High oil pressure

[Dennis O.]

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.

[Jim T.]

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.

Changing to a 180 thermostat like the factory installed in your 327 L79 is a good idea.

[Donald H.]

Re: High oil pressure

Dennis,

If you do some research on this forum you will fine some information about oil pumps. I have the same issue with my 66 L79, high pressure. Seems like most of the oil pumps you get today are higher volume and higher pressure than were originally in our engines.

From the research I did, the one that comes as a standard volume and standard pressure is the Melling M55, but there are some concerns with it breaking due to some thin casting. I also have a 1960 I am restoring and ordered a standard pressure standard volume from Paragon, and it was the Melling M55. We did put it in the 283, and I'm hoping it perform OK.

As far as harm, what I found on other threads is that no one thinks it's a good idea to run the high pressure, but they also seem to say it does not do significant harm.

[Timothy B.]

Re: High oil pressure

Dennis,

Too much oil pressure causes oil to be forced to the rocker boxes and leaves marginal supply available to the lower end of the engine. Check to see if the L-79 uses a 45 or 60 lb relief pump and change it out. It's not a problem to pull the pan on a mid year and correct this. Good info in the archives about M-55 Melling pumps and oil pressure, they are good pumps but be careful with the relief spring pressure. Also, don't even think about high volume oil pump.

Seems odd you had a overheating problem then the engine ran at 160*. You may have had trapped air causing the coolant level to be low.

[Norris W.]

Re: High oil pressure

I've got high pressure issues with one of my L71 cars, but since it's driven easy and usually not for long distances I have decided to let it go for now and see what comes of it. I used the same high volume Melling pump in it that I've used in most all of my cars, but think the bottom end clearances may be the reason, since they worked out on the close side of the tolerance on both mains and rods.

One of my fears with high pressure is load on the camshaft & distributor gears. When I was in college many moons ago I had an L79 crate motor in a '57 Chevy. When making a camshaft change to an Engle, I also thought it would be a good idea (for some reason that I don't recall now) to shim the spring up in the oil pump to have big oil pressure. It would peg whatever guage I had in the car back then, but wore the gears on the distributor and camshaft to the point they were knife edge sharp within less than 1000 miles. I subsequently put an L79 camshaft back in and removed the shims from the spring and never had any more trouble for the additional 30 to 40K miles I put on it. That memory bothers me with the L71 Corvette now, but I haven't pulled the distributor and looked at the gears as I should have by now. This car pegs the 80 lb guage on start up and never gets below 60 after warmup.

[Joe R.]

Re: High oil pressure

High oil pressure should not be a problem in SB engines IF the block was prepared properly and tolerances are followed closely. Block preparation is the key so check out "How To Hotrod The Small Block Chevy," and prep the block as they suggest.
If oil starvation is happening in the bottom end of the SB Chevy you will have NO oil pressure.
Remember how a dry sump system works, "Sports Fans"
In our SB (Wet System) the oil flying around in the oil pan is of little or NO use in lubricating. As long as the pump is getting oil and producing oil pressure the crank, rods, cam, lifters etc. are getting oiled.

JR

[Tom P.]

Re: High oil pressure

A HIGH PRESSURE PUMP IS WHAT CAME IN THESE ENGINES FROM THE FACTORY!!!!!
If you notice, the oil gauge has a higher limit than the gauge in cars with the lower performance engines!
This issue has been kicked around with so many debates since the Civil War days!
Personally, EVERY engine I build gets a high volume pump. I just recently replaced a 350 (with a 383), which I built, with 35yrs/300K+mi on it, which had a high pressure pump all its life---------------still running, tired, but still running. Most engines that I've seen, which are in good condition, that have a high volume or high pressure pump will peg, or nearly peg the gauge (80lb gauge) on start up when cold. After completely warming up and everything is normalized, the pressure usually settles down to around 55-60lbs.
Again, over the years, there has been lots of debate on std vs hi-pressure pumps-----------------some of it has been pretty hostile.
I can assure you, after reading MANY comments from various people, that I have a heck of a lot more experience with engines and engine building than a lot of folks, here, or on the Chevelle forum or on the early Chevy forums. And I've NEVER seen any adverse effects from using a hi-vol or hi-press pump--------------even on grandma's grocery getter engines. So that's my .02cents.

[Joe R.]

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.

Dennis,

I would highly recommend changing to a 180 degree thermostat. Here's a good thread on the topic:

https://www.forums.ncrs.org/showthre...=2667&uid=8745

As a matter of fact, here's the one I would use because it won't stick closed:

http://www.summitracing.com/parts/BRA-330-180/

Joe

[Timothy B.]

Re: High oil pressure

A HIGH PRESSURE PUMP IS WHAT CAME IN THESE ENGINES FROM THE FACTORY!!!!!
If you notice, the oil gauge has a higher limit than the gauge in cars with the lower performance engines!
This issue has been kicked around with so many debates since the Civil War days!
Personally, EVERY engine I build gets a high volume pump. I just recently replaced a 350 (with a 383), which I built, with 35yrs/300K+mi on it, which had a high pressure pump all its life---------------still running, tired, but still running. Most engines that I've seen, which are in good condition, that have a high volume or high pressure pump will peg, or nearly peg the gauge (80lb gauge) on start up when cold. After completely warming up and everything is normalized, the pressure usually settles down to around 55-60lbs.
Again, over the years, there has been lots of debate on std vs hi-pressure pumps-----------------some of it has been pretty hostile.
I can assure you, after reading MANY comments from various people, that I have a heck of a lot more experience with engines and engine building than a lot of folks, here, or on the Chevelle forum or on the early Chevy forums. And I've NEVER seen any adverse effects from using a hi-vol or hi-press pump--------------even on grandma's grocery getter engines. So that's my .02cents.

Tom,

From reading your posts you have much more experence with these engines then me and I am not trying to pick a battle about oil pressure..

The high pressure pump that's factory supplied on the solid lifter small blocks is 60 psi relief. Don't you think if a HV/HP pump worked better the factory would have used it. Can you give me one example where a high pressure high volume pump works better than the factory rated pump, did it make the engine last longer..

In the how to hot rod book JR refers to there is a section that describes how to restrict oil to the lifters and rockers and it also makes reference to NOT running to much oil pressure stating 60-65 PSI max. So why does a street motor need a high volume pump with a higher pressure than 60 psi?? The edge orifice solid lifters were used to restrict oil to the valve train because of the high reving motor.

In post #1 Dennis states the lowest oil pressure he has is at idle where the gauge reads 55psi, I think that's way overkill.

[Joe R.]

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.

Dennis,

I think you would be best off running the standard pressure and volume oil pump that came with your engine. Here's one thread on the topic:

https://www.forums.ncrs.org/showthre...=2667&uid=3287

Joe

[Stuart F.]

Re: High oil pressure

I replaced my oil pump, timing chain and sprockets back about 1992 just as a maintenance matter. I know that sounds crazy and probably unnecessary, but I had to drop the pan anyway to repair the drain fitting and bump out a big "off road" dent. I can't find the info on the pump I put in, but I recall it was probably a hv/hp unit as that was all the rage back then. I too have the hp gauge as it is the L-76 motor, but I can't say I ever noticed too high of oil pressure until I went to Rotella T 15w-40 oil. I now hot idle at about 45psi, and get well up near the peg at rpm. Some side effects noted are oil seeping up past my center intake manifold bolts, a little seepage past my new valve cover gaskets (recent valve adjustment), and some oil dripping into my under engine catch pan in the garage. I fear the worst may be a leaking rear main seal.

I doubt if returning to 10w-30 oil will help much, but I will probably try on my next change. Otherwise, I too may be looking at some extra work in the near future.

Stu Fox

[Domenic T.]

Re: High oil pressure

I have ran engines both ways without problems BUT I think the crank clearances need to be concidered.

When we ran engines with loose clearance for racing we needed high pressure to take up the space between the crank & bearings.

With normal clearance you don't need to go much higher than what the factory recomends, (street engines).

When I first shimmed a oil pump I asked a old timer why we didn't go ballistic with the pressure and he said going ballistic blew the babbit off bearings. I'm sure he was talking about really high pressure but after seeing water blasting to remove paint and other things, I believe what he said.

What Tim said about to much oil in the valve covers is a reason to foul plugs also because the oil level gets to high and sucked down the intake valve guides. Also the excess oil that squirts out of the rods causes the engine to run to wet, (to much oil under the pistons).

When the piston go's down to suck the fuel/air mixture it also sucks more oil thru the bottom oil control ring. Good for racing but can cause plugs to foul on the street.

DOM

[Tom P.]

Re: High oil pressure

Tim,
I don't advocate that every engine should have a hi-vol/hi-press pump. I'm only saying that in all of my years of engine experiences, I've never seen any adverse affects caused by hi oil pressure in the 50-60psi range. Also, I've never seen a COLD engine startup, with a stock or hi-press pump, where the oil pressure was at the "normalized" position (usually around 35 with stock pump and 60 with hi-press pump). On a cold start, the pressure is always high until the oil/engine is heated up, then the oil pressure drops to the normal level. Of course, this can't be observed if a car has idiot lights! A gauge is needed to see where the oil pressure is at any given time.
Also, not everything in existance is for everybody. That's why there are so many options in the world to choose from. And on ANY engine, I choose, and have chosen, for MANY years to install a hi-press oil pump and have never experienced any resultant problems.
Also, with a proper, full oil level in the pan-----------including stock pans, I've never pumped the pan dry with any of my hi-press pumps, including the 455 in my Cutlass with a stock pan. Although, I admit, ALLLLL of my small blocks (except the 400 in the Chevelle) have the big Vette pans (either the 57-62 or 63-later style).
Oh ya, and I forgot to mention, even at my age, I don't baby any of my engines. I frequently flog the crap out of most of them, and I want to be sure they get well oiled---------------------maybe that has something to do with my preference to a larger capacity oil pump.

[Dennis O.]

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.

[Duke W.]

Re: High oil pressure

Yeah, let us know if you seize a bearing due to insufficient oil film strength.

Duke