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Thread Title:

Isuzu NPR Diesel running hot

Created On Friday July 04, 2008 14:06 Diesel Talk
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Note Friday July 04, 2008 14:06 View thread in raw text format
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I have a 1993 Isuzu NPR Diesel Box Truck, it has recently started running hotter than normal. The radiator overflow has been replaced due to a hole was found in it, the thermostat was removed yet the truck still runs hotter than normal. While the truck is being drove down the road the temp starts to rise and stays high, however when the truck comes to a stop in traffic or at a light the temp starts to drop according to the temp needle. Any help would be great. Thanks
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Note Friday July 04, 2008 16:38 View thread in raw text format
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The first thing that comes to mind is maybe the fan clutch in not operating properly or falling behind at higher speeds where the engine is running at a higher RPM (and where the cooling system is needed most importantly). I would say check the fan clutch and how is the condition of the radiator? Is it the original radiator and has the coolant been flushed at the right intervals over its operating life? The radiator may be plugged up if it's old. When was the last time the water pump was replaced or is it the original? Another thing you could do is pressure test the cooling system if you have the pressure testing tool with the hand pump and built in pressure guage. Pressure test it to the max pressure measured in PSI that's stated on the radiator cap to see if you have any coolant leaks in your engine bay. Also, did you test the existing thermostat to see if it is sticking and not opening at the right temperature? The best test to do on it would be to put it in a stove pot with the water level higher then the thermostat's height measurement and heat it up to see if the thermostat opens at its recommended temperature. If it doesn't then the thermostat plainly needs to be replaced with a new unit. I'd suggest going to an Isuzu commercial dealership to buy that part at least if it's bad. Being that you have a 1993 NPR it probably won't be too bad as far as a price on a new replacement thermostat. And I wouldn't recommend running the engine too long without a thermostat as it's not going to solve or make finding the problem come about. Good luck and let us know what the issue is.

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