Cooling Question

[78 280zcar]

Well today I took the thermostat out and backflushed the radiator and the block and left the thermostat out because it was overheating, after I had done that car was running too cool, where does your guys gauge get up to when you are running the car at night, mine gets like a fourth of an inch before the middle of the gauge, is this good for the car to run this cool or is it only because I was running it at night, during the day (90 degree weather) it takes a while to get there but it goes to the middle, and should I put a thermostat back in it. I tested the coolant and water mixture with a tester and it is fine it is even below the line to where it is suppose to be.

I kinda like it because when I bought the car about two years ago it would always overheat and there was no thermostat in it. So I put one in it and it still overheated. Thanks in advance for any suggestions

[Bambikiller240]

Your car should have the Thermostat installed. The engine was designed to operate at a constant temperature and this cannot be acheieved with it missing.

First in your post you say the engine was overheating, then you describe the needle position as "a fourth of an inch before the middle of the gauge" which in a 240Z (and probably in a 280Z) is nowhere near "overheating", you need to clarify what is going on.

Gauges are notoriously inaccurate and readings at "a fourth of an inch before the middle of the gauge" will vary from car to car.

You need to buy a candy or cooking Thermometer which you can place in the radiator and observe it's readings as to when (what temperature) the thermostat opens, so you can tell if it is operating correctly and opening at the correct temperature. Also you can then compare it's reading to the position of the needle of your car's Temperature guage.

All of this is done while the car is standing still at idle (not driving it).

Either way, your engine needs the Thermostat installed in order to operate correctly. If it is overheating with a properly functioning Thermostat installed, you have other problems to deal with, and removing the T-Stat will not remedy them. Even if you back flushed the radiator it could still be plugged with crap, you could have a radiator hose that is collapsing while you drive and stopping the flow of coolant throught the system, you could have a bad radiator cap that doesn't seal properly or hold/maintain proper pressure, you could have a a failing water pump, or you could have a head gasket leak,

[sblake01]

Middle of the guage on a hot day is normal for a 78. That's where mine runs with the a/c on. I would replace the thermostat with a NISSAN thermostat rather than a Stant or whatever you get the local chain autoparts stores. We've discussed this in other threads. The Nissan thermostat has a larger opening than the others. If your car overheats only when you have a thermostat installed then either the thermostat is bad or it too high a temperature. Get a Nissan 180 degree thermostat

[ZmeFly]

In short VERIFY VERIFY VERIFY!! before you do anything.

A good meat thermometer in the radiator will tell you where you are as far as how hot your getting.

Never ever run without a T stat, just waiting for bad things to happen there.

[78 280zcar]

I have installed a thermostat, (180 degree thermostat), I put a new radiator cap on it. My car does not overheat when it is idling, I can let the car idle for a half an hour without it overheating ithe gauge stays right in the middle. When I take it on the freeway at around 70 MPH is when I start having problems, the gauge will go past the middle almost 1/4 of an inch before the 250 mark on the gauge. Any suggestions would be very helpful. Thanks

[Bambikiller240]

Next step is to examine the fan clutch for signs of the oil having leaked out rendering the fan useless. Also have your radiator checked. It could be plugged up with crap preventing full flow of coolant. After that I'd have the engine checked for signs of a blown head gasket. (most radiator shops can do that for you) Next (for me) would be to replace the water pump.

Slowly you go, step by step, inch by inch, it's a preocess of elimination.

PS 1/4" past the middle of the guage doesn't seem that terribly high, especially given the inaccuaracies of these gauges. You might want to think about the meat or candy thermometer suggested by several of us earlier. Run the car on the freeway to get it up to temp, CAREFULLY release the pressure from the radiator cap (assuming your cap has a lever to do this) then stick in the thermometer and see what it is reading in degrees F..

[mdbrandy]

I just got over my overheating problem on my '78 by replacing the fan clutch. However, my problem was opposite from yours - I could not idle for any length of time after the engine was up to temp without the temperature quickly rising. Getting the car moving (with air moving through the radiator) brought the temp back down. New fan clutch was the ticket.

For your problem, I don't know. My fan clutch was freewheeling, and thus not cooling enough. If yours is locked up instead, could it be fine at low speed, and putting extra stress on the motor/water pump at higher RPM, causing higher temps? Seems like a SWAG, but....

Since your problem is occurring at higher speeds, seems like it should not be a problem with moving air through the radiator (is the radiator clean outside?), so it has to be with moving hot coolant through the radiator. Thus, thermostat, blocked radiator, bad water pump, etc. are reasonable things to look at.

My guage is now pretty much rock solid right in the center.

[gundee]

I had the exact same condition. I did all the above suggestions and still ran hot on highway only.

I finally pulled radiator and took to rad. shop. He called me back and said it was so plugged it was beyond being cleaned.

They recored it (tripple) and temp. has been perfect ever since.

That happened when mine was 26 yrs old, same as yours.

[78 280zcar]

I have a new thermal fan clutch on it and a 1 year old water pump on it so I dont think it could be those, I checked to see if the radiator was pumping water when the engine was running and it was. grayghost, what did you do did you get a new radiator. Thanks for the help guys, I am kinda stumped on this one, I've been trying to fix it for the past 9 months or so. Also should I check to see if the front of the radiator is clear of debris.

[78 280zcar]

Does anyone know anything about the "water temperature thermal transmitter", it says in the book to test it disconnect the lead from it and connect the lead to a good ground and turn the ignition to "on" and if the temperature needle goes all the way to hot then the transmitter is bad. Well I did that and the needle went all the way to hot. Has anyone else tested this and what were your results, thanks.

[Bambikiller240]

Originally posted by 78 280zcar

............. I checked to see if the radiator was pumping water when the engine was running and it was............

Respectfully submit that no one can tell if the radiator is "pumping water". The water pump pumps it, not the radiator. You also cannot tell by looking at a radiator if it is "flowing" coolant sufficiently (unless it is COMPLETELY plugged up which would be very unlikely). This is something that needs to be checked by a Radiator shop.

[78 280zcar]

after the car is warmed up you can see it flow inside of the radiator cap. Any suggestions on the thermal transmitter?