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Hello, I'm currently having a VERY bad overheating problem. I drive a 1985 300ZX, non turbo.

I'm driving the car, and I usually run dead in the middle on the temperature gauge, recently (sorry can't remember how long ago, maybe 5 days ago) I started to overheat. Now it's VERY hot here in Nevada, and I just started having this problem recently.

The car will be fine in the morning, usually, and then towards noon when I have to take it out it gets very hot, it maxes out on the temperature gauge, and I start to get steam through my vents, as if my heater core was broken. I used to be ok if I didn't run my AC, however now it overheats withing minutes of being turned on. I've not tested it sitting in the driveway, but running it shoots up to above 270 in a matter of 5 minutes.

I recently replaced the thermostat on it, to no avail, and now the only other problems I can think of it is either a faulty water pump, the fan cinch is broken, the radiator has a blockage, or the water pump drivebelt is not spinning. The car is getting so hot that the 50/50 in the resivoir is boiling, and the car takes hours to cool down.

Can anyone give me any ideas as to what it may be, or any fixes I'll most likely want to try before I go ripping out the water pump? Thanks.

Mike
 

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Sounds like the heater core went bad on it. My old 2+2 did that, and it turned out to be the heater core. I just bypassed it so that I didnt have to switch the core out. IMO, if the core is leaking, it is the same as the cooling system leaking, so the proper pressure doesnt build up and the system doesnt cool down like it should...
 

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Blown head gasket? Exhaust into coolant leak?


If you have questions about coolant loss, you need to do the following:

* Check your rad cap for leaks. Replace it?

* Check the gasket UNDER the thing that the cap fits onto...a brass part.

* Check the condition of the small brass pipe (on the brass thing) that connects to the hose going to your coolant overflow tank...it can corrode seriously. I soldered a soft copper tube over mine and reconnected the rubber hose.

* Be sure the hose to the coolant tank isn't blocked and also check the inlet in the bottom of the tank...this can happen if stop leak has been used. Remove the tank and clean it & the hose out with water pressure.

* When done....use a permanent marker to mark your COLD COOLANT LEVEL when the car has sat overnight, so you can keep close track of any coolant loss cold....before starting it up.

* If you rule out coolant loss from the cap to the coolant tank, then you can tell if there is a loss elsewhere...and you will have an accurate idea of HOW MUCH COOLANT YOU ARE LOSING.

* You can use a flashlight to check for leaks around the waterpump, and top front of engine, & back between the valve covers. Also check heater hoses and radiator hoses and the radiator. Best bet is to do this just as the engine temp first gets near the center area on the temp gauge, when it's not so hot that the coolant totally vaporizes...you can still see small leaks. A flashlight allows you to concentrate on a small area.

* Symptoms of a blown head gasket: Start car cold with cap off and coolant visible...look for a stream of bubbles...if you see any, this is probably an exhaust into coolant leak. If you get serious bubbling in the resevoir when the car is hot and it overheats, this pretty much confirms it. I would replace the thermostat first & "burp" it, before removing the heads though.
 

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I do not know the answer to your problem with the information given; however, in a climate such as Nevada, (I am assuming Desert with, this year, low humidity) if you are getting condensation on the interior of the vehicle, it would almost have to be the heater core. My suggestion would be to bypass the heater core in the engine compartment immediately!

The biggest reason for this is the vaporized water escaping from the heater core will cause poblems with electrical connections (ie, Digital Dash, Security, and ever other system that is connected underneath the dash. As you know, there is not a lot of work space anywhere on a Z., which makes searching out these electrical problems created by unwanted water in unwanted places.
 
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