'04 Yukon 6.0L Oil Pressure Reading Lower Than it Used to

[Beer 30]

A couple of weeks ago, my oil pressure under normal driving conditions dropped from 40 to about 20, sometimes 30. No warning light has ever come on, no noise from the engine, oil level is full, no issues at all while driving and the pressure's never dropped below 20.

I'm suspecting that the oil pressure sending unit has gone bad - but I suppose it could also be that the oil pump itself is slowly failing.

Any thoughts? If the first thing to try is to replace the sending unit - how difficult is that job? I've watched a couple of YouTube videos and the approach the two guys took was completely different. One guy accessed it from the top of the engine, the other suggests going in from the side.

Earlier this summer people in this thread gave me the confidence to change the plugs, saving me a ton of money. When I was in high school in the early 70's there wasn't much I couldn't do on an engine, but that was a long time ago. Once fuel injection and electronic ignition came along, my backyard mechanic days came to an end - until I took on replacing those plugs because every shop in town wanted $1000.

Thanks!

 

[Danny3737]

$1000 to replace just the spark plugs?

 

[wjburken]

A couple of weeks ago, my oil pressure under normal driving conditions dropped from 40 to about 20, sometimes 30. No warning light has ever come on, no noise from the engine, oil level is full, no issues at all while driving and the pressure's never dropped below 20.

I'm suspecting that the oil pressure sending unit has gone bad - but I suppose it could also be that the oil pump itself is slowly failing.

Any thoughts? If the first thing to try is to replace the sending unit - how difficult is that job? I've watched a couple of YouTube videos and the approach the two guys took was completely different. One guy accessed it from the top of the engine, the other suggests going in from the side.

Earlier this summer people in this thread gave me the confidence to change the plugs, saving me a ton of money. When I was in high school in the early 70's there wasn't much I couldn't do on an engine, but that was a long time ago. Once fuel injection and electronic ignition came along, my backyard mechanic days came to an end - until I took on replacing those plugs because every shop in town wanted $1000.

Thanks!

How many miles are on the oil?
What kind of oil filter do you have?

Might get a mechanical pressure gauge on it to compare with what your dash is showing.

It could be a cracked o-ring on your oil pick up tube.

 

[Beer 30]

$1000 to replace just the spark plugs?

Danjy3737 - Yes!!! It's something like 6 hours labor to replace the plugs and another 2 for the wires. That's what shops get by 'the book' I hadn't done anything on a car since I was 19 and I'm now 62 but I had the whole job done by lunch.

 

[Beer 30]

How many miles are on the oil?
What kind of oil filter do you have?

Might get a mechanical pressure gauge on it to compare with what your dash is showing.

It could be a cracked o-ring on your oil pick up tube.

Wjburken - it kicked over 200,000 this summer. No oil drips that I've seen, but I'll keep looking. I've considered getting a pressure gauge but I read in one thread that what harbor freight sells doesn't have the right adapter. Maybe that's changed???

 

[wjburken]

Wjburken - it kicked over 200,000 this summer. No oil drips that I've seen, but I'll keep looking. I've considered getting a pressure gauge but I read in one thread that what harbor freight sells doesn't have the right adapter. Maybe that's changed???

You wouldn't see any drips if the o-ring on your pickup tube was cracked. It is inside your oil pan and connects to your oil pump. If the o-ring fails, the pump can draw in air. One way to test it is to put a couple extra quarts in your oil pan and park with the nose of your truck significantly lower than the rear. This puts the oil up around where the o-ring is and if doing this causes you pressure to increase, then you likely have a bad o-ring. It is a common point of failure.

Please check your oil pressure. I see a lot of people that see an output from a gauge that they don't like and instantly assume the gauge is bad instead of assuming the gauge is good and looking for why the gauge is not reading where it should.

 

[Beer 30]

You wouldn't see any drips if the o-ring on your pickup tube was cracked. It is inside your oil pan and connects to your oil pump. If the o-ring fails, the pump can draw in air. One way to test it is to put a couple extra quarts in your oil pan and park with the nose of your truck significantly lower than the rear. This puts the oil up around where the o-ring is and if doing this causes you pressure to increase, then you likely have a bad o-ring. It is a common point of failure.

Please check your oil pressure. I see a lot of people that see an output from a gauge that they don't like and instantly assume the gauge is bad instead of assuming the gauge is good and looking for why the gauge is not reading where it should.

wjburken - thank you very much. I'll try that this weekend. What will happen to the extra oil I put in? I assume I should drain it back out after the test?

Also - if a bad o-ring is the problem - any guess on how much that repair might be? My wife and I have already decided that with 200,000 on it, we're not going to sink a lot more money into it.

Thanks!!!

 

[iamdub]

wjburken - thank you very much. I'll try that this weekend. What will happen to the extra oil I put in? I assume I should drain it back out after the test?

Also - if a bad o-ring is the problem - any guess on how much that repair might be? My wife and I have already decided that with 200,000 on it, we're not going to sink a lot more money into it.

Thanks!!!

Don't take it to the shop that charges 2 hours for spark plug wires!

The O-ring replacement is one of those "4-hour jobs to replace a 20-cent part" kinda deals. You have to drop the oil pan, which is pretty straightforward on a 2WD but more complicated on a 4WD/AWD.

 

[Tonyrodz]

wjburken - thank you very much. I'll try that this weekend. What will happen to the extra oil I put in? I assume I should drain it back out after the test?

Also - if a bad o-ring is the problem - any guess on how much that repair might be? My wife and I have already decided that with 200,000 on it, we're not going to sink a lot more money into it.

Thanks!!!

Yes, take out the extra oil. You don't want to ruin any other seals or gaskets from the extra oil.
I had a similar issue with my 05 Express van. It has the 4.8. Not a ton of miles either. Started at around 143,000 miles. Oil pressure slowly went down, til it would go to 0 at idle. I think what started my issue was getting synthetic oil changes. Seems the former owner neglected getting oil changes! Anyway, took it to a buddy of mine. O ring was good, but you should've seen the sludge. I think the synthetic oil must've knocked some sludge loose and probably clogged some oil passages. Had my buddy put in a Melling HV oil pump, which actually didn't help right away. Pressure slowly went up for a few weeks. Now at cold idle it's 50 lbs. Are you pretty consistent with your oil changes? Have you gone from conventional to synthetic oil? Hopefully it isn't as severe as mine was.
I just wanted to give you an idea what could've or might've caused your issue. Taking it to a garage to replace a defective O ring--if that's what it is--I can't see being under $700. All labor. My buddy needed a lift(it can be done on the ground if need be)and he needed to take the lower front of the engine off--crank pulley, front cover (oil pump is there also)to expose the timing chain and eventually get to the oil pickup.
I'd look around and price out different shops--BUT--The cheapest price isn't always the best either. Check for any online reviews from any garage you're considering. Also check the BBB for any complaints. Also--when you finally find a garage, see if you can supply your own parts. That'll save you some money too. On an LS motor 200,000 miles isn't horrible. I've seen and heard these motors going 300-400,000 miles no problem. Imo, you'd be making a wise investment if you spent the funds to get it repaired properly--that's if everything else is in good mechanical shape. Just my .02.
BTW--Stay away from the shop who wanted to charge you $1000 to do plugs! They were flat out trying to rip you off! Straight up scumbags if you ask me.
Let us know what you decide and what you find. Good luck.

 

[Beer 30]

Thanks all!! I appreciate the advice. In the worst case, even if it does cost $700 or a little more, that would be about the cost of me registering a new vehicle. Our other taxes here aren't bad (western Colorado), but bend over when you want to register a vehicle.

I'll let you know how this turns out.

I bought out with about 90,000 on out and it had a great carfax with it. Apparently the former owner changed the oil often. I've changed every time the computer tells me to with synthetic and a quart of Lucas oil treatment.

I have a huge lust for an F150 with the 3.5L and the max tow package because it will add about 4,000 lbs to the max with this Yukon, but my bank account says to hold off

 

[Tonyrodz]

Thanks all!! I appreciate the advice. In the worst case, even if it does cost $700 or a little more, that would be about the cost of me registering a new vehicle. Our other taxes here aren't bad (western Colorado), but bend over when you want to register a vehicle.

I'll let you know how this turns out.

I bought out with about 90,000 on out and it had a great carfax with it. Apparently the former owner changed the oil often. I've changed every time the computer tells me to with synthetic and a quart of Lucas oil treatment.

I have a huge lust for an F150 with the 3.5L and the max tow package because it will add about 4,000 lbs to the max with this Yukon, but my bank account says to hold off

Be careful with the fords--they make your hair fall out--teeth fall out---go blind etc lol.

 

[wjburken]

Be careful with the fords--they make your hair fall out--teeth fall out---go blind etc lol.

Hey, I have a F150!
I still have all my teeth!
Hair..........Not so much.
Oh........I also wear glasses.

 

[JonnyTahoe]

Don't take it to the shop that charges 2 hours for spark plug wires!

The O-ring replacement is one of those "4-hour jobs to replace a 20-cent part" kinda deals. You have to drop the oil pan, which is pretty straightforward on a 2WD but more complicated on a 4WD/AWD.

You mean 10+ hours. It takes four hours just to clean the oil pan and related parts. I did this Job two years ago on my 4X4 Tahoe maybe if you have access to a shop with a lift but to do the job on your back in the garage or outside four hours is never going to happen.

 

[JonnyTahoe]

Danjy3737 - Yes!!! It's something like 6 hours labor to replace the plugs and another 2 for the wires. That's what shops get by 'the book' I hadn't done anything on a car since I was 19 and I'm now 62 but I had the whole job done by lunch.

They were looking up the wrong vehicle. Must of been one with the engine in sideways.

 

[Mudsport96]

wjburken - thank you very much. I'll try that this weekend. What will happen to the extra oil I put in? I assume I should drain it back out after the test?

Also - if a bad o-ring is the problem - any guess on how much that repair might be? My wife and I have already decided that with 200,000 on it, we're not going to sink a lot more money into it.

Thanks!!!

If it is the oring, 200k is well worth the repair if the truck is otherwise solid. I did the oring on the Silverado my father in law gave my daughter. The truck has 400k on it and after the repair she carries 40psi highway and 20ish idle.
It's just a bit difficult without a lift, but I did it over 3 days (only a couple hours a day and 1 day soaking pan in solvent) last winter. On a decent day i probably could have done it in 6 hours but it was 10 degrees in a non insulated non heated garage on the floor. Had to take warmup breaks and short days.

 

[mikeyss]

I'm pretty neutral between GM and Ford, but I will not knock the 3.5 Ecoboost..that motor is powerful and isn't a bad engine. There's a million of them running around these days, lol

 

[ScottTheEngineer]

My 6.0 had a failed oil pressure relief valve in the oil pan every so often the pressure dropped to 0psi. They had to drop the front diff to get to the oil pan to replace it. $1500
I had them replace the pick tube o-ring also. $2.50
I was quoted an additional 2,000 for replacing the oil pump.
I paid because I don't work on cars when its its below 40deg.
My average pressure after the replacement dropped to 40 psi where before it was 60 constant.
My understanding is that there are 2 pressure relief valves. One in the pump, one in the pan. The pressure sending unit is on top of the engine in the rear.
Also, if you have AFM lifters don't use the Lucas.

 

[cam3439]

Have you added any additives or cleaners to the oil? A clogged/failing oil filter (rare but it happens) can give similar oil pressure results.

 

[iamdub]

My 6.0 had a failed oil pressure relief valve in the oil pan every so often the pressure dropped to 0psi. They had to drop the front diff to get to the oil pan to replace it. $1500
I had them replace the pick tube o-ring also. $2.50
I was quoted an additional 2,000 for replacing the oil pump.
I paid because I don't work on cars when its its below 40deg.
My average pressure after the replacement dropped to 40 psi where before it was 60 constant.
My understanding is that there are 2 pressure relief valves. One in the pump, one in the pan. The pressure sending unit is on top of the engine in the rear.
Also, if you have AFM lifters don't use the Lucas.

Gen3 engine doesn't have AFM, so no pressure relief valve in the oil pan. On all LS engines, the oil pump has a spring-loaded valve to bleed off pressurized oil to limit the maximum developed pressure within the engine oil system as a whole.

On the Gen4 engines with AFM, the relief valve in the oil pan is a limiter for maximum oil pressure within the AFM system itself. Since the AFM system operates by varying oil pressure to lock and unlock the lifters, its pressure relief circuit has to be isolated from the engine's primary oil circuit. Otherwise, the oil pressure gauge would swing drastically as AFM engages and disengages.

 

[georgebuhr]

Definitely check the oring. Replaced mine at 200,000, at 350,000 now and still going strong, no oil pump necessary. This engine is solid as a rock otherwise.