Hello all,
Just a quick question to check whether my diagnosis of the cause of my overheating is correct, before i spend any money..
The car occasionally overheats causing the water to boil over out of the expansion tank, causing the low pressure light to come on.. like i said it is an intermittant problem, which leads me to the thermostat.. however i dont want to take it out, test it and put back in all to have to do it all over again, once i have the replacement if its def the cause, i can save some work and time?
any replies appreciated...!
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JH
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Does your radiator fan work? I had a radiator temp. fan switch fail.I have never know a thermostat problem to be intermittent.
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Being as its not happening all the time..ie Thermostat stuck closed..would think as GGH..Fan switch/or could be fan. try disconnecting the connections on fan switch and short terminals out..If fan works then it will be the switch. if fan wont kick in.fan
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Steve
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Check the expansion cap seal, it's very easy to miss. The actual seal is around the inner plug on the cap, so it doesn't matter how tightly it screws on, if this seal has gone it will leak. The tank is dual skin, the inner tank is the pressurised part, the outer simply collects water that bursts through the seal (or is vented in the event of overpressure) and vents it downwards away from the mechanic. If it's the black cap, as opposed to the later blue cap, I have been told that it is worth changing. No idea why, I'm just passing on information received. Problems with caps can be intermittent, as the seal might only fail on certain occasions. I'd suggest changing it anyway, they're only a fiver from VW dealerships.
Checking the thermostat is simple. Start the car from cold, and note the temperature rising on the top radiator hose.
WATCH YOUR HANDS ON THE ALTERNATOR. It will take fingers off if you catch them in the fan blades
The bottom hose will remain cool. Keep watching the temp gauge (or get someone else to sit in the car and watch it for you). As the temperature rises, you will eventually feel the bottom hose from the radiator warming. This is the thermostat cracking open and diverting water to the radiator. If the engine temp gets quite hot before this happens, which you can further test by turning the car heater on, then you might have a thermostat problem. The fan will (I think) only come on if water flows through the radiator, so if it never cuts in this might be a further indication of a dodgy thermostat. Needless to say, turn the engine off if you get high up the temp gauge with no sign of the thermostat cracking.
If it's the thermostat, you'll be pleased to hear it's not that bad a job, and the golf doesn't tend to suffer from airlocks.
I'd check the expansion tank cap first though, surprisingly easy to miss.
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I think I should clarify my previous post. Coolant boiling out of the expansion tank is a very common thing in the mk2, caused by expansion tank cap seal failure. It can be intermittent, it will sometimes hold the pressure, sometimes not. When it fails, the contents of the expansion tank are expelled forecefully, you'll lose all coolant in the tank and the warning light will come on. If you have no problems with the gauge (in terms of obvious overheat) and the pipes warm up as I suggested in my previous post, then I'm almost certain it's the tank cap seal.
If, however, you get excessive temperatures on the gauge and the lower pipe never gets hot, it might be thermostat - along with Stevo.o, however, I haven't come across intermittent thermo problems before. I'd be surprised if you ever needed the fan in this weather, unless you do a lot of crawling in traffic, so I don't think it would be that. The fan on my mk2 hasn't come on in over 3 months.
Matt
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Also check the expansion tank does not have any hairline cracks in it, I have had 2 Golf Mk2 GTis that have had small cracks in the expansion tanks which lose pressure and fluid when very hot...
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Any luck with this one?
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I ran the car up to temperature and observed what happened.. water (and coolant obviously) began to leak out of a mounting nut that holds what looks like a switch on top of the actual expansion tank.. as the pressure rose, the water began to build up in the recess and dribble down the side. The thermostat had opened, which means that can almost be ruled out.
However, i tried it again today and there was no leakage and no problems..
I may change the cap anyway as the expansion tank has boiled over a few times since i got the car over approx 18months and for a fiver, i may as well rule it out
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JH
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