Ideal Oil Pressure

[burgy711]

On my restoration I put a 1725 in unknown condition into my Series III. The motor was thought to have been a re-fresh and I did pull a couple of freeze plugs to find the insides to be looking like new. I've had the motor running now several months and things run great. The motor was bought in a large Rootes parts sell off that was then pasted through several hands before it came to rest with me so there is no way of knowing what I have.

What I noticed is that in gear and with a load on the motor say third or fourth gear going up hill or at higher RPM I will hit 75 pounds of oil pressure. Normal running in third or fourth in the 35 to 55 MPH range it will run around 50 pounds of pressure and at idle could drop to 25 pounds of pressure when good and hot. Should I have concerns with the 75 pounds of pressure? In past Alpines I'd be thrilled with 50 pounds and at idle 25 would be good too but I have not seen 75 pounds before.

 

[Nickodell]

Hi, Steve. Unless the gauge is faulty and reading high - unlikely due to the 25psi at idle and the fact that these are mechanical gauges - my guess is that someone in the past has tinkered with the relief valve. A popular, but IMHO unwise modification is to convert the spring to an adjustable one and then pump up the pressure way over what the designer intended.

There is a strange illusion that if you are getting low oil pressure in a worn engine you can magically restore it by increasing the relief valve blow-off pressure. Since this is designed at a max of 45-50psi, if the engine will not reach this pressure it is futile to increase the setting if the engine can't even give the standard pressure.

If someone has done this you can usually tell by the presence of a set screw and locknut sticking out of the end of the valve body. If there is, you might want to try reducing the setting by backing the screw out in small increments until you reach a 50psi max, then secure the lock nut.

 

[RootesRacer]

Hi, Steve. Unless the gauge is faulty and reading high - unlikely due to the 25psi at idle and the fact that these are mechanical gauges - my guess is that someone in the past has tinkered with the relief valve. A popular, but IMHO unwise modification is to convert the spring to an adjustable one and then pump up the pressure way over what the designer intended.

There is a strange illusion that if you are getting low oil pressure in a worn engine you can magically restore it by increasing the relief valve blow-off pressure. Since this is designed at a max of 45-50psi, if the engine will not reach this pressure it is futile to increase the setting if the engine can't even give the standard pressure.

If someone has done this you can usually tell by the presence of a set screw and locknut sticking out of the end of the valve body. If there is, you might want to try reducing the setting by backing the screw out in small increments until you reach a 50psi max, then secure the lock nut.

Well Nick, I have to partially disagree.

While most basic engine wont get an advantage out of increasing the oil pressure, the fact is that increasing the oil pressure by increasing the relief pressure has a twofold benefit.

1) The added pressure, will increase the flow of oil around the bearing clearances, which (particularly if the rod big end has a squirter slut cut) will allow the journal to remain cooler at higher RPM due to the increased oil across the journal.

2) The oil is not being pumped/worked as much since less of it will get bypassed back to the sump. If more pressure is developed before the surplus is dumped, less pumping losses are created and the pumping will heat and aerate the oil less than if it is pumping it around in circles.
Aerated oil is not such a good lubricant nor does it have good thermal transfer, which is why serious engines run a dry sump.
Granted the added oil pressure puts added strain on the pump drive gears, this too can be overcome with a squirt slot in the pump.

The difference between 45 and say 65 PSI increase is negligible WRT the design constraints of the relevant components, and has been shown in practice to allow longevity in properly equipped performance engines.

 

[Nickodell]

I agree totally with the benefit of increased oil flow. However, you've missed my main point - how does setting the relief valve to a higher pressure do anything for an engine that can't even reach the original design pressure? That's like increasing the pressure in a leaky tire to 100psi. You could set the relief valve to 200psi and it will still show a low pressure at the gauge and will not change the flow rate at all.

In nice and tight engines like Steve's, resetting the pressure to much higher pressures has been shown to increase the likelihood of trouble. More than one member has posted accounts of, for example, blown oil filter gaskets. I would also be suspicious of the flexible pipes to the oil cooler.

I suppose I'm always leery of people who think that they know better than the ones who designed to engine in the first place, the only exception being the use of modern technology in such things as oils and electronic ignition, stuff that wasn't around back then. You can be sure that if they had, the Rootes engineers would have incorporated them.

 

[V6 JOSE]

Nick,

Factories don't always do things the best. Sometimes they will compromise to save money.

In the oil pressure department, We have run engines with the relief valve set at 80 lbs, without any problems. I really don't think 75 lbs. from time to time, will hurt anything. If my engine showed the kind of pressure he says his does, I would be a happy, proud man.

Oil pressure much above 80 lbs., can wipe off the babbit that the bearings have as a facing.

Jose

 

[RootesRooter]

Steve,
Per the factory manuals, fully warmed up oil pressure in a 1725 should max at 45psi if the pressure relief valve is operating correctly. I think you need to either turn down the current relief valve (if it's been made adjustable by the PO), or replace it (they can be hard to find in good condition) and see what the pressure is.

Like others, I think 75psi is on the edge of blowing a oil filter base gasket. I'd avoid extended freeway trips til the pressure issue is resolved.

Dick Sanders

 

[RootesRacer]

I agree totally with the benefit of increased oil flow. However, you've missed my main point - how does setting the relief valve to a higher pressure do anything for an engine that can't even reach the original design pressure?

Well the engine/pump may not produce 45/75 PSI at idle, since the bearing clearances will leak more oil than the the pump can deliver, however at higher RPMs, the pump overcomes the clearances, and then the relief valve regulates the oil pressure. In my experience, a reasonably clearanced 1725 will produce 45 PSI (hot) from 2000 RPM on.

Any how, I'm not terribly concerned about idle oil pressure, the load is light and the journals dont heat up like they do at 6000 RPM at full load. Its then that I'd want the added pressure and the cooling the added journal leakage provides.

Lastly MANY engines run stock oil systems at 75+ PSI, and many use the same oil filters with the same rubber seal on the bottom we use. Ive only burst a filter seal once, and it turned out the old rubber ring stuck to the engine block (not a rootes engine) and there were two rings installed, the one against the block has no support on its outside so it pushed the seal out like a balloon.

 

[Bill Blue]

Ive only burst a filter seal once, and it turned out the old rubber ring stuck to the engine block (not a rootes engine) and there were two rings installed, the one against the block has no support on its outside so it pushed the seal out like a balloon.

Jarrid, good to see that you got caught in that trap. I thought I was the only one to ever do that and it was beginning to depress me. Company is good.

Bill

 

[Nickodell]

But remember, a pressure of 75psi for more than four hours requires immediate medical attention.

 

[howard]

But remember, a pressure of 75psi for more than four hours requires immediate medical attention.

YOU CAN'T SAY THAT! (He can't say that, can he?!?)

Nick- You can't say that! This is a family-friendly forum!!!!

 

[65beam]

oil pressure

oil filters are designed to take 200 to 250 psi before either blowing the gasket or bulging of the metal cannister. blowing the gasket is more common than distortion of the metal cannister,but i have seen it happen.when we first started pushing to open quick lubes we found some cars that had pressure relief valves in the engine that would stick and blow the filter loose.at that time the valvoline filters were made by either wix or champ labs and they worked close with us to solve these problems .some where in my attic i have the tech sheets on these problems and they state the particulars as far as what it takes to blow a filter.i need to look for them.i would assume the same still applies.

 

[RootesRooter]

I wasn't thinking so much of the rubber seal on the oil filter itself as I was the paper gasket under the base. Do modern cars really run 75psi? I'd imagined 55-60.