98 buick lesabre 3800 (k) engine

Hi,
The 3800 engine has oil pressure when you start it. It is around 45psi. When you drive it for just a few miles, the oil pressure starts to go down. The pressure really goes down at stop lights or idle, when you go to drive it, the pressure goes to a reasonable rate.

This happens when the engine warms up. For the first few miles, the pressure is good at idle and speed. The car runs fine otherwise. Is it a sign of a worn oil pump? Should I check compression, would that have anything to do with oil pressure.

All help is welcome and appreciated.

Gary

For starters I would suggest attaching an external OP gage to the oil sending port to verify the readings.

Should I check compression, would that have anything to do with oil pressureCompression has nothing to do with oil pressure! How many miles on the engine?

I just rebuilt the engine on a limited basis. New crankshaft, bearings, piston rings and all seals and gaskets. The engine had 150,000 on it. Reason for teardown was bad piston bearing which damaged piston rod. Its been replaced. I was having problem with oil pressure before also. Had heads magnafluxed and no cracks.

What brand of oil filter and oil viscosity? Have you changed the oil pressure sending unit? As Max suggested, you need to verify IC gage accuracy with a remote oil pressure gage!

To me it sounds like the oil pickup is getting clogged. Back in the day Quakerstate oil was made with as waxes for additives and would bake onto every surface inside of the engine (the Quakerstate treatment), when you ran engine flush to clean the system all that carbon from the breakdown of the cooked/burnt wax would find it's way into the oil pan and stay. After the oil change all that crap in the oil pan would clog the pickup screen and starve the engine for oil causing low oil pressure and thus damage. It acted just like you described, oil pressure fine when first started, start driving oil pressure drops, stop the car at a light oil pressure drops off the map, let the engine cool and begin again.

The block, heads, and parts were all cleaned at an automotive machine shop before assembly. The oil pressure sending unit that screws into the base that holds the oil filter is also new. II use 10w-30 and Fram filters

Sorry, I just caught that...You did all of that work and didn't replace the oil pump? The oil pump is the heart of the engine and should be replaced or rebuilt with any engine rebuild... but I digress. The problem with the wrist pin you stated above is often caused by inadequate lubrication i.e. crap in the oil passage, bad oil pump, too thin oil or overheating to the point where things burn the oil off the surface or swell to where there's too little space for the oil to get out of the hole.

Some things we need to know to effectively help you... Was this a problem that started during the first drive after the rebuild, or was it a problem before the rebuild? Did you replace the sending unit before or after you noticed the pressure problem? Have you checked the oil pressure manually as suggested above? Are you using the correct weight oil?

To me, since the oil pressure is good before a drive, it sounds like it could be either crap in the oil pan as I suggested above or a stuck bypass valve in the oil pump.

I use 10w-30 and Fram filtersTry 10-W40 and change the filter to a mobile-1, Wix, or Purolator pure one.

10w30 isn't thin enough to cause the oil pressure to go that low.

10w30 isn't thin enough to cause the oil pressure to go that low.The OP never mentioned how "low" the oil pressure is, so how do you know?

The OP never mentioned how "low" the oil pressure is, so how do you know?

By the way he described the problem "The pressure really goes down at stop lights" and the fact that you wouldn't notice a difference in oil pressure between 10/30 and 10/40 unless they really fu**ed up the clearances during the rebuild (in which case the oil pressure wouldn't be normal when the engine is first started). Even then there wouldn't be enough of a difference that you'd be able to tell between two oil weights that close in range from the in car gauge.

#1 problem here....

Never ever use a Fram PH3387a on any 3800 V6.... This is a disaster in its self... The Fram can drop oil pressure as much as 10-15 Psi in a 3800..

AC Delco PF47 in most cases can be found cheap at Wally World.. Make sure it has a PF47 sticker not painted on..

Usual cold start for any 3800 should be 60 Psi or better... Hot idle will be 30-40 Psi on an engine that is not tired.. The OP never said how low the oil pressure actually got..

As well I seriously doubt that the OP had a wrist pin issue.. Sounds more like he had a rod bearing failure...


To the OP...

The only way you will know what the true pressure, is to use a mechanical gauge to see what PSI you actually have.. Replace the oil filter with a better quality unit... Then test the oil pressure with a mechanical gauge... Until thats done we really can't tell you much more..

"The OP never said how low the oil pressure actually got" No, your right, but if it's getting low enough to worry someone competent enough to rebuild an engine into posting his worry on the internet, then it's probably deviating from it's known baseline and getting pretty low . Just an observation.
Also. when someone says " bad piston bearing which damaged piston rod" to me that says wrist pin as the piston rod is the wrist pin and connects the piston to the connecting rod. Now, if someone says the connecting rod and crankshaft were damaged, then I would think rod bearing.

The technical aspect isn't all you need to know when trying to give someone remote technical support, you also need to know people. Many times you need to read between the lines to give the best solution as people don't always give the whole story or straight answers. :)

From what he's describes, it sounds like normal operation. I observe simalary conditions. I observe similar conditions with my 3800 as far as the oil pressure is concerned from reading the cluster gauge. Oil pressure on start up is about 60psi (per gauge) and idles under 40psi and kind of fluctuates the whole time. The only time it doesn't is after a long drive then its dead steady and under the 40psi mark. Have observed this since I had the car which I've put 50k on myself.

The only time the oil light has ever came on was when a fram filter was installed. Real world experience as far as fram filters are concerned. Don't use them on a 3800!

Another side note. The only gauge on the cluster that is accurate is the speedometer :lol: . The rest of them are inaccurate as I have observed with my scan tool and as far a gas fill ups.

If you read between the lines also you could conclude that the OP is noticing things that he has never payed attention to before the rebuild. People tend to over concern themselves when the fix something becuase you want everthing to be right. Also the OP has not reposted which could be a sign that the problem (or precieved problem) is gone, or is no longer of concern.:rolleyes:

Just my :2cents:

Its very hard to read into people on the net, and sometimes hard to convey exactly what they are saying.. LOL.. Thats the bad part about the net and posting on forums..

Its rare for any 3800 to damage a wrist pin, its almost unheard of... Can it happen?... Sure its always possible, but uncommon... The L36 and L67 both use a floating wrist pin design... More than most I have seen 3800's spin rod bearings, this is usually after the oil has been contaminated with Coolant( Dex especially ), The bearings become pitted and its all downhill from that point...

Oil pump failures are also very uncommon on the 3800's... If a Pump is in good shape upon inspection I would reuse it in a rebuild... But with the inspection any scoring or scaring in the timing cover would cause me to replace the timing cover and pump..

I have my Old L36 sitting waiting for the day I build it.. Never had any oil pressure issues with it... Always had great oil pressure.. Didn't even have a wrist pin issue... I do think I was getting ready to pop the motor tho, Cylinder 4 has some massive piston to bore issues, Sounded a lot like bad piston slap when I pulled it..

In any event the real way to know what the oil pressure is would be the mechanical gauge..:)

Cman I agree... Fram oil filters = Skull with crossbones here:cool:

the OP is noticing things that he has never payed attention to before the rebuild. People tend to over concern themselves when the fix something becuase you want everthing to be right.
Ain't that the truth lol.

Although I know the OP is probably gone by now, I just like to answer peoples questions about how I get to my seemingly assumptive conclusions. I did professional level tech help and field service for a long long time and found sometimes you just need to use the powers of deduction and assume certain things in the lack of real info to get the job done. Am I right every time no but more than often , yes. :icon16:

"More than most I have seen 3800's spin rod bearings" GM has had this problem for as long as I can remember. More than once I've gotten into a GM car and got on the gas to hear Knock knock knock knock. Hey someones at the door, no wait it's the rod bearing.
Never threw a bearing in a ford, blown a piston out the side of the engine, but never threw a bearing.

"More than most I have seen 3800's spin rod bearings" GM has had this problem for as long as I can remember. More than once I've gotten into a GM car and got on the gas to hear Knock knock knock knock. Hey someones at the door, no wait it's the rod bearing.
Never threw a bearing in a ford, blown a piston out the side of the engine, but never threw a bearing.

100% True... I can't count how many 3800's I have seen spin a rod bearing.. Seems to be common place with high mileage or an intake gasket rupture allowing coolant into the oil.. Had a 3800 L27 start knocking... 20-50 got me a few more months in this Florida climate.. An L36 dropped oil pressure on me and tanked the #4 rod bearing.. Funny the other L36 has a cylinder #4 problem, but not a rod bearing..

And not long ago we yanked a 3.8 Split Port from a Mustang... Rod through the oil pan.. Amazingly tho the bearings looked like new at almost 150,000 Miles..