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    Results 1 to 4 of 4
    1. #1
      Join Date
      Feb 2010
      Location
      El Segundo, CA
      Posts
      268
      Country Flag: United States

      Ford Racing 347 Oscillating Coolant Temp

      Folks - I have a Ford Racing 347JR crate engine installed in my pro-touring type 56 F100.

      I recently got my coolant temp gauge working, and installed a thermostat (the original builder negelected to install one).

      The thermostat is 195°F as recommended by Ford Racing.

      I find that my coolant temp oscillates between 195 and say 215 or 220. Back and forth, back and forth. I have a SPAL fan controller, which reads a seperate dedicated temp sensor, and it also slowly comes on, goes to max speed, then slows down again as the temp goes down, also over and over.

      Maybe this is no big deal, but it does seem odd. I would think that the thermostat should open just far enough to keep the engine at a regulated temperature. But it seems to act more like an on-off swtich. Letting the coolant temp rise and then opening all of a sudden to allow a rush of cold coolant from the radiator into the engine, cooling it back down, closing the thermostat and so on.

      I considered it could be my coolant guage misbehaving in some weird way, but the fan seems to follow the same pattern and using a seperate sensor on the opposide side of the intake manifold.

      Just wondering what other folks experience is with this.

      Thanks,

      Gustave

    2. #2
      Join Date
      Feb 2006
      Posts
      478
      Do you have a coolant bypass installed? That is a little hose from the water neck to the water pump on a ford I think. That lets the coolant circulate and heat up evenly. Otherwise, the water in the heads will get super hot before the water at the thermostat heats up enough to open it. Then all the cold water in the radiator and block will come rushing through and close it back, and so on until it all mixes up good.
      Alex Godsey
      Somerset, KY
      Pro Touring 67 GTO
      461 Pontiac Power

    3. #3
      Join Date
      Feb 2010
      Location
      El Segundo, CA
      Posts
      268
      Country Flag: United States
      Quote Originally Posted by gearbanger View Post
      Do you have a coolant bypass installed? That is a little hose from the water neck to the water pump on a ford I think. That lets the coolant circulate and heat up evenly. Otherwise, the water in the heads will get super hot before the water at the thermostat heats up enough to open it. Then all the cold water in the radiator and block will come rushing through and close it back, and so on until it all mixes up good.
      Gearbanger, I think you nailed it. I'd given up getting a response here and just checked and saw your post. I do not have the heater bypass installed. I do not have a heater installed and did not realize the function of this bypass hose, so did not bother to install one. But the behavior you describe is exactly what I am experiencing. Thank you very much!

    4. #4
      Join Date
      Feb 2010
      Location
      El Segundo, CA
      Posts
      268
      Country Flag: United States
      Finally got the heater bypass hose installed and indeed that did solve the fluctuation issue. The coolant temp is now rock steady. Lesson for me, with no thermostat you can ignore the bypass, but with a thermostat you definitely need the bypass!







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