Edition 30 Overheating

[cpk]

Wonder if anyone has ideas around this...my 114000 mile Stage 1 Edition 30 has started to have issues with high coolant temperatures.  At first, the fan started coming on after anything but a very short journey, but no other issues. Then, I started noticing the coolant temperature creeping up above 90C.  An independent specialist checked for fault codes, ran a live test, replaced the engine temperature sensor and bled the coolant system with no effect, so the next change was a new main cooling fan/control module.  Again, no effect.  The problem has continued to get worse, and on motorway journeys, the coolant temperature gets very close to the red zone.  I regularly check the oil level and keep it topped up but after a motorway run at the weekend, the oil level light came on.  I topped it up, drove the car 170 miles home and it had drunk about half a litre.

What would you guys advise next?

[GVK]

Has it had a water pump on at all? Pump impeller could be spinning on the shaft.

[cpk]

It had the pump and cambelt done 7 years/50000 miles ago.  I'd actually booked it in to the garage to get the overheating fixed, and a new belt and pump done at the same time, but the mechanic advised holding off on the belt and pump until the overheating was fixed.

Is there a way I can tell if the impeller is spinning on the shaft?

Thanks for your help.

[FJB]

Take off the pipe at the top of the expansion tank and put it into a bottle, start the engine, if coolant goes into the bottle the pump is working.

[exodus_ste]

I've had similar issues with mine over the last year or so. Although the cause of mine is still unknown, my problem is slightly different - no cooling fans. Replaced the fan/controller pack a few months ago assuming this was the issue but it hasn't helped.

My problem occurs whilst sitting idling/crawling in traffic. As soon as i get 15/20 mph there is enough air passing the rad to cool it.

Weirdly, the fans work perfectly in output tests using vcds and occasionally they will work. Also, when the engine is over 90 and i turn it off, the fans come on! Work that bugger out!

I did confirm the pump was working using FJB's method. Also changed both temp sensors.

Have you got vcds? The fact yours is overheating during driving sugests you have no circulation or a thermostat is stuck closed possibly. Does putting the heaters on max temp and full power bring the temp down?

[cpk]

Mine is strange in that airflow definitely doesn't reduce the problem.  Sitting in traffic doesn't seem to cause too much of a problem, but as soon as I've done a few miles at motorway speeds, the temp needles rises way above 90C (and now it seems like oil is being consumed).

I'll try the water pump test as soon as I can.  I don't have VCDS sadly, but I'll be able to check if turning the heater on to full makes a difference later on.  The only VCDS info I have is when my mechanic scanned it as part of his investigations and he said there were no faults being logged.

[FJB]

I've had similar issues with mine over the last year or so. Although the cause of mine is still unknown, my problem is slightly different - no cooling fans. Replaced the fan/controller pack a few months ago assuming this was the issue but it hasn't helped.

My problem occurs whilst sitting idling/crawling in traffic. As soon as i get 15/20 mph there is enough air passing the rad to cool it.

Weirdly, the fans work perfectly in output tests using vcds and occasionally they will work. Also, when the engine is over 90 and i turn it off, the fans come on! Work that bugger out!

I did confirm the pump was working using FJB's method. Also changed both temp sensors.

Have you got vcds? The fact yours is overheating during driving sugests you have no circulation or a thermostat is stuck closed possibly. Does putting the heaters on max temp and full power bring the temp down?

You may have a faulty temperature sensor, the fans work from the one in the coolant flange, just below the vacuum pump. The temperature gauge runs from the sensor just below the main thermostat. At least this is the arrangement on my 06 GTI. 

[exodus_ste]

I've had similar issues with mine over the last year or so. Although the cause of mine is still unknown, my problem is slightly different - no cooling fans. Replaced the fan/controller pack a few months ago assuming this was the issue but it hasn't helped.

My problem occurs whilst sitting idling/crawling in traffic. As soon as i get 15/20 mph there is enough air passing the rad to cool it.

Weirdly, the fans work perfectly in output tests using vcds and occasionally they will work. Also, when the engine is over 90 and i turn it off, the fans come on! Work that bugger out!

I did confirm the pump was working using FJB's method. Also changed both temp sensors.

Have you got vcds? The fact yours is overheating during driving sugests you have no circulation or a thermostat is stuck closed possibly. Does putting the heaters on max temp and full power bring the temp down?

You may have a faulty temperature sensor, the fans work from the one in the coolant flange, just below the vacuum pump. The temperature gauge runs from the sensor just below the main thermostat. At least this is the arrangement on my 06 GTI. 

Sorry for the slght hijacking but it may shed light on your issue perhaps CPK. Thanks for the advice FJB, i did replace the sensor on the front of the engine when i did the thermostat a couple of years ago, and the one above the gearbox even more recently. Is there a way of checking output of these individually in vcds i wonder, to see what message they are actually sending 

[FJB]

When mine was playing up. it was not the sensor but the plug, I had a small oil leak from the vacuum pump cover that had got into the plug causing a dodgy connection. The sensors are ntc thermisters, you can test for resistance with a multimeter, the higher the temperature the lower the resistance, and vice versa.

[cpk]

Thanks for all the advice, and no worries on the slight hijack!  I've done a couple of long motorway journeys over the last couple of days, and turning the heater up to full definitely does bring the temperature down again.  Does that imply coolant's circulating, meaning the pump's okay?  To recap, I've had a new fan/controller, and a new temperature sensor...so, if the pump is okay, is that pointing towards the thermostat?

[exodus_ste]

Okay well by my reckoning, it could well imply that the stat isn't opening and allowing coolant to flow through the rad.

Not 100% sure how the cooling system works on these but i'm sure the pump will be working. It will pump coolant round the heater matrix system before the stat is supposed to open.

Think this also suggests it's the b**tard stat on the front of the engine thats the problem, not any of the inlines. Just my guess though, wouldn't wish that job on many people.

[pudding]

I'm pretty sure manual ED30s don't have the inline thermostat, well, mine doesn't at least.  Not sure if the DSG might has one, but worth checking/replacing if yours is a DSG.

The OP's problem sounds like the main pump to me.  The classic the faster you go, the hotter it gets.  Coolant system pressure is about 1 bar, so that is some pressure for the impeller blade to overcome.  What can happen with the plastic ones (as GVK said) is the impeller spins on it's shaft rather than moving the water.  The mechanical bond breaks down over the years.

The mechanic was wrong to hold off on the belt/pump change as the pump is the heart of the coolant system, and the belt is long over due as well.

You might also want to check the secondary pump as well, which lives in the primary thermostat area.  That pump supplements the mechanical one and also circulates the coolant after shutdown to prevent hot spots.  @exodus_ste , the fans can come on as part of that process, so I wouldn't be concerned about that.  So long as they don't stay on permanently.  The after run circulation process usually lasts for approx 5 mins.

As for the fans not coming on, if both of them work via an output test, it proves electrical continuity at least, so you need to investigate the signals from the sensors.

[exodus_ste]

I thought a manual had one inline stat, and DSG 2?

Pretty sure the coolant system pressure doesn't put extra load on the impeller of the pump. The whole system is running at 1 bar, and thats due to expansion from the temperature. The pump would see the load if it itself was creating the pressure. These are circulation pumps not positive displacement.

That said, if the shaft/impeller connection is a weak point that could still be the culprit.

I will stand corrected though if someone can tell me that it isn't the main belt driven pump that circulates coolant round the heating system. If running the climate at the highest temp allows coolant to flow around the matrix then doesn't that suggest that the pump is working?

Anyway, running with the cap of the reservoir and looking for a return flow will confirm.

Thanks pudding, however i have no idea how to check the output of the sensors. Can easily check for a resistance but not sure how it that and the actual temp correlate.

[pudding]

My manual only has the main thermostat.  Above the gearbox is just a plastic housing with a temperature sender in it.  When I bought an inline stat from the dealer, it did actually come up on his screen that it wasn't applicable for my chassis number, but I bought it anyway 

Yeah a visible return flow in the expansion tank is another sign the pump is working, but unfortunately the symptoms of an impeller spinning on it's shaft aren't there at idle usually, only at higher engine rpm where pulling/pushing the water presents more of a resistance.

That is a good point about the heater matrix. Another symptom would be luke warm heating at motorway speeds compared to idle. Is the heater matrix in permanent circulation, or only after the stat opens up?  Some older VWs didn't get a matrix flow until the stat had opened up.....hence the frosty experience over winter when they jammed shut.

I would use VCDS to check the sensor output.  Engine coolant temp for the main stat and I *think* the second sensor could be in the HVAC controller, I can't remember.  The sensors normally sit at 85 ish degrees on a run.

[cpk]

Just in case anyone was waiting with baited breath for the resolution of my problem  - it turned out to be the thermostat.  It was replaced (only after all the other expensive work), and the temperature gauge reaches 90C and stays there.  The fan starting up after switching the engine off has been cured too.

On the down side, the car appears to have lost its cruise control at some point during the process.  That's probably another thread though...