High oil pressure

[Dennis O.]

Re: High oil pressure

Duke,

Thank you. Given it's you, I will be taking your advice, notwithstanding the snide delivery.

Denny

[Joe R.]

Re: High oil pressure

Thanks for all the replies. First thing, I am going to change to a 180 thermostat. I don't even know why I asked; I guess I was just looking for assurance. Second, It did have the problem with overheating at idle that went away after a few hundred miles. I still believe it was because the engine was "tight" and loosened up after it was broken in, as I had no other cooling system problems, and haven't had to add any coolant since the initial installation. I think that may also be why the engine came with the 160 thermostat. The guy who built the engine did several dyno pulls and he probably saw that it ran hot.

I have read all about the hv/hp pumps here and several other forums. I am at the age now with pretty bad arthritis that the idea of crawling under pulling the pan has very little appeal to me except as a last resort. I will probably pull the distributor and check the gears this winter. The one thing that hasn't been addressed (except peripherally by Stu) is switching to a lower viscosity oil. Unless someone has some experience other wise, I think I will get some of the aforementioned 0-20 oil, add some zinc additive and do an oil change. If the engine holds normal (35+ at idle) pressures, I don't see what harm could be done. I'll let you know what happens.

Denny,

I believe that Shell Rotella T can be special ordered in 10W-30. There are probably other CJ-4 options that I am not aware of.

Joe

[Stuart F.]

Re: High oil pressure

Where would one expect to get them to special order 10w30? My usual purchases are made at Walmart or Sam's club. Perhaps a local NAPA store? My local store is in the process of moving into a larger store on a main street so they are not availabe as an outlet. Then there is a little Mom and Pop Auto store that I go to for Wix filters - ya, I'll try them. It's getting cooler now so the lighter weight is probably the way to go. Talking about highs in the 70's and lows in the 50's by Thursday - ye! Ha! my Vette loves the cooler air. Can't wait.

Stu Fox

[William C.]

Re: High oil pressure

Where would one expect to get them to special order 10w30? My usual purchases are made at Walmart or Sam's club. Perhaps a local NAPA store? My local store is in the process of moving into a larger store on a main street so they are not availabe as an outlet. Then there is a little Mom and Pop Auto store that I go to for Wix filters - ya, I'll try them. It's getting cooler now so the lighter weight is probably the way to go. Talking about highs in the 70's and lows in the 50's by Thursday - ye! Ha! my Vette loves the cooler air. Can't wait.

Stu Fox

Stu..My local NAPA orders Triple T 10w30 from the warehouse in Tampa..Bill

[Stuart F.]

Re: High oil pressure

Bill;

Thanks. I'll call around and see who can get it.

Stu Fox

[Dan D.]

Re: High oil pressure

The Advance Auto store in Webster, NY (near Rochester) carries Rotella 10W-30. Check one in your area. -Dan-

[Lawrence M.]

Re: High oil pressure

Where would one expect to get them to special order 10w30? My usual purchases are made at Walmart or Sam's club. Perhaps a local NAPA store? My local store is in the process of moving into a larger store on a main street so they are not availabe as an outlet. Then there is a little Mom and Pop Auto store that I go to for Wix filters - ya, I'll try them. It's getting cooler now so the lighter weight is probably the way to go. Talking about highs in the 70's and lows in the 50's by Thursday - ye! Ha! my Vette loves the cooler air. Can't wait.

Stu Fox

Around here (Chicago area) most parts stores carry the 10-30 Rotella in gallon jugs. I order it a case at a time in 1 qt bottles at my local NAPA.

[Duke W.]

Re: High oil pressure

I don't see a need to expend substantial effort seeking out 10W-30 CJ-4. Look at the recommended viscosity ranges in your owner's manual.

Since some current multi-vis oils were not available in the fifties and sixties, I'll use the data in my Cosworth Vega's owner's manual, which is the same as my '63 Corvette owner's manual other than the addition of newer multi-vis grades that were not available in the fifties and sixties.

10W-30 is suitable for cold starts down to about zero F; 20W-50 down to 20F. Split the difference for 15W-40 and you have 10F. These recommendations are for consistent cold starts. An occasional cold start below these temperatures will do no harm, but I doubt if many of us ever cold start our vintage cars below freezing. Also noteworthy is the note in the CV owner's manual that says straight SAE 30 is okay down to 40F cold starts.

Prior to switching to 15W-40 CJ-4 in all my cars a few years ago due to the reduction in S-category ZDDP, I always used dual rated (both the current S and C-category) 20W-50, and the lowest typical cold start was 40F.

The colder the cold start temperature the higher the initial oil pressure, so just warm the car up easy by only demanding minimal speed/load during the first few minutes of operation. And keep in mind that it will take more time for the oil temperature to achieve normal operating level than coolant.

Although there are reports of "excess oil pressure" with higher viscosity grades, there is considerable overlap in the absolute viscosity ranges of adjacent SAE grades, so the typical viscosity of a 15W-40 at any given temperature is not that much more than 10W-30.

High oil pressure due to installing the wrong oil pump/spring will do no harm other than increasing parasitic power loss, which increases fuel consumption and reduces available flywheel power.

The oil's ability to support internal loads and keep the journal from contacting the bearing is a function of hydrodynamic pressure and oil film strength. Hydrodynamic pressure runs from a few hundred psi at idle to several thousand psi at high revs, which are orders of magntude above pump delivery pressure. Delivery pressure just insures that oil is delivered to the bearing at some point in the load cycle where there is no load at the oil feed hole, and this is why the location of the oil feel hole is critical.

Our vintage Corvette engines were designed for "traditional" oil viscosity ranges. Some current engines are designed for lower viscosity oils like 0W-20, which have lower film strength due to the lower viscosity, but I would not recommend using such low viscosity oils in vintage engines unless you want to do an experiment at the possible expense of major engine damage.

Duke

[Michael H.]

Re: High oil pressure

I think everyone here has forgotten the real reason why the mech lifter engines were equipped with a higher pressure oil pump than the same basic engine with hydraulic lifters.
I posted the answer here a few years ago.

[Duke W.]

Re: High oil pressure

It wasn't until late in the '63 model year that mechanical lifter engines got the higher pressure relief spring, and the engineering reason behind this was never clear to me.

If you think you know, perhaps you could refresh our memories.

Duke

[Timothy B.]

Re: High oil pressure

Could it be due to the centrifugal throw off of oil out of the bearings at the higher RPM?

[Joe C.]

Re: High oil pressure

Well, I just passed 2000 miles on the rebuilt L79 in my '67 coupe. It shows extremely high oil pressure. It pegs the needle on start up at idle and the lowest I've seen is 55 lbs at idle after a 20 mile run. I checked it with another mechanical gauge and the readings appear right. I guess the re-builder put in the famous hi-volume/hi-pressure oil pump. When I originally got the car put together, it was real tight, and would overheat after idling for 5 minutes. After running a few hundred miles that problem went away. The engine starts and runs great, and now runs 160 all the time after warm-up (160 thermostat), and I have no complaints about anything else functionally.

A couple of questions :

1. Is there a possibility that this high oil pressure is harmful?

2. Would changing to a lower viscosity (I see 0-20 is available) with the proper zinc additive help any?

3. I am thinking of changing to a 180 thermostat because I think I may be running too cool now; would that be a good idea?

I don't race the car and don't run it all that hard. I did have a plug fouling problem, but that was solved by changing the AC 44 resistor plugs to a non-resistor AC 45 equivalent (Denso W14-U) and some carb tweaking.

Any help will be appreciated.

Were the main journals align honed? If your crank is small journal, then your bearing clearance should be .0021 +\- .0005. If the clearance here is on the small end of the range, your oil pressure will be on the high side.
You should be using Rotella in 10W-30 preferably, if not, then 15W-40.
The oil pump should have nothing to do with idle pressure when at operating temp since the high pressure pump relieves at 65-70psig and the standard pressure spring relieves at 55-60psig.

[Michael H.]

Re: High oil pressure

Could it be due to the centrifugal throw off of oil out of the bearings at the higher RPM?

It has to do with centrifugal force, but not quite the way you descrbe it.

Think about the oil supply to the connecting rod bearings and where it comes from.

Oil is sent down to the upper main bearing annular groove from above and forced into the crankshaft. It then travels through the hole drilled in the main journal and then out the other end of the hole to feed the rod bearing.

The inlet side of the oil hole, and the oil passing through it, is under a force, centrifugal force, that resists the pump pressure. As the crankshaft spins faster and faster, the force resisting the oil pressure increases and can eventually become greater than pump pressure which can/will starve the rod bearing.
Once the oil passes the center of the main journal, centrifugal force assists the oil flow instead of resisting it.

The RPM potential of an L79/350 HP is considered well within the safe operating range but engineering decided that the additional 1000 RPM potential of the solid lifter engine might possibly be getting closer to the point where the reverse flow/pressure could occur.

Pontiac racing engines had this problem years ago too but more severe as the diameter of the main journals was huge compared to Chevrolet engines. That increased diameter also increases centrifugal force acting on the oil which required even more oil pressure.

[Timothy B.]

Re: High oil pressure

Michael,

That's very interesting, would you agree then that the 55-60 psi oil pressure relief is adequate for high performance engines. If so, the stock M-55 pump (which I think is a good pump) with it's standard 55-60 psi relief is all that's needed in a high performance street engine overhaul.

[Dick W.]

Re: High oil pressure

Many moons ago, a wise old Indian by the name of Smokey Yunick, told me that 10# oil pressure for each 1,000 rpms was adequate for a race engine. Todays race engines, with the modern lubricants require quite a bit less than to to safely operate.

High pressure and high volume oil pumps in street engines today fall in the catagory of "Snake Oil" remedys.