High oil pressure

[Warmi]

A few days ago I noticed that during startup ( around 60 F ) my oil pressure went up to 90 or so PSI .. it seemed to vary with throttle settings ( higher RPM = higher pressure ).
Within 10-20 seconds it came down to what I consider normal range for my engine ( < 60 PSI ) and then was fine going forward. I stopped the engine, checked everything and could find anything and on the next startup and subsequent flight it was just fine ( upper 30s low 40s)
Well, today it happened again, this time went up above 100 and it varied with engine power but in the opposite direction ( more power = lower pressure ) - again 10 seconds later everything went back to normal ( it came down rather suddenly , within 1-2 seconds )
It seems that this only happens if the oil is cold , once it warms up everything looks good..

A few years back I had some issues with my sender with oil pressure going high but it was during flight only and it would come and go - basically different symptoms so I am wondering if this is another issue with the VDO sender or what ...

I figure the best way to check would be to plug a mechanical gauge and see what is going on - is there anything especial to this process ?.. do I just unscrew the sender and replace it with 1/8 NPT gauge fitting ?
Anything other to worry about when testing with the mechanical gauge?

Thanks

[3Dreaming]

The other option is to remove the sending unit and test it. With a couple of air fittings you can hook the sender to a compression tester and run the sender though its range while checking the resistance with an ohm metter. I found a chart online that had a graph with pressure readings compared to ohm readings.

Honestly I would just replace the sender and see if the problem goes away, and if it doesn't then start troubleshooting. I have yet to not fix an oil pressure problem when I replaced a sender.

[Warmi]

I already got myself a cheap oil pressure testing gauge from Harbour Freight with all sorts of fitting for just $29 so I will give it a shoot and see what it reports - I am hoping it is just the sender , it would be second one gone bad in my 500 hours with this plane.

Thanks

[3Dreaming]

I already got myself a cheap oil pressure testing gauge from Harbour Freight with all sorts of fitting for just $29 so I will give it a shoot and see what it reports - I am hoping it is just the sender , it would be second one gone bad in my 500 hours with this plane.

Thanks

Two in 500 hours is not bad for the VDO senders. One other thing if the manufacture will approve it is to remote mount the sender off of the engine on the firewall.

[Warmi]

You were right , it was the sender.
I got another one for about $50 and all is good again.

Thanks