Overheat at Idle - what needs replacing?

[dridge11]

Hey all, happy owner of a beautiful 71 here. Been driving it around plenty since I acquired it a few months ago. Even took a 6 hour round trip and AutoX'd this weekend no problem. The car usually runs cool under all conditions. Today on the way home, I noticed it running hot when I was sitting at a stoplight, made the rest of the 30 min drive home no problem once the car was moving at regular speed, the temp dropped back down to about normal. Got home, opened the garage, got back in and the temp was between the "half way mark" and the "all the way" mark.

Radiator is fine, water/coolant is full, fan was spinning at idle...so what is it?

Fan clutch or water pump?

Or something else?

Thanks in advance!

Edited August 6, 2010 by dridge11

[steve91tt]

I'm guessing fan clutch as the problem only occurs when the car is not moving. I had the same issue with a 300ZX a few years ago.

The car would overheat at idle or driving slowly around town. The fan looked like it was moving a bunch of air at idle but it turned out that it was not moving enough air. I replaced the fan clutch and all was good again.

Do you hear the fan get louder as the engine gets hot? If the mechanical fan thermostat is working correctly the fan should be much louder when then engine is hot than when it is cold. If the fan speed (volume) is not varying with temperature then you need to look at fixing the clutch. My fan is louder than the engine when I sit at a traffic light for a while but it's barely audible when the engine is cold.

Edited August 6, 2010 by steve91tt

[Gary in NJ]

+1 on the fan clutch. You could also make sure that the fan belt is tight and not slipping.

[Oiluj]

You can rebuild the fan clutch, it's not hard.

[Shade133]

definitely seems like fan clutch. fan is spinning, but possibly not fast enough.

[dridge11]

Much appreciated all...I'll investigate a bit more this weekend. I'll start the car up, take it for a brief spin around the block and park it, then see if the fan runs harder as it gets warmer.

Julio, any links to fan clutch rebuild instructions? Or just search for it on the forums?

[Shade133]

check it by having the engine off and hot and free spin the fan. see if you can feel any resistance.

[dridge11]

check it by having the engine off and hot and free spin the fan. see if you can feel any resistance.

I did that yesterday, it seemed to spin pretty freely.

Looks like this might be the rebuild link:

http://www.hammondsplains.com/newtechtips/cooling/index.htm

[Shade133]

ya if the engine is hot and it spins freely.. the clutch is out.

[dridge11]

Alrighty, I'll be undertaking my first project on the Z next week with my attempt to rebuild the clutch. Looks like MSA has a replacement if things go horribly wrong.

Any thoughts on replacing with an electric fan?

[Gary in NJ]

Any thoughts on replacing with an electric fan?

Yes, don't bother. The engine system works fine when kept in working order.

[AZ-240z]

Is your fan the early metal fan or plastic fan. Don't think the fan clutch for the early metal fans are rebuildable. If the metal fan clutches are rebuildable, or anyone has any experience doing that, I would be interested in hearing about it.

Dan