ZIPP IT

1967 Corvette with 427 390 hp. Motor was rebuilt before I bought the car. Not knowing what oil was in the motor assumed break in oil. Unsure of what kind of rebuild was done. Changed the filter and oil. Replaced with Chevron Delo 15-40 and noticed the oil pressure is 60# at idle and goes up to about 80# when revved up. I thought maybe the gauge was faulty, so I hooked up another gauge. Read the same. Cant remember what the oil pressure was before I changed it. Is this anything to worry about the car runs great.

JohnZ

Don't worry about it - just drive it.

SonnyAK

My '66 L72 runs very similarly and I've never had any issues. From what I understand that's pretty normal pressures for the 427's...

babbah

Mine runs 80lbs cold and 70lbs hot - "Not To Worry"

DansYellow66

Mine pegs over 80 when cold at idle. Drops down to 35 or 40 at idle hot. Your's probably picked up a HD pump sometime in it's past life. Better to have too much than not enough.

KSL '67 101234

Zipp It, see my post/threads dated January 1, 2014 titled "Can oil pressure be too high?"

Here is my original post: The oil pressure in my '67's 327CI 300hp engine is pegging well beyond the 60psi max reading upon startup, and stays there until the engine has warmed up. The engine is the original, was rebuilt with a mild cam, and has 10,500 miles on it. Oh, and the rumble at idle from the side pipes is a V8 listener's delight. A warm to hot engine still results in pressures between 30 to 60psi. Acceleration usually pegs the meter well beyond the max reading of 60. The high pressures occurred after recently changing to Valvoline 10-30 racing oil, and adding 8oz of STP. Prior to using Valvoline racing oil the pressure readings were well within the meter's range, and never exceeded 60psi. Can oil pressure be too high? Should I be concerned?

Review the other posts in the thread, but I'll update you here.

I changed the oil 2 times following the change that produced the high pressures with no significant difference in the high readings at start-up. For the 3rd change I used Valvoline 10W-30 Synthetic with a #L30001 oil filter from Purolator. There was a slight drop in pressure at startup, but nothing that indicates there is not a problem, or an unexplainable change. What I noticed about the oil filters though are the number and size of drain holes surrounding the threaded center of the filter. I never paid attention to a filter's features, but I do now. Like you, I also verified the oil gauges readings, and found them to be spot on throughout the pressure ranges.

Here are the stats from all 3 oil changes:

1st Change:
Oil - 5 qrts 10w-30 Valvoline VR1 Racing Oil
Filter - Mobil 1 #M1-301 which has 8 drain holes with a total diameter of approximately 1.563 inches.
Additive – 8oz STP
Miles driven after oil change - 200

2nd Change:
Oil - 5 qrts 10w-30 Valvoline Oil
Filter – Car Quest #85515 which has 6 drain holes with a total diameter of approximately 1.5 inches.
Additive – none
Miles driven after oil change - 200

3rd Change:
Oil - 5 qrts 10w-30 Valvoline Synthetic Oil
Filter – Purolator #L30001 which has 8 drain holes with a total diameter of approximately 2 inches.
Additive – none
Miles driven after oil change - 100

Following the last change the oil pressure was still high at start-up, but did drop to an acceptable pressure of 30# at about 150 water temp. That marked a significant drop, and change from the 2nd change using conventional oil (see the table below of oil pressure readings at various water temps and RPMs). So, I’ll drive it a bit and see how the summer ambient temps affect the pressure readings.

Now, you can accept what the posters say and just drive it. I, by nature, can’t. I am both puzzled and concerned by such a dramatic increase in pressure at start-up from simply changing the oil, and I’ve been changing oil in all my cars for over 40 years. What you and I have experienced is not normal, and “just driving it” could result in engine damage.

You and I can take our chances by “just driving it,” or we can continue to look for the cause of the increased pressure. In the meantime, before I “just drive it” I let the engine warm up (gas is cheaper than an engine repair) and ensure the pressure at 1500 rpm is running no higher than 45#.

Below are the oil pressure readings after the 2nd oil change in data and graph form taken as the engine, water, and oil were increasing in temperature:

rongold

Mine pegs past 80 when cold, and then settles down to about 40 at idle and 75-80 above 1200 rpm when hot. When I built the engine, I put in a stock L88 pump, which has the high pressure spring and 1/4" longer gears. Like Dan said above---better too much than too little.

AZDoug

Your oil pressure is governed by the bypass valve spring in the oil pump., and to a lesser extent, by how worn out your motor is, as in low pressure = worn motor/excessive bearing clearance, if pump is working properly

I would rather have 60 PSIG than 45 PSIG any day at cruise speed, warm.

A stuck bypass could theoretically blow your oil filter off, probably at about 200+ PSIG.


The factory Z28 302 was designed to run at about 60 PSIG. I have one of the Z28 pumps in my '61 car (427 SB), and cold, the gauge is pegged, I suspect the bypass opens at about 80 PSIG, at cruise, it runs 60,a nd about 45 at idle, warm.

FWIW, my Ferrari runs about 90 PSIG as normal. Higher RPMs like higher oil pressures.

Doug

Westlotorn

It sounds like someone built you a very good engine. I like your readings cold and hot and would make zero changes.

TCracingCA

Make sure the engine is vented good whenever seeing pressures in these ranges. I just vent to the atmosphere being that I am such an enviromentalist!!!!!

Second always take the time to warm it up before putting a load on it (just for the sake of bearing clearances and all!)

And if you take the screw on oil filters, go get the longer 2 quart truck filter!! If you are cannister, then just a Fram or quality one! Stay away from the cheap paper ones!

I would also recommend running the synthetics 20-50!

Ps sometimes I have seen rebuilders shim the bypass springs instead of putting a new one in. It is a trick of a thief to make a guy think it has all good bearing clearances and such and "Look how great the oil pressure is now! Pay me!" type conversation.
I would drop the pan and get the little putty clearance stuff and check a crankshaft bearing!

DansYellow66

Why did you put STP in your motor? I'm not exactly sure why it has not reversed course since you changed it out of your oil, but I would never have put that stuff in one of my engines in the first place - unless it was on it's last leg and I was still 100 miles from home. Other than that, except that my hot idle pressure looks to be higher than your small block readings, my engine runs that pressure if not more. It pegs the 80 lb gage at idle cold and it stays pegged until it warns up considerably. Rule of thumb is an increase of a "minimum" of 10 psi hot for each 1000 revs. My motor has a 7500 rpm valve train in it (not that I use it) so that it will peg an 80lb gage hot when accelerating is exactly what I'm looking for. My motor was built in about 1986 and is still going strong. I would not lose sleep over it.

KSL '67 101234

I added STP on the recommendation of a good friend, a mechanical engineer and long-time engine builder. After adding it and seeing the pressure readings I knew something changed but could not trace the cause as I did not take pre- and post-readings in steps. I want to give credit to the the technical people at Valvoline. Mike was very helpful and said the STP will affect the viscosity, but to what degree is based upon the engine's clearances, oil pump, as well as many other factors. His recommendation was to drain the oil when its very hot, and replace with either VR1 racing oil or standard Valvoline. He said the additives in VR1 will not affect the viscosity nor lead to an increase in pressure. His guess was that there was a mecahnical issue brewing and that it occurring following the oil change is conincidental.

As to Zipp It's post, I was very interested in following the comments, as his experience is very similar to mine.

JohnZ

Stop listening to that person.

KSL '67 101234

I was overcome by the irrational exuberance from the reality that I was about to change my Vette’s oil for the 1st time! I have once again regained my senses.....

claysmoker

STP?

claysmoker

Westlotorn

The original poster here said he bought this car with a new engine in it. Properly built a new engine will have good tight oil clearance between the Rods and Mains and Cam bearings. If this engine is set up by todays standards, normally ( .00175-.00225 ) he will have good oil pressure with very little drop off at idle. If they built it to old standards with large clearance on the Mains and Rods the pressure will be much higher at start up and lower when hot. Old standards for mains and rods were typically .0025 to .0035.
The extra clearance leaks a lot of oil when hot and your pressure drops at idle. Rev it up and the oil pump will put out enough to raise the oil pressure back up to it's relief valve set pressure, that is the pressure you will see if the engine is held at a steady RPM well above idle, like cruising on the freeway at 3,000 RPM.
Some modern engines are built with .001 to .0015 at the factory and have 100,000 mile warranty while many of these have red lines well above 6,000 RPM, some reach 8,000 RPM at the factory red line. Running old clearances are like running a flat head engine, technology has passed that era right by.
One of the big gains in tighter rod bearings is better oil control by the piston rings. The rings are lubricated by oil thrown off by the connecting rod bearings, loose rod bearings will provide more oil on the cylinder wall than the rings can control and the engine will use oil even though the rings and cylinder finish are good.
A friend and shop owner built his personal engine a Small block 400 with rods and mains at .001 as his personal test engine and put it in his Suburban. He towed with it, drove the snot out of it towing his trailer and keeping up with his buddies towing with their Diesels. His father borrowed this Suburban and was towing while on vacation and the radiator failed while the father was pulling a long hill, he caught it late and overheated it blowing the head gaskets. On tear down after about 2 years of use and abuse the Bearings were cherry and could go back in again. He normally shoots for .0015 today by choice but knows his ran great in a small block 400 at .001. He has a great rep for building high quality engines.
Some oil pumps brand new are loose and will spill more at idle giving the same oil pressure results as loose bearings, not common but it happens. The oil pump can be taken apart before an engine build and checked, the most common cause is too much clearance between the gears and the cover plate, you can check this clearance with plasti-gage to make sure this is not going to happen in your engine. If I remember correctly .002 to .003 was good but .004 or above would cause oil pressure issues at idle. High end engine builders will tear down every oil pump and make sure it is to blueprint before installation. This is adds 30 minutes to an hour to an engine build so it is not done by most shops.
If I was looking at your pressure readings I would be very happy and not concerned at all.

PS: a lot of engines for these old Corvettes are built with less than perfect oil clearances because the owners want to stay all original, the choice is made to run a crankshaft with .003 clearance because they don't want to grind an original or they don't want to add money to the rebuild by grinding the crank. These choices are fine and the engines will live a full happy life but you will live with low oil pressure at idle and may use more oil than a tighter engine. Both are good engines, but one is loose and one is tight. I prefer the tighter engine and I know the reasons for building it tight but both will run for many years even if your idle oil pressure is as low as 20lbs. ( but I want 45 to 60 at idle )