Need help with oil pressure

[rparker762]

For the last week since I bought my XJ, at start up the oil pressure rises to 60'ish, from there under load of normal driving it runs about 50 - 60. No big deal. Well today it was colder and rainy when I left. I started it up and the oil pressure was pegged out at 80 . I drove till it warmed up thinking ok its cold. Well as I drove you could see the oil gauge fluctuate between 60 - 80. Also it was acting backwards, meaning when on the gas it would drop to 60 ish and at a stop it would rise back up. Even after shes nice and warm.
I,ve read elsewhere that the sending units are crap and alot of ppl dont like Fram oil filters( what was on it when I bought it) but this is worrying me. It still runs great but......
It is a 96, 161,200 miles, 4.0 HO, auto, its stock as far as I can tell. And hardly been offroad by the looks of it.

 

[90Xjay]

Sounds like a sending unit more than likely. The pressure should read lowest when warm at idle in gear. But I've never seen one drop when you rev and raise when your off the throttle. Those factory guages are all running on voltage supplied by the sending unit. It's not your oil filter. Fram is a decent brand and the parent company Allied Signal makes a lot of other brands too.
I did hear, through a professional trade organization that Fram does use less material to make filters it sells to WalMart cause Walmart beats them down on price so bad, but heck I run a Fram filter most of the time.

Do you know someone with an oil pressure guage test kit? That way you can screw in a wet line and check it against your guage reading.

Other than that, you might look into a new sending unit. I just hate putting parts on before you know for sure what the problem is.

don't sweat it much either way, high mileage 4.0s still make good oil pressure, their main bearings are darn near bullet proof.