[Tim M]

I had a fair amount of oil leakage from the rear main seal area on a recent long WOT run of a stock LT1 engine with LT4 blower.

I cleaned it up and planned for a replacement of the seal - awaiting parts.

In the mean time, I've gotten no further oil leaks although admittedly I've only done short WOT bursts (300 miles).

I had already replaced the front main seal with an LS3 seal and understand the rear main seal is the next weak point if one's crankcase is over-pressurized for various reasons.

My question is, does the rear main seal 'roll' when failed and simply continues to leak under normal operation or is it possible it just passes oil/pressure when under duress and returns to normal?

The oil was coming from the lower bellhousing breather holes as well as the side access covers...all appeared internal to the bellhousing...

I suppose wishful thinking...

Thanks.

[laynlo15]

How much boost are your running?

[ss2fast4u]

catch can?

[toohighpsi]

Replace the seal and get the tune fixed - it's knocking.

[laynlo15]

Yes it is, me and Mike have been there on my Camaro just me pushing him to make more boost and power. Plus I didn't get the crank case vented as I was supposed to do. It will break some ring lands at some point. Been there also.

[Tim M]

Appreciate the posts folks...

laynlo15: I recall reading your ring land failure failed your RMS (excessive crankcase pressure). How much oil did it puke and was it constant?

Thanks.

[laynlo15]

Enough to oil the track down and try catching the car on fire it was smoking so bad. I also had a belly pan or diaper because we were running a lot of boost and it saved my ass from probably crashing the car. I was on an 1/8 mile pass when it happened and I checked to see where the other guy was and couldn't see the tree on the starting line so I got over against the wall but still put some oil down. The pass before was a 1/4 pass as I was running two classes that day, if that would have happened at 142 mph I'd been screwed. I'd guess a 1/2 pint was in the belly pan, maybe a little more. Yes I had two ring lands break, number 1 and 8. Sucked.

[Joshinator99]

Originally Posted by toohighpsi

Replace the seal and get the tune fixed - it's knocking.

Mike, care to elaborate? How do you know it’s knocking from an oil leak?

OP: if you can add a Mighty Mouse Wild catch can, I would definitely recommend it.

[toohighpsi]

Originally Posted by Joshinator99

Mike, care to elaborate? How do you know it’s knocking from an oil leak?

OP: if you can add a Mighty Mouse Wild catch can, I would definitely recommend it.

The excessive cylinder pressure as a result of detonation dramatically increases blowby - quickly past the limit of the crankcase ventilation system. The very low tension seals that are on the LT engines can't handle much crankcase pressure and are the first to go (front seal then rear seal). On the engine dyno we monitor knock with two "old school" methods - a copper sound tube bolted to the block routed into the control room and a flow meter on crankcase ventilation. These two little bits of information go a long way to keeping the engine alive under the most torturous testing.

Adding additional crankcase ventilation will help to prevent the seal problem, but if it's caused by detonation, it's a nice warning sign that something isn't quite right.

I personally feel the factory GM oil separator on the Camaro does a great job. If I'm running more than a "pump gas" boost level (6-7 psi), I'd upgrade the hose that runs from the separator to the the throttle body to a larger diameter (one I use is 1/2" or 5/8").

Sorry Tim, you'll probably have to replace the seal, haven't seen one fix itself yet...

[Joshinator99]

Originally Posted by toohighpsi

The excessive cylinder pressure as a result of detonation dramatically increases blowby - quickly past the limit of the crankcase ventilation system. The very low tension seals that are on the LT engines can't handle much crankcase pressure and are the first to go (front seal then rear seal). On the engine dyno we monitor knock with two "old school" methods - a copper sound tube bolted to the block routed into the control room and a flow meter on crankcase ventilation. These two little bits of information go a long way to keeping the engine alive under the most torturous testing.

Adding additional crankcase ventilation will help to prevent the seal problem, but if it's caused by detonation, it's a nice warning sign that something isn't quite right.

I personally feel the factory GM oil separator on the Camaro does a great job. If I'm running more than a "pump gas" boost level (6-7 psi), I'd upgrade the hose that runs from the separator to the the throttle body to a larger diameter (one I use is 1/2" or 5/8").

Sorry Tim, you'll probably have to replace the seal, haven't seen one fix itself yet...

Great info, thanks!

[Tim M]

toohighpsi: Agreed, very interesting information. The leak began on a track visit when I wasn't logging, but previous logs had shown very little knock thanks to careful tuning. Its evident that I've got a combination that the German 98 octane fuel does not fully support when used with gusto.

Dumb question, but can the RMS be replaced without pulling the oil pan? Rear engine cover? It appears one might be able to pry just the RMS out and tap a new one in.

I've got limited experience with LS/LT engines and since there doesn't seem to be a published book on the subject.

My trans jack arrived...still awaiting remaining parts.

Comment: I did a good clean up, added a METCO breather with check valve to the valve cover, and then exercised the car on the autobahn...very minimal oil residue was found on inspection. But it does need to be replaced - no question.

Thanks.