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engine overheating; no A/C or cabin heat

16 August 2007
My 1995 nsxt suddenly started overheating & providing no A/C or cabin heat. Has anyone experienced
a similar situation or can suggest its cause?
Would appreciate any help before taking to a dealership.....
Archie, Ontario Canada
Not a lot of information to go on.

Has it actually overheated (ejected coolant from the coolant tank) or is the gauge just indicating that it is running hot? If the gauge is just indicating hot, do you know that you are actually running hot? When the engine is cold, turn the ignition switch on and check the temperature gauge. Is it reading cold? A short circuit to ground on the sender wiring will cause the gauge to read high. Check the sender resistance to confirm that it is in spec. The gauges can also go out of spec. The service manual has test procedures.

Were the radiator fans running? The rad fans are off of a different temperature sensor than the gauge. If the rad fans are not running then the engine may not be overheating.

Does the radiator feel hot? If you have confirmed that the temperature gauge is operating correctly; but, the radiator was not heating up then I would be inclined to think that the thermostat has failed shut. You could also have a coolant pump failure; but, I have never heard of a complete failure of an NSX coolant pump. I can't remember the exact location of the rad fan temperature sensor; but, I believe that it is in the engine coolant loop and should not be affected by the thermostat operation. If the rad fans start up; but, the radiator remains cool that points a finger at the thermostat.

The lack of interior heat is a mystery. My car is in storage so I can't check the heater hose path; but, I thought that the heater loop was before the thermostat which should allow coolant to flow through the heater core and provide heat if the engine is overheating. I could be wrong on that.

Have you checked the coolant level in the expansion tank? All of the preceding assumes your coolant levels are close to normal. If something happened and you ejected a bunch of coolant then a lot of the preceding may be irrelevant. If something caused you to dump a significant amount of coolant you may want to have it towed to the dealership because there may be peripheral damage. A cooling system pressure check and chemical tests for coolant in the oil or combustion gasses in the coolant may be in order.
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Step 1 is to check the coolant level in the expansion tank. If there isn't any, there's your problem. If there is coolant at the normal level, you could consider (when the car is cold) opening the pressure cap and then cracking the bleed valve on the heater loop in the frunk area behind the spare tire. It's possibe you've had a leak and the system is vapor locked. As with Old Guy, I can't remember 100% if the heater loop is down-stream of the thermostat, but my knee jerk is that it probably is (just from experience driving the car in the winter). So if the coolant is full and you don't get any big bubbles when you crack the bleeder then I'd move on to the thermostat. If it's the thermostat it's a cheap part and replacing it isn't that bad, but re-filling and bleeding the system can be a little tricky. Good luck either way! Definitely don't drive the thing if it's overheating.