Overheating after a time of stop start traffic

[Minesabora]

Hi, I have a 2001 Bora V5 with the 170bhp engine. It has now done 131,000 miles and going well, by and large. However, it has started having problems that only seem to appear in specific circumstances. Normally, she runs at 90degrees, regardless of what we're doing or how loaded the car is. When towing our caravan, she will be fine towing at 60. But when sitting in a traffic jam on a motorway she gets overheated after about 10 minutes, when the temperature starts to creep up. It continues to rise until we are moving again; once we reach about 30mph, the temperature starts to fall. Given the state of our motorways, this is not a comfortable experience. I have had it checked by a variety of garages, including an independent VW Audi specialist and they have all said that they cannot replicate the fault and all seems to work fine. It seems that it is an airflow problem and it is as though the fan cuts out when it has a lot of work to do. Any ideas anyone?

[mikeybutch]

Can you check if the fan has come on when this happens?If not then the sensor seems to have failed.Other wise could the waterpump be failing or the coolant need changing?

[Crasher]

The fans are not coming on. Check the fuse on top of the battery.

[Minesabora]

Can you check if the fan has come on when this happens?If not then the sensor seems to have failed.Other wise could the waterpump be failing or the coolant need changing?

Thanks mikeybutch; Yes, had a problem with the fan fuse some time ago, so this was the first thing I checked; fan works. Sensor replaced recently because it was giving an error message but this hasn't resolved the problem and I have changed the thermostat in case this was it - also have drained and flushed the system. Problem persists. However, I think I may have found the problem source. I had not been aware of problems associated with G11 & G12 anti-freezes (I wasn't even aware that there was a G12) in consequence, on rare occasions when the header tank needed a drop more coolant, I topped up with the standard mixture I have used for many years. I suspect this will have produced a gel that has settled in lower parts of the system and causes problems when the engine is under particular strain. If this is the case, my problem now is whether there is a way to deal with the gel short of stripping the engine?

[Minesabora]

The fans are not coming on. Check the fuse on top of the battery.

Thanks Crasher, please see my reply to mikeybutch!

[mikeybutch]

Thanks mikeybutch; Yes, had a problem with the fan fuse some time ago, so this was the first thing I checked; fan works. Sensor replaced recently because it was giving an error message but this hasn't resolved the problem and I have changed the thermostat in case this was it - also have drained and flushed the system. Problem persists. However, I think I may have found the problem source. I had not been aware of problems associated with G11 & G12 anti-freezes (I wasn't even aware that there was a G12) in consequence, on rare occasions when the header tank needed a drop more coolant, I topped up with the standard mixture I have used for many years. I suspect this will have produced a gel that has settled in lower parts of the system and causes problems when the engine is under particular strain. If this is the case, my problem now is whether there is a way to deal with the gel short of stripping the engine?

You may well be on to something cos the problem reminds me of sludge which used to build up in radiators and effectively reduced the cooling to the top part only.You can check by feeling the bottom of the rad when the engine is hot and if it feels cool then thats where the sludge is.I did not know that its caused by mixing these coolants but maybe the rad can be flushed in situ or taken to someone with the knowhow.I would be surprised if the engine is badly affected cos it has not boiled ....yet!