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Old 12-19-2020, 06:38 PM   #1
vanman23
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Default Should I change the rear main seal

The engine is out from a timing belt break. We've redone the heads but did nothing to the short block. There is no indication of a rear main seal leak. The engine has 170K miles on it. 05 OBXT AT

Should we let sleeping dogs lay?
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Old 12-19-2020, 06:41 PM   #2
JDMRosa04
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Never hurts to do, easy and cheap
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Old 12-19-2020, 06:54 PM   #3
NighthawkSTI
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at 170,000 miles I think its good insurance to put a fresh rear main seal in, especially if you plan on keeping the car for awhile. They actually dont have a reputation for leaking the crankcase cover can though. I changed my rear main seal at 87,000 when I did my clutch just to get the experience, and for piece of mind. I didnt want to do $700 in clutch parts to have a leak a couple years later.
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Old 12-20-2020, 10:15 PM   #4
DrD
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I agree - at 170k miles, given the cost and how easy it is to do now vs. after you put everything back into the car, it would be foolish not to.
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Old 12-20-2020, 11:32 PM   #5
vanman23
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Thatíll be the plan then to replace it. Iíve heard of stories in which they started leaking after a new one was put it.

What about the oil air cover?
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Old 12-21-2020, 01:09 PM   #6
NighthawkSTI
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Quote:
Originally Posted by vanman23 View Post
That'll be the plan then to replace it. I've heard of stories in which they started leaking after a new one was put it.

What about the oil air cover?
I read about the instances where it would leak after installed new, but those are situations where either the installer put a scratch on the crank when forcing out the old one with a makeshift "tool"(which will create a path for oil to escape around it and or tear up the seal), or they didnt install it properly, most commonly seating it too far back allowing oil to bypass it and come out, or tearing it or bending the metal spring inside it by installing it cocked.

I bought a disc from a subaru tool vendor that fit over the new seal and has a collar on it so that as the new seal is tapped in "squarely" it seats it at the correct depth and wont allow it to go further.

I left the crankcase covers alone and did just the seal. Of course if they look like they are leaking remove them and put new silicone sealer

Last edited by NighthawkSTI; 12-21-2020 at 02:17 PM.
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Old 12-21-2020, 03:11 PM   #7
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The rear main crank seal on EJ engines is a royal pain to remove, even with the correct tool. I'm not surprised many replacements end up with a leaking seal, because it is quite easy to scratch the bore.

When I was replacing the HGs on our EJ253, I asked a trusted friend who owns an independent Subaru repair shop his opinion. He said "Don't touch it if it's not already leaking." I couldn't leave well enough alone and after much cursing and breaks taken, I finally got the old seal out.

This is truly one of the cases were if it's not broken, sweet baby Jesus, don't bother replacing it.
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Old 12-22-2020, 10:46 AM   #8
DrD
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Quote:
Originally Posted by vanman23 View Post
What about the oil air cover?
My school of thought would be if you have a polymeric seal (particularly if it's also a dynamic seal (seals on a moving interface)) that's going to require that either the engine or transmission be removed in order to get it if it leaks, I would replace it. A static seal, if it's not leaking, is probably ok - but if it got distorted or otherwise damaged while the engine is out and starts leaking in a month, it's not going to be a happy day for you.


It sounds from the posts above that the EJ25 RMS is difficult to remove without scoring the bore in the block or the crank, so that's something to consider - that being said, 170k miles and 15 years is a lot for a dynamic seal, though, so if you are going to be driving the car for years more, given that the engine is out of the car now, and the seal is right there, I'd replace it.
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Old 12-22-2020, 12:22 PM   #9
Brokebecauseofsubies
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Rear main seals are pretty cheap to do and it would hurt to freshen it up
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Old 12-22-2020, 05:59 PM   #10
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I think it was $7 at the dealer if I remember correctly.
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Old 01-01-2021, 12:41 PM   #11
mike_n
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I would definitely replace it especially if you don't know if it's been done before.
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Old 01-01-2021, 04:10 PM   #12
AliBenn
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Like replacing T-belt and not replacing tensioner(among other inexpensive parts)
RR the seal
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Old 01-03-2021, 10:57 PM   #13
CaptainSlowbaru
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If your separator plate is aluminum, replace it. I don't remember when Subaru changed from aluminum, but the latest design is stamped steel, and they tend to not leak. Also, there is a wrist pin access plate back there with an o-ring. Might as well replace that too- sometimes they seep oil.
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Old 02-27-2021, 09:42 PM   #14
SubiSIR07
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I absolutely would. You just did all that work pulling the engine out you won't want to do it again because you skipped replacing one gasket. Better insurance to change it while it's out.
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Old 03-07-2021, 07:36 PM   #15
yliu14
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Quote:
Originally Posted by vanman23 View Post
The engine is out from a timing belt break. We've redone the heads but did nothing to the short block. There is no indication of a rear main seal leak. The engine has 170K miles on it. 05 OBXT AT



Should we let sleeping dogs lay?


Always change your rear main seal, pilot bearing, throw out bearing when you at that stage. Use OEM parts. You donít want to pull the transmission out just for a cheap seal. Unscrew the plates at the back of the engine and reseal them by using black RTV.
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