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Hot Rods Flathead cooling

Discussion in 'The Hokey Ass Message Board' started by spqr67, Mar 22, 2014.

  1. Fordoors
    Joined: Oct 22, 2012
    Posts: 43


    I'm new to flatheads, so this might be a "known issue"...I recently installed a newly rebuilt flathead in my shoebox. Before it was dropped, I had the radiator refurbished and all the gauges in the dash gone through. Now that she's up and running, I can't get the operating temp anywhere close to the mid point. She consistently runs hot. I replaced both sensors as well.
    Any thoughts?


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  2. R Pope
    Joined: Jan 23, 2006
    Posts: 3,309

    R Pope

    Are the sensors the right ones? The one with two wire connections is a real gauge indicator,it grounds through the single wire sender. The single wire one opens contact when it reads hot and the needle goes straight to "Hot". I would get an infrared thermometer and see what it is really running at for temp.
  3. Super Streak
    Joined: Nov 22, 2011
    Posts: 257

    Super Streak
    from Florida

    Make sure the thermostats are out. Check that your running a 50/50 ratio of anti- freeze and water. Check that your timing is correct. Make sure your exhaust is not clogged. That the fan belt is tight. That your water pumps are good. Have you flushed your engine to make sure all the passages are cleared out. Flatheads can be a P.I.T. Ass when it comes to running hot.
  4. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,493


    I have found the temp gauges seem to read more hot then the motor acutually is,I built a 51 for my dad that the temp gauge read almost hot but a thermometer in the radiator said 180.

  5. kendall66
    Joined: Apr 3, 2011
    Posts: 96

    from iowa

    timing has to be dialed in. this is a must.
  6. s nichols
    Joined: Feb 7, 2012
    Posts: 7

    s nichols

    use 2 mechanical gauges ( one for each bank ) donot rely one original gauge for accurate readings--- make sure tune up is correct
  7. ginuine555
    Joined: Jun 17, 2006
    Posts: 104

    from louisiana

    Just remember not to let your wife know you are taking her cooking thermometer. I found it can make things a lot hotter around the house and the cooling down period can take much longer than a flattie . In fact don't even let her know you are returning it after you use it if they don't know you have it. Just stick it back in the drawer.
  8. junkyardjeff
    Joined: Jul 23, 2005
    Posts: 7,493


    Bought some from the tool man that comes to work so no need to take one from the kitchen.
  9. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,270

    Rusty O'Toole

    If you take out the thermostats you must use a washer to control flow. Old gauges can be inaccurate, they were kind of a cheap gauge to begin with. Best check it with another thermometer or gauge.
  10. prpmmp
    Joined: Dec 12, 2011
    Posts: 1,062


    Why would you need to take out the thermostats? If you have 180 stats in then the motor will stay at that temperature as long as your radiator is the right size and good. I have 180's in my 8BA and stays at that temperature in cold and hot weather. Pete
  11. tubman
    Joined: May 16, 2007
    Posts: 5,145


    I'll second the motion on an infrared thermometer. You can get one for about $40.00, and they are useful for a lot of things. I found out our oven was running 40 degrees less than the control knob was set. It made the little lady happy for a change.

    I used mine when it started to read higher than normal on the dash gauge, and found out it was still running 175-180. Checked out the sending unit with an ohmmeter and that was the problem. Changed the sending unit for a good one and all was right with the world. I then used it to check out the differences in temperatures on various locations on the engine, which was quite interesting

    I'll stick my nose out here and say that unless you have a modified engine build, any one who mentions no thermostats and/or washers is not giving good advice.
  12. neb-rivet
    Joined: Mar 25, 2012
    Posts: 69

    from Nebraska

    Leave the thermostats in. I went through all the "fixes" years ago on my 8BA and found it was not obvious but the block had a crack. The exhaust leaked into the water and pushed water out making me think it was overheating. You need to really know the water temp as others have described. I drove the car carefully for a year then replaced the block. Now I am back to no heat problems no matter the air temp, 50/50 antifreeze mix and no pressure on the radiator.
  13. Fordoors
    Joined: Oct 22, 2012
    Posts: 43


    Thanks for all the great suggestions. Think I'll pickup a therm as noted above to see what the actual temp is.
    Strange thing today...changed out the fluid and took her for a spin. She ran cold for about 10 minutes and then sprang up past the hot mark (higher than its ever been). Frustrating.
  14. uncle max
    Joined: Jan 19, 2006
    Posts: 905

    uncle max

    Burp the system... You could have an air blockage.
  15. 56shoebox
    Joined: Sep 14, 2011
    Posts: 1,106


    Drilling a small hole in the rim of each t-stat will eliminate air locks.
  16. Fordoors
    Joined: Oct 22, 2012
    Posts: 43


    Last question (maybe). I've replaced just about everything I can (fluids, wires, sender, thermostats w/1/8 hole drilled) and I still get goofy readings from my gauge. A quick reading from an IR therm confirms the motor is running at about 165. But the gauge goes to mid point, then straight past hot after about 10 minutes of idling. It's gotta be the gauge. That said, any tips on best way to repair the old gauge? I could install a new mechanical but I'm a fan of nostalgia and would prefer to keep the stock appearance.
  17. Untill you find a good gauge use a good mechcanical for now.

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