Perkins 4108 senders part deux

[BigAl.NZ]

Originally Posted by waterman46

Nice pix! Wish my motor was half that clean.

Since senders 2 and 3 are in parallel, those must be your oil pressure and water temperature alarms. Its possible the 3 wire sender contains both the oil temperature switch and the oil temperature gauge sender. Disconnect one by one and observe results.

As for IR measurement, I would not be surprised to see a few degrees difference (though 10 is kinda high) between the internal temperature of the oil or water, and an IR meter measurement on the outside of the engine - maybe also affected by the surface condition where you are measuring. I would first calibrate the IR meter by placing a piece of metal in a pot of boiling water such that just a small part of it is sticking up into air, and measure that with your IR meter. And see if different metal surfaces cause different temperature readings. I have used IR meters on electrical components and always found the readings to be somewhat flaky.

I think I found the issue and have posted this for the benefit of anyone else. I was chasing ghosts....the gauge is reading correctly (and the engine is running a bit hot).

I confirmed the gauge is correct by putting the sender in the water and using a thermocouple (not IR gun) to test water was at 100.

I then used the thermo couple to test the temperature on the body of the sender (which was out of the water). It was a whole 10deg lower than the water temp.

So when I was using the IR gun on the body of the sender in the motor it was also a whole 10deg lower.

Moral of the story is that the body of the engine (including the sender) can be up to 10deg cooler than the coolant temp being measured.

Now I need to check the various other things to see why running hot.

Cheers

AG