240z Overheating When Idling

[lm71z]

I noticed that the temperature on my 240z is fine when I'm driving it(just under 1/2), but it sometimes rises to 3/4 when the car is idling at a stoplight. What's causing this problem? Could it be the radiator?

[Carl Beck]

Could be the radiator

Could be a lose radiator cap or one not holding proper pressure

Could be a fan fluid coupling (thermostat control)

Could be a lose fan belt

Could be an idle mixture set way to lean

Could be a timing issue

Could be a weak water pump

Could be it's low on coolant

Could be a thermostat not opening all the way

Could be a thermostat that is missing

FWIW,

Carl B.

[lm71z]

What do you mean by idle mixture? Could someone tell me how to properly adjust the idle on a 240z? How should the idle screws on each carburetor be adjusted and how should the main idle screw be adjusted?

[JonnyRock]

This is a common problem with Zs. However, if the temperature is just rising and not actually 'overheating' you don't need to worry about it too much. My temp gauge sits at about 3/4 at all times. I have overheated a couple of times and have made small changes (fan shroud, ceramic header, replaced water pump) which all helped slightly.

But again if it's not actually overheating, don't worry too much.

[ozconnection]

I'm with Carl on this one. I hate having to watch the temp guage to see "what's it gonna do?"

Time to become a detective or pretend your on CSI. Investigate everything that's been suggested to you. There must be a reason for it!

And isn't it winter in the northern hemisphere ATM!? Man if she 'overheats' now, what's she gonna do in summer!! :paranoid:

Fix it now or fix it later: either way you gotta get it sorted.

Cheers.

PS, Could also be a blocked radiator core, damaged fins or corrosion in the coolant passages in the head and/or block or a grubby engine with thick coats of grime that's preventing adequate cooling

Edited February 21, 2009 by ozconnection
added some stuff

[lm71z]

Could it be a bad fan clutch that's causing the problem?

[Zs-ondabrain]

Could it be a bad fan clutch that's causing the problem?

Could be.

First things first, Flush the system. This will knock out any loose crap that may cause blockage. (let's everything move better)

Go buy a thermostat (180 should be fine but you can always do a 170 or 175)

If you live in a normally warm or hot climate, a fan shroud is almost a must. If you don't have one, get one. (Directs that air where it needs to be)

Check the belt and pulley on the water pump. And while you're at it, how much tension does the clutch fan have. The more resistance, the better cooling affect of the fan.

These are my own top 4 things to check and do. Your situation may very but you can't go wrong with a good flush, new thermostat, shroud and water pump and fan inspection.

Dave.

PS. I have an Aluminum Radiator and it NEVER moved past the mid point while sitting in 95 degree Anaheim heat, while stuck in traffic, idling in stop and go traffic, Never. Something to think about.

Edited February 21, 2009 by Zs-ondabrain

[240Z-Fan]

Could it be a bad fan clutch that's causing the problem?

This is exactly my thought. If the clutch isn't looking up then it will run hot when stopped. When driving, it will have enough air flow to cool without the fan.

If it were the radiator you would have problems at higher loads, ie freeway.

With the engine cold, see if the fan spins easy. It should be stiff cold. If it is easy, the clutch is bad.

Al

Edited February 21, 2009 by 240Z-Fan

[DeesZ]

Carl Beck did a good response to the question about testing a fan clutch a while back in this forum. Here's a link to it. Thanks Carl!

http://www.classiczcars.com/forums/showthread.php?t=25817&highlight=cardboard+clutch+fan