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Old 05-18-2005, 01:01 PM   #1
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Default Very low oil pressure

Greetings:

I'm kind of stumped on this one. I have a '98 Bonneville SSei with 97,000 miles, and recently the serpentine belt that runs the supercharger broke. I noticed it the next morning (no warning light or anything unusual showed up on the gauges) when I went to check my oil level.

I had the car towed to my mechanic, who found the problem was caused by a seized idler pulley, which he replaced. He also replaced the water pump at the same time just as a preventive measure since he had to take off so much stuff to replace the pulley anyway.

However, since making the repairs, the oil pressure has dropped to only a few pounds above zero. The needle does move, but not a lot, and when I start the car and it is cold, the valved make some noise, but it goes away when the engine reaches operating temp. There must be oil circulating, or the engine would have seized already or something else catastrophic would have happened.

I had my mechanic change the oil pressure sending unit and the oil, and he thought the oil seemed cooked - he thought it might have overheated the oil when the supercharger belt was off, even though the engine temp showed normal.

Even with the new oil pressure sending unit, the oil pressure still shows very low, although it has been coming up about 1 lb a day, but not much. My mechanic thinks there may either be a lot of sludge or carbon crud blocking the oil intake screen to the oil pump. He said it might correct itself, and I added some CD-2 oil detergent to the oil to see if it might clear/clean it up.

I have scoured the internet, and it sounds like the next step would be to drop the oil pan and examine/or replace the oil pump, and my mechanic agrees. We haven't done the usual checking of the oil pressure with a mechanical gauge, but we already did replace the oil pressure sending unit, and I've been getting the low oil pressure still. What is odd is that the pressure is highest (in the red zone) when the car is stopped and idling.

Any thoughts? This is kind of scary as I don't want to seriously damage the engine.

Regards,

mld
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Old 05-18-2005, 02:33 PM   #2
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I don't understand that last part about highest in the red zone when idling. I'm thinking you mean the pressure drops off when you aren't idling.

First thing... get it checked with a mechanical gauge asap. Do not run or drive it until you know if you have pressure. Although it sounds like you have. So if damage was going to occur it already started. You could have two bad senders, but doubtful.

Don't like the valve noise comment and assume that'* new? Why did everything magically go to h*** right after he worked on it?

Anyone????? Which side of the motor is the oil pump? Didn't I hear someone say the water pump was part of the timing chain cover? If so I bet he dropped something in and now it'* blocking the pickup or a return hole so you can't pickup oil or it'* not there to pick up. If so he owes you a new motor. (Friend of mine had this happen.) (Started the car, ran for a little while, turned it off and no oil showed on the dipstick for 5 minutes.)

If the water pump isn't part of the timing cover then I'd say look for a pinched wire. The mechanic was on the side with the sending unit (passenger) and moving things to dig in there.
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Old 05-18-2005, 02:57 PM   #3
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When I start the car, the oil pressure needle (and the other gauges) do the usual light show and swings, and it settles at the absolute bottom below the zero. After the engine warms up, the needle moves up to the bottom of the red zone, but no higher.

When cold, you can hear some valve clatter, but it goes away as the engine warms up and the oil pressure needle moves up.

All of this is new since the seized pulley arm was replaced. Oil pressure was normal before that, although there was a small lead at the oil pressure sending unit.

Frankly, I was surprised by this. I thought that the only problem that the broken serpentine belt would cause was a lack of supercharger boost, and I can't see the connection from lost boost to lost oil pressue, especially given that the supercharger has its own permanently sealed oil reservoir that is separate. The mechanic thought perhaps that effected air intake to the engine and caused the oil to overheat, but I am doubtful.

By the way, there is no oil leak, and the dipstick shows it to be full, so there is plenty of oil in the block.

I am really curious about the connection between the water pump and the engine internals. Could the mechanic have messed something up when he changed the water pump, or could the loss of the supercharger serpentine belt result in block overheating and loss of oil pressure?
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Old 05-18-2005, 07:12 PM   #4
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You will need to get a mechanical gage on the car...

When the pulley went out, did it leave the water pump useless?

Even then if it did you would have noticed via the temp gage unless the block had no water in it... I'm sure this was not the case...

When the water pump was done, did the mechanic remove the entire front timming cover to do so? The water pump is not a bad job on these cars... But some of the parts in the way on the Supercharged enginers can make it fun to say the least...

I'm wondering what the oil really looked like... Black as in not changed for a long time or a graphite barbecued color.... What you describe almost has me believing that the bottom end is impending doom... The bottom end may be getting so hot that its frying the oil... If this is the case then the engine is over with and will have to be rebuilt no matter what you do... Its rare that an oil pump will fail in the lifetime of a 3800, but its possible...

My largest concern is what the oil actually looks like, and smells like... Along with the ticking / noise that goes away when the engine warms up... These engines should have a bit of lifter chatter upon cold start, but it should be for a very shorty period of time... Once the lifters have pumped up, it should be pretty quiet...

Its also possible that the oil sump screen may be clogged... Is the oil pan bent or deformed in any manner?

Have you owned the car from day 1? Has the car always had its oil changes? The last time the oil was changed did the oil pressure change at all?

Right now I'm thinking that the bottom end of the engine is in trouble...

These engines typically run at 25-40 Psi hot idle, and 60-80 psi at cold start...

Rule of thumb is 10psi for every 1000 rpms...

Please have the oil pressure checked with a mechanical gage...

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Old 05-19-2005, 03:19 PM   #5
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I'll make sure to get a mechanical gage on the car.

The oil pressure was normal prior to the pulley seizing. The water pump worked fine, and temp was normal. My mechanic recommended changing it because it was the original with 97,000 miles on it, and it was a lot of work to get the parts out of the way in order to replace the pulley, so it seemed like a good idea.

I was with him when he changed the oil. The oil looked black, and he said that it smelled burned, and was very watery. I recently bought the car used from an out of state dealer (believe it or not, I had the car checked out by a AAA-certified mechanic before I bought it), although I suspect that the oil hadn't been changed for a long time. I don't have the mechanical history, beyond Carfax.

I also suspect that the oil sump screen is clogged. The oil pressure dial on the dash stays at absolutely zero until the engine temp hits 175 degrees, then I think some valve opens to circulate the oil somewhere and the pressure goes up (still in the red zone) and the lifter chatter audibly goes away. I have low oil pressure, but not zero oil pressure.

I'm waiting for a part to come in, and I think I will invariably have the shop drop the pan to see what is going on. I don't think the pan is bent.
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Old 05-19-2005, 05:08 PM   #6
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The AAA mechanic I'm sure did a thorough job. Some things can be noticed and some cant. Best of luck..totally agree with dropping the pan. See first hand. Be prepared to consider putting a new oil pump in.
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Old 06-03-2005, 04:43 PM   #7
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Bad news - it looks like bad engine bearings. I need to replace the engine. Luck of the draw. Does anyone know where I can get a rebuilt 98 SSEI engine?
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Old 06-03-2005, 05:23 PM   #8
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Why not put in oversize bearings?
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Old 06-04-2005, 12:32 AM   #9
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Quote:
Originally Posted by Damemorder
Why not put in oversize bearings?
I agree... no need to scrap it just yet...
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Old 06-05-2005, 11:59 AM   #10
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I'd say its possible to put a crank kit in the engine, and a new oil pump as well... But buy the time you have spent the money on doing so you could have almost paid for a rebuilt engine with a warranty...

Personally, I love to rebuild it, But thats not for everyone..

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