its COLD, and don't put anything in the overflow. You want to leave it empty or on the LOW point. As you drive the radiator will fill the overflow and go back in as it builds pressure.

If you leave both full it could cause the problem you are having. Give me a call if you are still stuck on something.

 

ok, but what i don't understand is why the car would be fine for about 3000 miles and lots of running the car hard, and then after this particular session of spirited driving it would decide to do as it has.

 

I hate to be the bearer of bad news, but I had this same issue awhile back. Turned out to be a blown headgasket.

Leakdown test results?

 

I agree with bigpurp. I had this issue on my old turbo integra. It would be fine on the dyno but once i went for a long drive the coolant would overflow from the resevoir. Good luck!

 

after running the car hard that night i was driving normal for a few miles. then i coasted downhill at roughly 35 mph. that is when i noticed it overheating

 

my car is also doing the same things yours is... the coolant doesnt flow back from the overflow tank, and i need to prop the front of the car higher than the rest so the coolant can flow back into the engine... or i have to bleed the system like i was changing the coolant.... i did a pressure test and coolant system pressure test and the results were within 10% for all cylinders and the pressure test lost .5 of psi over 30 mins... i have not done a leak down test yet... but am almost completely sure i have a blown headgasket... and i am running FI as well... get it tested and see if you have any oil in the coolant... or coolant in the oil... for the former you see an oily residue at the top of the radiator, and creamy mayonaise in the oil for the latter...

If my compression test is within 10% for all numbers. 1 cylinder 198, 2# 195, 3# 185, #4 192 should i do a leak down test as well?

 

well, i installed the mugen thermostat and fan switch, samco hoses, and arc rad cap tonight and so far so good. i haven't gone into boost yet but the car is not overheating at all. tomorrow i am going to finish getting all the air out of the system and make a few hard runs and see how it goes.
also i am going to test my old rad cap at work tomorrow to see if it possibly had anything to do with the overheating. i have not done a leakdown test. what should the compression test numbers be at with a 3mm headgasket?
soulcoughing - are you running a stock headgasket?