'91 Jetta diesel overheating

[dermie24]

Hello,

I have a '91 Jetta diesel that I am having overheating issues with. I had a mechanic change the thermostat and that did nothing. There is no white smoke out the tailpipe and no water in the oil. I believe I have stumbled upon a couple of my problems. But I have a couple of questions before purchasing parts.

1. The expansion tanks seems like it has two chambers. There is a small chamber in the middle with the cap off and then the rest of the tank surrounds that. When adding coolant, should there be some in the outer portion of the tank or only the inner chamber? I think my problem here is that this tank is cracked and leaking coolant when the outer section of the tank tries to fill.

2. I am also having fan trouble. Even when the temperature guage is above 3/4, the fan will not turn on. I did turn the A/C on and the fan runs. Poking around in the engine compartment I noticed wires going from the motor to a coil looking thing down by the radiator. It looks like this part has seen better days (lots of corrosion, rust, and cracking). Is/was this the thermostat that should make the fan turn on normally? What else can I check to determine why the fan doesn't cycle by itself?

I don't know if we can attach pictures here, but I could take pictures of the pieces I'm describing and send them to anyone by e-mail who's willing to help! Feel free to PM me with your address.

Thanks,
John

[Doug Tatham]

If I remember correctly there are a few places where temperature is sensed. I believe that the radiator has a couple sensors that screw into it (top right) with wires attached and they are for the AC. More importantly, the coolant pipes coming off the front and side of the engine have temperature sensors and I think one of them controls the fan. I never looked up which sensor controls what.

[Jake58]

Your fan problem sounds almost like your thermal switch isn't working. This switch is located in the lower right side of the rad. It will have a plug with 3 wires plugged into it. I believe the red\white and red\black colors are for the 2 fan speeds and a red wire for power. You could test this switch I guess by taking it out and dipping it in boiling water to see if you get any continuity between the contacts. The wires run up to relay located in the upper right side of the rad as well. You might want to check the connections there as well. Also check the fuses. I think No. 13 fuse (10 amp) and No.19 fuse (30 amp) in the panel are for the fan. Seems like every Jetta Diesel with AC from this era has a fan problem. I just bought 1990 and it has a fan problem which I hope to tackle this week. Good Luck