944/1 pushes coolant out when thermostat closed
 

1984 944 NA
So heres a brief background. Ive been losing coolant since january or so. Slowly sometimes, faster other times. I had never seen evidence of where it was going. Not in the oil, not on the ground, not excessive in exhaust.
Well finally recently I did find water in my oil, and oil in my water. So i did the cooler seals. They were fairly obviously corroded and bad. I did 3 back to back cleanings with seafoam and recycled oil and let me tell you.... milkshake for days.
now my oil is clean.
however, im still losing coolant.
now though, it starts coming out a minute or so after i park, and upon testing a minute ago, it starts coming out as the car is warming up (it starts a few minutes into warmup), until the thermostat kicks open. then it doesnt come out until i turn off the car.
with the car off for about a minute, it will start coming out again, and let me tell you, it doesnt come out super fast, but it loses a lot. like a quart or two out the overflow.

I believe i have sufficiently burped the system each time. I did drill a hole in the top of the thermostat before installation last time.
I have done a compression check, and they are all within 15 percent, however i will be doing a leakdown hopefully soon. It runs well, but im still suspicious that it may have HG issues.
i THINK i either have not burped the system well enough, and the pocket is expanding and pushing it out, or i have a HG breach that is allowing exhaust into the cooling system.
other ideas?

thanks!

A bad coolant tank cap will do this also. Only replace it with a porsche cap, as there seems to be too many issues with the aftermarket caps.
Sunset is pretty local to you, and I find their prices to be close if not cheaper than most other vendors.
But start with that, should be pretty cheap to try.

i have tried 3 caps, admittedly all aftermarket and all different. i may swap with my other 944s aftermarket cap which i at least know to be good and see what happens

I have a behr coolant tank cap from a running 87 S. If you're interested. $10 shipped.

Turn the heater on full hot, then run the car and bleed it. You have air in the system.

I will say, i just pulled the BEHR cap off my autocross 944 and ran it parked until it warmed up, and turned it off. no puddle. a day or two of driving will tell.

well i was quite skeptical about the cap thing, but it seems to be holding after a good amount of driving!
thanks guys!

Its been almost a week, and no problems! That stinking cap did the trick.
Thanks guys. Now I just noticed a small drip from one of the hoses on the heat control valve. What a pain in the butt place to get to. Ill have to do that sometime this week.

Don't wait too long on the heater control valve - if that lets go it can cause several other issues.