Aidoneus

My 1991 383 stroker with ATI procharger running 8 lbs of boost keeps blowing coolant out the thermostat housing under heavy load. First noticed it on a dynopull, going over 4K under load made coolant shoot out the thermostat housing. In normal driving, even over long distances, everything stays dry, same thing if you just rev it in neutral.

Replaced the gasket today, careful to scrape off all the old gasket material and adhesive and cleaned up with solvent - went out for a drive, came back, still got coolant spraying around in the same vicinity it was before. I'm assuming it's still coming out of the thermostat housing since it's wet in the same areas it was wet before, but I can't be 100% certain this time since I didn't have the advantage of seeing it on the dyno. In normal driving, even over long distances everything stays dry, it's only when I'm really getting on it. Any ideas?

JBB

Could slow the pump down with different pulleys if you primarily race it.

Corvette Kid

Did you run a fine file over the thermostat housing surface to see if it was true? I've seen plenty of these get distorted.

comp

boost pressure into the coolant

Corvette Kid

Alarmist! (I didn't want to start off with the worst case senario....)
Actually though, it wouldn't be hard to rig a temporary pressure gauge into the cooling system and see what kind of pressure it's building during hard runs.

Mr6spd

Interesting thought: If your cylinder combustion pressures are getting by your head gasket, It would pressurize the coolant. It would be interesting to run it Naturally aspirated up to high RPM and see if the same thing happens ... or not!

Do you have a high flow thermostat? Is your pump bypass plugged?

Aidoneus

Hmmm, hand't thought about the boost pressure getting into the coolant, that makes sense though.

I did run a file over the housing before reinstalling gasket.

Can I simply disconnect the hose from the ProCharger without any problems? Will it run like crap if the F.A.S.T. engine management is expecting boost and it isn't there? Can any damage result to the ProCharger if I eliminate the backpressure by disconnecting the hose?

cv67

Whose water pump are you running?

comp

i'd try checking pressure's,,, rad. cap first

Aidoneus

I must be missing something, how would I go about this? If it is boost pressurizing the coolant, and it leaks back out from the themostat housing, how would I test pressure at the rad cap? Is there such a thing as a rad. cap with a pressure gage that reads the maximum pressure, not the current pressure?

Pete K

The pressure test kits come with adapters that allow you to test the cap.

Aidoneus

Ok, just found this kit on Summit Racing - http://store.summitracing.com/egnsea...5&autoview=sku

This must be what you were referring to. Can you leave this in the car though while you drive it?

Also, I was never aware there were "high flow" thermostats. But it does seem that pretty much all of them are, so since it's a 180 degree aftermarket thermostat, I guess I would say "yes" it is? Do you think that could do it? If it's feasible, that's a cheap and easy thing to try.

Corvette Kid

Running it at rest, warmed up with a standard cooling system pressure tester hooked to the cap opening (not pumped up) might show something. If the boost is getting in there, it's likely leaking compression into the system all of the time, just much more pronounced under heavy load of course. It should not build up over three or four lbs. under these conditions. If it continues to slowly build, there's a compression leak. What I originally suggested was hooking a pressure gauge into the cooling system temporarily, mounting it in view such as taping it to the windshield and going for a ride. This should tell the tale in short order. Still, I find it curious that it leaks from the thermostat housing rather than just expelling it from the pressure cap. (Assuming it's building excessive pressure) Have you checked it for proper operation?

redvette6spd

Mark did you go out to DRM for your tune. shoot me a pm I have been trying to get out there my self for a re tune he has been really busy

Aidoneus

Thanks everyone, I think I'll order the kit from Summit and see what I can find out. I'll let you all know. Thanks again

Aidoneus

Well, got the kit from Summit and pressurized the system up to 25 lbs before it started leaking from a hose fitting right next to the cap, but nothing from the thermostat housing. Then I let the pressure off and started the car. It built up to 9 lbs. at idle before I shut it off. The coolant pressure had been steady at 180 since about 5 or 6 lbs. So it does appear to be a boost leak. Head gasket seem like the most logical place to start?

Aidoneus

In thinking about this further, a head gasket leak doesn't make sense. My procharger only provides boost to 8 psi. The coolant pressure should reach 15 psi (right?). If there was a head gasket leak, the procharger wouldn't pressurize the coolant, coolant would leak into the cylinders since the coolant pressure is higher than the boost pressure. Rethinking it, maybe the thermostat housing is warped and heating it up to 180 or warmer causes it to leak. So, I heated the car up with the pressure tester hooked up, then shut it down and manually pumped it up to 25 psi again. This time it leaked from the thermostat housing where it didn't when it was cold. So how would you go about figuring out if the problem was with the upper thermostat housing or the base and how would you correct it? Particularly how would you correct it if it was the base?