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green hornet 01-28-2013 12:27 AM

cooling system does not warm up
The cooling system in my 96 nissan 4cyl. pickup never warms up. Temp guage stays at bottom. Figuring a stuck open thermostat, I changed it for a used one that tested good by itself in a hot water test. When I drove it the first time after the replacement, the temp went to the top within 10 minutes of driving (to work). Parked it, came back a few hours later and started the engine while eating lunch. After about 15 to 20 minutes of idling, the temp reach a little less than half the guage (about 30 degrees downward from horizontal) turned off engine to return to work. 3-4 hours later I drove about 10 - 15 minutes with NO movement of the guage and no heat! It's now acting the same way it did before changing the thermostat. I tested the thermostat which I took out (in a container of heated water) and it also tested ok. Unlike the reported cases of air in the system, my temp guage does not go up. What can cause a thermostat to stick open even when it tests ok? Is it possible that I have installed the thermostat incorrectly (backwards). I installed the thermostat with the 'stem' end, the part with the springs, toward the engine (away from the connector that connects to the hose).
Could I have two thermostats that test ok, but don't work when installed? In the case when the thermostat was first installed, it appeared to be stuck shut, then opened up then stuck open, never to return to closed. What am I missing? I don't want to replace the thermostat again if it is not the problem. I don't believe in diagnosing problems by replacing parts until the problem 'goes away' without knowing why. Help, its cold and I and my engine don't like it.

Cusser 01-28-2013 04:42 AM

My suggestions: use a Nissan or Stant brand thermostat, and in the heat range of the specifications, NOT a lower temperature optional thermostat. And bleed out ALL the air of the cooling system. Run with cap off and front end higher, check/add coolant after each trip (after radiator has cooled - safety) for a week. Use the cooling system air bleed valve if your truck has one (my '98 4-cylinder Frontier has one).

If the truck is new-to-you or has done this every winter (assuming your winter climate is cold), maybe block off half the radiator with a sheet of cardboard for the winter.

If the truck is something you have history with, and this is the first winter you've experienced this, again suspect thermostat and air in system.

Gregg the G 02-15-2013 03:43 PM

Be careful with putting cardboard in front of the rad. if you have an automatic trans. you could over heat the tranny.

smj999smj 02-19-2013 12:52 AM

I wouldn't even recommend the Stant thermostat. Best to stick with a genuine Nissan thermostat. These engines are known for trapping air. There is a bleeder at the front, top of the intake manifold. Turn the heater to "max heat" and jack up the front end to help purge the air out. A Lisle Spill-free funnel kit works great for purging the air out!

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