Rear Main Seal - MP340

[BrentP]

Hey guys,

have any of you ever seen a rear-main seal go in the 5.7L? Mine is a marine power, but you know, a GM block is a GM block. Been cleaning on the boat, about to take it in for yearly maintenance. Noticed engine oil coming from (what appears to be) the connection between the transmission and v-drive. I do a visual on the motor pretty regularly, and just noticed it. Ran the boat for probably 2-3 hours over the last month with no major issue. Engine oil is a little low (but not empty by any means) and was last changed about 16 months ago and was clear at the end of the summer when it was 12 months old (I know. I'm changing it now, the last guy changed it in July and I wanted to get on a spring cadence). It looks like its coming from both sides and is above and below, which suggests the crank shaft is slinging it around in the bell housing.

Full disclosure: My old man is the engine dude, I'm just repeating what we discussed.

Anything else on the back of the engine that could fail and cause something like that to happen? It does NOT look like its coming from the valve covers or anything like that.

If it is the rear main, I'm being told the engine has to be pulled and flipped over, so they can get to everything that needs to be services. Parts are cheap, labor is long.

On the bright side, It'll make replacing the impeller and spark plugs a breeze!!

-BP

[AJMichael]

I know that on my last truck the rear main took a crap and dropping the trans was the big part then being able to access the seal was no prob, but that’s a truck. I know I have a seal leak on my trans in my 02 21V and wondering if that’s a doable self fix.

[KoolAid]

Seems to me that you would pull the trans and Vdrive which is a lot easier than pulling a trucks transmission. Drop the oil pan and swap the rear main seal. I don't see a reason to pull the engine. Never done it on a boat, only a Tahoe.

[BrentP]

Both dealer mechanics I spoke with said we needed to pull the motor if that was the cause. *sigh*




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[sandm]

I would think the big challenge is trying to drop the oil pan with the tight clearances and lack of depth underneath the engine?
trans/vdrive would be the easy part

[chpthril]

What gen/RPO 5.7 are those blocks?

[UNSTUCK]

[boatwakes]

The above rear seal is a 2 piece which is not what you have. The rear main can be replaced in the boat if you have access to the pan bolts but honestly it'll take an hour to prep the engine for removal to perform the replacement. Here's a pic of the oil seal we all have (except 6.0 GM engines, but theirs are still 1 piece). There are lifter valley plugs back there that can leak but I've never seen it. If you want to remove the engine I can do a write up for you including parts. Keep posting to this thread so others can benefit.
Question for you, what oil was used prior to the leak? There have been problems with seal compatibility and certain oils.

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[chpthril]

Boatwakes,

is seal portion serviceable from the aluminum piece or is that a single assembly. If one piece, doesnt look too bad to swap is those male torx bolts come out.

[boatwakes]

The seal is removable from the housing. FWIW I have yet to see one let go in a marine 5.7. The housing is still siliconed to the pan so it needs to be removed after the pan is loosened and/or removed. All the gasket material and silicone need to be removed and a new 1 piece oil pan gasket installed if its not there already, silicone the corners and re-install the pan.

If it is leaking, after the old seal is removed the crankshaft rear face where the seal is made needs to be inspected for corrosion and pitting, that could tear up the seal too.

[BrentP]

Boatwakes,

We free are making a list, what would cause oil to escape the back of the motor if it’s not the rear main?

(Going down the list of stuff to inspect)


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[UNSTUCK]

At the back of the engine you have the oil pressure sending unit, which could leak and run oil down the bell housing. Either of the valve covers could be leaking and doing the same. Inside the bell housing you have the rear main seal and the rear cam shaft plug that could be leaking. There may be two oil galley plugs in there as well. I don't remember if this particular block as them or not. I don't know your boat, but I would check to see if there could be an oil line (perhaps to a cooler?) that runs back there that could be leaking. If it's all dry back there get ready to pull the trans and get a look inside there. Maybe you could just separate them enough to look in there with a scope or flashlight and mirror. Probably wont be to hard to see where the leak is coming from then decide how you want to tackle it. Run the engine for a while before removing the transmission.

[BrentP]

Thanks, we'll keep looking.... Interesting that we've never seen one fail boatwakes... Hrm...

Regarding oil, I'm not sure - it was services last by the old Austin Tige Dealer (Ski Dock). Not sure what brand they used oilwise...

[boatwakes]

Pull the starter (if it's the rear mounted one in the bellhousing) and inspect it for oil. If it's not being flung around by the flywheel and the starter is dry, your rear main is not the culprit.

[BrentP]

So the dealer put some dye in the oil and inspected, and they don't see an active leak (suggesting its very slow at best) after running for a while. The tech's initial suggestion is based on where they saw the oil on the outside of the engine, it's most likely an intake manifold leak, albeit a minor one. He noticed that the engine idled rough when it was cold which he felt backed up that assumption if of a potential gasket issue there.

We've had very few mechanical issues with the boat (Power seems good, gas mileage doesnt seem completely beyond terrible, no major issue with stalling or anything once the boat is warm).

So the strategy is either pay them 1250 bucks for something that MIGHT be wrong, or just wait and see if it gets way worse. *Shrug*

I have them putting in new plugs, full fluids change, etc. I figure if there is a big gasket failure in the intake MF, we'll probably see issues with the plugs.

Let me know if you guys have any thoughts. The service manager suggested that fixing it at this point may not be worth the money given we've not had substantial mechanical issues, and we dont have clear evidence of a substantial oil leak.