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Chevy express oil pressure

TSexpediter

Seasoned Expediter
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I have same problem on two expess vans. 4.8 l gas engine. Sudenly the oil pressurre running low. Both engine are 400 kmiles. They no burning oil no smoke. Should I change the oil pump, replace the engine or should I run with low pressure untill the engine is completly done? Idle 8 psi , when running on the hwy 20. Did somebody have the same problem? Thank you
 

chefdennis

Veteran Expediter
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My 05 4.8 runs 30 at and idle and 50 at 70mph...i use nothing but ams oil and their filters and change the filer every 5000 miles, oil at 20,000

Before I went with a major decision, id change the oil to a straight 30 weight and use a good oil filter, not your normal $6.99 filter but a good one...
 

purgoose10

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If your not running above 40pds at hwy speeds and that many miles I would change the pump. It's not hard and it's a lot cheaper than a motor. You can change it out in a couple of hours if you know how. While your changing it I would look at the number 1 rod bearing and check see the wear. Change the rear main seal. Simple job if you have the place to do it.:cool:
 

chefdennis

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A straight 30 weight oil verses a 5-30 or a 5-40 weight..the straight 30 weight does not thin out to a low viscosity when it gets hot like the multi weights, it remains a constant 30 weight where a 5 - 30 will thin out as it gets jot...thats what the numbers mean it will never ge thinner then a 5 weight and never thicker then a 30 weight...id even consider going to a straight 40 weight from this time of the year if you run mostly up north, and see if that improves the situation...if it does, that will indicate that the clearences in the motor are reaching their outer limits with all those mile, and that is to be expected...changing the oil pump will help for sure because it wears also and the larger clearence in it will also reduce the pressure...but before Id invest in that or a motor overhaul, id change the oil to a straight weight and use a real good filter and see how it goes...
 

greg334

Veteran Expediter
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Before you do a thing, put a mechanical gauge on the oil port and check the pressure.
 

buckwheat

Seasoned Expediter
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Before you do a thing, put a mechanical gauge on the oil port and check the pressure.

Excellent advice. With 400k on the clocks the most likely cause will be bearing clearances coupled with a tired oil pump. Although the mechanical gauge won't tell you exactly where the problem is, it will rule out the sending unit and send you to the next place to check. Straight 30 or 40 wt. oil will sometimes help to get the pressure up for a time and improve lubrication to the upper engine. With that low of pressure though, the top of the engine is probably starving for oil. I've majored several engines in my garage over the years and you'd be surprised how badly one can be worn and still run relatively quietly. Broke the crank in a 350 Pontiac V-8 once and drove it home 18 mi. At idle you couldn't hear a thing. But rev it a little and............
 

Fr8 Shaker

Veteran Expediter
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I'm having the same problem and my mechanic said it could also be the gauge itself. He said it actually has a little motor that runs it. It was doing it on my original motor and doing the same on current motor which has 77,000 miles on it.
 

greg334

Veteran Expediter
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Well a few things.

If you have bearing wear, it doesn't always show up as low oil pressure however if the thrust surface on the rods are worn, then you will have a drop in oil pressure big time. The same goes for the thrust bearing, if it is worn, then it shows up as low oil pressure and that also means another problem, a possible transmission or torque converter issue.

Oil pumps are known to wear, and depending on the replacement pump, you can go through a couple of them.

if you have a gauge replaced, it has to be "calibrated" by a GM tech. The sending unit is different, that goes through the ECM.
 

Jason2

Expert Expediter
Owner/Operator
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use a/c delco filters MADE IN USA only.check filter made in usa not made in mexico. there is a difference. parts man brought it to my attention.
 

guido4475

Not a Member
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While in Laredo I met a Panther Driver with a Chevy who had the same problem, and it ended up being his oil pump.He replaced it and it has been fine since.You wouldnt believe this guys van, how spotless it is.I mean real spotless.It has something like 600k on it.
 

TSexpediter

Seasoned Expediter
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Thanks for your answers. I took the van in a shop ,they will tested this afternoon. I hope that is the oil pump. I will let you know.
 

quickpickup1

Seasoned Expediter
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On my 04 express with a 6.0 l, it had a simular issue.It ended up being the o-ring on the pickup tube.It was not sealing properly and was drawing air in from the oil pan and supplying the oil pump with a oil/air mix.When You pull out the dip stick you may see very small bubbles on it that dissapear very fast.
Another thing to Check is the pickup screen,make sure its not plugged.Definately check out your oil pressure with a mechanical guage first and go from there.
sending unit
wiring
gauges
hope this helps you.
 

TSexpediter

Seasoned Expediter
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The mechanic said that the screen is was clean. Changing the pump expensive and you still don't know the result just after you install it. So I bought an used engine with 100 k and replace it. 650 for the engine 1000 for labor. Now is ok. Thanks
 
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