Oil Viscosity vs Pressure vs filter?
 

I have about 500 miles on a new rebuild 300/327 in my 67. I used Shell Rotella (sp?) 30 weight Diesel oil. The engine runs good but the oil pressure is high. It starts off scale and finally comes down to 60 PSI at freeway speeds and 35 when ideling. All of the new oils have higher viscosity than I'm used to? All of the Vavolene VR1 oils that I see are 20-50 weight and the Chevron 400 is 10-45? these are both CJ-4 compliant.
I want to change my oil now at 500 miles to try and bring the oil pressure down but wonder if the higher warm weights will actually increase the oil pressure? Also, I noticed in an other oil thread that high oil pressure causes the oil to bi-pass the filter?
John

High oil pressure is more a function of a high volume oil pump than oil viscosity. Going from a 10W40 to a 20W50 for example would have a marginal impact on oil pressure. What kind of an oil pump was put in when the engine was rebuilt? High volume oil pumps are really unnecessary in most street driven cars.

Oil Pressure vs Viscosity
 

The oil pump is supposed to be a standard volume as the engine is meant to be only a "grocery getter"!

Wow that seems like high oil pressure.

What oil pump did you install in the motor? I've heard that the general rule of thumb is 10 lbs for every 1000 RPM is adequate for a regular street motor. Maybe a race motor would need a bit more. My 327/300 runs 30 at idle 45 at speed hot. It's an older rebuild.

I use the Rotella 15w-40 (?) multi weight in my '66 and '71, mostly due to the suggestions of fellow forum members.

Try changing the oil AND filter. Maybe the filter has some breal in lube in it that is causing the higher readings? That high pressure may give you problems down the road. Also verify that your dash gauge is correct. Try hooking up a cheap Autozone mechanical gauge just to check the reading.

Good luck.

Sounds like you have the high pressure pump. Not the high volume even though you could have both.

Find out what kind of pump was put in it. If it's the high pressure pump only, just change the pressure relief spring to the standard spring.

If it's a high volume/high pressure pump, I'd replace the pump.

At 500 miles with no problems related to having a Too High an Oil Pressure you can afford to relax this concern a bit. What kind of Oil Filter System are you using? Spin On or Can? The Can's are a pain but do a better job all around. A Multi Weight should help your situation somewhat. Al W.

Engine builders today routinely use high volume pumps, whether you specify or not. If you experience no other problems like oil usage or leakage, I would forget it. If you don't want that much pressure, change the pump.

You definately have a high volume or pressure pump. standard pumps only run 35-45 lbs. Standard perf engines need no more than that, period. The tag on the pump will say hv or hp, then the pump number. Standard pump will just have the number.

10 lbs for every 1000 rpm is for racing and high perf engines, but best not to exceed 70 lbs.

The problem with high volume pumps is if you are running a stock 4 quart pan, (5 with filter), and not the 365hp 5qt pan, (6 with filter), you stand a very good chance of sucking the pan dry at high rpm. Chevy hp tech literature says that a 4 quart pan can suffer starvation around 5000 rpm, if 1 quart low. That is with a stock pump. I have seen way too many freshly rebuilt Chevy motors with high volume pumps and spun bearings.

I like to run standard Melling pumps, and shim the pressure relief spring to give 50-60 lbs hot, at speed. All my engines are high performance.

Also, high volume pumps take more force to turn, accelerating timing chain and distributor gear and cam gear wear.

BTW, all chevy oiling systems routinely by pass the pump, especially when cold. They are purposely designed to do this to prevent problems caused by plugged filters, since Americans in general tend to be lax about maintenence. I remove the bypass and plug the hole with a short 3/8 bolt and locktited nut. All of the oil must then go through the filter. Keeps you from spitting metal throughout the entire engine, if you hurt anything. Been there, broke that.

Just go easy until the engine is thoroughly warmed up, since the filter now will see full system flow, which it did not before. I have seen spin on filters expand with rpm, when cold. That is why I prefer the canister filter. It is tougher, it holds over a quart, and has more filtering area. Bigger is better.

Rich

Oil Viscosity vs Pressure vs filter?
 

Update: I changed my oil at 500 miles to Shell Rotella 15-40W. The oil pressure is a little better. It now idles at 50PSI cold and 35 warm. At speed it is lower but still at about 70 PSI.
I picked up my short block with the pan on it so I never saw the oil pump ... 3 months later the engine builder doesn't recall! I suspect in this economy he might have used anything he had laying around i.e. high volume or pressure???
When I installed the new engine I converted it to a spin on AC 454 filter. Thinking back, when I converted my 57 to a spin on I also saw a rise in oil pressure but since it was the only change I made I didn't think much about it?
Before I rip off my pan to check the origin of the new pump I think that I will convert it back to a canister filter (yuk) to see if there is a pressure change.
How are the standard, high volume and high-pressure Melling pumps marked?
Thanks for all help! :)

I was loving your advice until this statement....WTFO ?

Good thread (other than the mtce comment), My fresh rebuilt 327/365 is also running similar high pressures, I did have to go to the 4 quart pan (long story, its in a BB car with power steering and won't clear the power cylinder), so now I am worried about starvation if its a high volume pump..
For oil choice with flat tappets are folks going diesel spec oils to get the additives they took out of conventional motor oil? how about synthetic oil for diesel, and lower viscocity?

The Shell Rotella or Chevron Delo can be special ordered in 10W-30.
You are better off with the old fashioned canister filter because it has more filter area and does a better filtration job.
Assuming that you already have a standard volume/standard pressure pump installed, ask the engine builder whether or not the mains were align bored and honed. If they were, then the machinist might have set the tolerances on the tight end of the range. This will result in higher oil pressure.

Engine does seem pretty tight, that should wear in pretty quick though?

It is true.

Now, I dunno if Euro or Japanese are any better, but the general trend among the American car driver is drive it until the oil pressure light goes on, and when it goes on, just add more oil.

That of course is an exaggeration, but not by much.

When i worked in a service station, I don't know how many cars needed 3 or 4 quarts of oil added, and I can think of at least six times I went to change oil and nothing came out of the drain plug because the oil was so thick it sludged up into a semi solid goo that congealed in the pan and under the valve covers. Looked like black jello.

And that was just the oil portion, the belts, hoses, tires, etc were horrors of their own.

Doug

My Dad had a simple maintenance routine, change the oil, filter and do a tune up every time the muffler falls off.

Add a qt of MMO (Marvel Mystery Oil) It will lower the viscosity and also keep the engine clean of any deposits forming.

Synthetic oil is "thinner", weight for weight, than conventional. Might help if you just need to reduce pressure 5 to 10 pounds. But you might need Bar's Leaks to keep it from seeping through your valve cover gaskets, etc.!

I agree that a performance pump of whatever kind has a greater effect than viscosity, however.

I want to hear some feed back this suggestion, Marvel Mystery Oil. I've used it to clean out motors but not run in a fresh rebuild.

I too suffer from high oil pressure with my fresh built 350 with Rotella 15-40. I put the Summit 7qt pan with Melling high volumn pump, wasn't supposed to be high pressure.

I've never encountered a problem in nearly 50 yearss using MMO, but I'll let others chime in. You can lower the oil pressure in your pump by putting in a weaker pressure relief spring.

If you chart the viscosity of oil from cold to hot, you will find that there is very little real difference in viscosity of oils at higher temperatures. The hot viscosity makes little difference in hot oil pressures. Single weight oils make little difference either. The only difference in them is the rate of change. Multi weights start out thinner, cold , and just don't change as fast with temperature. When they all get hot they are all thin.

When my 31 and 33 Cadillacs were new, there was a recommendation to add a quart of kerosene to the oil for ultra cold temperature operation, so I guess adding MMO to the oil would not hurt anything since that's what most of those snake oil products are. But they were dealing with mineral oils. Modern oils are much better, especially cold, so I wouldn't recommend the Kerosene thing. Just use a good multi weight and forget it or change the pump.