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Old 01-31-2013, 10:24 PM
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Very low oil pressure after about 5 minuted running

1995 buick Lesabre 3.8 V5 engine with 180k miles At start up has good oil pressure of about 70 pxi The computer controlled engine at start up runs about 1500 pm for a minute or two and then starts ramping down as the computer skows down the engine t0 around 1000 rpms ( estimated) at this time the oil pressure drops several pounds as the engine is starting to warm up the computer steps it down about to more steps until normsl idle speed of around 750 rpms is reached each step down in speed drops the oil press until at idle speed the pressure hangs on but is constantly wavering at 30 i033 psi , (I am using an external test gauge) the oil pressure holds up at39+ pounds for a couple more minutes the engine temp gauge is displaying about 170 degrees and all of a sudden the pressure drops to near but not quite 0 pressure, before shuting down the engine I increased the rpms slightly to see if the oil pressure would go up ans it did go up asmall amount. Some history about this car might be related to the problen. poor engine manteanace for 1 . infrequent oil changes. The owners kids washing the top of the engine with 2500 lbe pressure washer caused the thtottle valve position podition trans itter in about the 3K rpm range. A while after this was fixed the oil pressure starting a little eractic some days the pressure was ok then on some days the presure was very low. I have a very close friend who happens to be the best mechanic I have ever known, tells me that high milage CM 3.8 ingines have a history of oil pump ware. it not only involves the worn impeller but the allumin outside plates is worn and schored alowing the oil slip past the impeller to t suction side. To me this seemed to be most of the problem but did not explain the oil pressure going to almost 0 psi after idleing at 750 rpms at a pressure of near 30 psi, If the oil slipage past the impeller had to be near 100% after runing at an aceptable oil pressure as it warmed up for 5 or 6 minutes and then sudenly troping to 0. that does not sound right. A very littlr thought was given to the oilpressure regulator sticking open and was quickly discounted as to do this the regulator would have to work in reverse of its normal mode as it normally bypasses the oil flow at high pressure to lowerit and should be off

tight at low pressure. A badly worn oil pump causes low oil pressure but a suden drop after 6 minutes of running to near 0 psi
The design of the oil pump is centhical rotating impeller in a very close fitting housing. A few thousants wear on the outer cover plate will increase the slipage back to the suction side and greatly decreases the pump to mantain pressure high enough to cause the oil pressure regulator to open to decrease the pressure to the limited pressure maybe 60 or so lbs I realy dont know what the highist design pressure is for this engine is but it seems erelevent to the problem. This pump is more efficent at the faster speed even if it is near worn out. As the pump is runing at the start up high idle of 1500 rpms when first started it could put out only 60 or so lbs, probaly not enogh pressure to open the pressure regulator bypass. ac the pressure increases so does the oil slipage from output to the suction side.
what if at near mormal warmed up engine some of the oil is liquified and flowing normaly thrue the sump screen and the oil pressure is fair and can get by but like a frozen river in the soring thaw has the problem when the ice cover breaks up and starts to flow down stream with the liquid water somer where down stream the ice wile cause a restriction. This engine has had very dirty sludged up oil. What if some old grey headed fort decided to run a motor flush through the engine befor changing oil If the rngine is heavely sludged up this flusht may cause globs or chunks of sludge to fall into the pan this sludge globsho not drain well and probally lightly stick to the pan. cold fresh oil does not bother it at all when it is put in the engine . If a large amount of this sluge is near the oil intake screen it may when the engine is close to warm up tempt my cause the glob to come loose and be sucked to the screen and stop oil flow to the pump If at this time the engine does not have a knock prompt shut down will avoid damage but if not a main will sound off soon. this is my first tine to be in your forum. please coment whether this might be possabke

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Old 02-01-2013, 07:03 AM
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Many years ago we had a Buick Park Avanue with the 3.8. It was fresh overhauled, had great power, and really ran great. Oil changes were regular and on course. However by the time the engine got 150,000 miles on it the bottom end was loose and rattling as evident on a cold start. Once the bearings in the bottom end get worn the oil pressure starts to head south once the engine and the oil is fully warmed up. The only thing you can do as a band aid is install a high volume oil pump or run a heavier oil. Even so I can't speak for your engine, mine with regular oil changes was gone by 150,000 so my thoughts are yours without regular oil changes likely has the same problem. Also keep in mind, just about all gauges are not accurate below 10 psi, some as high as 20, so the quality of the gauge can play a role.
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Old 02-01-2013, 09:20 AM
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I have had a number of Park Avenues and LeSabres with the 3.8 and never had a problem with oil pressure. My current 2002 Le Sabre has over 180,000 miles and the oil pressure says it is running at 129 psi. Frankly I don't believe it is that high. Most of my cars had 260,000 miles on them before I got rid of them. In my opinion the GM 3.8 V6 is one of the best most reliable engines ever built.

Are you reading the oil pressure from the computer or a oil pressure guage? What weight oil are you running? I run 5W30 synthetic on all my Buicks and never had a problem.
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Old 02-01-2013, 11:30 PM
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Quote:
Originally Posted by taylor23 View Post
This may be happen when oil is leacking on any inside part of engine. For overcome this problem check all the pipes from which oil runs.


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Last edited by painted jester; 02-01-2013 at 11:58 PM.
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