All Things Mk5 > How to Guides / Troubleshooting

Edition 30 Overheating

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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:

--- Quote from: exodus_ste on November 06, 2019, 09:40:46 am ---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?

--- End quote ---

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:

--- Quote from: FJB on November 06, 2019, 04:18:05 pm ---
--- Quote from: exodus_ste on November 06, 2019, 09:40:46 am ---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?

--- End quote ---

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. 

--- End quote ---

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  :thinking:

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?

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