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Hi everyone, first time posting, but long time reader. I usually try to avoid posting when I can, and  just browse the threads and read about related problems and figure it out from there. Even though I've found many threads that are similar to the problem Im having, I still can't narrow it down to my next step. so if anyone can help, it would be greatly appreciated. 

 

Ok so, BAD oil leak problem with my friends 2005 GMC Sierra 1500. It's had this leak for a while, but it's gotten to the point now where it's starting to leave puddles. I power washed the entire area, and I actually got it pretty clean. Today when I looked again to see if I could trace the source, I had a much clearer picture of where the leaks are actually coming from. From what I've read it seems as though it could be the valve cover gasket, the crankshaft sensor, the rear main seal, or even the oil pan gasket. My problem is that to me, it looks like it's coming from almost all these places. I looked inside the bell housing and I don't see it looking completely soaked in oil. It does however, look like the leak is mainly coming from in front of the bell housing behind the engine, in between the two. I'll attach some pictures. These would be from overnight after I power washed it, so the oil hasn't blown anywhere from being driven or anything. Thanks so much to anyone who's got any ideas! 

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Edited by Brittney Trefry
Forgot to say thank you
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I had the same leak on my 2002 at 180k miles.  It just started to leak and put drops on the driveway.  I kind of went over boad to try and fix it but after it was all said and done.  All was well.

 

I started with the valve covers and  intake. Why intake, because it makes it way easier to get to the oil pressure switch.  My big hands don't do well in tight places.  When that didn't fix it, next was the oil pan.  I had seepage along it on both sides.

 

So that didn't fix it so next was the rear main seal.  Low and behold, once the transmission was pulled back you could see where the leak was at the seal.  Changed it out and all was well, nice and dry all over.

 

Sorry couldn't help much but that was how I attacked my leak.

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probably the rear main seal but check the top rear and make sure its not running down the back of the engine. a dye test with ultraviolet light will confirm it. standard trans? usually caused by bad thrust bearing

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10 hours ago, txab said:

Don't forget to check oil pressure sensor up top as well. Not uncommon for the crank sensor to leak as it ages

Thanks for the response! So I ended up checking both of those. Unfortunately, neither were the culprit. I was hoping one of them would be, since the alternative is a lot more of a  headache

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10 hours ago, richard wysong said:

probably the rear main seal but check the top rear and make sure its not running down the back of the engine. a dye test with ultraviolet light will confirm it. standard trans? usually caused by bad thrust bearing

So I added the uv dye, ran the truck for a bit and did another check. Inside the bell housing looked clean surprisingly. It really appears to be coming mostly from the oil pan gasket AND the valve cover gasket. To answer your question, yes, standard trans. I noticed that the line on the side of the trans had a lot of oil on it. Is that the shift linkage ? I don't think he has oil cooler lines. How would I check for a bad thrust bearing. Thank you for the response 

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10 hours ago, Black02Silverado said:

I had the same leak on my 2002 at 180k miles.  It just started to leak and put drops on the driveway.  I kind of went over boad to try and fix it but after it was all said and done.  All was well.

 

I started with the valve covers and  intake. Why intake, because it makes it way easier to get to the oil pressure switch.  My big hands don't do well in tight places.  When that didn't fix it, next was the oil pan.  I had seepage along it on both sides.

 

So that didn't fix it so next was the rear main seal.  Low and behold, once the transmission was pulled back you could see where the leak was at the seal.  Changed it out and all was well, nice and dry all over.

 

Sorry couldn't help much but that was how I attacked my leak.

Thanks for the response. Totally sounds like a standard process I would go through lol. Actually those were the steps I planned on taking, so thanks for sharing, it helps me figure out what I should do if I get t wrong. I hope to God it ends up not being the rear main seal! 

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It is fairly common that the rear main seal goes out.  If you already changed out the oil pressure switch/inspected it, the rear main seal is where I would look to next.  It wouldnt hurt to actually change the valve cover gasket as mentioned already by others.

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3 hours ago, Brittney Trefry said:

Thanks for the response. Totally sounds like a standard process I would go through lol. Actually those were the steps I planned on taking, so thanks for sharing, it helps me figure out what I should do if I get t wrong. I hope to God it ends up not being the rear main seal! 

Hope it isn't but it seems to be the weak link.

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to check the thrust bearing take a pry bar and see if you can move the crankshaft forward and back tolerance is in the thousands so there really should be no detectable movement. with standard trans the clutch puts pressure on the thrust bearing causing wear. if there is play save yourself agravation and just pull the engine, replace the bearings and reseal/gasket the engine. a LOT easier on an engine stand than under the truck

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On 10/25/2021 at 2:05 PM, Black02Silverado said:

I had the same leak on my 2002 at 180k miles.  It just started to leak and put drops on the driveway.  I kind of went over board to try and fix it but after it was all said and done.  All was well.

 

I started with the valve covers and  intake. Why intake, because it makes it way easier to get to the oil pressure switch.  My big hands don't do well in tight places.  When that didn't fix it, next was the oil pan.  I had seepage along it on both sides.

 

So that didn't fix it so next was the rear main seal.  Low and behold, once the transmission was pulled back you could see where the leak was at the seal.  Changed it out and all was well, nice and dry all over.

 

Sorry couldn't help much but that was how I attacked my leak.           

 

I heard that as the main bearing wear the crank falls lower and this is what makes the rear main seal go bad. It makes sense but that means the real fix is a crank grond with new bearings and a seal front and back.                                                                                                        

 

Edited by dna9656
wrong question
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I replaced the oil sending unit, the valve cover seals, oil pan, and timing chain cover and front crank seals. I still got a leak; that leaves the rear main seal and I THINK there is some sort of plunger/ plug up in the upper left rear corner of the block I'm not sure but if some one can shed some light on this I sure would appreciate it. I'm told the REAL fix for that ream main is a crank grind (to resurface the main crank journals, replace the main bearings and the 2 seals at each end of the crank shaft; reason being as the crank bearing wear the crank rests lower relative to where it resides when the engine is new, this puts more weight on the bottom of the front and rear seals causing them to leak. Now I think you can drop the crank without pulling the engine but reinstalling the crank would be at least a 4 handed job; esp. while on your back as most of us don't have a lift. Even doing it this way you still have to pull the transmission back, pulling an engine with this many sensors is not my idea of a good time. Following this and other forums it seems that a lot of engine sensors/wiring just break if they are disturbed so you could also count on replacing sensors and the wire harnesses that serve the sensors. If you do this I would be checking out www.partsgeek.com.

Edited by dna9656
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38 minutes ago, dna9656 said:

I replaced the oil sending unit, the valve cover seals, oil pan, and timing chain cover and front crank seals. I still got a leak; that leaves the rear main seal and I THINK there is some sort of plunger/ plug up in the upper left rear corner of the block I'm not sure but if some one can shed some light on this i sure would appreciate it. I'm told the REAL fix for that ream main is a crank grind (to resurface the main crank journals, replace the main bearings and the 2 seals at each end of the crank shaft. reason as the crank bearing wear the crank rests lower relative to where it resides when the engine is new, this puts more weight on the bottom of the front and rear seals causing them to leak. Now I think you can drop the crank without pulling the engine but reinstalling the crank would be at least a 4 handed job; esp. while on your back as most of us don't have a lift. Even doing it this way you still have to pull the transmission back, pulling an engine with this many sensors is not my idea of a good time. Following this and other forums it seems that a lot of sensors just break if they are disturbed so you could also count on replacing sensors and the wire harnesses that serve the sensors. If you do this I would be checking out www.partsgeek.com.

With all the millions of these engines out there and some over 400k miles on them, I think you are overthinking this.  Change out the rear main seal and all will be good.   I wouldn't do any more than that for the most part.

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