the car will over heat after it runs at idle for about 15 minutes, however, the aux.(electric) fan will NOT come on.

If I remove the bleed screw and let it idle again, as the temp goes above normal the aux fan WILL come on and cools things down and does not overheat, but air/steam does come out of the bleed screw hole.

I cannot find any water leaks anyway. It has a new OEM radiator and alum. thermostat housing/hoses.

Am I correct in thinking that somehow air is getting into the system which is causing the overheating? I am not seeing any milky substance in the dip stick or overflow tank that is normal for HG failures. I have bleed the system over and over again but still am getting air into the system.

HG failure??
:eyecrazy:help

If the failure is one that allows combustion gases into the cooling system, an easy check is this: Run the car up to temp. Shut it down. Several hours later (when the engine is cool), open the radiator cap. If there's still pressure in the system, then you've got a HG leak.

-tammer

hmm, tried that, did not really notice any pressure...

It is possible to have a blown head gasket with these engines that allows the coolant to escape via the exhaust system in the form of steam at such small amounts that it is virtually undetectable....without pressurizing the coolant system. I know, it happened to me at Second Creek O'fest race a few years back. No tell tale signs of any milkiness in the oil system and no pressurization of the coolant system...only the coolant level would decrease slightly during each run until the water pump would catch a small air bubble and cease pumping properly....causing the engine to overheat. Once I refilled and bled the system, all was well again for a short time until enough coolant had escaped (via super-heated [invisible] steam ) through the exhaust to repeat the cycle once again. If you are running big cams, sometimes all it takes is one time running just a bit hot to stretch those OEM head bolts just enough to allow the headgasket to blow. :(

Hope this helps. ;)

It is possible to have a blown head gasket with these engines that allows the coolant to escape via the exhaust system in the form of steam at such small amounts that it is virtually undetectable....without pressurizing the coolant system. I know, it happened to me at Second Creek O'fest race a few years back. No tell tale signs of any milkiness in the oil system and no pressurization of the coolant system...only the coolant level would decrease slightly during each run until the water pump would catch a small air bubble and cease pumping properly....causing the engine to overheat. Once I refilled and bled the system, all was well again for a short time until enough coolant had escaped (via super-heated [invisible] steam ) through the exhaust to repeat the cycle once again. If you are running big cams, sometimes all it takes is one time running just a bit hot to stretch those OEM head bolts just enough to allow the headgasket to blow. :(

Hope this helps. ;)

thanks.

Was the new radiator installed before it started overheating?

sorry to jump in, but.... I'm trying to figure out if my HG went too. Got milky dip stick and antifreeze was in the hoses going into the intake elbow... sup with that? Is this a sure sign of a blown head gasket? 95 e36 m3 3.0

Was the new radiator installed before it started overheating?

new radiator was installed over the winter and worked just fine for the first 25 minute session at VIR.

I blew mine at VIR last year. Passed every test. Did 6 E36 headgaskets last year, everyone of them passed every test. So small, but they were junk. And to the guy with anti freeze in the intake... Sure sounds like it and if that is true, should be an easy test.

Hey "philsans5"
test, what test? you went through 6ea? was that oem's? did you go to the metal ones?

No, 6 different cars. Leak down test, any mechanic should be capable.

new radiator was installed over the winter and worked just fine for the first 25 minute session at VIR.

Since many of the other possible solutions are pretty time consuming, I would recommend trying this first. Put the old radiator back in to see how the car runs. That's assuming it is still useable.

If I were in your situation, I would try to get the car back to the way it was before it started overheating. Maybe one of the new parts you installed is defective. :dunno

Oh, when the car overheated, did it get to the redzone or was it slowly rising past operating temp?

i think i can make a pretty good prediction... blown! was just wondering if it could be anything else... like cheaper!

I think what's happening here is that you do have a small head gasket leak that is pumping air into the cooling system. That would be consistent with the aux fan not engaging because the top of the radiator fills with air and/or the pump is stiing in an air bubble and can't circulate coolant. In either case the upper portion of the radiator, where the thermoswitch is) is cooler than it should be. Opening the bleed screw allows that air to vent, which floods the radiator with hot coolant.

A qualitative test is to properly bleed the system, drive the car until the temp starts to rise (but don't allow it to overheat), and then re-bleed. If a significant amount of air is released then or on subsequent bleeds, you have a head or head gasket problem. The definitive test is to pressurize each cylinder with 180psi for several minutes while monitoring cooling system pressure with a sensitive gauge. A rise in cooling system pressure indicates a leak. A negative result on a cold engine required the test to be repeated on a hot engine.

In my experience head gasket leaks cause overheating under load rather than while sitting at idle. I've had a few that were fine under normal street driving and ideling, but would sent the temp sky high on the second lap. After a cool down and burp would run fine on street and at idle. On track same thing would happen again.

What you describe with the the fan not comming on until you open the bleed screw makes it sound as though the coolant is not circulating properly as the fan temp sensor is in the radiator. Could be caused by a bubble in the system, but this should work its way out afetr repeated bleeding.

Let it idle until it's up to temp and then check the radiator hoses with your hands. If either is not hot, then it's not circulating properly. Might check that your thermostat was not installed backwards.

Most shops have a test kit that can check for by-products of combustion in your cooling system. This to me would be THE most definitive test.

Most shops have a test kit that can check for by-products of combustion in your cooling system. This to me would be THE most definitive test.

Yes it is. And those 6 cars passed that test too. Basically, pressure and heat of multiple laps will show it, NOTHING else did for us.

Yes it is. And those 6 cars passed that test too. Basically, pressure and heat of multiple laps will show it, NOTHING else did for us.

That's why it's nice to have the test kit at the track.

We had one and diagnosed a blown head gasket on a J-Stock E30 M3 at Laguna just last weekend, potentially saving a guy's S14.

thanks for the info guys. Everything I read points to HG failure.

so, while I am getting it fixed, what else should be done to a stock 3.0? I guess it is a good time for cams. What about new valve retainers? Anything else?

thanks,
matt

hey matt...
might want to consider complete head rebuild. mainly the keepers/retainers. pulled the #6 plug today and found out my issue is NOT a head gasket. looks like i dropped a valve. 95 3.0 s50!
know of any s52's for sale?