Lucas 20W50 - good for my low oil pressure GM 350?

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I have a 1991 GMC Sierra K2500 that suffers from low oil pressure to the point that the "check gauges" light flickers on when the engine is hot and A/C is running.
The engine is otherwise running very smoothly, pulls strongly and never makes any bad noises. Oil burn is moderate less than 1 qt per 2,500 miles.

I have another thread to discuss diagnostic and repair, but this thread is mainly to seek feedback on oil.

I am going to try a 20W50 to see what it does for oil pressure readings. The local parts store has a pretty good price on Lucas Oil 20W50. Is it any good, or shoul I stay away from it?
 
If you have bad pressure then you have bad flow. a 20w50 would limit the flow even more. I would get a quote for a new pump installed. You might say [censored] it and put a new pump in.
 
Originally Posted By: abycat
If you have bad pressure then you have bad flow. a 20w50 would limit the flow even more. I would get a quote for a new pump installed. You might say [censored] it and put a new pump in.


I have learned from numerous sources that changing the pump is unlikely to make a significant difference - the pump creates flow, but not pressure, which is more dependent on wear tolerances inside the engine.

In this thread I am mainly hoping to get some good feedback on Lucas 20W50.
 
Lucas is good for chainsaw bar oil.
What else do you need to now about it?

You can buy a pail of 15W40 CJ-4 at Canuck Tire for $59 which is as good as it gets for very little money.
 
Rotella SAE 30? Defy 10w40?
I was stationed with a buddy who had a 315CI, He ran Berrymans mixed in with Rotella sae30 for 500 miles on his mid eighties chevy truck, ran a can in the oil and a can in the gas tank, afterwards he switched to QSGB 10w40, his Oil pressure went back to normal after the "clean up"
 
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Originally Posted By: GumbyJarvis
Rotella SAE 30? Defy 10w40?
I was stationed with a buddy who had a 315CI, He ran Berrymans mixed in with Rotella sae30 for 500 miles on his mid eighties chevy truck, ran a can in the oil and a can in the gas tank, afterwards he switched to QSGB 10w40, his Oil pressure went back to normal after the "clean up"


This was paired with a Napa Proselect filter.
 
Hmmmmm, no love for Lucas, Eh?
I have set my mind on trying a 20W50, was hoping Lucas was good since it is inexpensive but I suppose it was not to be.
 
Define inexpensive? It must be old slow moving stock, wouldn't matter in this engine.
 
Originally Posted By: Chris142
Have you actually checked the pressure with a real gauge?


I assumed that was done but yeah that's a great idea.
 
an adjustable brand new oil pump is 52$ which would fix the pressure and volume problem on the most worn engine and it's an hour to replace for the backyard mechanic. I just don't want to see you cause more problems with oil starvation. a new oil sender is under 20$ or even cheaper from a wrecking yard. hopefully you only have a bad sender and have great pressure.
 
Sounds like wear at the bearings. It time for a refreshing.
Climate permitted a heavy oil will help. Sae30/40, 20w-50, 15w-40, and alike.
Lucas is a choise, if priced the same as cheap dino. It is a bandaid for worn bearings.



Harvey
 
Originally Posted By: sr17
Hmmmmm, no love for Lucas, Eh?
I have set my mind on trying a 20W50, was hoping Lucas was good since it is inexpensive but I suppose it was not to be.


Lucas isn't really that great, even their synthetic doesn't look good on paper.

Probably be better to pick up some HDEO. Inland Kenworth has 5 Gallon buckets of Delo 400 for $65. There should be one close by, Burnaby or Langley.
 
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As Chris142 asked; Have you actually checked the pressure with a real gauge?
Those GMT400 trucks with the small block notoriously had bad oil pressure sending units. I've replaced a bunch of those. A crowfoot makes the job easier. Given the year, make and model, I would first replace the oil pressure sending unit.
 
Every GM 5.7 that leaves my yard (marine) leaves with 20W-50. They tend to stay that way for half of forever, too.

I wouldn't run Lucas. Go to the Wally World and dump in some Supertech 20/50.

You said yourself that the engine is likely on its way out. I wouldn't even begin to waste the effort of getting under there, getting the pan down, and changing an oil pump for an engine in that condition.

The only reason that oil pan should come off is to swap it onto the new longblock.
 
Originally Posted By: Michael_P
As Chris142 asked; Have you actually checked the pressure with a real gauge?
Those GMT400 trucks with the small block notoriously had bad oil pressure sending units. I've replaced a bunch of those. A crowfoot makes the job easier. Given the year, make and model, I would first replace the oil pressure sending unit.


I have a mechanical gauge, but this thing is such a pain to get at that I just ended up throwing in a new Delco sending unit to save the extra steps. New sending unit produced no change on the gauge in the dash. Btw. what is a crowfoot??
 
Originally Posted By: DoubleWasp
Every GM 5.7 that leaves my yard (marine) leaves with 20W-50. They tend to stay that way for half of forever, too.

I wouldn't run Lucas. Go to the Wally World and dump in some Supertech 20/50.

You said yourself that the engine is likely on its way out. I wouldn't even begin to waste the effort of getting under there, getting the pan down, and changing an oil pump for an engine in that condition.

The only reason that oil pan should come off is to swap it onto the new longblock.


Yeah, the fact that the marine version of the same engine is running with 20W50 is what made me think that this might be viable.
I am not entirely sure that it is on its way out after all - no smoke and minimal oil consumption. No weird noises associated with the low hot oil pressure situation, just a couple of knocks heard in the first second of a cold start.
 
Someone pointed out that there is another port to hook up mechanical gauge near the oil filter. Turns out oil pressure is ok.

I put in a fill of MAxLife 10W40 that I already had on hand.

Thanks for the feedback on Lucas.
 
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