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 Post subject: Solved - Coolant spitting out though expansion tank overflow
PostPosted: Sun Aug 18, 2019 10:14 pm 
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Location: Nottingham
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Gents (with apologies for cross-posting from the PCGB forum),
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?

(Note: new OEM expansion tank, tank cap, rad and head gasket also all fitted less than 10K miles ago).

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

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Mark

Porsche 944 S2 1989 Alpine White (204,600 miles and ready for another 204,600)
BMW e36 328i Sport Coupe 1998 Titan Silver


Last edited by MJL944 on Sun Nov 03, 2019 11:33 pm, edited 1 time in total.

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 Post subject: Re: Coolant spitting out though expansion tank overflow pipe
PostPosted: Mon Aug 19, 2019 9:04 pm 
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Location: Bolton U.K.
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I wouldn't worry too much. Try a bleed first it could just be an air lock. Mine always settles to the low level on the header tank when cold and just blows off excess above that. No obvious leaks but I suspect the head gasket may need a look at sometime. I'm preparing a new cylinder head for a swap this winter.

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 Post subject: Re: Coolant spitting out though expansion tank overflow pipe
PostPosted: Mon Aug 19, 2019 10:49 pm 
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Thanks for the reassurance Endoman. I'll attempt a bleed.

From past experience, I know my S2 will also only accept a fill to the min coolant level line before overflowing.

It's just the suddenness of this issue that concerns me - there must be a reason why one section of the cooling system appears to be out of action, and I'd like to understand why.

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Porsche 944 S2 1989 Alpine White (204,600 miles and ready for another 204,600)
BMW e36 328i Sport Coupe 1998 Titan Silver


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 Post subject: Re: Coolant spitting out though expansion tank overflow pipe
PostPosted: Mon Aug 19, 2019 11:20 pm 
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Joined: Sat May 28, 2011 10:17 pm
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Just to chime in my Turbo did just this when I recently refilled it after the big service, I must have bled it 3 times, once with the nose in the air and the front of the car on ramps (and this is after back-filling the block using a hosepipe down the elbow on the head so I know the block was full of water!)

Make sure that the heater valve is working and set for maximum cabin heat before bleeding, a vacuum leak at the heater controls can cause the valve to fail (not sure if it fails open or closed).

The turbo dribbled water from the overflow twice and then I remembered something you both said about never filling it up to the maximum line on the expansion tank... :lol:

Mine is now about 1/2 way between minimum and maximum when cold and when hot sits at maximum.

I still had to bleed it a couple more times, just keep getting the engine up to temperature until the fans kick in and the turn off (this is the important bit so you know that the thermostat is opening and letting the water into the radiator - if this doesn't happen then something is wrong with either the radiator fans or the temperature sensor in the radiator). Crack the bleed valve open until no bubbles appear and then top up the expansion tank if it drops.

I do remember an issue in the past where my expansion tank cap failed and caused a similar incident - I know you said that yours is reasonably new but they can and still do fail or it could be faulty, I read on another forum that there was a bad batch of radiator caps.


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 Post subject: Re: Coolant spitting out though expansion tank overflow pipe
PostPosted: Tue Aug 20, 2019 9:56 am 
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I've never had any bleeding issues with the nose up and the heaters cranked up. Most turbo's object to a full expansion tank and happily sit somewhere between min and halfway. Can't speak for S2's.

Stuart

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 Post subject: Re: Coolant spitting out though expansion tank overflow pipe
PostPosted: Tue Aug 20, 2019 10:12 am 
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the 968 is exactly the same, always ends up at half way between the marks

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 Post subject: Re: Solved - Coolant spitting out though expansion tank over
PostPosted: Sun Nov 03, 2019 11:39 pm 
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Just to (hopefully) close this off for future reference, Wh1t3Kn1ght 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 some other German text and the plate on the bottom of the spring is slightly larger and the rubber seal is noticeably more substantial.

I never knew a coolant cap could fail in such a way and display such symptoms (and researching cap issues lead to some interesting and confirmatory threads on US 944 sites), so thanks for pointing me in the right direction.

I do like a cheap fix!

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Porsche 944 S2 1989 Alpine White (204,600 miles and ready for another 204,600)
BMW e36 328i Sport Coupe 1998 Titan Silver


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