I have a 95' LT1, I don't know the history of the engine but it has been rebuilt recently. While driving at highway speed for about 5 minutes, I carry about 45 PSI oil pressure. After 15 minutes, same speed, the pressure is down to 25 PSI. Would it be a good idea to run a thicker oil, maybe 10W40 or 20W50? What's everyone's thoughts?

 

It is normal for oil pressure to drop somewaht as the engine heats up, although 20 PSI drop seems more than normal. Depending on how the engine was rebuilt makes a difference in the viscosity of the oil needed. Try a good brand of 10W40 and see if it holds up better. The rule of thumb for minimum oil prssure is 10 PSI for every 1000 RPM

 

Are you running a automatic or a six speed?

The reason I ask is the 6 speed has double OD so the rpms are lower at higher speeds compared to the auto which has only one OD, (though when in 5th for the manual, you are close to that of the automatic).

But, unless you are driving at 3k rpms at highway speed, you are fine with what ever viscosity oil you have in it now. The reason it's dropping so much is because the engine is warming up and the car isn't under hard stress there fore the pressure doesn't need to be so high. 5w-30 or 10w-30 would be the only two oil viscosity I'd go with, anything more I'd think would be over kill.

 

Thanks, it is a six speed. Yeah, it only turns about 1300 rpm at 55mph, I guess I won't worry so much. Like you said, just put in a good oil and should be OK. I used to think thicker was better, I've learned recently the thin stuff is better.

 

Yup. Just put some good oil in it and you'll be good to go. You only need multi-viscosity oil if you live in cold climates (hence the W in 5W-30). I'm sure you knew that all ready though seeing as you are intelligent enough to call it "viscosity" and not "weight". If I lived in Arizona or somewhere else where my car saw 100* weather, I'd most likely just run straight 30.