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I have a 1998 Chevy Silverado K1500 with the 5.7 350 engine. It has 235,000 miles on the truck. I bought it brand new and I have never beat the crap out of it. What is causing the oil pressure to drop while the truck is at a complete stop? Is it the oil pump gone bad?
I attached some picks of what the oil pressure does while driving and sitting at a complete stop. They go from 70 MPH down to a complete stop. Notice the RPM, speed and oil pressure.Driving no matter the RPMs or speed the oil pressure remains the same. After I am at a complete stop (stop light) the oil pressure goes way down. Why?
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I doubt it is the oil pump. It could be the sending unit, though. If you just start the engine and let it idle, is the pressure higher than when in your photo coming to a stop? What weight oil are you using? Worn crank bearings + hot weather + thin oil = pressure drops. Also, a rule of thumb says that 10psi of oil pressure at 1000 RPM is still acceptable.
I used to have the same problem in my ol Dakota. I have to agree with the first responder that it is more then likely you sending unit. Given you are still getting oil from your pump as witnessed buy the rpm changing oil pressure you are still getting functionality
You have almost a quarter million miles on the truck. Your engine bearing clearances aren’t as close-fitting as they used to be.
Having said that, I wouldn’t say you have an issue. You’re still making over 20 psi oil pressure at only 600 rpm, and almost 50 psi at 1,200 rpm. Very respectable numbers, especially when you consider the mileage.
Based on the pics, I wouldn’t worry a bit about the pressure. I see similar numbers in trucks 10 years newer. At idle, about 25-30 psi, and 40-50 psi driving down the road. As much as I like making money, if that truck came through my bay with that complaint, I wouldn’t recommend overhauling the engine over it. Now if it were dropping completely to zero at an idle, I would say you likely have a relief valve sticking open, pretty common on new trucks.
Your problem is a common condition known as old.
Age and wear have increased the bearing tolerances in your engine and they are no longer tight enough to maintain high oil pressure at lower RPM when the pump volume is low. It could also be partially the pump getting old but mostly it is the engine getting old. My experience with the SBC it’s probably the cam bearings that are causing the issue but I would be bet the main and rod bearings are not exactly perfect anymore either.
Good news is a SBC only needs like 5psi of oil pressure at idle to keep alive, if you are getting 30 or over driving down the road it should be fine.
If you want to get really proactive you can pull and oil sample for analysis and see what bearings are wearing most and how far into the shell they are.
[quote=”Tesla77″ post=142370]Driving no matter the RPMs or speed the oil pressure remains the same. After I am at a complete stop (stop light) the oil pressure goes way down. Why?[/quote]
Well it’s not exactly the same RPM at all driving speeds, but I understand what you mean. The reason the oil pressure goes so low at idle is that the pump is just turning slowly compared to the 5000+ RPM redline it’s designed to be alright with.First of all, your oil pressure is very good at idle. I remember the minimum spec was 6 psi at idle on a 1998 Yukon with a 350. I remember the vehicle owner was concerned about 10 psi at idle. Idling is also a situation of minimum bearing load, so oil pressure (which is what supports bearing load) does not need to be high. I have a modified VW engine that makes between 5-10 psi at idle when the oil is over 180°F (hot). It makes at around 20 psi at lidle when cold (under 150°F. It has 240k miles on it with a high volume oil pump, and makes 60+psi at speed while hot.
My idle oil pressure does not concern me at all, despite the fact that engine has had a aftermarket cam in it for the last 13 years that has put additional lubrication load on the lifters and cam lobes. The lubrication load on the valvetrain components is constant. Regardless of RPM/oil pressure, it takes the same amount of force for a cam to push on a lifter every time it comes around. I also have beat on the engine severely for the last 15 years right up until 4 hours ago , and it’s fine with that oil pressure. A old 350 SBC is very different from a old VW 8v, but oil pressure is a far more universal thing.
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