Late 1961, 2x4, 245hp, 4spd

Temperature has been fine until recently. Had a water pump leak out of the weep hole and replaced the pump. Temp ran fine dead on 180. Several weeks later, temp starts to jump. Up to the high line and a little past ~200? And yes it is on hot days, but I was running fine on hot days just a week or 2 ago. If I run the heater it drops some but when I turn off the heater it jumps right back up. I replaced the thermostat which was a 160 with a 180 as I believe it makes no difference since the engine should run around 180. I checked the new t-stat in hot water before I put it in and it starts to open at ~178

This didn't help. Temp still runs high. Checked the connection on the sender. This was fine. Coolant level in expansion tank 1/2 full when cold.

Now here is the thing that just doesn't make sense...as I pull into the garage and stop, the temp reads ~200-210 or so. With my foot on the brake and the transmission in 1st I ease out the clutch and load the engine a little bit and the temperature immediately DROPS!?!?! I unload the clutch and it goes back up immediately. Tried again and same thing. WTF is this???

Any inputs on solving this issue would be welcome

 

If you check with IR gun you'll see what real temp is. You know it can't really be changing that quickly when you step on the clutch

 

I know this but I am trying to figure out why it is happening.

 

The gauge has 12 volts on one side the other side goes up to the sensor and reads resistance to ground with change in temperature. So the only thing that makes sense with the clutch is if the pedal is bumping against a wire and causing a change in resistance in a connection or a fluctuation in the 12 volt supply.

 

Its not like the needle jumps...its smooth down and back. I will try to take a video of it and post it. In the meantime gotta figure out why it is running high in the first place...

 

Check to make sure the connectors are good (clean them while you are checking) with the temperature sending unit and behind the gauge. Sounds like something is slightly loose.

 

As I said earlier, you need to verify that it's actually high and not just the needle moving

 

Totally different troubleshooting if it's a temperature issue or a wiring issue

 

Check your motor to frame ground. I suspect loading the engine is torquing it enough to make the ground better, or worse. I can't recall if dead short to ground pegs the water temp gauge or the other way around..

Doug

 

Also check the wiring harness ground wire that connects to the valve cover, or coil hold down bolt, or where ever.

This sounds like a classic feedback issue with a bad ground, somewhere.

Doug