Oil pressure check

My '88 used to live life at 40psi pretty much all the time. I couldn't get any 5 qt jugs of Castrol 5W50 so I went with 10W30 this last round and I switched my oil filter from Fram engine destroyer to Wix engine saver.

On the XJ and the ZJ my oil pressure has risen to levels I've never seen before- most dramatically on the XJ. It starts off cold at around 60psi now and then drops down to 40 after it's warm. I had a spare oil pressure sending unit and swapped it in to check and they both agree my oil press. is now higher.

I'm a little concerned and wonder if you guys have any thoughts or wisdom. Thanks.

I use Castrol 10W-30 dino oil, and my pressure is pretty much the same as yours, 60 psi at cold start-up and 40 when warm. I think that's normal.

It seems to me a 5W would have slightly less viscosity than a 10W when cold, but then the same as the 10W-30 when warm.....

its completely normal. nothing to worry about.

A cold engine typically shows 10 to 20 psi more than when warmed up, depending on make and grade of oil.

The FSM defines normal oil pressure (warm engine) as 13 psi minimum at 650 RPM idle, and 37 to 75 psi above 1600 RPM. Your results are well within spec.

Okay thanks... I was kinda worried. You get used to your XJ's numbers and when they change suddenly it usually means something is wrong or different.

What do ya'll think about using 5W50? Seems to me like it would be great to have an oil that's nice and thin cold and thicker when hot. I know the owners manual says 10w30 but they didn't even make snytec when my XJ rolled of the line....

thanks again for your help!

The owners manual for the 2000 calls for 5W30 in cold climates. That wasn't an available viscosity when I bought the '88, which calles for 10W30 or 10W40.

I ran the recommended 10W40 in the '88 for about 175,000 miles, changing the oil and filter religiously every 2500 miles. Eventually, the oil pressure began to drop, especially on long highway trips with heavier than usual loads (such as when heading out for a weekend at Paragon, loaded with clothing, spare parts, tools, etc.). At that point I switched to Mobil-1, using 10W30 in the winter and 15W50 in the summer. Oil pressure came back up to slightly over 40 psi on the highway. I would have preferred to see 50+, but 40 is better than 27 so what the heck.

But with the 5000 mile oil change interval I adopted to partially offset the higher cost of synthetic oil, it seemed like I was always running summer oil into the winter, or winter oil into the summer. Then I discovered Castrol had a 5W50. Sounded interesting, so I asked around. Turns out Castrol makes the factory synthetic oil used in Volkvagens and Audis. That's good enough for me. I now run Castrol 5W50 exclusively in the older vehicles (2 MJs and an XJ), but I run conventional Castrol 5W30 dinosaur oil in the 2000 and follow the 2500 mile interval. I'll probably change over to synthetic somewhere around 20,000 miles or so.

I guess that's a long way of saying I use the stuff and I like it.