Solved - Coolant suddenly being spat out though the expansion tank overflow pipe

MJL944 · Aug 18, 2019

Gents,
Your advice/wisdom please.

My 1989 944S2 suddenly spat out about 3 tablespoons or so of coolant through the small overflow pipe just under the coolant expansion tank cap. This happened last night, right at the end of the car's weekly 1 hour run-out and seemingly as soon as I switched the engine off.

I touched all the coolant hoses and they were all the usual hot temp except for the small coolant pipe that runs from what I understand to be the water pump 'elbow' joint, and which travels up and level with the top of the radiator, then goes under the AFM before coming to a T-junction just under the expansion tank. The cool section of pipe I'm referring to is the long section of the pipe shown here (thanks to Woolies website) > link to pic of coolant pipe

The long section of that coolant pipe was only mildly warm at best (especially in the middle) so it looks as though coolant flow through that section is suddenly pretty none existent. The last time I touched that section of coolant pipe (to reseat one of the slightly broken plastic clips that holds the pipe in place correctly) was only a couple of months ago and the pipe was red hot then as usual.

A new water pump (a genuine Porsche part and eye-wateringly expensive!) and thermostat were fitted by a local indy 12 months ago and I've had no noticeable issues since other than there was a sudden slight coolant leak back in January from the tiny coolant pipe that leads from the top corner of the radiator directly to the expansion tank (it joins the rad just above the radiator top hose) and this was sorted by my local OPC. I did notice that that small pipe was cool as well last night.

Any thoughts as to the issue?

Is it possible that it's just some air in the system as this pipe is just about the highest point of the coolant system (although the pipes through the throttle body seem about the same level and they were hot)?

If it's just air how has this happened and is it just a matter of performing a quick bleed?

Might some debris that's been lurking somewhere for the past few moths have suddenly shifted to cause a blockage (maybe something disturbed by last years water pump change or the replacement of the plastic bracket for the small coolant pipe changed by the OPC)?

Or, (shudder!), is this water pump related?

Any thoughts appreciated so I can decide whether to call the local Indy (who fitted the new pump) or my (more convenient) OPC to investigate.

Thank you.
Mark

944Turbo · Aug 18, 2019

Without the pipe temp, I would say maybe a weak expansion cap spring or cracked seal, so start by checking out the expansion tank cap.

It could be a blockage but that is unusual except I think the waterpump elbow needs to be drilled for turbos and that sometimes doesn't get done and also the small thermostat for the turbo coolant plumbing can fail - been a while since I have played with this area so I cant remember exactly how the plumbing works.

If it wasn't for the strange pipe temps, It could be the coolant being pressured by a small leak in the head gasket allowing a cylinder to pressurise the coolant - you can test the coolant to look for combustion gases.

good luck,

Tony

MJL944 · Aug 18, 2019

Thanks for the reply Tony.

Expansion tank issue was also my first thought but the new OEM expansion tank and cap I had fitted in 2014 (under 10,000 miles ago) seem perfectly OK. I took off the expansion cap and had a very close look today.

Head gasket was changed as part of the same 2014 job, as was the fitting of a new OEM rad (this is a very well looked after S2!) and the coolant is beautifully clean, pink and oil free so I think I can confidently discount HG issues.

If the thermostat or its seal has stuck somehow or even shifted slightly, could this cause a blockage through that pipe? The flow through the water pump elbow joint looks very narrow so wouldn't take much to block?

944Turbo · Aug 18, 2019

MJL944 said:
Thanks for the reply Tony.

Expansion tank issue was also my first thought but the new OEM expansion tank and cap I had fitted in 2014 (under 10,000 miles ago) seem perfectly OK. I took off the expansion cap and had a very close look today.

Head gasket was changed as part of the same 2014 job, as was the fitting of a new OEM rad (this is a very well looked after S2!) and the coolant is beautifully clean, pink and oil free so I think I can confidently discount HG issues.

If the thermostat or its seal has stuck somehow or even shifted slightly, could this cause a blockage through that pipe? The flow through the water pump elbow joint looks very narrow so wouldn't take much to block?

sorry was thinking turbo - not much knowledge of the s2, does that pipe stay cooler if the thermostat is open and sending the coolant to the rad? How full is the coolant tank, turbos tend to vent a bit if the tank is full to max - usually best not to go over the half way point between min and max when cold. Are the fans running ok when hot?

Tony

MJL944 · Aug 19, 2019

Yes fans run OK when car is hot - they'll often be on for a minute or so after I've parked up.

Coolant level is/was at the min mark on the expansion tank as it always is. Any higher and my S2, like your Turbo, will just spit it out.

In nearly 7 years of ownership, other than a couple of obvious but small leaks which were easily fixed, the coolant system has caused no problems which is why I'm rather spooked by this sudden issue.

MJL944 · Nov 3, 2019

Just to (hopefully) close this off for future reference, Tony was correct to suggest that a failing coolant tank expansion cap was the cause.

Fitted a new £15 coolant tank cap supplied by OPC Nottingham and no more coolant is being burped through the overflow pipe as the engine is switched off (which the car continued to do 2 times out of 3 for the past 2 months - particularly when the coolant temp was just below triggering the cooling fans to come on when the engine is switched off, at which point an alarming amount of pink fluid would be burped onto the garage floor). The section of coolant pipe that was cool to the touch before is now hot as the system is correctly pressurised.

What I hadn't realised was that the failing cap was an after-market part (purchased and fitted in April 2014 by a garage who suggested the cap should be changed - it had lasted less than 10,000 miles and is the type you can buy for £8 on eBay).

The OPC part is stamped with Behr (the maker's name) and other German text and the plate on the bottom of the spring is slightly larger and the rubber seal more substantial.

Never knew a coolant cap could fail in such a way and display such symptoms (and researching coolant cap issues lead to finding some interesting and confirmatory threads on US 944 sites), so thanks for the heads up Tony. A nice, cheap fix!