Fluctuating Coolant Temp
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Senior User
Joined: Sep 2009
Posts: 289
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From: Van Nuys, CA
Fluctuating Coolant Temp
Folks - I have a Ford Racing 347JR crate engine installed in my 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
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
Lead Driver
Joined: Oct 1999
Posts: 6,765
Likes: 547
From: Kalispell, MT
Thermostats can be bad out of the box - you might try a different brand. Above 195 or so (its approximate) the t-stat should stay wide open.
Unless your fan setup is cooling it below 195 - where it should start closing.
You could check it in a pan of water with a thermometer to see what it's actually doing.
Unless your fan setup is cooling it below 195 - where it should start closing.
You could check it in a pan of water with a thermometer to see what it's actually doing.
Thread Starter
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Senior User
Joined: Sep 2009
Posts: 289
Likes: 3
From: Van Nuys, CA
Thermostats can be bad out of the box - you might try a different brand. Above 195 or so (its approximate) the t-stat should stay wide open.
Unless your fan setup is cooling it below 195 - where it should start closing.
You could check it in a pan of water with a thermometer to see what it's actually doing.
Unless your fan setup is cooling it below 195 - where it should start closing.
You could check it in a pan of water with a thermometer to see what it's actually doing.
I've considered I might have the fan coming on too soon, and sort of fighting the thermostat. I can reprogram it to come on at a higher temp.
g
Fleet Mechanic
Joined: Aug 2010
Posts: 1,994
Likes: 3
From: Morgan Hill, CA
Do you have a good digital thermometer? Maybe you should verify that the temp is actually swinging 20 to 25 degrees. It could be that your gage is overly sensitive in that range.
You could try measuring the temp of the outside of the radiator....right at the top hose connection. The metal will be a little different than the coolant inside, but it'll be close to the coolant temp inside. Any changes in temp will show up.
You could try measuring the temp of the outside of the radiator....right at the top hose connection. The metal will be a little different than the coolant inside, but it'll be close to the coolant temp inside. Any changes in temp will show up.
Thread Starter
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Senior User
Joined: Sep 2009
Posts: 289
Likes: 3
From: Van Nuys, CA
Do you have a good digital thermometer? Maybe you should verify that the temp is actually swinging 20 to 25 degrees. It could be that your gage is overly sensitive in that range.
You could try measuring the temp of the outside of the radiator....right at the top hose connection. The metal will be a little different than the coolant inside, but it'll be close to the coolant temp inside. Any changes in temp will show up.
You could try measuring the temp of the outside of the radiator....right at the top hose connection. The metal will be a little different than the coolant inside, but it'll be close to the coolant temp inside. Any changes in temp will show up.
Gustave
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