Interesting loss of oil pressure issue GM 6 Liter

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BobsArmory

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So I have a friend of mine that I have done oil changes for him and his family for years now. He has a 2008 GMC Yukon Hybrid with a 6 liter motor that he bought used with about 120,000 miles on it. The first owner was the Canadian Govt. Uses about 3 quarts of oil each OCI no matter what oil is used. Runs great.

When he bought it the used car lot sent it over to the local "Fast Eddies Oil Change" for a fresh OCI. A few days later he called me up in a panic stating that the oil pressure warning light was on and the gauge dropped to near zero PSI. I went over to his house, couldn't find anything wrong but did a complete oil change replacing the made in China filter with a Fram Ultra and 6 quarts of M1 EP 5w-30. Bingo, everything worked with no issues.

Since then I have done all his oil changes with no issues using oils such as M1 EP, Valvoline Maxlife Syn and Pennzoil Ultra with Fram Ultra filters with no issues.

Fast forward to last week. His current set up is PU 5w-30 with an FU filter, 53% left on the OLM. He calls me up with the same problem. Oil pressure dropping light going on. I go over, start up the truck when it's cold. Jumps to about 70 PSI and after 4 minutes or so it slowly loses pressure to about 10 PSI at idle and as usual, can't find any glaring issues. Drain the oil and replace with PP and an ACDelco filter. Bazinga! No problems, great oil pressure and no warning lights.

So what's the deal here? Why is this happening? What am I missing?
 
FYI, Last week when I did the oil and filter change it was about 12F outside. My 2009 Chevy Silverado with the same 6 liter jumps to about 60 PSI at those temps with the same oil. His was 70 ish PSI at a cold start.
 
Oil pressure sender screen clogged. Seems to be common on this generation. I would start there.
 
Last edited:
Originally Posted By: caravanmike
Oil pressure sender screen clogged. Seems to be common on this generation. I would start there.
Replace the Oil Pressure sending unit. Your engine still has good oil press, but bad sending unit. This happened to a friend.
 
Originally Posted By: caravanmike
Oil pressure sender screen clogged. Seems to be common on this generation. I would start there.


If the screen is clogged wouldn't it make more sense that it would have low PSI upon start up since the oil is thick? Then as it heats up and the oil thins out it more easily flows past the screen?
 
Originally Posted By: tig1
Originally Posted By: caravanmike
Oil pressure sender screen clogged. Seems to be common on this generation. I would start there.
Replace the Oil Pressure sending unit. Your engine still has good oil press, but bad sending unit. This happened to a friend.
+1 it needs a new Oil Pressure Switch.

My mom's Buick did this. New sensor, no more oil pressure light.
 
Originally Posted By: caravanmike
Oil pressure sender screen clogged. Seems to be common on this generation. I would start there.


That happened to me not too long ago in my '08 V8 TrailBlazer.

Those screens doe not have any oil flow past them so they can collect sludge.

I had the sensor replaced at the same time due to the mileage.
 
It's Probably the sender replace it with one from the stealer and use Mobil 1 High Mileage with a Fram Ultra oil filter and it should be good to go.
Those gauges are not exact at all.
 
Going to throw a crazy one out there. Had issues with Fram filters on our old Equinox 3400 and my current S10. Equinox would tap like no other for a while, as did the S10 when it's cold. Strangely on the S10 the oil pressure would stay high (internal bypass kicking in I'm assuming) even after warm-up. Went to non-ecore AC Delco's on both and no more issues. Still needing to cut open the one that came off the truck. Not saying there is anything wrong with Fram filers, just my personal experience.

Now, given the mileage, still wouldn't be a bad idea to replace the sender.
 
I'm using Ultras. No pressure issues, don't burn any oil in a 6500 OLM OCI thanks to a soak.. If it were me I would immediately change the oil filter and see what happens. Then the sending unit. If it turns out to be the filter let us know and DO NOT throw it away!
 
Before spending $450 at the stealer to replace sending unit and screen under it, change your oil and use a Wix XP filter with full sythetic Amsoil 0W-30. Could also be pump or O ring in pickup. Or bearings could be loosening in engine and sucking air.
 
Originally Posted By: Mortjr
Before spending $450 at the stealer to replace sending unit and screen under it, change your oil and use a Wix XP filter with full sythetic Amsoil 0W-30. Could also be pump or O ring in pickup. Or bearings could be loosening in engine and sucking air.
It HAS to be Amsoil? Why?
 
The filter is still in the back of my truck. I plan on opening it up when I get a chance.

Originally Posted By: LeakySeals
I'm using Ultras. No pressure issues, don't burn any oil in a 6500 OLM OCI thanks to a soak.. If it were me I would immediately change the oil filter and see what happens. Then the sending unit. If it turns out to be the filter let us know and DO NOT throw it away!
 
Originally Posted By: Mortjr
Before spending $450 at the stealer to replace sending unit and screen under it, change your oil and use a Wix XP filter with full sythetic Amsoil 0W-30. Could also be pump or O ring in pickup. Or bearings could be loosening in engine and sucking air.


Originally Posted By: DoubleWasp
The sending unit is $450?


Its $35.73 I bought one a week ago.

Thanks to krismoriah72 for the link


http://www.ebay.com/itm/162084838855?_trksid=p2057872.m2749.l2649
 
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I just took a peek on Amazon when somebody quoted $450. Its actually $31.25. But whats interesting is what I noticed for "frequently bought together". A screen! If there actually is a screen ahead of the Pressure sender Maybe all thats wrong. Its clogged! Finding out is free
smile.gif


https://www.amazon.com/ACDelco-D1846A-Original-Equipment-Pressure/dp/B0016HPUS8/ref=au_as_r?_encoding=UTF8&Make=GMC%7C48&Model=Yukon%7C558&Year=2008%7C2008&ie=UTF8&n=15684181&newVehicle=1&s=automotive&vehicleId=1&vehicleType=automotive
 
Another vote for sending unit. Had same issue on 08 5.3 Trailblazer. Bought AC Delco for around $40 on Amazon. Not too hard to change. Worst part is reaching it.
 
I thought that was wrong.

I haven't had to buy a lot of LS engine parts for my fleet, but that price was jiving with what I know about parts pricing for this engine family.
 
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