30W vs 15W40 & Very high oil pressure

[Adam King]

Hi All-

I just changed the oil in the 1988 Silverado 1500 that I bought while I was in Kuwait. The filler cap and the owners manual say that 30W is the "prefered" weight unless it gets cold, then they suggest 15W40. I don't know what the guy was running before but now I sometimes bury the needle on the oil pressure gauge when going down the freeway at about 65-70 mph. It idles at about 50-55 psi. Anybody else have this happen?

It could be a bad gauge or sending unit too, I haven't checked yet, but it wasn't that high before I changed the oil, at least not that I saw.

The Army runs 15W40 in all the HMMWV's and the old 6.2L Chevy's year round so that was what I went on. Did the oil recommendation change when they started with the new style rockers and should I be running 30W during the summer?

-AFK

[john8662]

The oil weight preference for these engines hasn't changed through the years, but the specification has.

The recommended oil weight is 15w40, and most of us run this weight year around. I run this weight in the winter and in the 100*F summer heat.

As for the high oil pressure situation, you could replace the oil sender just for a reference.

You may also consider doing an engine flush...

My current truck does exactly what you're describing, I'm of the opinion that more oil psi is better than low oil psi.