Stupid Question about oil pressure.

[Gregory M.]

I went to change the oil in my newly acquired 1968 435hp coupe. The manual says crankcase capacity is 5 quarts plus one quart for filter. So after I change the oil I start the car and the oil pressure guage is nearly pegged on 70lbs...I run it a few minutes, shut it down, and then check the dipstick and I am a quart over...wtf?

So I call a buddy, whose opinion I value, and he says the higher oil pressure will not hurt and when the car gets hot the oil pressure will come down. So I idle it for a while and then take it for a spin. When warm, and at idle, the oil pressure comes down to 50-55sh but pegs on 70 with a little rpm. Then it starts pushing a little oil out the rear of the valve cover gaskets on both sides. Do I dump a quart of oil or change my valve cover gaskets?

GM

[Duke W.]

Re: Stupid Question about oil pressure.

I have no experience with your engine configuration, but have run other engines a quart over in track events with no ill-effect. It was a "trick" used by racers back before SCCA allowed dry sumps.

If oil is being pushed out the valve cover gaskets it is more likely to be a crankcase pressure issue than oil pressure, so check your PCV system and valve.

You say this car is "newly acquired". So how did it behave before you changed the oil? What SAE viscosity range oil are you using?

The '67 AMA specs list normal hot oil pressure of 50-75 psi @2000 for all 427s, and '68 is probably the same. The '67 427 oil fill capacity with filter change is also listed as 6 quarts, so you should verify if you have the correct dipstick.

Call GM customer service 800-222-1020, and ask for the '68 "restoration package", which includes the AMA specs - lots of useful tech. info. It is complimentatry, but they will want your VIN. You should also buy a chassis service manual and assembly instruction manual.

Duke

[Joe L.]

Re: Stupid Question about oil pressure.

Greg------

The total capacity of your system, with filter change, is 6 quarts. Period.

After changing a filter and installing 6 quarts of oil, if you get a 1 quart over reading on the dipstick, then I would suspect one (or, more) of the following exists:

1) A non-Corvette oil pan has been installed on the car at sometime in the past. These will fit perfectly but they have 1 quart capacity less than a Corvette pan;

2) A dipstick has been replaced with an improper one for the oil pan and/or dipstick tube installed on the engine;

As far as the oil pressure goes, it doesn't sound too far out-of-line to me. In any event, I don't think it has much to do with the leakage from your valve covers. Most often, this condition is caused by distorted valve covers. Sometimes, a HIGH VOLUME oil pump (which your application did not originally use) may cause "flooding" of the upper valve train area and exacerbate valve cover leaks. However, this is a rare condition with a big block. It's THEORETICALLY possible and I've heard of it, but I've never seen a case of it.

[Gregory M.]

Re: Stupid Question about oil pressure.

I only started the car and ran it for a short time prior to the oil change. The cold range was 45-55sh and I noticed ithe dipstick seemed a quart low. Riddle me this, Batman:

1) Does the volume of oil (in other words being a quart over) effect oil pressure?

2) Does oil pressure exist under the valve covers or just in the crankcase and lifter valley?

I am being told no to both and if that is the case, and the AMA specs call for normal hot oil presure in the 50-75 psi, I should change my valve cover gaskets and add the quart back. They currently have rubber gaskets and in my experience corks seals better. Note that the 1967 had an 80lb gauge whch was decreased to 70lb in 1968, so there must be a difference in the AMA specs. If the normal range dropped proportionately as well, say from 40-65, it would seem the 6 quarts readings I am currently getting are normal and I need new gaskets.

I am going to order the restoration package...thanks for the heads up...

GM

[Clem Z.]

no to both questions. BBC put a lot of oil

upstairs because of the type of lifters but if the oil return passages in the head are clear there should be no buildup of oil. toss the rubber gaskets and get corkprene ones.

[Dennis B.]

Re: Stupid Question about oil pressure.

I would first try to determine that you have the proper oil pan. These cars can have a varied past.

[Gregory M.]

Re: Stupid Question about oil pressure.

What should the pan look like? I know it has a 7/8 drain plug centered facing rearward and not off to side like a SB...any other indicators?

GM

[Duke W.]

Re: Stupid Question about oil pressure.

I'm not sure about BBs, but all vintage SB pans up to your era have the plug centered at the rear of the pan. Any with side plugs are "incorrect" replacements.

If you can post of photo of the pan, the BB experts can probably tell you if it correct of not.

Also post some dipstick measurements and post a photo if possible, and they can do same.

There have been many cases of improper dipsticks.

Duke

[Joseph T.]

Re: Stupid Question about oil pressure.

Greg..this is either a picture of the pan from my 68 427/390 or from a 70 454. Others more familiar with pans can comment.

I have other pictures of you need them.

Joe Trybulec

[Gregory M.]

Re: Stupid Question about oil pressure.

Thanks for the picture...I will have to check mine but my dipstick does enter from the pass side between the #4-6 exhaust manifold ports...

GM

[Joe L.]

Re: Stupid Question about oil pressure.

Joe-----

The external configuration of the Corvette pans was, essentially, the same from 1965 through 1974. There were some small differences in features, but the configuration portrayed in your photo would be applicable to all.

[Gerard Q.]

Re: Stupid Question about oil pressure.

If the oil pans are essentially the same why would my 71 sb require 5 qts w/filter.....I've always thought GM V8's required 5 qts although I've never owned a bb.

[Joe L.]

Re: Stupid Question about oil pressure.

Jerry-----

By "all the same" I was referring to big block oil pans, not small blocks. Many big block oil pans were designed for 5 quart oil systems. Corvette was an exception. That's why it's an often-used piece for certain non-Corvette applications that it will fit (sometimes with mods to the vehicle it's being installed in). In fact, that popularity may be the primary reason that this pan is still available.

For small blocks, virtually all 1963-74 Corvette oil pans were the same EXCEPT for most 63-72 with mechanical lifters. The widely used pan was designed for a 5 quart oil system. Most 63-72 with mechanical lifters used a pan designed for a 6 quart oil system.

Corvette oil pans were generally not used for any other Chevrolet application, big block or small block. The exception was 1975-79. Those year Corvettes used the same oil pans as passenger and/or other Chevrolet cars. Virtually all other Chevrolet applications for big block or small block used 5 quart oil systems.

[Gerard Q.]

As always Joe, thanks for the detailed explanation *NM*

[Clem Z.]

SHP corvette oil pans both BBC and SBC

came with a trap door system so the oil would not run away from the oil pump pickup during "spirited driving" no other chevy pans used this system