Low oil pressure at Idle.

96 Bonneville SE 3800 vin K, 264K

I’m thinking the Oil pressure relief valve may be clogged or obstructed.? If the valve is staying partially open at hot idle could this be the cause of my sudden onset of low oil pressure. Can I get at this valve without taking the Oil adapter off the engine?

Problem began suddenly one month ago. Driving short distance, less than 10 miles oil pressure went to zero. Chimes rang constantly. Stopped car immediately ; let rest. Oil level a ½ quart low; coolant okay. Did not appear to have oil in coolant, or coolant in oil. Drove about a mile home without chimes. Pressure low but around 20-30 psi. This car normally about 40-44 2000 rpm operating temp about 195F; and maybe 35-38 at hot idle.

This car had UIM replaced in 2005. Since that time car loses 48 ounce of coolant every 1000 miles. No visible external leaks.


Action to date..

Changed sending unit (put in BWD sending unit), oil and filter (acdelco PF47) that day. After change, Oil pressure about 40 when cold and 38 when at operating temperature and 1700-2000RMP. However idle at a traffic light about 22 psi just above the redline or touches the redline. Most of time above the redline but as you wait at idle it will ratchet down to redline. Once at redline gauge will jump a little bit.

Since changing the oil now have about 700 miles on it. I intend to change the oil again at 1000 miles maybe sooner.

Took to dealer. Dealer ran a compression test and added tablets to coolant. Results CY 1-215; CY 2-195; CY 3-210; CY 4-210; CY 5-220; CY 6-205;


Drove the car on the interstate the other day about 50 miles; PSI 40 at 2000 RPM, got off interstate at light, PSI ratchet down to about 20-22 eventually touching redline. Light green PSI jumped back to 38-40. Operating Temp about 200F

Changed PCV yesterday. Not any noticeable PSI change on low range.

This car was running very good; and it still is. However this oil issue is concerning and I am trying to find the root cause and correct it.

I am hesitant to drive other than local because I do not want to be stranded.

Questions:

My concern is what caused the immediate problem. Was it a clogged oil filter? After I changed the oil and filter things improved immediately but not back to normal when hot.

My thought is if the filter was clogged could the relief valve also be part of the problem? What clogged the filter (sludge?). I know that lost coolant has to going somewhere.

Please advise. Thank you for your assistance and advice.


Jim

48oz of coolant every 1000mi? thats just not right....oil problem sounds to me like main/rod bearings.Time for a new motor.I've been down that street before...

My car'* the same year and trim, and I have the same problem.

I took it to a shop after my engine died [blew an air uptake or some crap]

After they were done with it, the oil pressure would go low at idle. Sometimes touching that red line, and causing that god awful and constant dinging.

But as soon as I hit the gas, shot right back up to 40 PSI.

I wonder if there are any sensors that could go bad that would cause this problem? Or if they were improperly installed or something? They replaced the Oil Pressure Sending Unit too, which maybe is put in wrong?

I was gonna check the relief valve, but I don't want to take all the stuff off and risk putting it back on wrong and killing my engine.

But my pressure has been like this for about six months now, and the car is still running fine.

I just wish I could get a straight answer as to what'* wrong. Some people say bad sensors, some people say bearings, some people say relief valve; I'm not going to be keeping this car forever, I know that, but I just want the beeping to stop

About the coolant; I seem to be losing a tiny bit every once in a while..
What color is yours? I know mine isn't the right color, it'* got a bit of a red tint to it, but i'm just wondering if yours does too.

Thank you for the responses to date.

I use dexcool and the color in the overflow bottle is a redish color.

I just picked up the new pressure relief valve items. I'll post what I find. I share the same thoughts of the difficulty of the task and do not know if the outcome will be positive. I agree with you from what I understand there are many things that could cause low oil pressure. I plan to tackle the job soon.

My oil psi issue occurred suddenly.

When I initially changed the oil and the filter the pressure came back up on the the upper end around 40 PSI where the car has normally operated. However the lower end was still low especially after about 20 minutes of driving and operating temp was 195 or closer to 200. When in drive at a light on hot day the needle touches the red indicator on the gauge. I couple of times it the car felt like it wanted to stall.


Thanks again.
Jim

I have the exact same problem in my 96 SE but it doesn't touch the red line. No one has been able to give me a straight answer yet, but my car is going in the shop next week and we will see what they say. I will be sure to let you know right away what they say and if it fixes the problem.

I to am having this problem, thats is why i found these forums.i just broke my cherry posting this post!!.. I just bought the car for $2200 its a 1995 w/ 125k it'* a florida car and there is nothing wrong with execpt the Low oil pressure after the car heats up. but as soon as i step on the gas it goes back up to 40 psi. there is no pinging or knocking. The car runs fine! Also i would like to note, The U.I.M. was just done. Along with all the vacuum lines, before i bought it. it also has a slight oil leak. im not sure where it is, i plan on adding some die to and buying a black light. also i average 27mpg

P.*.
I love this car. It is one of the best cars i have ever bought. I know its a 1995, but this thing is ROCK SOLID and i would drive this car to cali if i had to. So long as this oil pressure problem is nothign serious.

Here is a picture of the car started. it is 96°F out side.


Here is the oil pressure as i accel


Here is the oil pressure when i come to a complete stop after running the car for 10-15 mins.

Thank you everyone again for the input and responses.

Great dash gauge pictures. Those photographs depict exactly my 96 Bonneville’* low oil pressure situation.

I changed my oil pressure relief valve yesterday. Since then I have put on about 80 miles and have not noticed any significant change/improvement. On the high end, cold oil pressure is probably slightly higher maybe 60 pounds or slightly more. When at operating temperature oil pressure is about 40 psi constant; come off gas and then pressure is about 38 PSI.

However, at a light and at operating temperature oil psi is still right at redline. The only slight difference is when at low idle, the oil pressure gauge appears to be more steady and not jerky.

One other observation is I believe when operating temp is about 200 or above that is when at idle the oil pressure is at the redline. With a slightly cooler operating temperature the oil pressure gauge may read about 25.

It is interesting several members are experiencing almost the exact same issue.

I’m pondering my next step.

Jim

Wish we could some of the forums Guru'* know what there doing to post! Thanks

From the pictures I see, the pressure at an idle isnt a major issue thats going to hurt the engine. Even my GXP flucuates from idle to cruising, older car do it a bit more. But that is t on the low side. What weight is the oil. Have you changed it recently. And was the filter changed. Oil pressure sending units go weak. 3800 oil pumps are pretty bullet proof, so the first thing to look for is the oil. Have you changed it since your owned it? Filter? Oil relief valve is a possibility. I have seen a trend for older car members to go 5W30. Not a good move. Stay with recommended weights. We'll get Bill Boost in on this in the AM. He'* the guru gramps in this dept.