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Thread: Low Engine Temp

  1. #1
    Building Boost MSheff's Avatar
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    Feb 2013
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    Carl Junction, MO
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    Low Engine Temp

    Working on my '84. This started by having no heat in the cabin. Thought it was a blocked heater core, so unhooked the lines going to the heater core and flushed with a garden hose. Got lots of gunk out of it and was flowing good. Got so much gunk, I changed the coolant ran some flush through it and it all seems good. Went ahead and changed the thermostat (192 degree). Still no heat and temp gauge never got to the N on the gauge while driving. Found a leak around the thermostat housing, replaced housing (old one was far from a flat face). Also, put in a 195 degree thermostat. lifted front of car opened radiator cap and let it run for a good while to let out any air. Let it cool, made sure coolant level was full and put on radiator cap. Started it and ran at 2000 rpm for a while and watched the temp gauge raise up to the A. Radiator fan kicked on. Temperatures taken with infrared temp gauge:

    Thermostat Housing 195
    Upper Hose 197
    Lower Hose 184
    Heater Hose #1 198
    Heater Hose #2 165
    Outside Temp 42

    I didn't put a thermometer on heater air, but felt pretty warm, about what I would expect. All was good so took off on a drive. Temperature gauge went down to the left of the N and stayed there. Heater air moved cooler as would be commensurate with the dash temp gauge.

    And by the way, the temp gauge has always been low. I thought just a bad gauge and a clogged heater core.

    The car will just not warm up on the road. Seems like a stuck open thermostat, but this is the 3rd one I have had on it with same results. Could be air pocket in the system, but have done all I know to remove any air.

    Looking for ideas...

  2. #2
    Some Boost
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    Jun 2012
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    Acworth, GA
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    Do you have a stock radiator? Have you pressure tested the system after all of the changes? Test your radiator cap to makes sure it can hold 16 psi pressure. Do you have an AC condenser installed?

    My first guess would be the the cooling system is not holding pressure. My second guess would be a leak in the vacuum system and your heater door is closing and you are getting vent air mixing with the warm air.

  3. #3
    Building Boost MSheff's Avatar
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    I do have a stock radiator. Haven't pressure checked and don't know about my radiator cap. I will check. Curious, if my system isn't holding pressure, why would that cause low temp?

    I don't think I have a blend door issue, just because when I look at the temp gauge, then reach down and feel the air coming from the heater it is about what I would expect.

  4. #4
    Some Boost
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    May 2012
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    San Mateo, CA
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    The engine does not need to be fully hot to get good heat. It’s pretty common to get a lot of crud in the heater core. A word of warning, when I find crude and do several chemical flushes, the water pump will start to leak shortly after.

    the heat blend door is mechanical and is right behind the glove box on ac cars.

    Put your hand on the heater core pipes. One will start out cooler than the other but both will end up getting hot. Maybe 10 minutes.

  5. #5
    Some Boost
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    Jun 2012
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    I don't know the thermodynamics of why the system will run cooler if not pressurized, but from my personal experience that is what happens until such time as you loose to much fluid for the system to function correctly.

    A trip to Harbor Freight to get one of the IR temp gauges may be helpful in tracking down your issue.

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