1995 Bonneville Low oil Pressure

[RDLDRDLD]

I get low oil pressure when the car idles or when the oil heats up. Replaced the oil sending unit and the problem is the same. Looking for a diagram of the oil pump replacement if anyone has one. I have seen where some say the engine can be worn enough that it won't get pressure - the engine runs smooth and does not knock. It might be wishful thinking, but I think it comes down to a flaky guage or the oil pump at this point- Could also be the oil pickup. Anyone else have these symptoms- what fixed the problem for you?

[ricebike]

can be the pickup if some gasket material clogged it...

lack of oil change? too much sludge in the engine would restrict some flow...

online manuals on the internet that are haynes/chilton type at one auto parts place...

other than hooking up an oil pressure gauge, we won't know

[RDLDRDLD]

After I replaced the sending unit and hooked up a mechanical gauge to verify pressure is low, using thicker oil. I am to the point of replacing the pump- oooorrr?
I have seen some threads about putting a heavier spring in the oil filter housing to increase the pressure. It is a trick used by race car mechanics, and some Farmers use this trick to get some more life out of hydraulic systems. It is my understanding that if you put a heavier spring in the oil filter housing and the pressure comes up- it means the pump is good. Can anyone shed some light on this? I am about 1500 miles from my next oil change when I will give this a try. BTW- My engine runs great, no knocks, it just gets below the red pressure line and the dinger goes off. I have some fairly thick oil right now-but once it gets warmed up it still hovers around the red line at idle.

[Jrs3800]

First what kind of 95 Bonneville do you have? There were 2 engines used that year.... The L36 Series II 3800 and the L67 Series I 3800( Supercharged )

Next being that you are using thicker oil the spring for the bypass valve is not going to buy you very much oil pressure.. And its very rare that these oil pumps fail..

If you have an intake failure or have had an intake failure as well as a lower intake gasket failure the engine could possibly be done.. But it would help to know what engine you have..

[RDLDRDLD]

I have the series II 3800. I thought when I bought this car, 6 years ago, it was leaking oil from the manifold. I tore it apart and put in all new gaskets, but there is a real slow leak somewhere still. Guy told me it was prob warped - not worth fixing. The car has been this way for 35,000 miles and has not developed any knock or gotten worse, so I don't think the engine is shot. The car is not worth putting any money into. It is a runner. If putting a spring in there can raise my pressure reading 5 lbs. it would be fine for my situation. I have talked to several people and they say if your getting 15-20 pounds on a mechanical guage, it is enough to lubricate the engine.
(The annoyance for me is that the dinger goes off and it is not the same dinger as the lights and seatbelt. I would like to know if there is a way to disable this cluster alarm dinger as well without disabling the entire cluster.)
If this car dies- I really don't care. I don't think it is very close to dying - so I will keep brake, oil, and coolant in it. My son drives in 2 years and I know my son - whatever car he drives will take a beating.

[Jrs3800]

I do understand what you are saying..

The spring pressure for the bypass may not gain you anything if the pressure is dead low.. But the next time you are there you can try adding a hardened washer inside the plunger to help stiffen up the spring.. This can help add pressure, but in your case it may not do much of anything if at all.. But worth a shot..

You can get away with running 10-40 in that motor, 20-50 would be pushing it... I ran 20-50 in my 95 Series I( used the same crank as the series II ) and drove it 3000 more miles till I pulled the motor..

[rayp40]

I have had the same problem with my 95 Bonne SSEI for 3 years now. I have pulled the oil pan and checked the intake and found nothing abnormal, also changed the sending unit..no change. Mine has plenty of oil pressure when the engine is cold; 45 psi..and drops to 5~10 when hot and the engine goes below 1000 RPM. Above that speed I get 15-20 psi and it always stays above 35 psi above about 1500 rpm. I have been driving it this way for 3 years.


The oil pump on the beast is simplicity itself, but getting to it is not so simple. You need to remove the front cover of the engine to get access. If you've ever thought about this, you quickly decide against it. According to the shop manual, you need to remove the right motor mount..they call it the "Torque axis mount," the drive belt(s) and the damper pulley. Although they don't specifically tell you in the manual, you also need to drain the coolant since the water pump and water outlet are part of the front cover assembly. They also don't tell you that you need to support the right end of the engine since you have the motor mount off.


Anyway, my opinion is that the main bearings are probably worn, since I have 150,000 miles on the car. If I ever decide to replace them I will post the results. Good luck.

[Jrs3800]

I agree, there is a good possibility on the series I engines that the Mains could be worn.. Mine was at 180,000 Miles... But with the series I engines the usual cause of lower oil pressure is the #1 Main and #1 cam bearings wearing..

The series II's are a bit different..

[rayp40]

Jrs3800: Thanks, appreciate your second opinion.

[RDLDRDLD]

I guess I don't understand how this Series II could be that bad at 170k. I ran series II in a 2000 Impala 290k and it ran like new when it got totalled (due to an idiot driver). I thought the series II was pretty much bulltet proof. Maybe GM used better bearings in 2000 than they did in 1995.

[Jrs3800]

Have you had the 95 since new?

A lot of the time with the 3800 series II the usual cause has to do with the lower intake gaskets or the upper intake failing and allowing coolant into the engine.. If the leak is internal the oil can become acidic and pit the bearings, from there sooner or later failure will happen..

My original 95 engine went 161,000 miles before I had to pull it... It had a massive upper intake failure.. I didn't catch it right away( didn't know that much about intake failures back then )... I drove that car 80,000 More miles... I never had any oil pressure issues or problems with the bearings in the bottom end... I pushed the motor soo hard I simply wore it out.. The Piston to bore clearance was bad..

The second engine I used was short lived and did see an upper intake rupture... Motor only made it 80,000 Miles.. The 3rd one is still running today( 2 years later ), it never had any upper intake or lower gasket issues.. 20,000 + miles later the motor still runs great... Total mileage on the motor is 80,000 Miles now..

Most of the 3800's do get serious miles... I do look at the 95 3800 series II as the first year of production.. I should have never bought it in its first year, but it did give me great service..

I have a couple of friends with 97's and they still run great with next to nothing for issues.. One has 200,000 on his and it runs like new..

[rayp40]

Thanks for your replies. I did not buy this car new; I got it in 1997 and it had 17K miles on it. Other than the A/C compressor failing, it has required only normal maintenance.

Regarding the intake gaskets failing, it does not appear that's a problem as the coolant level has always stayed full.. However, now that you mention that problem, that's probably true of my wife's 96 Buick Regal..also a 3800. No low OP on hers, but need to add coolant about once a month.

[Jrs3800]

You have a leak someplace... Find it very soon... I add almost nothing to my cars.... Might add a little every 4-6 Months.. Watch it close..