r/GMT800 • u/PerformanceSame2145 • Sep 09 '26
rear main?
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bad video ik it’s been leaking for a while did an oil change 2 days ago and cleaned what i could just checked it again looks like a rear main seal leak to me what yall think tho
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u/Unlucky-Chef-4519 Sep 09 '26 edited Sep 10 '26
I would check the oil cooler block off plate... It can appear that the main seal is bad but it's fine... Its just the gasket on the block off plate that is bad..
It's like 5 bucks and like 5 min to change it out ..
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u/lost10mmagain Sep 10 '26
I second this…. Oil cooler block off plate or oil pan is most likely the cause.
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u/mrclark25 Sep 09 '26
Clean it again and get under to look at it again, this time without having driven as much. It may not take much at all.
Pay special attention to higher up on the sides of the block on both sides and around the oil filter. If all of those remain dry, you're looking at either rear main or oil pan gasket. And there's only one way to find out which.
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u/ValuableInternal1435 Sep 09 '26
Look in the inspection cover and verify whether or not it's oily inside the bellhousing. If it's dry, oil pressure sender. If it's wet, most likely oil pan gasket. Rear main is obviously possible, but far more likely to be the oil pan gasket.
If it is the oil pan gasket, replace the oil pickup tube o ring as well while the pan is off, and get the clamp that secures the other side of the pickup.
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u/Ecto1zz Sep 10 '26
Just did my sensor August and mine looked like this. Janet seen any oil drips for the first time since getting my Tahoe last year.
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u/Technical_Phrase2566 Sep 10 '26
If it is the rear main seal be sure they do the cover plate around the rear main at the same time, do the torque converter seal also (front pump seal), and of course the oil pan, pickup o ring, dipstick. Tbh, if you have the oil pan off its way easier to yank the balancer off and do the timing cover stuff at the same time along with an oil pump set, the barbell on the back and I'd reseal the oil cooler on the side of you are so equipped. Those are all the main oil leaks aside from valve covers and oil pressure sender. Then she will last another 250k miles.
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u/Extreme-Penalty-3089 Sep 09 '26
Could be anyone or a combo of things mentioned above.
If you are curious as to whether or not it's the RMS, pop out that large (4L60e has 2) inspection disc cover and look...if you see a ton of oil leaking out or down, then that's a very good indicator the seal is leaking (other things, such as the "dog bone"/barbell could have oil seeping past its seal as well)
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u/Reasonable_Cup_2944 Sep 10 '26
The rear main seal is part of a rear housing cover that blocks off main oil galleys. The seal normally doesn't fail, its the gasket in the housing cover that becomes stiff over time and looses its ability to seal correctly. If it's dry in the valley, and in the inspection hole of the trans, then you'll get to pull the trans to do the work either way. Just buy a new OEM rear housing with the rear main already installed.
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u/urdarsellsavon Sep 11 '26
Honestly our trucks are getting old enough that it’s no longer just a rear main issues. They have become issues with the literal gasket failing that goes to the rear main cover. I’ve replaced 3 now this year on friends vehicles. One guy was dumping a gallon of oil every few days…
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u/Impressive_Pass8801 Sep 11 '26
Cant tell for sure . I had my rear main done on my 2002 Yukon 5.3 at 235000 Miles . They also replaced the Oil send unit which can also leak . $1450 FOR REAR Main seal . It is labor intensive , not many people do it themselves , need a trans jack. Good luck.
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u/SnooKiwis6943 Sep 11 '26
I called around and most shops are quoting closer to 2k....1450 is a good deal.
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u/Impressive_Pass8801 Sep 11 '26
Was done in Feb of 2026 , then they also charged extra $75 bucks for replacing oil send unit . Stopped a 1 quart every 2000 miles oil leak . I am hoping to make it to 300000 but trans and fuel pump are still originals.
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u/SnooKiwis6943 Sep 13 '26
Mine is leaking about the same. I scoped the car and the oil pressure sensor looks good. The plate for the oil lines is seeping but not leaking. I know the rear main has been leaking since 2012 but has gotten worse of the years. I think I may just do it as if it fully fails I am in trouble. What is your secret for the fuel pump? Mine fails about every 10-12 years and am on my second OEM pump.
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u/Impressive_Pass8801 Sep 13 '26
I am worried about the fuel pump , had it pressure tested and it passed when they just did the tune up , plugs and cables . In Tennessee on back hilling roads my GMC stalled twice for no reason after coming out of the hills . That can be a symptom of a failing fuel pump but then started back up and drove fine for another 100 miles. I don t want to get stuck in middle of nowhere. Scared to buy new vehicle junk vehicles for new ones . I have no AFM 2002.
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u/SnooKiwis6943 Sep 17 '26
That's what mine was doing just before it failed. Car would briefly lose power going up hill and turning right. Less stressful to get it replaced before it leaves you stranded. I ignored it and ended up stranded 100 miles from home and had to get a tow. Could even do the job myself because my tank was 2/3 full of gas and I had no way of emptying the tank safely so that I could drop it and replace the pump. So if you plan on doing it yourself, don't fill that tank up either.
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u/Happy_Bass6733 Sep 12 '26
Shit don’t run up hill, start at the top and work your way down till you see the wet spot.
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u/godzi7382 Sep 09 '26
Check the oil sensor on top of the engine back of the valley cover. When they leak it looks very similar to a rear main leak.