Yummybud924

Actually I mean the expansion tank pressure cap. I noticed that even when I open it when hot there is no sound of pressure being released.

Does this mean my cap is bad or could it be something else? According to the temp gauge the car never gets close to the red mark. Actually when it gets hot it just goes to the centre of the temp gauge and stays there and the fans come on.

just wondering if this is normal or if the expansion tank should be pressurized.

Erzengal

Yes, it should be pressurized. Also, do be careful "checking it" when hot, that can be quite dangerous.

Yummybud924

I know, I wasn't putting my face over it lol. But I removed it right after parking it and no pressure at all.

so is it just the cap? or could it be something else. The car is not overheating or anything (at least not according to the temp gauge).

shiners780

Use a cooling system pressure tester to test the cap. The one I have has an adapter for testing caps, so you can check to see if the cap is holding pressure.

jbaeng

Any more information on this topic?

I have the same question, my cooling system keeps my '88 944 NA at the lower temp indicator line consistently, but the water in the expansion tank stays cool and unpressurized. very strange. i put in a new water pump last month when i bought the car (towed it home). I had some external leaks that I fixed by checking hose clamps on the radiator and though I was home free. i had to add a few cups of water after every drive. The level was unchanged when i got home and checked the level in the expansion tank when hot (actually, a bit higher due to thermal expansion) then the next day it would be about half way down in the tank. no puddles, the oil is clean and no evidence of coolant leaks, and the water in the cooling system is clear and no indication of oil. so where is the coolant going.

My original theory was air pockets in the cooling system just coming out as I run the car. I did the venting procedure but was convinced yesterday i had all the air out. I pulled into my garage and the level was good. I went to check my tire pressure and noticed a puddle of coolant under the car. It appeared to come out of the expansion tank overflow tube. Almost all the entire tank contents were pushed out somehow. i filled it back up, ran it for a while, no level change... I’m driving it today and still the level looks good.

so I’m looking for some help here. if i had pressure in the tanlk I'd be a lot happier. The only thing left I see is to find a pressure tester and go that route (I actually picked one up at sears for ~$100 but returned it when I stopped the external leaks). I’m just glad the temp is good and controlled unlike yummybud924 above.

Sorry this post is so wordy, just that I’ve put so much (and $$$) into this car after picking it up last month and love driving it. i sold my 911SC a year ago and was dying to relive my late '80s with a 944. a sweet well balanced car. Unknown to me was now that these cars are in their 20s, all the bells and whistles’ that are all gismos and electrical in nature do not age well. But all you need is time and money (and help from the rest of you people!!!) to get it back.

thanks...


thanks...

MAGK944

Both of mine do the same, zero (or very little) pressure in the tank when hot, coolant has never leaked, never gets close to the red temp mark, fan cuts in well before. Both have had the water pumps and caps replaced. Never had a problem, though I am curious why it doesn't build pressure.

Guessing that the caps are the wrong type/psi rating.

Wallace

If the cap is leaking or if the cap is not COMPLETELY closed, coolant will leak out of the expansion tank tube after the car is parked.

One day, after working on my car, I went for a drive. I parked the car, and came back out a little while later and found a river of coolant coming from beneath my car. I feared the worst, but I could see it was coming from the overflow hose from the expansion tank. I checked the cap and it was not quote closed all the way. No problems since then.

I've also read, that it may not necessarily be the cap that's causing the leak. It may the be the expansion tank that's been warped from heat, or it has a small crack somewhere.

I would do things in this order:
- check make the sure the cap is tight
- pressure test the cap and/or buy a new one
- check for cracks/imperfections on the expansion tank and/or replace

MAGK944

Anyone know what the correct pressure rating on the cap should be? Mine is an OEM cap says 'BEHR 150' and purchased from 944Online. All my hoses are new and both tanks were replaced less than six months ago.

Never any overheating problems even here in FL, but am curious as to why there is no significant pressure build up.

jbaeng

Well, I drove the car today and the tank level was hanging in there when i checked periodically during the day. I let it sit and cool down and when I checked the tank it was low again with the level down near the bottom.

where is the coolant going?? no smoke, the oil level is constant and clean, compression check was good.

any thoughts or ideas?

Lizard944

You most likely won't be able to find a leak unless you pressure test the system. Go get the free loaner from autozone. I had the mysterious coolant loss and was fearing a head gasket. When I pressure tested, it was leaking from the left lower radiator, and the seal around the oil cooler housing. You don't need much pressure to find a leak.....maybe 5-10psi. Oddly, I could never find a drip or leak after driving the car and letting the coolant system pressurize naturally. It took the pressure tester to find the leaks.

jbaeng

yup, great advice. i'll run back to sears and get the tester tonight.

544DRS

Y'know? I've thought about this too, but didn't think much of it. I'll have to do the pressure test thing.

Put that on the list!

Nick

jbaeng

Yes, i take one think off my list and then have to add two or three more!!!
it never ends...

Yummybud924

I replaced the cap and now when I take it off I hear pressure beign released and I don't have any overheating prolbems or anything like that. Think it was just a bad cap.

jbaeng

I'm going to an Autozone right now for a tester, so i can test the cap also.