Oil Pressure non-gauge: revisited...

Kit Sullivan

Registered User
OK, so I understand that the factory gauge is really just an 'on-off' idiot light masquerdaing as a gauge.
How come mine acts like it does? At first cold start-up the needle moves to the 'M', and will drop to the about the 'R' as soon as the temp needle finds its normal place (exactly half-way on the gauge).
Once the engine has been running for a while and in traffic and all fully warmed up, the needle sits slightly above the 'N', and at a 70-mph cruise it rides right on the 'O'.
If it is only ON or OFF, why does it move around like this?

The car does not have the modification and still has the original oil sender in place. (looks just like the temp sender)
 
Pretty obvious that the electrical resistance in the circuit is changing with temperature. There is a resistor in that circuit that may be heating as temps change or the contacts inside the oil pressure sender are being affected.

The lower the resistance in the circuit the more current flow and the greater the needle deflection on the guage.
 
Yeah, I agree with that...I was just wondering why it is happening. Wasn't the whole reason Ford 'rigged' the system this way is so it won't fluctuate like this?
 
Yes...it was. But then again...your car is AT LEAST 11 years old. I would suspect the problem lies in the oil pressure sender. Mine on one of the cars was fine for 14 years then started wavering around finally picking up the check Guage Light until I replaced it.
 
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