Sky high oil pressure

I had a pretty good, long ride this weekend and, besides the engine running very hot, I've been pretty happy with the way it's running.

The temperature I think is a function of a number of things, including a couple of uninstalled rad seals and the 100 degree outside temperature.

Even though the engine was running very hot (230 by the cluster gauge) the oil pressure still remained pegged at full the whole time I ran it. I know very little about the engine, oil pump or components.

I have not yet attached a reliable gauge to the back of the block to verify so a faulty gauge is a possibility, but I don't think that's the case.

I am using Rotella 15W40. I would have thought that heating it up that much would have lowered the operating pressure but not noticeably. Would reducing the grade help appreciably? Other places to look?

Pegged, but what's the max on your scale?

Twin_Turbo said:

Pegged, but what's the max on your scale?

Click to expand...

The max number is 70. I would guess another 30 to the stop.

First thing is to confirm with a hamdheld mech gauge.

I guess it was the gauge after all

Tested tonight with a hand held and pretty reliable Mac gauge and got the following results:

Cold High idle: 75 PSI
Cold Revving to keep from stalling: Over 80 PSI (top of range for that gauge)

Switched to the high range gauge

Sightly warmer idle: 65 PSI
Warmed up idle (in gear): 60 PSI
Cruising speed: around 75 PSI
Enthusiastic acceleration: around 80 PSI

I don't think the high range gauge read as accurately as the low range one but didn't want to switch back and try it again as it was a little to late. I also noted that the Oil Pressure gauge from the cluster no longer goes below 35 PSI. Looks like it's toast. No big deal as I intended to swith to an electric one that Darrow gave me anyways. Guess I'll have to do that sooner.

I'm still thinking that the cold idle is a little high at 75 PSI. Should I switch to a slightly lower viscosity grade next change?

You don't know what oil pump you have ? It's very likely a Melling M55HV (high volume) - same pump I have.... I also have 75psi pressure at cold idle. not sure if a standard pump can get the pressure that high.... maybe....
My cruise pressure is lower though, cruise with warm oil is about 50-60psi, hot idle 30psi... Autometer electric gauge...

Other things that can cause high pressure: no bypass ... either a non bypass oil filter adapter or a disabled bypass in combination with a restrictive or plugged filter....

Maybe your oil flow is restricted - the pump would work against the restriction and pressure would be high but flow would be low.... remove valve covers and make sure you get plenty of oil at all rockers - just to be safe.....

Chances are high that you have some kind of Melling pump. The performance pumps usually have a 70 psi relief spring, in fact that's the highest Melling has.
If you truly are running over 70, then oil is continually going over relief which will cause the oil to heat and degrade much more quickly. Having a high oil pressure in itself isn't all that bad, but the relief part is. Problem is the relief port flow can't handle enough volume from the pump to even keep it at 70 psi and that is why you get more than 70. Certainly won't help any engine running temps either.
About the only thing you can do is lower the viscosity to have less than 70 psi when hot and/or pull the pump and go to a stock one. If you have the stock 60 psi spring, then the relief problem is even worse.

I've gone so far as to drill a couple holes in the front oil plugs for the timing chain and slot the dist lower land to squirt the cam and dist gear, and still run 60 psi hot with 10w30, but with a select 25 pump. The extra oil certainly doesn't hurt those areas either.

Sounds like you have to mauch oil pump for the bearing clearances you are running, The most pump we will put on a SBC is a 10552 oil pump which is a 10 more volume over a stock pump. Some times with high oil pressures it will cause premature dist. gear wear.

Becareful of the 15/40 Rotella as its fomulated for the newer engine and is very low in zinc ait use to be 1400 PPM of zinc and now is down to 800 to 850 of zinc.

Check out this link
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1415835#Post1415835