1999 Vortec 5.7 high oil pressure - possible checks
02-21-2013, 04:06 AM
#1
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1999 Vortec 5.7 high oil pressure - possible checks Hi all, I have a question about a truck I am looking to buy. It has a few issues, one in particular worries me. High oil pressure that stays up even when warm.
The truck in question is a '99 Silverado Z-71 5.7 with high mileage, around 170k.
Starting off the truck sounded smooth for having that many miles. But after driving a bit, I noticed the oil pressure while warm at idle, in neutral, was up around 60psi and raises to 80psi with throttle...and this never changed the whole test drive.
I did the regular checks, and the oil seemed fairly new with the correct level on the stick. I mentioned to the guy that runs the dealer that I would've crawled underneath to look the truck over but with the ground half covered in ice, I didn't. That's when he said a could use their wash bay if I wanted. I asked if I could come back this weekend, and he said that was fine.
Doing a little research I read that an easy check for the pressure sending unit is to unplug it and the gauge should jump one way, then ground the wire and it should jump the other. This should tell me that the sending unit is good and the problem is probably internal. Does this sound correct?
I have read of other checks to narrow it down, simple things like new filter, or putting on a mechanical oil gauge, but being I don't own the truck I can't get to far into things.
Are there any other things I could do while I am giving it a second look this weekend?
Sorry, long rant is long...
The truck in question is a '99 Silverado Z-71 5.7 with high mileage, around 170k.
Starting off the truck sounded smooth for having that many miles. But after driving a bit, I noticed the oil pressure while warm at idle, in neutral, was up around 60psi and raises to 80psi with throttle...and this never changed the whole test drive.
I did the regular checks, and the oil seemed fairly new with the correct level on the stick. I mentioned to the guy that runs the dealer that I would've crawled underneath to look the truck over but with the ground half covered in ice, I didn't. That's when he said a could use their wash bay if I wanted. I asked if I could come back this weekend, and he said that was fine.
Doing a little research I read that an easy check for the pressure sending unit is to unplug it and the gauge should jump one way, then ground the wire and it should jump the other. This should tell me that the sending unit is good and the problem is probably internal. Does this sound correct?
I have read of other checks to narrow it down, simple things like new filter, or putting on a mechanical oil gauge, but being I don't own the truck I can't get to far into things.
Are there any other things I could do while I am giving it a second look this weekend?
Sorry, long rant is long...
02-21-2013, 04:12 AM
#2
Aside from a mechanical gauge, nothing will really tell you for sure. While rare, sometimes the needle can slip. Even a scan tool will only tell you what the sending unit is picking up.
My guess is if it's not the sending unit is a stuck pressure relief valve.
My guess is if it's not the sending unit is a stuck pressure relief valve.
02-21-2013, 04:31 AM
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And a bit more info that may or may not be related to the problem...
I also noticed the temp never got close to 200°. I don't remember the #s on the gauge, I think it was 150° then 200°…it sat closer to the 150 (or what ever was printed on the gauge)
Maybe with freezing temps added with the truck not getting up to operating temps is something, but I don't think pressure would stay between 60-80psi even then.
Edit: I did get an SES code scanned but the only thing that came up was o2's...
I also noticed the temp never got close to 200°. I don't remember the #s on the gauge, I think it was 150° then 200°…it sat closer to the 150 (or what ever was printed on the gauge)
Maybe with freezing temps added with the truck not getting up to operating temps is something, but I don't think pressure would stay between 60-80psi even then.
Edit: I did get an SES code scanned but the only thing that came up was o2's...
02-21-2013, 09:47 PM
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If I owned the truck I could answer that. It's at a small lot so it could be running straight W30 for all I know.
Idk what I'm gonna do yet. I could just ask him to send it to the main Chevy lot to get checked out but I don't trust them (the big name lot) to actually do the test and tell me the findings...
Idk what I'm gonna do yet. I could just ask him to send it to the main Chevy lot to get checked out but I don't trust them (the big name lot) to actually do the test and tell me the findings...
02-22-2013, 06:07 AM
#6
It probably had a rod knock and they put 60-70 weight oil in it. I vote for a mechanical gauge then maybe pull the pan. On a side note, my old 3.4 v6 Firebird would run about 80 cold and 60 hot. I know they are totally different engines, but just sayin. And I ran 5-30.
