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Old 07-18-2021, 01:34 AM   #1
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Main Seal Leak

A mobile mechanic fixing my dash air conditioner said I had a small main seal leak in my caterpillar diesel. Researching this, I found such a leak can quickly become a dangerously fast leak. Has anyone heard of success or problems of using BlueDevil Rear Main Sealer to protect against this happening? I would take it into Freightliner, but these days they can take weeks to even look at your vehicle. Thanks.
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Old 07-18-2021, 04:11 AM   #2
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Get a second opinion and no magic elixir.
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Old 07-18-2021, 06:33 AM   #3
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A mobile mechanic fixing my dash air conditioner said I had a small main seal leak in my caterpillar diesel. Researching this, I found such a leak can quickly become a dangerously fast leak. Has anyone heard of success or problems of using BlueDevil Rear Main Sealer to protect against this happening? I would take it into Freightliner, but these days they can take weeks to even look at your vehicle. Thanks.
nope never heard of it but I use Liqui Moly in my truck.

It should slow a leak down, you might need 2 for a diesel.

1 works on a gasser.
Best case, it buys you time to have it looked at better.
Worst case, it does nothing for you. These products really only work on dried out seals and revitalize them. If it is torn, nothing really fixes them. It might slow it down some though.
My rear main leaks, one of these made it more of a spot than a mark where it parks.
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Old 07-18-2021, 07:47 AM   #4
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I've never had much faith in any "mechanic in a can" solutions.
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Old 07-18-2021, 12:04 PM   #5
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In , 11 years and 45,000 miles the amount of dampness around the bellhousing vent plate , (that collects annually after I clean it when changing oil ) , hasn't changed .
JMHO: Remove the plate , and clean , wipe around inside the bellhousing , and monitor for drips after a long trip , if you're only seeing dampness and no drips , leave well enough alone.
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Old 07-18-2021, 06:13 PM   #6
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In , 11 years and 45,000 miles the amount of dampness around the bellhousing vent plate , (that collects annually after I clean it when changing oil ) , hasn't changed .
JMHO: Remove the plate , and clean , wipe around inside the bellhousing , and monitor for drips after a long trip , if you're only seeing dampness and no drips , leave well enough alone.

This is the correct answer!! Monitor the situation and leave well enough alone unless the leak gets progressively worse. My Cummins has had a dampness around the rear main seal since new but nothing more in 8 years and 57,000 miles.
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Old 07-19-2021, 03:40 AM   #7
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Quote:
Originally Posted by Skip426 View Post
In , 11 years and 45,000 miles the amount of dampness around the bellhousing vent plate , (that collects annually after I clean it when changing oil ) , hasn't changed .
JMHO: Remove the plate , and clean , wipe around inside the bellhousing , and monitor for drips after a long trip , if you're only seeing dampness and no drips , leave well enough alone.
IMO more oil comes out of the slobber tube than the rear main crankshaft seal. Leaking crankshaft seals are the result of IMO lack of use.
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Old 07-19-2021, 06:34 AM   #8
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IMO more oil comes out of the slobber tube than the rear main crankshaft seal. Leaking crankshaft seals are the result of IMO lack of use.
I totally hadn't considered lack of use. I bought this 20-year-old MH with only 80k miles on it.

Thank you all for your ideas. I'm going to clean it, watch it, and add some sealer.
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Old 07-19-2021, 06:52 AM   #9
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I have not yet verified this, but I think the dipstick our ours is miscalibrated. Filled to the "full" mark, our engine leaks out the rear main seal. Let it get down to the "add" mark and it just stays there (for 4500 miles' worth, at least).
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Old 07-19-2021, 09:11 AM   #10
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Get a second opinion and no magic elixir.
+1 - right on Twinboat!
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Old 07-19-2021, 06:41 PM   #11
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nope never heard of it but I use Liqui Moly in my truck.

It should slow a leak down, you might need 2 for a diesel.

1 works on a gasser.
Best case, it buys you time to have it looked at better.
Worst case, it does nothing for you. These products really only work on dried out seals and revitalize them. If it is torn, nothing really fixes them. It might slow it down some though.
My rear main leaks, one of these made it more of a spot than a mark where it parks.
Sorry. One of those nights when I canít pass it up.

I have the same problem. Iím thinking about going to my Dr. tomorrow morning.
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Old 07-19-2021, 06:49 PM   #12
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Please tell us what engine you have and what quantity of oil you used at last oil change with filter change.
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Old 07-21-2021, 04:25 AM   #13
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You don't say what engine or year you have.
Note that many diesel engines have a crankcase breather/filter at the top of the "slobber tube". If that filter (or screen) gets clogged up, higher than normal crankcase pressure builds up in the engine which then pushes oil out of the seal (the weakest seal is where the leak starts).
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Old 07-21-2021, 06:42 AM   #14
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Sorry. One of those nights when I canít pass it up.

I have the same problem. Iím thinking about going to my Dr. tomorrow morning.
Lol
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