Catastrophic Rear Main Seal Failure (1 Viewer)

[winestonecowboy]

Posted this on my main vehicle thread, but figure I'd make one here for visibility

Have not experienced any oil leaking since owning my 100 (around 10k miles now I believe), but I started noticing a few drops of oil in the past couple of weeks - nothing crazy. Oil pressure was reading same as it always has, and dipstick when I checked it a couple of weeks back was reading fine. I figured I'd just let it ride and keep an eye on it until the next oil change.

Well, it seemed to get way worse in the past couple of days, so I crawled under there and dropped the skid plate, and my god what a mess. Oil everywhere - transmission was covered in it. Went up top to check the dipstick - bone dry. Straight to the mechanic. I read up on this one and was hoping it was not a rear main seal.. just got the call. Lucky door number three: rear main seal. Mechanic said it's completely busted, and that he's never seen one this bad, which honestly tracks with what I saw under the truck. It looked like something exploded. $1500 to fix, which absolutely blows. My upcoming trip is now officially canceled.

I have not found any other experiences of such a drastic failure on this, and honestly haven't found too many reports of this happening on 100's at all. My question is: since a catastrophic failure like this seems to be pretty rare, should I be having my mechanic look into something else that could have caused this?

 

[winestonecowboy]

Also, while this is pretty much already blowing my budget, is there anything additional I should consider tacking onto this job while he's in there?

 

[SteveH]

Before replacing it, you might try to find out if it blew due to very high crankcase pressures, indicating another problem (cracked piston, etc.). A full compression test and oil pressure test (just to determine general engine health) might be a good first step, especially since you said there was no oil on the dipstick.

 

[winestonecowboy]

Before replacing it, you might try to find out if it blew due to very high crankcase pressures, indicating another problem (cracked piston, etc.). A full compression test and oil pressure test (just to determine general engine health) might be a good first step, especially since you said there was no oil on the dipstick.

100%. Going to have him check crankcase pressure and ensure PCV valve is all good.

 

[NearJetties]

There is another oil seal on the back of the engine - it’s probably that. I had a bad leak that was not as bad as yours but way way worse than a typical rear main leak. It’s behind a 2nd plate so make sure they do it.

 

[winestonecowboy]

There is another oil seal on the back of the engine - it’s probably that. I had a bad leak that was not as bad as yours but way way worse than a typical rear main leak. It’s behind a 2nd plate so make sure they do it.


View attachment 3889511View attachment 3889512

What's this seal called?

 

[excessive]

its very rare for them to fail like that. usually just start weeping and gets worse and worse

 

[andrewderrick]

Never heard or seen it on a Toyota but it is quite common of the Audi/VW engine's. Bad PCV will cause them to fail. So my thoughts would be - bad PCV, it's not actually the rear main (something else that is under pressure is just dumping), or just an anomaly.

 

[Bisho]

I think the “while you’re in there’s” depend on whether your mechanic is dropping the tranny or pulling the motor to fix it.

If pulling the motor, it’s the perfect time for headers, a timing belt job or a steering rack.

 

[LJE]

What's this seal called?

That's the rear oil gallery seal. Unlike the rear main seal that's just going to have sorta 'ambient' crank case pressure on it, that o-ring has the full pressure of the oil pump pressing against it - the other end of that passage (at the front of the engine) is the output of the oil pump.. My guess is @NearJetties is correct & that's the seal that catastrophically failed.

IIRC, it's the exact same O-ring as what's at the front of the engine (sealing the oil pump to the block).

According to PartSouq, the P/N for the front/rear O-ring is (at least for my 05):

RING, O(FOR OIL PUMP)​

Part number: 9672124025​

 

[winestonecowboy]

That's the rear oil gallery seal. Unlike the rear main seal that's just going to have sorta 'ambient' crank case pressure on it, that o-ring has the full pressure of the oil pump pressing against it - the other end of that passage (at the front of the engine) is the output of the oil pump.. My guess is @NearJetties is correct & that's the seal that catastrophically failed.

IIRC, it's the exact same O-ring as what's at the front of the engine (sealing the oil pump to the block).

According to PartSouq, the P/N for the front/rear O-ring is (at least for my 05):

RING, O(FOR OIL PUMP)​

Part number: 9672124025​

Excellent - appreciate the heads up on this

 

[2001LC]

A failure, that blows out much oil that fast. Is almost certainly the oil galley rear O-ring. @NearJetties pictured and @LJE named. If it failed, very likely oil pump O-ring (front oil galley o-ring) will also. Why?

O-ring failure is not tied to excessive crankcase pressure, as is the main seal (crankshaft seal). It's almost always, due (assume factory installed O-ring) rubber of O-ring damage. Excessive heat and or use of "High Mileage" oil.

Even not changing oil often, more so with conventional oil. Seals get coated with gunk/carbon, which dries out rubber of seals. We then use a good synthetic oil and or engine oil flush, which cleans seals. Seal already shrunken, from being drying out, then leak.

The million mile (only 5 years) 4.7L nor countless 250k, 350k, 450K mile 25 years old 4.7L. They're Not leaking at O-rings. So it safe to assume, something caused this to happen. Maybe as we go beyond 25 years, will see more. But todate, I've not.


Some will post "High Mileage" oil will not hurt. Fine, post away! But I'll not use it.

 

[NearJetties]

A failure, that blows out much oil that fast. Is almost certainly the oil galley rear O-ring. @NearJetties pictured and @LJE named. If it failed, very likely oil pump O-ring (front oil galley o-ring) will also. Why?

O-ring failure is not tied to excessive crankcase pressure, as is the main seal (crankshaft seal). It's almost always, due (assume factory installed O-ring) rubber of O-ring damage. Excessive heat and or use of "High Mileage" oil.

Even not changing oil often, more so with conventional oil. Seals get coated with gunk/carbon, which dries out rubber of seals. We then use a good synthetic oil and or engine oil flush, which cleans seals. Seal already shrunken, from being drying out, then leak.

The million mile (only 5 years) 4.7L nor countless 250k, 350k, 450K mile 25 years old 4.7L. They're Not leaking at O-rings. So it safe to assume, something caused this to happen. Maybe as we go beyond 25 years, will see more. But todate, I've not.


Some will post "High Mileage" oil will not hurt. Fine, post away! But I'll not use it.

If you look closely you can see the o ring was actually split. I’m guessing the previous owner ran high mileage oil or there was a manufacturing issue with that particular o-ring or run of o-rings. The one on the front of the motor is weeping so again pointing to it drying out from high mileage oil being used for a time.

This is what the leak looked like

 

[bcarbs]

Keeping an eye on a slow suspected RMS leak on mine as well. Dropped some ATP-205 in few weeks back hoping for a simple fix and some worry free procrastination. Consider me subscribed!

 

[2001LC]

If you look closely you can see the o ring was actually split. I’m guessing the previous owner ran high mileage oil or there was a manufacturing issue with that particular o-ring or run of o-rings. The one on the front of the motor is weeping so again pointing to it drying out from high mileage oil being used for a time.

This is what the leak looked likeView attachment 3890607View attachment 3890608

Can I ask a few question:
So this is your 1998 with how many miles?
Was rear O-ring soft and pliable, or semi hard?
Any signs of overheating or running hot? Like swell water hoses or clogged radiator fins!
Have you seen under head (valve) covers. Was it gunky or clean?

Keeping an eye on a slow suspected RMS leak on mine as well. Dropped some ATP-205 in few weeks back hoping for a simple fix and some worry free procrastination. Consider me subscribed!

Sometimes leaks from front engine, dipstick tube or head covers, look like RMS weep. Study area (pictures) clean and watch.

Also, PCV system, must work as designed. Or we get weeps and leaks, on seal like dipstick O-ring, rear main, cams & crank. Due to excessive crankcase pressure.

AT-205 can aid all rubber (Seals and O-rings). I've found they must be clean, to allow AT-205 to soak-in properly. So I use 2 cans of BG's EPR engine oil flush first, to clean seals. Then 10 oz. of AT-205 and fresh synthetic oil & filter.

If been running synthetic oil, for last few changes. That also does, a good job of cleaning seals.

 

[winestonecowboy]

Update: this thread likely saved me from a second RMS failure, as the oil gallery seal was completely toast in addition to the RMS. Huge thank you to everyone here for the heads up and the part number. No clue what would cause such a catastrophic and rare issue, but I'm glad it's resolved.

Truck is back in my hands and all seems well (except for the other 10 things I need to work on), but the AC decided to mysteriously start working again, so I'll take what I can get!