91 Olds Cutlass Supreme 3.1 Oil Pressure

[2Tired]

Hey..,

 

I have a 91 Olds Cutlass Supreme 3.1.., and the Oil Light has come on occasionally.., usually while sitting at a light., in gear.., on the brake.., when you accelerate or put in neutral.., the Oil Light goes out. So.., I removed the Oil Switch.., and the opening seemed quite thick with 'sludge' like material.., although it seemed to flush out ok.., the port on the block had same sludge-like material.., which I flushed out also.., then I installed a manual type Oil Pressure Gauge.

 

My question is.., what is the 'Oil Pressure - PSI Range' for this engine..?

 

I primed the oil tubing feed line from the engine to the Pressure Gauge.., so there was no air in the line.., but when I shut the car off.., there seemed to be air in the line. The instructions did not say anything about priming or purging the tubing to the Gauge.., but I did it anyway.., thinking it was the logical thing to do. Anyway.., it seems to work correctly.., having started the vehicle several times since installation of the Pressure Gauge.

 

After start-up.., when the engine is cold.., the Oil Pressure is very good..., then as it warms up.., it drops down to 20 or so.., but when you drop it into gear.., and sit with the brake on.., it can drop to @ 10 psi.., or so.., then when you accelerate.., the pressure comes up again to @ 20.

 

Is 10 psi normal.., when warm.., and sitting with your foot on the brake...?

 

What is the safe minimum pressure..? Would changing from 10w30..., to 20w50 be a better choice..., being that the car now has over 130,000 miles..?

 

I was just interested to know what the 'normal'..., and 'minimum' Oil Pressure is for this engine.

 

 

If you knoweth..., grasshoppa awaits.

 

 

Thanks.

[RobertISaar]

everything you're seeing is normal, and don't jump up to 20W-50, while it will most definitely raise your oil pressure, it will significantly lower the flowrate of the oil at the same time.

 

normal would be the oil pump pressure relief valve opening at ~60PSI, which you'll only ever really see when the engine is cold.

 

also, why 10W-30? LH0's spec 5W-30, when at full operating temp ~(100*C), both oils will act more or less the same, but when cold, the 10W is going to be noticably thicker, and thicker oil moves slower/requires more power to pump/etc.

 

if you were to move up to a thicker oil due to pressure being unacceptable at operating temp, 0W or 5W 40 would be the next logical step up in viscosity(not counting certain "high mileage" 5W-30s).

 

as long as the lifters don't start clattering around due to not enough pressure at a hot idle, you're seeing enough oil pressure at that operating range.

[2Tired]

Thanks for your reply.., good info.., could use 5w40.., it rarely drops past - 5 where I live.., so just use 10w30.., so 5w40 is a good suggestion.

 

I was concerned with the Oil Light coming on a few times.., so I picked-up an Oil Pressure Gauge and installed it.., just to make sure what pressures the car actually had when at operating temperature. I thought that oil pressure would have been a little higher than @ 10 psi at warm idle., in drive.., on the brake pedal.., but anywhere else.., the pressure is well above that.., just at warm idle.., on the brake.., is where I have some concern.

 

Am I correct that the Oil Switch closes @ 3 to 6 psi...? If so.., @ 10 psi seems a little close.., perhaps 5w40 would help a bit there.

 

Finding sludge in the Oil Switch opening.., as well as in the block port.., is likely the cause of the Oil Light coming on a few times.., hindering proper flow rate to the Oil Switch.

 

It is somewhat annoying finding this crap here.., as the oil is changed regularly.

If I utilize 5w40.., any suggestions for an additive.., Lucas.., Bardahl..., perhaps an 'Oil Flush' before next oil change..?

 

 

Hopefully this sludge at the Oil Switch was the only problem.., I guess I will see in the next few days.., observing this Oil Pressure Gauge.

 

 

Thanks.

[RobertISaar]

oil pressure switch will close AROUND 4PSI... after being in use for so long, it could be 1 or 10, you never really know. it's only purpose(other than turning on the low pressure light/oil pressure guage) is to provide an alternate +12V source for the fuel pump, should the fuel pump relay fail.

 

additives = waste of money. these days, oil is VERY highly understood and very closely controlled, putting other oils/chemicals into oil that MAY defeat it's own additives isn't a good idea.

 

Lucas is just a REALLY thick oil with no real additives to it.

 

oil flushes.... there's a couple of different views on it. automatic trans fluid can do some really good cleaning in an engine, i wouldn't use more than a quart and not for very long. i've used a quart of kerosene with success before, but put no more than 50 miles of LIGHT driving on the engine before changing the oil.

 

0W or 5W-40 would increase the oil pressure you see at full temp in all conditions, but i'm not so certain you need it. "low" oil pressure isn't necessarily a bad thing, since pressure is simply a measurement of restriction to flow. you can have 100PSI of oil pressure and absolutely destroy an engine due to lack of oil flow. certain engines seem to need abnormally high oil pressure to live(3800s for example), but most are happier with relatively low pressure.

[2Tired]

Thanks for your reply...,

 

 

Some interesting information.

 

 

I will drive the car for several days.., and see what this gauge is telling me.

 

After that.., although the car is not quite due.., I will change the oil.., perhaps to 5w40 if the pressure has consistently been anywhere close to 5 psi at hot idle, in gear, on brake. Also for the purpose to get a clean oil filter on the car.., and purge any sludge in the system..., the lifters are a bit noisy at hot idle.., so I would like to see if that can be addressed also.

 

 

So.., if the oil pressure at hot idle, in gear, on brake.., is stable 'above' 5 psi .., "all-is-well"...?

 

Or.., what should the minimum pressure be.., in order to not activate the Oil Switch @ 4 psi.., should the minimum pressure not be several points above the Oil Switch activation threshold..?

 

 

If the pressure consistently stays above @ 6 psi .., I will re-install the Oil Switch.., and see if the Oil Light comes on any more.., if it does.., I guess the Oil Switch is crap-ola.

 

 

 

Thanks for your information.., I appreciate it..!

[White93z34]

Interestingly enough the owners manual - I believe states that that is normal... however i've never seen a single person till now mention it.

 

maybe add in some ATF or seafoam 50 miles before next oil change?

[RobertISaar]

the owners manual does call it normal... because it is. an engine with significant mileage will have some slop in the bearings. the 90GP was at ~190K last i knew and at a full temp idle(and i set the idle low on that car, like 600), it still made a good 10PSI on 5W-30.

 

if the lifters are making noise when at full temp, you need a thicker oil or a higher volume oil pump. obviously, one of these is much cheaper and easier than the other.

Edited March 12, 2013 by RobertISaar