Acceptable oil pressure; 3800 series 2

[default]

Bought 98 Bonneville with 163k and typical old GM oil pressure gauge dance. Replaced sending unit and changed oil with 10w40 DEFY and a PL10111. Now I get 40psi cold start pressure, and 20+ warm, but it doesn't seem to want to go much higher than that, ever, almost like the relief pressure is set at 40psi. Is this normal? I've never had one of these big iron block engines before.

Before its asked, the upper plenum looks sorta fresh and the intake gaskets appear to be leaking a bit externally, for now it will get some bars leak. I'll deal with it correctly in the spring with a new plenum, the good fel pro LIM gaskets and aluminum elbows.

 

[beast3300]

Those gauge clusters are notoriously inaccurate. You should be around 40 psi at idle warm. I wouldn't worry about the readout. 10w40 is unnecessary for that engine.

 

[GMBoy]

Actually , with those miles you're doing good. I think the old basic rule of thumb was 5psi per 1000rpm at a minimum. But, I like to see 20+psi at idle.

 

[donnyj08]

Originally Posted By: beast3300
Those gauge clusters are notoriously inaccurate. You should be around 40 psi at idle warm. I wouldn't worry about the readout. 10w40 is unnecessary for that engine.


I agree. and 10w40 is pretty heavy for that engine. back it down to a 5/10w30

 

[Warstud]

I think you should be around 50-55 psi at cold start (idle). Around the same psi at highway speeds when at hot and 25-30 psi at hot idle.

 

[JR]

I know a few people who run nothing but 10w40 in there3800. I have 99 buick regal series2 3800 w/ 169k, i have qsud 0w20 and acdelco filter to go in after cristmas. I also rum straight whiskey(e85), i average 28.1mpg. 0.8 mpg better then e10 regular gas.

Kc

 

[default]

Thin oil concerns me in old cars with unknown histories after spinning a rod bearing in a 1992 5S-FE Camry so hard it seized in seconds(I didn't even hear it rattle) with a sump full of GTX High Mileage 5w30 with 2500 miles on it, I was running a nice NAPA Gold filter too. It was allegedly a well maintained car with 185k miles and showed it when we dropped the pan and found no sludge or heavy varnish, just a big pile of bearing metal on top of the balance pack below the #2 rod journal. I've run 10w40 in every cheap DD beater I've ever had since.

Back to the Bonneville, if I get bored I'll put a mechanical gauge on it. I didnt know the clusters had problems, I thought it was just the sending units.

 

[ls1mike]

Drive it. My Buick doesn't even have a guage. Those pressures are fine for that car and guage is most likely reading low. I have had 3 3800 serious two cars. When my Bonneville had 260,000 it's idle pressure hot was 18 to 20. It is still in use by a buddy of mine with 310,000 on it.

But...CHANGE your gasket NOW.

 

[beast3300]

Well the 3800 will take a lot of abuse without maintenace. As long as there isn't coolant in the engine then you're good. My 98 Supercharged Regal got 30-50 passes a year (6 years) at the local dragstrip starting at 175,000 miles on the engine and ending at 225,000 miles with a range of Pennzoil 5w30 to Pennzoil full syn 5w30. That motor is in my garage currently.

The 03 supercharged Regal has 180,800 miles on it with only one trip to the dragstrip before they closed for winter.

Either way I beat the [censored] out of these cars with wide open throttle many times a day. I can attest to the durability of these 3800s. The 98 Regal received 6 month/whatever mileage oil changes and the 03 will get the same. I keep the oil level in the safe range, do not worry.

 

[dailydriver]

Originally Posted By: ls1mike
When my Bonneville had 260,000 it's idle pressure hot was 18 to 20. It is still in use by a buddy of mine with 310,000 on it.


...BUT BUT BUT 'common knowledge' says a domestic nameplate should NOT be able to do that, least of all a GM.

 

[default]

Incredibly steep gears in these cars. The engine doesn't make many revolutions in 300k compared to say, a 91 Accord.

 

[sciphi]

If the gaskets are leaking externally, change them NOW!!! Bar's Leaks will be worse than nothing since it's giving a false sense of security. Also, it won't work with the design of the LIM gaskets. Folks have tried, and purchased themselves another 3800 as a result.

For the oil pressure, the gauge and sender are known liars. I'd also use 5w-30 oil, since that's the right hot weight.

 

[default]

Update:

Changed gaskets, aluminum framed fel pro kit and a dorman UIM w/ revised stovepipe.

Changed oil again after a couple laps around the block, L10111 and mobil super HM 10w40, having deiced against running a larger PF52 sized filter(hangs too low). Then I gt it plated and road legal, and hit the road.

Hot hwy cruising pressure is now 25-30 psi going by the stock gauge w/ new sender. No bueno. It will pull then needle into the red(under 20psi) when its all warmed up and idling in gear. Never will it climb past 35 or so. Fearing for the engine, and out of curiosity, a bottle of STP was introduced, no change in pressure was noted.

My thought now is either a bad gauge, or a bad relief valve spring. If the bearings were shot I would think the STP would have brought the pressure up, and the pressure would be dropping lower at idle. Next time I have time to drive it back home(gently), I'll hook up a real gauge and see whats up.

 

[Boss302fan]

10W30 in Michigan is the heaviest oil I would use in your car... If it was Summer, then maybe 10W40 but not in the Winter months. Also, STP does nothing... Mobil super HM is fine by itself. Pretty much any 10W30 HM oil is a heavy 30 weight oil and is all you really need.

 

[Boss302fan]

What did it cost you to do the lower and upper gaskets? My sons 2003 Monte Carlo SS with 67K miles is close to maybe needing to have those replaced.I am getting to lazy to do it myself.

 

[default]

Originally Posted By: Boss302fan
10W30 in Michigan is the heaviest oil I would use in your car... If it was Summer, then maybe 10W40 but not in the Winter months. Also, STP does nothing... Mobil super HM is fine by itself. Pretty much any 10W30 HM oil is a heavy 30 weight oil and is all you really need.


The car appears to have EXTREMELY MARGINAL OIL PRESSURE, thicker oil brings up pressure, STP is an oil thickener. If it made 40lbs on the highway with 30wt in it, I would be running 30 wt in it. This is an engine that dates back to the 60s.

I think the UIM was around $65 on rock auto, the LIM gasket kit I got for around $55 on amazon. Dont forget the coolant elbows, those are under $10, some blue loctite for the LIM bolts, and two 1/4" grade 8 washers for the two LIM bolts that are into a blind hole, some people think the bolts are too long and part of the problem.

 

[[email protected]]

Im really surprised nobody has mentioned this but..

The only real way to know the engines true oil pressure is to hook up a mechanical oil gauge to the block. Its also possible you got a lazy oil pressure sending unit out of the box. Do NOT trust the gauge on the dash.

Had a 93 Bonneville with the Series 2 3800..great engine. Junked at 290,000 miles. Didnt burn oil, ran as smooth as the day we bought it with 60,000 miles. Sub frame rotted and took the unibody with it - not repairable.

 

[default]

That's my current thought/plan. The behavior does not line up with any oil pressure issues I've ever heard of/read about. It never goes extremely low, or as high as it should. Usually a washed out lower end or pushed out cam bearing will give 0 at idle and still pump up properly when revved

 

[steve20]

Originally Posted By: [email protected]
Im really surprised nobody has mentioned this but..

The only real way to know the engines true oil pressure is to hook up a mechanical oil gauge to the block. Its also possible you got a lazy oil pressure sending unit out of the box. Do NOT trust the gauge on the dash.

Had a 93 Bonneville with the Series 2 3800..great engine. Junked at 290,000 miles. Didnt burn oil, ran as smooth as the day we bought it with 60,000 miles. Sub frame rotted and took the unibody with it - not repairable.


Exact same thing happened to my BIL with his Bonney-about the same mileage too. He lives in upstate NY = salt

 

[default]

Well, turns out the gauge was right, pressure dropped into red on the highway, pulled off and it went into warning buzzer range. Glitter in oil, turned over hard on restart, I managed to limp it to a parts store, bought a new filter and a bottle of STP and limped it home, still going near 0 at stops and now rattling above 2500 rpm. Debating used engine vs selling for parts and washing my hands of the whole mess.