Best temperature for a running flathead

H

hfh

New member
I'm running a flathead with 180 degree thermostats and an electric fan that starts when the coolant temperature in the radiator reaches 185 degrees. At a traffic light on a hot day my gauge climbs to 190 or 195. When I am moving on a hot day the temperature ranges between 180 and 190, depending on whether the road is flat or hilly. Is there an optimum temperature? Is it 180 or is 190 or is 195 alright? Should I make it so that the fan starts at a lower temperature? Thanks for your thoughts.
 
Remember it just a gauge as to temperature so accuracy may vary. Sounds good to me . As long its not making steam you should be on the right side of too hot.
I am presuming your fan cools it down enough to turn off?
What radiator cap are you using?
 
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The hotter the better, but there are other limiting factors. I would want 185 to 195. Like Talkwrench posted higher would be better, but without a pressurized system it can be problematic. There are also issues like under hood temps, etc. Like everything it is a trade off.
 
JSeery said:
The hotter the better, but there are other limiting factors. I would want 185 to 195. Like Talkwrench posted higher would be better, but without a pressurized system it can be problematic. There are also issues like under hood temps, etc. Like everything it is a trade off.
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Why is higher better. 180 is perfect if you have a fan that will hold it
at 180 but that's tricky. My 39 P/U will hold 180 all day long at a fast
idle at over 100 degree outside temperatures. These 32 to 48 engines
were not designed to run over 200 moving down the road. This picture
is a commercial fan on a 35 roadster I gave to one of my son's. He
drives it in hot summer in the country and small towns and it never
gets hot. {200} I couldn't find the 39 P/U fan picture but I just posted
it about a week ago. G.M.
 

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Thank you all for your comments. I have a 7 lb cap. The fan is on when needed and off when not needed. I like to drive it on country roads here in rural Massachusetts. I am 10 miles from the nearest traffic light.
 
Have a similar set-up in my '52 F1. Here in Arizona even when it over 100 out I can run my a/c and a long stop light will bring my temp gauges up to about 200, then the go back down to 190-195 after a couple of blocks. I am running 50/50 coolant and have never had it boil over on me. Knock on wood as it's suppose to be 114 here today.
 
hfh said:
Thank you all for your comments. I have a 7 lb cap. The fan is on when needed and off when not needed. I like to drive it on country roads here in rural Massachusetts. I am 10 miles from the nearest traffic light.
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I would switch to a 4 lb cap which is all you need. I did heat tests here
in SW Florida for a year on the same 40 mile lunch trip on a 4 lane
highway for most of the driving. Wind speed and direction have a lot
to do with cooling. Going into the wind can cool the engine 15 to 20
degrees. G.M.
 
I ran my '39 pickup to 70 mph this past weekend on a state highway. Outside temperature was in the mid 80's and at 70 mph my temp gauge was at 180 degrees.
 
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