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01 sierra oil fluctuation

4K views 15 replies 3 participants last post by  Egoresb1 
#1 ·
I have a 2001 gmc sierra 4.8l spectre intake with k&n filter. Flo master duals and just had it diablew tuned. Noticed today at idle it slightly runs rough and my oil pressure fluctuates about 5 to 10 psi up and down on my gauge. Going down the road it'll hold roughly 60 which is normal and 80 when I hammer down. Also normal. What could possibly be going on here? I doubt it's the tune as mr lew knows what he's doing . Could I have a oil leak I'm not seeing? Bad sensor? Etc?

I run 10w-30 castrol high mileage oil and a purolator or car quest filter.and a quart of Lucas oil additive(don't remember which one off top my head) if that info helps. I've been running that oil combo for years. Except the Lucas I recently started adding to correct this and it did for the last few oil changes.

Also truck has 200k miles.
 
#2 ·
My truck does the same thing. A fluctuating oil pressure could be due to a possible blockage on the pickup tube. Do yourself a favor and dont waste the money on lucas. Spend the extra few $$ and put a good synthetic oil in. I would run a can of seafoam in the oil to clean everything out or some amsoil engine and transmission flush..
 
#4 ·
It's mostly after driving a while. At cold start my rpms are higher and oil pressure stays up towards 60 but not quite. Yes it dances lightly and my rpms have a mild fluctuation and engine runs a little rough. Almost like a bad head gasket but not nearly as harsh. And there's no apparent oil leaks. I just recently changed valve cover gaskets because they were leaking. Which I thought was the cause. Seemed to disappear a while but now it's back still no leaks. Hard to tell if front main seal is leaking as I can't clean it good enough. And leakage from valve covers went just about everywhere.
 
#5 ·
The oil I use the castrol high mileage is part synthetic. I don't want to put a pure synthetic as it breaks down a lot of carbon sludge etc which is good but on a high mileage engine in past experience gives major problems. Leaks form everywhere. I'd be better off pulling the motor and doing a rebuild with brand new gaskets everywhere which is what I had to do in my dads truck after he switched to royal purple at 175k miles on his 5.3. Spunk leaks on every sensor and seal that you can think of.
 
#6 ·
It could be a sludge / blockage issue... And a good flush might answer it.

But I would guess the pickup tube is grabbing some air. I have repaired a similar symptom with a bad seal on the pickup tube. Oil pressure would dance, though slightly more aggressive than yours. After verifying it was indeed fluctuating, i dropped the lower end to find the pickup tube seal as a culprit. It's an expensive job to have done, perform further diagnostics prior to diving in.

That said, leaking gaskets on the top end could be to blame also. I would perform all the less expensive diagnosis first to rule out the cheap fixes...
 
#7 ·
Ok. What takes place to change that? Drop the pan and I should be able to deal with that right? Or do I need to take everything off the front to get the pump off? If that's the case ill wait and change the chain and sprockets for timing while I'm in there. Preventative maintenance and save some cash on gaskets and seals for the front the engine.

Running a flush just seems like a temporary cover up but I'd like to get into detail and fix it for my truck to last another few years.
 
#12 ·
Ok great. Ill try and see what it does. I tried to take a short video and its like hit or miss thing. It did it when I stopped at the parts store and I tried to video when I got home and it was holding a steady pressure on the gauge?

If it were an air leak wouldn't it do that all the time? Maybe I'm having a slight misfire causing it to run slightly rough and throwing my pressure off?

Ill try again to get another video if I see it happening again. Ill also check pressures with a gauge.
 
#13 ·
If you have a friend with a scanner, even a Diablo intune, it can be set to read live for missing fires. And no, the air leak generally changes with temperature. Expansion, contraction, heating , cooling ....

Dont rule the mis fire out without running diagnostics... Cant stress it enough. Ideally, no money is spent without certainty of the failing part.... I would rule everything out before dropping that pan...
 
#14 ·
Yea. Well I've problems with bad gas as well as faulty plugs and injectors. I have an Intune which I obtained a diablew tune with. I also have a obd2 scanner. Ill see if I can get it to pick up intermittent misfires and whatnot as well as oil pressures etc before I spend any cash. I also just tanked up and added a fuel treatment/ injector cleaner. If it disappears then obviously it's fuel related. Ill also pull plugs and check for too rich/lean as well as build up due to bad fuel or slobbering injectors. Ill also change fuel filter... It's time for that anyway. Thanks for all your help. Ill be back after I can completely diagnose all the info you've given me. Hopefully i can figure out exactly what's wrong. If not I need to replace my timing chain and sprokets anyhow so while I'm in there ill clean up everything and replace what need be. I hope it's fuel related because it could be a simple easy quick repair. I'm not looking forward to timing chain replacement as that's about 400$ repair for all the gaskets and whatnot that will need to be replaced. Trying to wait until I can see symptoms that that NEEDING to be replaced to get the full life out if them which could be risky. But if it comes down to bad/faulty oil pickup ill do it all at once and save the 45$ on needing 2 pan gaskets if that makes sense. Thanks again. And please advise if you think it could possibly something else beside anything stated previously.
 
#16 ·
Well no go for any misfires. Everything seems to be operating correctly. Still can't figure out why this is a hit or miss problem. Can't seem to figure out exactly what's causing it...

Did notice it is worse (when it does do it)when I drive it hard petal to the metal most obviously because its getti g hotter although my coolant temp remains at roughly 205 degrees which is normal for my truck. Doesn't seem to be overheating or loosing coolant. Still stumped on the subject. Don't want to change parts without needing to.

Should I even be worried about it? As long as I'm still maintaining good pressure I should be ok?
 
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