Oil and additive recommendation - low oil pressure

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3
Good morning everyone. I have a 1996 k1500 5.7L with approximately 355,000 miles on the original motor (See attached picture). This was my grandfather's truck that I have been restoring since he passed away. Once I got it running again, I noticed that the oil pressure was low, about 20 psi when driving and 10 psi at idle. The truck has traditionally seen Castrol GTX High Mileage 10w-30 every 5,000 miles with an ACDelco PF52 oil filter. At the last oil change, I used 2.5 quarts of oil along with 2 quarts of Lucas Oil Stabilizer (4.5 quart overall capacity) in an attempt to raise my oil pressure (don't attack me, that was before I found this website and learned that Lucas is the devil's nectar). Overall, the oil pressure was raised and the truck has been driving good ever since, although the oil pressure is still slightly low, about 32 psi when driving and 18 psi at idle. Well it is nearing my next oil change and I am looking for recommendations. My current plan is to do a Liqui-Moly 2037 engine flush, and then bump my oil up to Castrol GTX High Mileage 20w-50. I was thinking possibly add in some MMO as well? I live in south Georgia so it never gets super cold here. I would love to hear your thoughts and any help that you may be able to give will be greatly appreciated! I hope everyone has a Merry Christmas!
 

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MolaKule

Staff member
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21,950
Location
Iowegia - USA
I also recommend checking the oil pressure with a mechanical gauge before doing anything too drastic.
Sensor and gauges get out of calibration over time so that would be my first check as well. Oil pumps wear over time and pressure can fall due to the pump.

As others have stated if the oil pressure is really that low then a pan removal would be in order to check the pickup screen for sludge.

it sounds like the oil girl needs new bearings, an oil pump, and a new oil pressure sensor at minimum.

In the meantime try a 40 grade oil and if the pressure doesn't rise, then the aforementioned items probably need attention.
 
Messages
7,262
Location
Roanoke Virginia
I’d get a gauge and check pressure. I do think a 20W-50 oil would help it they make GTX in 20W-50 I’ve used it and it’s great stuff so that might be something to try too. And nice truck I really like that body style. Also nice white lettered tires they fit it really well.
 
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7,006
Location
Suburban Washington DC
in an attempt to raise my oil pressure (don't attack me, that was before I found this website and learned that Lucas is the devil's nectar). Overall, the oil pressure was raised and the truck has been driving good ever since, although the oil pressure is still slightly low, about 32 psi when driving and 18 psi at idle.
Well apparently it did the job it was supposed to as those numbers are fine. Why not continue with that? If you want to experiment, maybe go to 10W50 first before 20W50.
 

bb04089

Thread starter
Messages
3
Ok so to address some of you guys on here. I have not checked the oil pressure with a manual gauge recently. However, when I got it running approximately a year ago, my mechanic hooked his gauge up to it then and it was low, reading the same as my dash gauge. It does burn some oil but not much. Its time for my 5,000 mile oil change and the oil level has dropped from the top of the dip stick marker to the halfway mark. What I have gathered from your responses so far is that I need to change out my bearings, oil pump, and pressure sensor as well as change to a heavier oil. I also think I may use the Liqui-Moly 2037 when I do the oil change unless any of you guys have any objections to that.
 
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5,727
Location
down in the park
Check the true oil pressure at speed, as the oil pressure should track closely with RPM which it doesn't seem to do in your case? Could be only the pressure reading is more off the higher it reads. 10 psi at hot idle isn't concerning, but at 4-5x idle rpm it should be 40-50 psi...

If the values are true, check the oil pump and bypass valve first.
 
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1,819
Location
RI
If you replace those parts there’s no need to use a heavier oil. A quick and easy way to check if the rod bearings are worn when you have the pan off, try to move the big end around with your hand. If there is a good amount of free movement, they’re tired. You won’t really be able to check the mains this way. You’d have to remove the main caps and then roll the upper ones out. All the load will be on the top for the rods, and the lowers for the mains. They will be the most worn out of the set (providing you don’t have a line bore problem)
 

wtd

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2,761
Location
southwest Mo.
First off, nice truck. I love that body style and still own the 98 ext-cab Z71 that I bought new.

Where did your mechanic hook up his gauge to? Was it a mechanical gauge? My truck only has 139,000 miles on it and it runs on the factory gauge about 20 psi when it's hot in gear and around 50 driving down the road.

I personally would try running a 10W-40 high mileage like Castrol before trying the 20W-50. Any unusual engine noises?
 
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35,800
Location
NY
Verify your oil pressure with a good mechanical gauge as others mentioned. Report the readings back before you drive yourself crazy trying to resolve an issue you may or may not have.
 
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5,011
Location
Southeast
I’d get a gauge and check pressure. I do think a 20W-50 oil would help it they make GTX in 20W-50 I’ve used it and it’s great stuff so that might be something to try too. And nice truck I really like that body style. Also nice white lettered tires they fit it really well.

this is good simple advice.

pressure drops either because the pump isn’t making it, or because the oil is released quickly downstream. It will escape quickly when bearings become worn. the thicker oil makes it harder to escape quickly.

does the the engine knock or make any notable noise if it’s on 10-30?
 

OVERKILL

$100 Site Donor 2021
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46,202
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Ontario, Canada
If you aren't inclined to look at doing the rod bearings (which are probably what's worn) then I'd step up to a 15w-40, skip the Lucas, and see if that makes things acceptable. It'll go many more miles on that setup.
 
Messages
2,343
Location
WA
when you don't want to dump more $ into an old car and you are not a mechanic (i.e even more $$$) ... I've read people play with different oil filters to somewhat manipulate or control the oil pressure. :unsure:

any merit in that?
 
Messages
5,727
Location
down in the park
not really. Oil filters can ony lower oil pressure on the gauge. If the oil pressure sensor is located downstream from the filter the indicated pressure gets lower as the oil filter gets loaded. I have seen vehicles that say to replace the oil filter when the max oil pressure drops by 15 psi (close to the bypass valve opening pressure)
 
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