A quick oil pressure question

[dhen]

Hi,

I've got a rebuilt engine that runs and sounds great. It's a long story, but I didn't drive it in really hot weather until recently. Normally when I drive it it will be at 70 PSI on the highway and 25-30 PSI at idle. Now, on really hot days (95 degrees +), the oil pressure will sometimes go down to 20 PSI idle and 60 PSI highway.

I want to be clear that I don't think I have a problem, but I like to know what my engine is doing.

I have conventional oil 20/50 viscosity. I am not running water lines to my T28 turbo. Is the oil possibly degrading because it the heat? Should I switch to synthetic?

If I didn't have an oil pressure gauge, I wouldn't even notice this. I'm just trying to understand, but I also like to be careful.

Thanks

[sjbsuperman1425]

Sounds like my car. I run 10w-40 Castrol GTX and at normal operating temperature my oil pressure is about 20-25psi and around 50psi on the high way. This is with my oil temps being at max...220*F

[sjbsuperman1425]

In short, I wouldn't worry about it.

[dhen]

That's kind of what I was thinking. I don't have an oil temp gauge anymore, but the oil was 240 on the highway when it was 70 degrees. I've heard this is good because it cooks off any moisture.

Thanks, I was just wondering.

[Izento]

Yup, you got it. You want oil hotter than 212 F because that is the boiling point of water. 240 is kind of high for 70 degrees ambient temp, I would be more concerned about your temps if it's at 240 F and you aren't in stop and go traffic/not beating on the car. Also, my oil pressure is around 60-65 psi when driving 65 mph. 20-25 psi at idle when it warms up to about 220 F. I haven't driven it in the summer, but normally it's around 60-70 ambient degrees here. I run 10w40 synthetic. So as far as oil pressure, you're fine.

[float_6969]

LOL! I have yet to have this stupid engine build more than about 12psi of oil pressure when hot and idling. Probably why I keep having issues with noisy lifters. After mic'ing everything out with this engine rebuild, I'm about 90% sure that the builder that built the engine the first time ground the rod journals down to the lower limit of OK and bored the rod bores out to the upper limit of OK. I suppose it's possible that it came that way from the factory, as the measurement are in spec, but JEEZ are the rod bearings loose.

[dhen]

I believe 12 PSI at idle is normal, according to the manual.

After I posted this I talked to an old hot rodder I know that's been working on cars for more than 50 years. In short, yes it's normal to see a small dip in oil pressure when it's really hot outside. Kind of strange that 10 more degrees can do this, but normal.

Just to confirm I took it out this morning before it get hot outside. 22-25 at idle and 70 at 3,500 RPM (my cruising RPM), so all is good.