mk2 golf overheats

Have you confirmed that the relay (usually located in the engine bay on the fan shroud) is (a) getting +12v constant and (b) working properly? If the thermoswitch is known-good, the relay would seem to be suspect (well, that or the wiring).

Relais only come into play for after-run w/ some engines and a/c. For normal fan operation the fan is directly powered from the battery via the thermo switch. To op: What does the temp gauge read? Goes it all the way to the right, does the red light blink? If not it may not be overheating. If it still leaks somewhere _at_ the new filler cap there may be two causes:

- the reservoir is cracked? Do you still have the old rectangular bottle or the new ball style reservoir? The old one is prone to cracking at the seem.

- it is possible that the over pressure relief valve in the new cap opens because pressure in the system is indeed too high, if temperature stays within normal range at the same time this may be caused by a blown head gasket Did you have the system pressure tested? Tested when engine hot or cold?

Ingo

Don't have A/C. The temp gauge reads quite cold usually but when stationary or steep hill climbs in hot weather the gauge will shoot up to half way and sometimes a little beyond. Which is when i know the water will be overflowing out of the filler cap. Haven't had it pressure tested though as it's not so much a leak, it's a case of water expanding beyond the exp tank when hot. The fan does not seem to stay on long and never seems to move into boost speed. Your suggestion about the water pump seems a good one to check, i had mentioned that to more clued up mates but have been told it wont be that! Replaced parts are radiator, thermostat, filler cap, fan motor and fan thermoswitch!!! As a temporary measure i have disconnected the fan thermoswitch and installed a manual switch direct to the fan which i have running constantly in this baking hot weather (at normal speed). I have since had no problems and no loss of coolant, just the inconvenience of having to lift bonnet up at start and end of every journey! Could just be dodgy wiring!?!?! Thanks

You sound like you are overheating if you have boiling coolant. My Jetta runs over half normally and doesn't puke coolant. Have you ever had it checked for head/gasket failure?

Hmm...ok, so I was definitely mistaken about how that worked. My car's harness *seems* to be as follows:

1. One red wire (presumed to be +12v constant) emerging from the harness and going to both the relay and the thermoswitch
2. One red/white wire coming out of the harness and going directly to the fan
3. One red/white wire coming out of the thermoswitch and going directly to the fan (well, merging with red/white wire #2 and going to same fan terminal)
4. One red/black wire going from the thermoswitch to the relay and another from the relay to the fan.
5. Brown ground wire to the fan and to the relay

Schematic:

However, the harness is somewhat mangled (the relay holder corroded badly enough to start smoking when I neglected to disconnect the battery while washing the engine bay, and I tried to patch it back together as well as I could), so it's entirely possible something is misconnected. I did use the Bentley in trying to figure the harness out, but since I don't have AC I also tried to just get the AC-related wires out of my way as much as possible.

So do I have my fan miswired? It definitely comes on in afterrun mode, and it definitely comes on during running (I noticed when trying to set my timing). Of course, if I've managed to disable the higher speed, that might explain why I've been sometimes getting ungood oil temps.

--Kevin Broderick kbroderick (at) smcvt (dot) edu

Possibly. I sent you a shematic, may it is easier then to try to line your description up with the shematic I have here.

There are two kinds of afterrun:

1. the thermoswitch in the radiator is directly powered by the battery, it will switch on the fan in one of the two speeds solely dependent of the water temp inside the rad.
2. the after run relay will power the fan after you shut down the engine _if_ the temp switch located at the engine head tells it that it's too hot in the engine compartment - this is to prevent vapor lock in the fuel lines.

Why do you mention oil temperature? I thought we're talking about water temp?

Ingo