Oil Question

[rod7515]

I have a 408 that has a roller cam with solid lifters and roller rockers. It may have about 1000 miles at most on it since it was built and during that time it’s always had 20-50 penn grade oil. The last oil change I had to buy partial synthetic oil. I’m noticing that oil pressure is lower with this oil. Probably 15 lbs cold and 10-15 lbs once warmed up to normal operating temps.
Is this a normal thing and what happens if I go to full synthetic 20-50?
Thanks Rod

 

[mbaird]

Synthetic oil tends to be thinner than traditional oil. I just went to a synthetic 15-50 from 10-30 dino oil in my Mazda B2600.
Pressure went up a little but is much more stable once hot .
20-50 seems pretty heavy for a new build . Was it built with bearing clearances on the high side ?

 

[rod7515]

If I remember it was .0015. I’ve run the 20-50 from the first start. I haven’t had any issues and when going to the partial synthetic noticed the slightly less oil pressure. I do think you are correct as it seems to keep a more constant pressure once warmed up and at a stop light/sign. What changes would I see if I went to full synthetic and should I be using any ZDDP additive with synthetics ?
Thanks Rod

 

[mbaird]

I don’t think the additive is needed with full synthetic.
Go to speed-talk.com and read up on oil tech . Those guys high level engineers and builders .

 

[Scody21]

there is nothing to worry about there. The first power pull of my 340 it was at 102 PSI on the Penn 30wt BR oil. I changed it to 10-30 Penn partial syn, and now about 70 PSI cold and 50 psi hot at idle. I would just stick with the partial 20-50. For the Cosworth racing engines my brother builds, (60’s/ 70’s tech engines) he runs .0008 mains and .001 rod/ cams bearings, we run 20-50 Penn in all of them.

These pics are right before the teardown. This motor was about 10 minutes from blowing up as we found some dumb **** from the last builder. When one of these blow up, it’s a 100 grand of ****…

 

[Bewy]

Go to the Penrite.com. website & look for the description of 'Friction Modified' oil. FM oils are 'thinner' to give better economy. Penrite make oils that are NOT FM'ed, which is what I use in my engines & engines that I build.

Not saying that the above is the reason for the oil pressure loss [ between different oils ] , cut it certainly could be. Usually a 10-15 psi loss at idle, hot; applies to syn & non-syn oil.

 

[rod7515]

Thanks guys for your insite.
Rod

 

[S'cuder]

Rod, two 20W-50s can have slightly different pressures as yours do because the viscosities have to fall in a range. They can be on spec without being exactly the same.

Avoid using additives. There's no way to know how they will work with the oil's chemistry.

Mobil 1 15W-50 is a quality full synthetic with a good amount of ZDDP blended in. It's also reasonably priced. Maybe try it next time. Good luck.