Porsche Enthusiasts Club Forum

Ok, this is officially driving me crazy now. Having gone to the trouble and expense of replacing the radiator and fan and some hoses, I'm still having intermittent overheating i.e. coolant venting out the expansion tank. I have in the past year pretty much refreshed the entire cooling system from head gasket replacement, waterpump, new belts, thermostat, heater core, fan sensor, cylinder head sensor, expansion tank etc.

So, having replaced the radiator and fan yesterday and refilling with fresh coolant, I took the car for a test drive last night and all was fine. I left the car over night, rechecked the coolant level this morning and topped up. Decided to go for another drive as I had also changed the throttle cable and replaced the throttle cam with a linear response one (excellent upgrade for £25!). Anyway, went about 1/2hr from cold no issue all was great temps indicate steady in centre of guage. Stopped for about 10mins with engine off, then got going again. Noticed that now the temp was almost up to top white line, and fluctuated between middle and top white line. Got into town and the temp started to creep up, 5mins later I pulled into a friendly garage, whilst chatting coolant started to vent from the expansion tank vent line. Checked the radiator and it was cold right across.

So, I have yet again drained the system this afternoon and pull the thermostat. It looks pretty much new, as it should as its only been in since last July when the waterpump was done. I did notice that it wasn't sealing properly (coolant draining past it), and it was lose I could rotate it freely and it wobbled around. Its a Wahler rated at 83deg, with rubber seal around the edge, a thin washer and circlip, also checked the inner seal and its fine. I've checked its operation in a pan of boiling water, put it through 3 cycles and it opens and closes without sticking, I dont have a thermometer unfortunately.

I just cant get my head around whats going on.

Hi

New radiator blocked ?? you tested its flow before fitting ? i.e fill with water with hand or something over bottom hose stub then when rad is full release hand and ALL water SHOULD flow out of rad within a couple of seconds.... you can do this when fitted as well as long as rad cap on overflow bottle is removed...

All the best Brett

Yep, it flows fine. This is not a new problem, the symptoms are exactly the same as before I replaced the rad. Which is why I have investigated the thermostat as I am running out of ideas as to why its doing this.

Hi

Ok rad fine...so reverse the problem....

What happens if you fill the ENGINE with water while blocking outlets then release them ??

Same result SHOULD be as for rad..i.e ALL water drains almost instantly ???

IF not then you need to find the blockage...did i hear somewhere that you cannot run a 944 engine without a t`stat ? if you could then run engine without and see if it helps ...

All the best Brett

I've not tried that experiment, but when I remove the bottom hose from the rad it will dump all the coolant (approx 8lts) as long as the expansion tank cap has been removed. If there was a blockage I would assume that I'd not be able to fill the system fully. I would also expect it to over heat properly whilst driving.

I believe the engine can be run without the thermostat just not advised as it will take forever to get to temp (if at all) and will use more fuel as a result. Nothing catastrophic will happen. I might actually try this tomorrow. If nothing else to prove the cooling system is flowing properly.

Hi

I have run many engines when I was a Race mechanic, without a t`stat to test if its working or jamming...

It takes the engine LONGER to get to normal temp but it will slowly get to normal temp...

If your problem vanishes you found the problem...the stat...

All the best Brett

Fingers crossed.

Been reading posts on other forums regarding similar problems, nearly always turned out to be related to the water pump either belt slip or pump knackered, pump and belts were done last year so I really really hope this is not the case.

Was it a pump with plastic impeller ?

They been known to come loose

Do 944 pumps come with a plastic impellor?

FWIW I'd be tempted to fit a BEHR thermstat with the right seal if it loose but potentially buy another header tank as well.

I know Steve here (Carrera RSR) had issues with water coming out of the vent hose. He changed his HG a couple of times as well. In the end it turned out that his expansion bottle was not sealing. I'm fairly sure his thread is up somewhere on here.

Thanks everyone for hearing out my pain and for your suggestions!

Finally, I have success! The route cause of my recent low speed / idle overheating was..................................................................................

the belts needed re-tensioning.

The belts and water pump were replaced last July, and having done ~2.5k miles since then they must have 'worn in' a bit. My car has the old style manual tension adjustment (no spring or hydraulic tensioning unit). Basically, the timing belt was partially slipping past the waterpump pulley once the engine was warm and therefor not driving enough coolant around the system when going slow or idling. Probably didn't need the new radiator but seeing as it was most likely still the original and 30yrs old its probably no bad thing to have replaced it. I put the thermostat back in and made sure the circlip was properly seated and it was much more secure than before. Been out in the car all afternoon in a mixture of conditions, stop start traffic in town, country road blasts, stopping and idling for a while, basically a full work out and it stayed cool as a cucumber the entire time with the needle sitting just above the bottom white line instead of between middle and top white line.

I do believe I have a fully functioning and efficient cooling system, at long last. And the engine feels noticeably better for it.

that's what assumption gets you.

a better man than I once said assumption is the mother of all f**k up's and he was right.

I assumed you had checked the belts were at the correct tension

This is why belts should be checked at 1000-1500miles.
PS Never seen or heard of a 944 with a plastic water pump impeller. Tends to be more modern stuff.

"assume nothing, my good fellow". Despite having been extremely hands on with this car since I've owned it it's all been new to me. The waterpump and belts are one of the few things i've not done myself and took it to a 'specialist' to be done early on in my ownership. So, having not previously looked beneath the covers I had assumed the car had some kind of self-tensioning mechanism (and the specialist neglected to mention that the belts might need re-tensioning), that and the fact that the pump and belts were new and recently replaced I had counted them out of the analysis myself. It wasnt until last night reading through a bunch of posts on various forums and checking Clarks Garage, that it dawned on me that the belts may have lost some tension.

We live and learn. And next time "state the bleeding obvious" I may have missed it

Glad that your problem was sorted! As an aside - my 944S2 started overheating (into the red) and it was the rad cap that had perished - not a normal 'motor trade' item, being 150 pressure, so a BEHR OPC was fitted - problem solved. My temp guage always seemed to run a bit on the hot side (middle range) anyway but nothing too tragic but still of a concern. I eventually, after a bit of research, changed my rad switch and thermostat (the units work in temp. variation tandem) to a 'hot' climate, from the USA.

I am not sure if this helps anybody - unless you are racing/track or going to tour Europe in the summer!

Dave
CT
South Africa

When EMC changed my engine and the belts on it, they said that it would need retensioning after 1500 miles. Sure enough, I went back to get it redone.