[stevev968]

Hi guys,

I changed my water pump on my 968CS about 10 months ago due to the old one showing signs of leaking. All has been going well until a few weeks ago when all of a sudden the red light came on. No sooner had I pulled over when I noticed the temp needle dropping from the 10 o'clock position down to the first white line (7 o'clock) in literally 4-5 seconds. I drove home and a had few more trips afterwards and all was fine - no overheating.



I then drove it again a few days ago and the same symptoms appeared... overheated whilst driving, then temp dropped to normal. I noticed that my overflow is ever so slightly leaking some coolant through the radiator cap, hence I do believe it's under immense pressure and definitely overheating rather than a faulty guage. From the symptoms I suspected I had a problematic thermostat.



After reading the forums here, I decided to change it myself and succesfully changed the thermo to a new one. (After changing it I noticed by the manufacturing date that the thermo had indeed been changed when the new pump was installed earlier this year). Anyhow, I then started the car and simply idled it. Sure enough after 15 min. it overheated again.



Now, I did lose some coolant when I pulled both the bottom hose and the thermo out. So, I was thinking that after a while I would see the overflow level drop down to make up the loss, but it never did. Should I have be bleeding the system for air locks possibly (where do I do that?).

Unfortunately, nothing changed in the overflow level and it didn't get hot at all in that area so water was not circulating even when hot. My water pump exterior got to about 70 degrees celcius (measured with laser temp gun)... also the thermo fans did not come on at all (aircon was off) . However, I do know that they were coming on when I was driving although that could be due to the air-con being turned on. (what's the difference with the thermo fans when you have aircon on vs off?).



So, does anyone have any idea where I should look to next? Is it the pump that maybe has a fault or a radiator blockage?



Any suggestions are much appreciated as I'd like to get the car on the road for the festive period.



Regards,

Steve

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[Rutger Gert-jan]

Hi,



First of all bleed the system, the screw sits on the front end of the engine, near the cover of the fuel rail. There also a coolant hose attached to the little "housing" where the screw sits in....



And if I am correct, one (or two) of the fans start spinning when the AC is switched on...



Good luck,



Rutger

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[flash]

these radiators are NOTORIOUS for blocking over time - much of this is because people fail to heed the warning, and put either tap water or phosphate coolant (or both) in there - this is not a chevy - distilled or de-ionized water and phosphate free coolant ONLY



i agree, make sure it is properly bled - turn on the heater - get it to operating temp, then crack the screw - repeat until only coolant comes out, and no air bubbles



a couple of things to check:



did you put the thermostat in the right direction?



are the fans both kicking on at roughly about 8 oclock on the gauge at low speed, and 10oclock at high speed?



is there a crimp anywhere in the radiator or overflow hoses? watch them as the car heats up - they could be collapsing - old hoses do that



when you changed the water pump, how was the belt tensioner? a weak one of those will cause less drive on the pump, and result in overheating - pete recently had a car in his shop that did that

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[Ryan]

I am with Flash on the belt to the pump or even the pump itself. I have seen the impeller separate from the shaft and only work at low speeds. Sounds like what is going on with your temp when you pull over. It could be a bad water pump again! Did you get a rebuild or new pump? It is getting hard to find new pumps.

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[stevev968]

Hi guys... thanks for the advice. Some more updates:

I tried to bleed the air this morning... undid the screw and idled the car with heater on until it was hot, but there is no water at all going through the top hose and across the elbow where the bleed valve is. The temp got to just under the 10 o'clock position on the guage and I then turned it off. I was able to open the overflow tank without any issue and no pressure build up at all.



So, does this point to radiator blockage or pump not working you think? I am not seeing the dramatic temp falls that I used to see whilst driving although I am now idling it so not sure if that affects it somehow.



I am worried that there is limited water inside the engine and that parts of the engine may be getting hotter than others if the pump is not circulating the water - is that a valid worry?



How do I see if the belt is slipping to the pump .. do I need to take the covers off to see the tensioner? ps. all the belts were changed 10 months ago in a major service whe I did the water pump (not that that matters with faults like these I guess).



Flash... the car has been serviced all its life by a reputable Porsche specialist so I don't think they'd be using bad coolant etc. Yes, I installed the thermo the correct way ( I also boiled the old one and it works just fine)..



Thanks again for any ideas...



Is it easy to remove the radiator to flush it out? Any instructions anywhere?

Steve

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[flash]

sounds like either MAJOR blockage, stuck thermostat, or failed water pump



while still possible, it would have a very screwed up belt tensioner to completely fail like this - i would think there would still be some signs of flow



none of the hoses collapse when the engine is running?

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[tloof]

I too had an overheating problem about 9 months ago that I discovered was a stuck closed thermostat when I pulled it all apart (it wouldn't open in boiling water). After replacing the thermostat, timing & balance shaft belts, and new cam chain & variocam sliders it ran cooler but still gets close to the 10 o'clock position in hot stop & go traffic. I didn't replace the pump when I originally pulled it all apart because it looked like it was in such good condition, but in retrospec maybe I should have (no big deal if I need to though since I do have all the tools for setting the belt tension and such). I personally suspect that the real problem is a slightly clogged radiator that just needs to be either flushed out or replaced...what do you think Flash?



BTW, just for everyones info both fans are supposed to turn on whenever the AC system is activated, but when not the first fan is supposed to turn on at 95 degC (203 degF) and the second one at 102 degC (215.6 degF) if the stock Porsche temp switch is used. I changed out to an aftermarket temp swith from Paragon that turns on the first fan at 85 degC (185 degF) and the second fan at 93 degC (199.4 degF) because of the overheating problem I was having, and it does lower the temp when the fans kick-in, but not enough to keep it at half scale in hot stop & go traffic (if the radiator is bad as I suspect, then nothing is going to really help). Since the stock thermostat is supposed to open at 83 degC (181.4 degF), then my first fan is now turning on only after an additional 2 degC of coolant temp rise so I really shouldn't ever get all that much hotter than the thermostst set point itself...perhaps I should change back to the stock 95 degC temp switch? In my opinion I doubt that the pump is ever really a problem in these vehicles unless the shaft seal totally blows out entirely since the impeller is always going to move water (I suppose if the timing belt tensioner isn't tensioning up the timing belt enough then the pump might slip enough to get the proper water flow required, but if that were the case then the belt will most likely jump a few teeth on the cam sprocket causing severe engine damage via a valve hitting a piston!).

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[stevev968]

Hi guys,

Just a follow-up on my overheating.

Got the car back from the workshop and turns out it was a massive airlock. I and they have no idea how that could have happened. The level in my radiator overflow tank did not change since my last service in March last year.



I tried to bleed it when I was self-diagnosing but I could not get any water to come through the bleed screw at all... maybe I should have let it heat up a lot more...



Anyhow, car is running low temps again at this stage and it's about 106 degrees outside... the guage is just a whisker under the first quarter mark.

Thanks again to everyone here for chiming in....

Regards from West Australia,

Steve

968CS M030

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[ldeprat]

When bleeding the cooling system on these cars, it's a good idea to raise the front end or park the car on an incline facing upwards. Helps get all the air out!

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