2006 Yukon Oil Pressure Drop After New Heads Installed

[YukonOwner06]

Hi forum members. I have an issue with my 5.3 Yukon engine that perhaps I can get some assistance with. I am the original owner and the vehicle has 137K miles on it. On a dreaded road trip the "Engine Overheating" message popped on the display. The coolant reservoir was empty so once the engine cooled down I refilled it and noticed over the course of a few months the coolant in the reservoir needed to be refilled.

I took the Yukon to a reputable engine shop. They discovered a small hairline crack on the right head. They replaced both heads and less than a few days I noticed the oil pressure dropped from 40 PSI to 20 PSI which eventually dropped below 10 PSI. Fearing there was an issue with the oil pickup, I had the O ring on the oil pick up replaced. It did not improve the oil pressure.

I am still trying to diagnose this pressure issue, but would the installation of new heads (perhaps not the exact replacement heads for my vehicle) cause the oil pressure to significantly drop?

 

[mattbta]

@Fless please move to Engine section.

@YukonOwner06 I suffered cracked heads 2x on my 2004. It has taken a number of short oil change intervals to allow my pressure to stay up past 500 miles on the oil. My theory is that despite the first couple of changes, there was still residual coolant/oil mix in the block and would clog up the oil filter. I noticed on fresh oil/new filter the pressure would be great and then after 500 or so miles, it would drop to ~25PSI at idle. I put a can of Marvel Mystery Oil in it when this happened, drove for a half hour to hour and then changed for fresh. Rinse/repeat a number of times.

Unfortunately, I was lazy so I can't tell you the number of times I did this. Now I can go 3000 miles and keep "normal" pressure. My normal is a little lower than 40 at hot idle, which might be bearing wear. Hopefully yours can be rectified by 4-5 short OCI's. If it persists, there might be substantial wear from the coolant being in the oil. Good luck.

 

[drdave81]

How are you reading oil pressure? The gauge in the cluster or an actual mechanical gauge in the block? If you're basing it on the cluster, confirm it with a mechanical gauge first. Then go from there. What is cold pressure at? Is it always low or start normal and drop as it warms up?

 

[OR VietVet]

How are you reading oil pressure? The gauge in the cluster or an actual mechanical gauge in the block? If you're basing it on the cluster, confirm it with a mechanical gauge first. Then go from there. What is cold pressure at? Is it always low or start normal and drop as it warms up?

This, plus, did the oil pressure sensor get changed when doing the heads? You did not say. Also, with coolant running mixed thru it, the oil pump is suspect as well. Needs a mechanical gauge put on it.

 

[YukonOwner06]

@Fless please move to Engine section.

@YukonOwner06 I suffered cracked heads 2x on my 2004. It has taken a number of short oil change intervals to allow my pressure to stay up past 500 miles on the oil. My theory is that despite the first couple of changes, there was still residual coolant/oil mix in the block and would clog up the oil filter. I noticed on fresh oil/new filter the pressure would be great and then after 500 or so miles, it would drop to ~25PSI at idle. I put a can of Marvel Mystery Oil in it when this happened, drove for a half hour to hour and then changed for fresh. Rinse/repeat a number of times.

Unfortunately, I was lazy so I can't tell you the number of times I did this. Now I can go 3000 miles and keep "normal" pressure. My normal is a little lower than 40 at hot idle, which might be bearing wear. Hopefully yours can be rectified by 4-5 short OCI's. If it persists, there might be substantial wear from the coolant being in the oil. Good luck.

Thanks for the suggestions. What is the benefit of using the Marvel Mystery Oil and how would that help with the oil pressure to increase? I will try this suggestion out and jump back into the thread to post my results.

 

[mattbta]

Thanks for the suggestions. What is the benefit of using the Marvel Mystery Oil and how would that help with the oil pressure to increase? I will try this suggestion out and jump back into the thread to post my results.

Didn't help the pressure. I was trying to get the excess/remainder of contaminated oil out of the motor using the MMO at the end of the interval.

 

[YukonOwner06]

This, plus, did the oil pressure sensor get changed when doing the heads? You did not say. Also, with coolant running mixed thru it, the oil pump is suspect as well. Needs a mechanical gauge put on it.

How are you reading oil pressure? The gauge in the cluster or an actual mechanical gauge in the block? If you're basing it on the cluster, confirm it with a mechanical gauge first. Then go from there. What is cold pressure at? Is it always low or start normal and drop as it warms up?

I am reading it off the instrument cluster. I have not done a manual reading just yet. The oil sensor was replaced a couple of times to determine if it was the oil sensor the root of the issue. Upon start-up the oil pressure on the instrument panel will be at 20 PSI and will remain at the level until the engine warms up. Upon increasing the RPM's I get, 30 PSI at 2K RPMs and 40 PSI at 3K RPMs. Its when I drive my Yukon for awhile the oil pressure will drop down to 7-8 PSI at idle which triggers the Low Oil Pressure notification and chime.

I cannot say how long my original head had the crack and the coolant was mixing in with the oil. It just seems after the heads were replaced the oil pressure just dropped significantly to the warning level. Would it be reasonable to replace the oil pump in hopes that is the culprit?

Again thanks for all of your replies and responses.

 

[Doubeleive]

you could do the old trick of adding a quart of trandsmission fluid also, run it for a day or two and then change the oil
that might help clean out any residual blockage

 

[Fless]

Have the oil & filter been changed since the head job?

 

[rockola1971]

you could do the old trick of adding a quart of trandsmission fluid also, run it for a day or two and then change the oil
that might help clean out any residual blockage

Ive told this technique to 100's if not 1000's of people. I always get that same surprised look. This technique was taught to me by the old timers. Now I am getting to be one of the "old timers'. A quart in the fuel tank also will clean your injectors too. It was originally used to clean out the old school carburetors too. Ive used it on autos, motorcyles, dirtbikes, 3&4 wheelers, lawnmowers....the navy wouldnt let me try it on Jet engines though.

 

[OR VietVet]

Ive told this technique to 100's if not 1000's of people. I always get that same surprised look. This technique was taught to me by the old timers. Now I am getting to be one of the "old timers'. A quart in the fuel tank also will clean your injectors too. It was originally used to clean out the old school carburetors too. Ive used it on autos, motorcyles, dirtbikes, 3&4 wheelers, lawnmowers....the navy wouldnt let me try it on Jet engines though.

Used to use a quart either added directly to the crankcase or would use a vacuum hose, with engine running, and stick the hose in the ATF a little at a time and had to butterfly the throttle to keep running and wait till all gone and white smoke gone at the tailpipe.

 

[nonickatall]

I use one Liter Diesel in the crankcase and drive appx. 20 Miles without heavy acceleration. I did that to my truck at my last oilchange. The oil was like honey at the dipstick when i filled in the diesel. And when i swapped the oil it was black.
The oilpressure increased after the oil change a few points.

It was funny when i stopped at the fuel station and took the tap to fill 1 Liter in my engine. The looks where worth every cent ..

 

[YukonOwner06]

This, plus, did the oil pressure sensor get changed when doing the heads? You did not say. Also, with coolant running mixed thru it, the oil pump is suspect as well. Needs a mechanical gauge put on it.

Apologize for the delayed response. The oil sensor was changed out several times after the heads were replaced.

The oil pressure dropped 10-15 pounds after the heads were replaced. The oil pump was not replaced as this drop in pressure was not discovered until after the new heads were installed. The oil pressure will be at 30-35 at startup and while driving, but when I come to stop and idle it drops down to 10-7 and I get the warning chime and message on the instrument panel. They put on a mechanical gauge and it showed 35 PSI at start up but they did not let it run for a bit and then measure it at idle. I suspect they were not wanting to see that idle measurement.

 

[YukonOwner06]

you could do the old trick of adding a quart of trandsmission fluid also, run it for a day or two and then change the oil
that might help clean out any residual blockage

So add a quart of transmission fluid to the engine oil and then change the oil?

 

[YukonOwner06]

Used to use a quart either added directly to the crankcase or would use a vacuum hose, with engine running, and stick the hose in the ATF a little at a time and had to butterfly the throttle to keep running and wait till all gone and white smoke gone at the tailpipe.

Are you suggesting to add a qua

Ive told this technique to 100's if not 1000's of people. I always get that same surprised look. This technique was taught to me by the old timers. Now I am getting to be one of the "old timers'. A quart in the fuel tank also will clean your injectors too. It was originally used to clean out the old school carburetors too. Ive used it on autos, motorcyles, dirtbikes, 3&4 wheelers, lawnmowers....the navy wouldnt let me try it on Jet engines though.

Are you suggesting to add transmission fluid to the fuel as well? I have never heard that before and wouldnt that damage the fuel system parts? I am all ears that this point to solve this issue. Thanks

 

[Doubeleive]

So add a quart of transmission fluid to the engine oil and then change the oil?

yes (to the oil), as for adding it to the fuel tank I have never heard of that one.
adding it to the oil will not hurt anything

 

[nonickatall]

You can also use one Quart Diesel in the engine. That works as well. I did that at my truck last time, I made an oil change. The oil was before like honey and after that it was black, full of carbon. So that worked very well, but I guess that will not solve your oil pressure problem.

But it's worth to try it.

But if this not solve your all pressure problem I would look for this two valves.

In the oil pan, there is a pressure relief or bypass valve which is there to prevent for no oil pressure when the oil filter is clogged, if this valve fails it can cause, no oil pressure.

And there is an oil pressure relief valve in the oil pump, which at least control the oil pressure.

This can also be a problem in your engine.
Probably because of the work on your engine something stuck in one of these valves.

 

[Tonyrodz]

Apologize for the delayed response. The oil sensor was changed out several times after the heads were replaced.

The oil pressure dropped 10-15 pounds after the heads were replaced. The oil pump was not replaced as this drop in pressure was not discovered until after the new heads were installed. The oil pressure will be at 30-35 at startup and while driving, but when I come to stop and idle it drops down to 10-7 and I get the warning chime and message on the instrument panel. They put on a mechanical gauge and it showed 35 PSI at start up but they did not let it run for a bit and then measure it at idle. I suspect they were not wanting to see that idle measurement.

Just curious--when the oil pressure drops low do you hear any drivetrain noise? Which heads did you have--which ones do you have now? I'm experiencing similar--but not exact issues with my Express van. Has the 4.8 with the 862 heads.

 

[rockola1971]

Are you suggesting to add a qua

Are you suggesting to add transmission fluid to the fuel as well? I have never heard that before and wouldnt that damage the fuel system parts? I am all ears that this point to solve this issue. Thanks

Tranny fluid serves 3 purposed inside the transmission. It is used as a coolant, hydraulic fluid and a detergent. Tranny fluid will not hurt your fuel pump, lines, seales nor fuel injectors. It will clean your injector nozzles. Dump a quart into your fuel tank and run another when you feel like it. Worst you will get is some smoke out the tailpipe. It will clean your injectors out. You can run it in your lawnmower, dirtbikes, ATV's and doesnt matter carb or fuel injection will benefit.

 

[RAMurphy]

Interesting. I assume the type of transmission fluid would not matter.