Rear Main Seal Leak

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Horsehammerr
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Rear Main Seal Leak

Post by Horsehammerr »

Since I started using Synthetic Oil I've developed a slight weep down across the oil pan. In the past with other GM motors this was a sign of rear main leaking. This has become evident over the last 18,000 miles of synthetic oil use. I wonder, does this new oil flow so good that 134,000 mile old seals can't hold it back ?? :?:
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Post by F9K9 »

I have heard that but, have also heard that the synthetic conditions the seals. I wouldn't worry about weeping or I might bump up to 10-30W oil at the miles you are at.
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Post by Horsehammerr »

I do run 10-30w from May thru November. I started out with 10-30w Syn.Oil. I really like how clean it is after 6,000 miles use. I change oil and WIX filter every 6,000 miles. Back in Dino. days I always changed at 3,000 miles and my Castrol was always coal black. I asked Castrol about this and was told thats clearly doing a good job cleaning. :shock: I do wonder how long I have left on this rear main ?? :?: 8)
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Post by F9K9 »

Horsehammerr wrote:............I do wonder how long I have left on this rear main ?? :?: 8)
Maybe as much as 100K or more. I wouldn't sweat it until you are adding a qt between changes. When it starts to get really bad you can substitute Barr (sp?) rear main seal treatment for a qt of oil. It will slow it down or stop it for a while. I had good luck with it in the heeps but, I have no clue on long term side affects.
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Post by DLP »

I have 130,000 on mine and have had a leaking rear main for about 20,000. I use 5/30 and change it every 3,000 like clockwork. I never see oil trails that wind drives towards the back of the truck. But I have a half dozen drops on the floor in the mornings. I do have the leaking oil lines. But I keep them wiped down so I can tell how much I am loosing out the rear main. Between towing trailers, leaking and maybe burning, I have never been more than a half quart low at change time. Like already said above, Don't worry too much until it gets to be a big problem. I do feel bad about leaving spots in friends cement driveways. I worry about oil additives gumming up the motor.
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Re: Rear Main Seal Leak

Post by MoJoe »

Sorry to dig up an old thread, but I guess that is why we search first. :mrgreen:

So, I too switched to Mobil 1 when I bought my truck with 70k miles on it. I now have 79k on it, and have changed the oil twice with Mobil 1. The bottom of my pan is wet, and I get a few drops each day after driving on the floor coming right off the drain bolt (not the bolt that I can tell).

My question is, I know it is a straight forward but labor intensive to replace the rear main. First off, could it be coming from another source, if so where should I start? Distributor, valve covers, etc. Thanks.

Also, how is yours holding up Horsehammerr?
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Re: Rear Main Seal Leak

Post by F9K9 »

I would clean up the pan and motor and make sure that you know where it is coming from first. Replacing a RMS is labor intensive on our 4.3L engines. The transfer case and tranny needs to be removed to get at it. Unless it is bad, I wouldn't fool with it unless you have to have the tranny pulled for service. I am still running the Bar (sp?) additive in my heep without ill effects. I don't don't really know why I am running it since it is $10 a qt and that would buy a lot of oil. My rms had a pretty bad leak and it is stopped for now. Replacing the seal does not mean it will not leak again within months. The crank may be scored and if, it is then, it will eat up a new seal pretty fast.
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Re: Rear Main Seal Leak

Post by roadrunner »

Just another reason I don't run synth oil. :) Over 102k and no leaks anywhere to be found as long as Reed keeps his ducks home that is. :lol: In my experience all or nearly all oil stop leaks are primarily seal softeners. They soften up old hardened seals to help swell them to stop leaks. Some successfully some not. Usually once used the seal remaining life is shortened even though it seals up for a while. Once the softened seal material wears away it starts leaking again and anything other than replacement is dubious at best. Bear in mind also that most synthetic oils are thinner and more prone to "oil creep". I have encountered this with some dino-oils as well that creep and seep where others do not. 8)
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Re: Rear Main Seal Leak

Post by MoJoe »

Thanks for the replies guys. I will clean up the pan and pay attention to it. Also, would it be wise if it is the rear main, to switch back to a dino oil, or possibly a heavier syn?
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Re: Rear Main Seal Leak

Post by F9K9 »

I'm running mobil 1 in both rigs and I don't see any leakage.
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Re: Rear Main Seal Leak

Post by roadrunner »

MoJoe wrote:Thanks for the replies guys. I will clean up the pan and pay attention to it. Also, would it be wise if it is the rear main, to switch back to a dino oil, or possibly a heavier syn?
If it wasn't leaking with a particular dino-oil I'd opt to try going back to it and see what happens. Couldn't hurt. 8)
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Re: Rear Main Seal Leak

Post by MoJoe »

roadrunner wrote:
MoJoe wrote:Thanks for the replies guys. I will clean up the pan and pay attention to it. Also, would it be wise if it is the rear main, to switch back to a dino oil, or possibly a heavier syn?
If it wasn't leaking with a particular dino-oil I'd opt to try going back to it and see what happens. Couldn't hurt. 8)

Right, as soon as I bought it I switch to syn. Makes sense to go back, but I will wait to change time. Hopefully I will see it go away.
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Re: Rear Main Seal Leak

Post by Cherokeez71 »

I know this s is a 2 year old thread but my 2002 s10 crew cab had a oil leak. So I tore down the trans. Found out the rear main seal was fine but there is the piece that holds the rear main. It's U shaped. It was leaking witch once I got that out GM put sealent only at the tops and no sealent at the bottom and half way up each side. Once that was fixed it stopped leaking.
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Re: Rear Main Seal Leak

Post by HenryJ »

Awesome tip. Thanks!

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Re: Rear Main Seal Leak

Post by Cherokeez71 »

Forgot to mention you will have to unbolt a couple engine oil pan bolts to be able to get that U shape piece out and in.
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Re: Rear Main Seal Leak

Post by ApproachMedium »

Cherokeez71 wrote:Forgot to mention you will have to unbolt a couple engine oil pan bolts to be able to get that U shape piece out and in.
Probably a long shot, but can you find a picture of this or possibly a diagram of where its located? My trucks last place its leaking appears to be the rear main seal. Probably something I shouldn't care/worry about with 251k but I have just been curious. The motor is slated for replacement with a 4.3L crate motor when it finally dies. Which seems like it will be never.
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Re: Rear Main Seal Leak

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G
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Re: Rear Main Seal Leak

Post by Cherokeez71 »

Here is the best pics I could find it leaks from the bottomm
http://repairguide.autozone.com/znetrgs ... 216598.jpg
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Re: Rear Main Seal Leak

Post by ApproachMedium »

OK Cool thanks.
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Re: Rear Main Seal Leak

Post by Cherokeez71 »

Sorry best I could find