Silverado With Oil Pressure Issues

[ArrestMeRedZ]

I'm seeking advice.

We've got a couple of 2006 2500 HD Silverados with my wife's landscaping business. Both were owned since new, and have between 120 and 130k miles on them. I've been lucky enough to get the maintenance responsibilities of the trucks in the last year and a half. This usually consists of a crew dropping a truck off at my house sometime after the change engine oil indicator comes on, the brakes stop ginding (yeah, I said stop) and the truck won't stop, or something else catasrophic happens.

One of the trucks developed a problem with oil pressure. At idle, the dash indicated zero pressure on the gauge, and the idiot light came on with warning chimes. No unusual engine noise.

I got the truck and changed out the oil and filter with my standard PP 5W-30 and PureOne filter (the change oil indicator had "just come on"). Didn't help. Next, I changed out the oil pressure sender switch (thanks for the location of that beauty, GM). No change. Then, I bought a manual gauge to hook up and check the pressure. After finding the correct adaptor (metric 16 x 1.5 male to 1/8" N.P.T female in case you are interested) and then tearing up my hands to get it installed (thanks again for the location, GM) I checked out the pressure as stated in the manual:

R.P.M______Minimum Pressure (P.S.I)______Actual Pressure (P.S.I.)

1000_______6_____________________________12
2000_______18____________________________20+
4000_______24____________________________40

While the test met spec, I still have a problem with it because at idle, the manual gauge read very near zero. The idiot light and chimes seem appropriate when idling, even though the system passed the test at higher RPMs.

The truck did overheat a couple of weeks before this problem (small coolant leak, and they didn't bother to check the coolant level). It got hot enough to turn on the idiot light, but apparently was just over the limit (temp gauge was just into the warning area). No indications of a blown head gasket or warped head - it still runs great, with no unusual noises, and no fluids where they shouldn't be.

I'm at a loss as to what do do next. I don't want to put the truck back into service with an obvious problem, but I'd hate to have to tear the entire front of the engine apart to replace what may be a good pump.

 

[OVERKILL]

It most likely needs bearings. How difficult is it to get the pan off to check a rod?

 

[Cup of Joe]

The tested PSI is after the truck has been FULLY warmed up?

 

[Steve S]

Add a can of STP or some kind of motor honey to thicken the oil up as a diagnostic tool. Cheaper than a 15w-40 oil change, the cost is minimal and will not hurt anything. This will see if a thicker oil will have a difference in idle oil pressure. The pressures seem to suggest all should be fine. Does the engine cancel cyls when overheated?
Was the oil pressure low at idle before the last oil filter change? I had a work van that I really liked due to the way the side doors opened that had an idle bearing knock and the idiot light would come on at idle ,I added a qt of 90 wt gear oil and the van ran 3 years before the company retired the van. At the miles on the odo and the price of a new crate G.M. motor I would milk the engine . G.M. crate motors aren't super expensive.

 

[ArrestMeRedZ]

Overkill, the pan isn't too bad, and that was my next step (that I hoped to avoid), primarily to check the oil feed tube o-ring and the filter screen. No other indicators of bad bearings though. Rings seem fine, no knocks, low oil usage, no smoke, etc.

Tater, the coolant was at full operating temp for a while. 105 degree F. outside air temp, and I ran the test multiple times, so I think so, but I'm not positive. I'll check it again to make sure the oil was at full temp. The idiot light did come on after the recent oil change just after start up, well prior to the oil heating up.

SteveS, will MMO do the same thing as STP? I've got that on hand. I don't believe the '06 6.0 had the cylinder cancelling technology. Pressure was low at idle before and after the filter/oil change I just performed. 3 months ago at the previous change, it was normal.

 

[daman]

Do you ever hear the lifters ticking/hammering??

is it idling abnormally low?

 

[Cup of Joe]

Do not use MMO that will thin your oil even further. Trying STP will thicken the oil faster then changing the oil. Some STP or the dreaded lucas will thicken it right up if the pressure goes up at full operating temp could be a worn engine or bad pump. More likely worn engine from the sound of things.

Just a thought 105F ambient temps used by knuckle heads performing landscaping. I would not be using a thin 30wt I would be using 15w40 personally. Coolant temp does not mean oil temp so the pressure will likely be even lower after it is worked a bit.

 

[oldmaninsc]

Are you sure it isn't just a problem with the dash gauge? I know you said you replaced the sending unit but maybe the gauge itself is bad. Over on Trailvoy.com we have had a LOT of problems with various gauges going bad. Something about the "stepper motors" on the gauge.

 

[440Magnum]

You could go up to a 40 grade and probably get a lot more life out of it. If its not making noises, then nothing catastrophic is happening most likely. Its just getting tired, the oil pump clearances are getting large, and the bearing clearances are getting large too. Throwing a new oil pump at it would be a good idea too, but for a beater work truck that's just *barely* missing its pressure specification, and then only at idle) I really think just bumping up a grade or two would do the trick. Try something like Rotella 15w40 or T6 5w40 (of course that's what i'd have been running all along in abused work trucks).

 

[MrCritical]

Of course with this engine you risk sticking the rings with 15-40. At least that's what GM tech told me.

 

[ArrestMeRedZ]

With no significant valve noise (I've heard an oil-starved valve train before, and it's not pretty) and a verified good sender, I thought it might be a bad dash gauge, but the manual gauge that was a PITA to connect read close to the same, especially at idle.

Idle speed is ok.

I'll give the STP a shot. If that doesn't work, I'll drop the oil pan and see if anything jumps out at me. I bought a new pump and pan gasket before I "discovered" the pump is mounted around the crank, and you have to remove the chain covers, sprockets, chains, crank pulley, gear, etc., etc., before you can get to it. That's a little more work than I want to do with the limited work space I have available (it's a crew cab, and it's questionable if it will fit in my garage).

 

[daman]

if your not hearing any valve train noise pressure is sufficient,,8-10psi per 1000 rpms is the norm i would try a thicker oil,,10w40HM or 15w40,5w40 first.

all your pressure listings look fine except idle.

 

[OVERKILL]

Originally Posted By: daman
if your not hearing any valve train noise pressure is sufficient,,8-10psi per 1000 rpms is the norm i would try a thicker oil,,10w40HM or 15w40,5w40 first.

all your pressure listings look fine except idle.


While this is completely correct, if the pressure has dropped (which it has) then there is a reason for this and it is likely wear.

 

[daman]

Originally Posted By: OVERK1LL
Originally Posted By: daman
if your not hearing any valve train noise pressure is sufficient,,8-10psi per 1000 rpms is the norm i would try a thicker oil,,10w40HM or 15w40,5w40 first.

all your pressure listings look fine except idle.


While this is completely correct, if the pressure has dropped (which it has) then there is a reason for this and it is likely wear.

correct as well...but if that's the case and it's wear that's a shame these engines are top notch and will run and run and run with out issues.

it was most likely abused maintenance wise.

 

[daman]

We have three of these in the yard two 6.0 and a 8100 and they get used like a red headed step child BUT always maintained properly.

 

[OVERKILL]

Originally Posted By: daman
Originally Posted By: OVERK1LL
Originally Posted By: daman
if your not hearing any valve train noise pressure is sufficient,,8-10psi per 1000 rpms is the norm i would try a thicker oil,,10w40HM or 15w40,5w40 first.

all your pressure listings look fine except idle.


While this is completely correct, if the pressure has dropped (which it has) then there is a reason for this and it is likely wear.

correct as well...but if that's the case and it's wear that's a shame these engines are top notch and will run and run and run with out issues.

it was most likely abused maintenance wise.


Agreed. The LSx engines are known to be very reliable. I think your theory as to why the engine is now no longer healthy is a sound one.

 

[mechtech2]

How about checking the pressure on the 'good' vehicle?
You have a handy reference.

But.. bearings and/or oil pump are faulty. Too much clearance in either or.

 

[Trav]

If you can the oil pan off with the engine in the truck the bearings and oil pump can be swapped out pretty easily before the crank gets damaged with the engine in place.
Not ideal but you can get plenty of more miles out of the engine.

 

[ArrestMeRedZ]

It might be while before I can get to it. I don't want to start until I'm sure I can finish the job. I'll keep you all posted.

Thanks for the inputs.

 

[wapacz]

Do you happen to have hour meters on these trucks. Just asking becuase it would be a bit interesting to see if the one with the oil pressure issues had more hours on it than the other 2.