oil pressure fluctuating

[teamsmith]

I've taken my truck out on the road for the first time following the engine swap. Renix computer, 98 4.0. I'm reusing the renix oil pressure sender. When I start the truck, oil pressure is about 60 and settles to about 50 at idle. However, it seems to fluctuate based on pushing the gas pedal. I can make the needle move by revving it. Also,when I'm coasting downhill in gear the needle floats up to the max. It never drops below 40 (center of dial). Also, the needle movement seems to be a little 'floaty' like it moves fairly erratically instead of gradually. Could something be wrong with my sender? It just seems odd that it's bouncing around like that. I have new oil in the engine.  

 

Any thoughts? 

[Jeep Driver]

The 'bouncing' part tells me that you have a bad connection, check your wire/connector or replace your sender or check ground to gauge cluster. Or your sender is not making a clean contact with the block. I would run a fine bead of thread sealant about 3-4 threads up from the end of the sender, that way the sender can make contact with the block and I can still get some sealant on upper portion of the thread.

 

As for the fluctuation- it should........increase RPM and increase pressure. Mine rests around 35-40 at idle and I can increase to about 50 by tapping the throttle. (whether gauge is accurate......another matter)

[teamsmith]

thanks. I'll check the wiring. Very well could be that we snagged it during the install. 

[Bobolink]

Agree it sounds like the single wire insulation is damaged. Any grounding of the wire will peg the gauge to the high side. 

[1987Comanche]

 I don't think you have anything to worry about but, for piece of mind, I'd put a mechanical gauge on it to verify.  Get the engine good & hot, then hook up the gauge. 10psi per 1,000 rpm is a good rule of thumb.  a 4.0 in good shape should be around 15psi at hot idle. Oil pressure should jump to around 30-35 as soon as you rev it up.