There shouldn't be any change in oil pressure at operating temp using 10W-30 or 5W-30 because both oils have the same high temp viscocity. However, when engine is cold there is certainly a difference in how easily the oil flows - 10W being harder to pump compared to 5W.

You might want to try 5W-40 and see how that affects oil pressures with a cold engine and engine at operating temp.

 

Yes, I'm wondering if the 5 quart jug I bought was mislabeled or something. I've never seen this happen in nearly 50 years of changing oil.

 

Well, I can't find any conventional Pennzoil 10w30 near me, or really, any non synthetic oil.

Also, I've used Pure One oil filters for years, I had one on hand, but now can't find any at the local auto parts stores. Thought I'd change out the new oil filter too just in case it's a crappy counterfeit.

Well shoot, I was prepping the old Jeep for a 500 mile road trip tomorrow morning for my grandson's birthday party. Not sure what to do now.

 

Based on my shade tree knowledge you need 10 pounds per 1000 rpm. As long as you are in that range you’re ok. In order to get a lower winter/cold number they use additives, I’ve read many articles about how that will affect thickness on the other end even if they say it won’t.

 

Based on my shade tree knowledge you need 10 pounds per 1000 rpm. As long as you are in that range you’re ok. In order to get a lower winter/cold number they use additives, I’ve read many articles about how that will affect thickness on the other end even if they say it won’t.

Yeah, it's interesting because before I changed the oil, the pressure has been steady and consistent for the past 8 years at around 45psi, didn't really fluctuate much.

Now it seems like the oil pressure is fluctuating with the rpms which it never did before.

Did a cold start this morning, pressure was at 45, but I decided against the road trip I had planned til I figure out what's going on.

 

Now it seems like the oil pressure is fluctuating with the rpms which it never did before.

Fluctuating oil pressure after an oil change was a sign of a bad oil pressure sending unit twice on my 93 4.0. New senders fixed it both times. Especially suspect if you used motor flush before the change.

 

In my ‘98 ZJ owners manual it lists 10/30 for temps above 0*F and 5/30 for those below. It does say 10/30 is preferred.

 

Interesting, I don't have the owner's manual but the factory service manual I have doesn't appear to specify viscosity.

Here up north it's hot in the summer and really cold in the winter.

I change the oil every 3000 miles due to the temperature variations here, and a lot of short trip driving.

 

If you get winter temps close to or below zero you could just use the 5/30 in the winter & the 10/30 the rest of the year; that’s what I’ve done with mine all these years….

 

I use 5W-30 or 5W-40 full synth year- round, I change the oil every 7500 mile. Zero issues. Winter temps generally are around 10...20°F and can drop down to negative double digits, summer temps 60°F...80°F.

Why 5W-40 instead of 5W-30? I've seen it a number of times when towing that at engine operating temp the oil pressure won't stay as high as it does with 5W-40. It's well within spec., but noticably lower with 5W-30. We don't have motor oil coolers in these and oil volume is fairly low on the 4.0 and 5.2/5.9, so motor oil tends to get fairly hot in heavy use especially during summer. This means -30 thins out more than the -40 does.