Jetta radiator fans and ac

[platatomi]

2002 Jetta VR6


My fans don't come on except when running the a/c. The car sometimes overheats when stopped in traffic, but has no problems otherwise.


I am going to check the thermal switch for the fans, but I'm not sure how the ac ties in to this issue.


I've looked at the schematics, maybe I missed it but is there a separate thermal switch to activate the fans to keep the ac cold? The fans cycle on and off correctly with the ac on, but do not run at all otherwise.


Thanks for your thoughts.
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'69 Beetle daily driver, fixing things as I go...

Update -

No longer daily driver but still fixing things...

[ps2375]

There is a thermal switch for coolant temp, but the common denominator is the fan control module located on the underside of the battery tray. They have been known to fail in the past, but I would try a new rad switch first, as it is much less costly, and at this age, it could've failed.

[platatomi]

Thanks, will do.

Any thoughts as to why this seems so variable. Like one day I can idle for a half hour, no fans running, and stay at 190*, and the next day at the same ambient temp, it starts creeping over 190* almost immediately upon stopping. Engine all warmed up already in both cases.
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'69 Beetle daily driver, fixing things as I go...

Update -

No longer daily driver but still fixing things...

[ps2375]

When was the last time the thermostat was changed? Or even the water pump?

[platatomi]

No idea honestly. It's at 143k, bought at 130k. I figure it has had work done recently because the timing chains are quiet and the auto trans seems good. Only have had electrical issues besides a tiny leak in the radiator.
_________________
'69 Beetle daily driver, fixing things as I go...

Update -

No longer daily driver but still fixing things...

[ps2375]

What color is it? Green is not the normal color of the factory coolant, that is either yellow or orange, I can't remember anymore. If it is BROWN you could be having problems as the G-12(factory)stuff does not mix with the green stuff, there is a non-factory prestone that will mix with the G-12 out there. And stay away from the RED stuff, I've not heard too much good about that stuff.

[platatomi]

I've been adding the right stuff. Keeping it 50/50 G12 to distilled water. The coolant looks clean and transparent. The leak is very slow, so I've only had to add maybe a gallon of coolant the last 8k miles.
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'69 Beetle daily driver, fixing things as I go...

Update -

No longer daily driver but still fixing things...

[platatomi]

Haven't had a chance to check things out yet but noticed something today.


It seems to start overheating only if it has been driven, then the engine shut off and quickly restarted. I have confirmed this happening several times now, vs if I drive 50 miles and never stop the engine, it will not get hotter than normal when idling. No fans running in both circumstances.


So that's pretty strange. It makes me wonder if the temp gauge is working correctly? How would I test for that? As far as I can tell, its readings and behavior seem perfectly normal.
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'69 Beetle daily driver, fixing things as I go...

Update -

No longer daily driver but still fixing things...

[TDCTDI]

If it idles & stays in the proper range but it starts overheating while driving at speed, then you probably have a bad water pump impeller. The factory ones have a plastic impeller that will crack & spin on the shaft as the RPMs go up.

Another possibility is that your car may have an auxiliary water pump. When this pump goes bad, (may also be your coolant leak) it will blow a fuse that also sends power to the cooling fan relay. This fuse is in the panel in the dash.
(I don't remember which one)
The other fuse that controls the fan module is on the main fuse panel on top of the battery, this fuse is the green 30 amp furthest to the left. Check this fuse anyway, if it has any signs of corrosion or arcing, replace the panel & the fuse. ONLY USE DEALER FUSE PANEL! Aftermarket ones will fail in 3-6 months.
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Everybody born before 1975 has a story, good, bad, or indifferent, about a VW.


GOFUNDYOURSELF, quit asking everyone to do it for you!


An air cooled VW will make you a hoarder.


Do something, anything, to your project every day, and you will eventually complete it.

[platatomi]

By auxiliary pump do you mean the small electric one that runs after stopping the engine? I can tell that is working because I can sometimes hear it running.

I have ruled out the main pump because it stays cool when driving, only gets hot when idling, since the fans never turn on. But I'm not sure how it could possibly not overheat if its already warmed up and idles for 20 minutes or more.
_________________
'69 Beetle daily driver, fixing things as I go...

Update -

No longer daily driver but still fixing things...

[kamzcab86]