Running too HOT

[MakDiesel]

my '72 is still in the tuning stages but I can't leave it running long b/c it'll sit right between the 120 and 250 on the temp gauge but after driving it around in the parking lot to check the carbs ill leave it at idle for maybe 30 sec and then the needle skyrockets to 250 and I shut it off immediately.....Also I've checked the hose that runs from the thermostat and the radiator while it idles and the flow is very low or not at all....So far I've changed the thermostat and flushed the system.....i dunno whats blocking it or might be the pump....any of you have this problem?

[Royce]

Are you sure it is really heating up! If you shut off your engine with the water temp at 250 there would be water shooting out the overflow on your radiator. Maybe the flow is low because the thermostat is not open yet because it really isn't heating up!

Buy a confectioners(sp?) thermometer at the grocery store (that goes to 250+ degrees F. When the car is running, take off the radiator cap and put in the thermometer and see what temp the water in the radiator is. If it is less than the temperature required to open your thermostat than there you go.

It is common for an old water temp sending unit to fail and give you high readings.

Hope it helps!

[MakDiesel]

The first time I took it out on the road (ever) was yesterday. I had had hood release problems so it was without a hood for this particular run. While idling at a stoplight, I noticed small jets of water shooting out of the front of the car and landing on the fender, thus overheating at the overflow bottle.....after changing the thermostat, same result.....the one I replaced looked to be in good shape....I'll try the boiling water trick tomorrow to see if it was defective but it looks to me like there is something else amiss.

P.S. -- Is it safe to jus take the thermostat out completely, thus always having full flow? It's getting summer now so I won't be needing the heat.

[JEFF]

If you leave the thermostat out it may very well solve your over heating problem...... BUT it will be hiding the underlying problem. Your car should not be overheating. Is you coolant new? Is it mixed 50/50?And is it full? Is your fan belt adjusted properly? When your belt is at the right tension you should be able to flex the belt between the crank pully and the alternator about 1/2 to 5/8 of an inch by hand. Does your fan clutch work properly? Does your water pump drip coolant out the weep hole at the bottom of it? If it "weeps" replace it. If all of those things are correct then your cooling system may need a good cleaning. Most/all good autoparts stores will have a do-it-yourself kit to clean your system. It should be the kind made to "ungunk" the cooling passages.

- Jeff

[2ManyZs]

FWIW, be careful you don't keep overheating it, as the head will end up being warped.

Many things to check, radiator, water pump, etc...

Rnning without a thermostat usually ends up with the coolant passing through the radiator to fast to transfer the heat and it will end up running hot. Best to use some sort of restrictor or just a new thermostat in a lower temp, perhaps yours is a 180 that is sticking, you could try a 160 and see how things go.

Also, when you get it to the point you can let it idle without overheating and think you have the problem solved. You might be wise to do a compression check and leakdown test on all the cylinders to rule out a blown headgasket or warped head due to it being overheated in the first place.

[Royce]

I agree with 2manyZ's that a restrictor plate, not NASCAR style, in place of the thermostat is better than no thermostat at all. But this is typically only done in race cars as even with a restricter plate it can be hard to get the engine up to operating temperature if you are running a fan. And if all the metal parts aren't up to operating temperature they will wear more quickly. Best to solve the problem properly than to go with a bandaid fix, removing the thermostat, which might just mask one problem but create others. I think checking the thermostat in hot water is a good place to start.

[MakDiesel]

Replaced the thermo ($4) and it still climbs too high after a relatively short time....used the old thermo/boiling water test and it worked...so the old thermo was fine. I suspect either the fan clutch, water pump, or clogged heater core......after some investigating I noticed after it ran hot the radiator cap had virtually no pressure yet while removing the thermostat housing it was pressurized enough to spray/bubble antifreeze out b4 it cooled down....there is either a block or no/low flow or both....water pump isnt 'weeping' that I can tell...I'd notice too cuz my 280zx had a 'crying' water pump for a good month b4 I found the time to replace it instead of carry a gallon jug w/ me at all times. Top radiator hose still feels limp and empty at idle...dunno what's up or how to check the other suspects (pump, fan, core)

[MikeW]

Keep in mind that 240Z radiators were never quite up to the task in warm climates. When I bought mine years ago it also had a tendency to run hot (in the summer in Savannah). I pulled the radiator and took it to a radiator shop and had them redo the core (from 2 rows to 3 or 3 to 4, I can't remember). Not only did that add cooling capacity but it cleaned it out. The cooling fins get damaged and the tubes get squeezed and plugged over time. After that the temp needle was rock solid even while idling in hot weather. Having the car overheat is one way to quickly do a lot of damage so it's worth it to make sure the cooling system is functioning well.

[korg_geek]

I'd say MikeW's on to something there. My Z's radiator worked fine for a full year, until I decided to take it for a three-hour drive in 80 degree weather. Then I had a nice coolant storm over the hood. I'd suggest double checking to make sure how large your radiator ACTUALLY is, my 73 had a stock radiator in it but couldn't take temps over 75 for more than an hour or two before it overheated. All the lines were clear, thermostat worked fine, etc etc.

If all of that is true in your Z, taking your thermostat out should make matters worse. In that case, your radiator simply isn't big enough to chill your coolant, and it'll keep circulating hot water back through the system continually, even at high speeds when you have a heavy gust of air cooling it off. A shop would probably give you the option of swapping it out for a larger one or just cleaning your present one - get a new one. I'd say at least a 3-core. Its not that expensive and takes about 10-15 minutes to swap out.

As an added hint: if you have more than a couple of inches of room between your fan and your radiator, you probably don't have a very thick core. 2.4L engine might not sound like much to cool off, but with the tiny factory radiator that came installed, sometimes it doesn't do the trick!

[MakDiesel]

Called back to autozone to see what temp. the thermo was set at they had sold me....192 degrees! Looked at the one I pulled from the 240 to begin with.....192 friggin degrees! No wonder it ran so high....it only cut on a mere 28 degrees before I ran out of gauge! Anyway, took the hot one back for a twice as expensive but much more sensible one....and the lowest they had 160 degree...should be in tomorra.....also looked into getting a 4 row radiator....cant find one for a 240z unless I get the big bad Motorsport version...that'll set me back $300....Anyone know of cheaper alternatives yet still 4-row cooling capacity? Also will be pulling the clutch fan apart to clean/regrease it to stop the seizing...all in good time to get her tagged and on the road w/o worry in 95+ degree heat :classic:

[Royce]

This brings up an interesting point. I have always wondered why go with a 160 degree thermostat???

You want the engine to warm up all the way and operating water temp for a L6 is about 180 degrees. I have heard that they run well at 190 as well.

With a 160 degree thermostat I would think that in the summer, once your thermostat opens it is not likely to close and the water won't get a chance to sit in the radiator and cool. During the winter, your engine may never reach operating temperature. I would think a 190 thermostat would be better, especially if you are going to go with a 4 row radiator. If your car continues to overheat because it is not because it has a 190 degree thermostat.

A general rule on overheating I have always heard is... I you overheat at crusing speed it is most likely your radiator. If the engine is overheating while idleing than it is the fan. Of course this assumes the rest of the cooling system is functional. But these are the two most common starting points.

What do you think gang?

[Daniel]

I have a 4 row rad. and run a 190 thermo.I have had this setup for years,no trouble,the engine loves it.I do have the flex fan and therefore have no fan clutch.My stock rad. was made into a 4 row at the local shop.I think perhaps your fan clutch is bad/weak.I think I read that when the car is at normal temp (and of course OFF!):stupid: You should not be able to turn the fan very easily by hand.That means its engaged.The other thing is perhaps an air bubble is not allowing you to put in the proper amount of coolant.I haven't had that trouble with my 240 but,I have a jeep that needs to "burp" two or three times after you refill the thing from empty.Also make sure the channels between the radiator tubes are clean.I've seen mud/grass block the flow although those were off road cars.I have also seen a thermostat installed upside down cause trouble.I'm not sure if that could be done on a z.Timing too far advanced I believe can also cause temp issues.