Mk 3 Golf 92 1.8 Overheats

Raylo:

It could be that your fan is shot. Just for giggles, use a rubber mallet or small block of wood and give the fan (center of bearing, and NOT HARD) a few thwacks... This might free up the fan brushes a bit. If the fan then runs, you have a worn out fan. It is quite common for these fans to fail due to worn brushes. "Back When", I have actually taken such a fan apart and replaced the brushes (OK, it was a Mercedes but still a VALCO fan).

WATCH YOUR FINGERS when thwacking the fan.

Peter Wieck Wyncote, PA

Maybe the fan has a poor ground . Meter the ground wire on the fan connector' it should be close to zero ohms.

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Isn't the fan isolated? I thought both "hot" and "ground' went through the connector. If you mean on the vehicle-side, the OP stated that he got 12V at that connector. Perhaps I was mistaken to assume that he used the two (three) points within the connector to measure?

You are absolutely correct if he measured from the connector to the frame.

Peter Wieck Wyncote, PA

Yes my thought was he had the neg lead of the meter on the bat. term. just due to closeness of the terminals and to aviod letting the smoke out.

Realize that 12V open circut is not 12V loaded. Make sure when you test for voltage at the fan your fan is connected to the connector (learn how to 'back-probe'...) Bet you find the 12V is not there when the fan is connected to the circuit.

Thanks for getting back so quick, with regards to the fan it definitely works on both low and high speed when directly connected to the battery, I have also measured the earth resistance to ground and it is zero ohms so I don't think its a bad earth problem and lastly the point about checking voltage with connector plug connected to the fan is a very good point, the only thing is I have a problem doing this as I can't get the meter probes to make contact with the 3 connection points (eth, low and high speed terminals) because the back of the connector it is fully insulated, any ideas.

Not familar with the term back probe, looked on the net, do you mean back probe pin kit (2mm) which enables you to get past the weather packed sealed connections.

Thanks for help much appreciated.

Raylo, Your circuit description seems to be the same as my 1996 VW Jetta. Your troubleshooting logic makes very good sense to me. The only thing I can add is in reference to PeterD's suggestion about 12V open circuit and 12V with a load. There is a difference.

The principle goes like this: One time a friends car would not start. When she turned the key, it just made a "tic" sound. I saw corrosion on the battery terninals, so I tapped the connection sideways causing the battery connector to rotate a bit. The corrosion caused contact resistance. So, even though 12V was present, the contact resistance dropped the current down low enough so that the starter solenoid did not have enough current to energize. You probably know, but the formula is V=IR. When R goes way up due to corrosion-contact resistance, 12V is often present, but I goes way down. Sometimes I miss the obvious, but you may have corrosion somewhere in the connection for the wires feeding the fan. I don't mean the fan connector, unless you have a split pin inside the connector itself (just look inside the fan connector end), but you probably have to trace the line back to some power connection point.

Best wishes, Mike

Thanks for lesson (ohms Law) its been a long time since I picked up a meter and carried out electrical tests, I now can see the obvious in that its not the voltage its insufficient current due to high resistance in the circuit which is preventing the fan from operating, I was thinking of carrying out a load test using a lamp e.g a 21w 12v bulb to check the cooling fan circuit from the fuse to the thermo switch and to the fan to determine where the bad connection is, I will check tomorrow and let you know how it goes.

Thanks again

Best regards

Ray

I don't have a schematic for you vw , but in mine there's a rad. fan relay that is activated with the thermo switch closing. Maybe it has burnt/carboned contacts.

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Raylo, In case my logic is wrong, you can also spear the wires with a safety pin using pliars and get some direct voltage readings. The unloaded voltage to the fan may be 12v (that is at the fan connector without the fan connected -- when it should be spinning), but when connected, and when it should be spinning, the voltage as measured with pins spearing the wires may drop significanly below 12v. I think this may indicatate corrosive resistance at a feed connection to the fan. I'm not totally sure. Also, remember that your bulb is a different resistance than your dc fan motor. My 2.0 liter VW Jetta circuit has a 30 Amp fusable link. 30 Amp x 12 v = 360 Watts. Your bulb is only

21 Watts. So, your 21W bulb may light up just fine, and the motor may still not spin because it requires much more current.

Knock this one out of the park and let me know! Mike

ps - Keep your mind open for other ideas. I have been wrong before.

Hmmm I am still not up on the title "Mk" I guess. When you say Mk3 does that means it could be a 1992 Jetta or Golf????? Hahaha stupid me, I thought it meant 3rd generation Golfs or Jettas which should have started in 1993 or 1994. Now is this a Mk3 or a 1992 Golf or both?

On the '94 and up Golfs, located almost underneath the coolant bottle should be a module for the radiator fan. I have replaced 2 malfunctioning ones, 1 shorted out on a '97 Jetta due to coolant getting into it and the other in a '98 Jetta would not shut off the fan until the battery died.

later, dave (One out of many daves)

I am thinking that the ROW gets body styles sometimes a whole year before the US does... I think that happened with the A4 at least... anyway what I didn't see in the original post was a check of the fan relay, I assume that there is one, that is what I would look for next. If thermoswitch is getting voltage and works, fan works when hotwired, it's gotta be something in between, only thing there is relay and associated wiring.

nate

Hi Mike

I have done load test using a 21w bulb at the Fan connector with thermo contacts bridged and at the incoming side of thermo switch from battery and bulb does not light up, I then traced the wiring which goes back to the fuse box, tried looking in the fuse/relay box a mass of wires, thought I could see the red wire coming into a air conditioner relay (car does not have aircon) and the wiring diagram in the Haynes manual does not show it going through a relay, anyway struggled to remove it, checked it out, operates to batt/eth and contacts making with a reading of 0 ohms so put it back. Checked wiring and can't see any problem.

I am at a bit of a loss, another message indicated a radiator control module located by the coolant bottle but I have had a good look and can't see one, the Haynes manual mentioned this as well but no explanation how it works but said it was by the front left turret but I could not find it, If I knew exactly what it looks like I might be able to find, the wiring diagram does not show this module in the haynes manual.So for the moment I have decided to take break.

Ray

A couple questions if you don't mind Dave? the module , must contain two circuits for the two speeds ( schweet! ) i'm asking if you can or did open it to see if there's repair possible? ( I'm guessing the mod. must have just two relays in it or is it more advanced?) And in your opinion , was it coolant from someone who was adding to the bottle so it's location was a poor choice though maybe the plan of having the module in the engine compartment rather than running the heavy wiring through the bulkhead and back is more economic. < guessing a bit there Thanks in advance.

the current capabilities of the thermo switches of today can't handle the load of the fan, ( as someone else pointed out your's maybe 3?0 watts) so a relay able to handle the load ( watts ) is used a an interface. the thermo switch /s closing activates the coil in the relay/s and closes the contacts in the relay that then supplies power to the fan. your jumping the the 1 to 2 or the 1 to 3 > is likely operating the relay/s because your open ended voltage test ( not under load ) showed there is some kind of interreaction between the thermo sw. and the relay , though not enough to handle even your 21 watt load test. If the fan module is NOT completely solid state( which i doubt is the case), you should be able to locate said module by have the ignition switch 'on' then by jumpering the thermo switch ( either one ) you should hear and audiable click ( the closing of the relays contacts snapping closed ). a thought or three --- did just ask dave for input) then

Yes I believe that this module will control the speed of the radiator fan with the engine on/off. It should be solid state and probably relies on a few inputs to turn that fan on/off. I think you can break it open but I don't think you can adjust anything inside of it.

JMHO but very BAD PLACEMENT to put electrical items like this under the coolant bottle. The plugs are on the bottom but there is a cap maybe for a fuse at the top. I think if you spill some coolant, while adding some to the bottle, and the module is not properly sealed coolant can enter that module. It was not pretty when I saw this thing smoking. 8^o So I will stress to others to make sure that these modules are sealed at their tops. ;-) Wiring runs should be kept short for devices that require more amperage, so relays help do this.

Too much stuff is getting more and more complicated. Bring it back to the KISS (Keep It Simple Sam) way of doing things! I think I will start driving my '70 Beetle in a few years! lol

I read that the OP does not A/C and may not have this module, so maybe it is just his relay or a fuse.

Again JMHO later, dave (One out of many daves)

On some of the 85-92 Jettas USA with A/C I have had to repair the wiring near the radiator fans due to corrosion or battery acid damage. Either the terminals are damaged or maybe even the wiring too. Check the wiring around the battery! A little water and baking soda usually neutralizes the acid.

I can't find a good picture of a Jetta's radiator fan module in the engine compartment. They should look like this though

good luck! later, dave (One out of many daves)

Thank you Dave , LOL keep it simple sam : kiss , i like that