Weird oil leak - 1972 350 SL 4.5 - PeachParts Mercedes-Benz Forum

ptspringer · #1 05-13-2009, 10:51 AM

I recently had my transmission rebuilt on my 1972 350 SL 4.5. The transmission had been leaking fluid (not oil) that came out the grating in the bell housing.

After the transmission was rebuilt and reinstalled I picked up the car and drove it home. Looking under the car, I could see a steady drip of oil from the bell housing, and returning to the tranny shop, we traced the source of oil, and found it coming from an untapped ~1/4" hole in the rear of the (117) engine block, low on the drivers side. There was no oil inside the bell housing.

I was able to inspect another 450 SL motor which had the same untapped hole, but no leak.

I'm guessing that the hole was drilled through the main oil galley tunnel to create an oil path to rear engine bearing, and then the outside portion of the hole was plugged from the inside. I've read that the factory used ball bearings as oil galley plugs on some diesels. If such a method was used on this car, then the plug may have come loose. The oil leak has nearly stopped on its own (the tiny gap between plug and hole wall filling up??) , but still I'm wondering what I should do about it.

Could someone who knows the 117 motor, please confirm if my guess about the purpose of this hole is correct. If so, I'd like to tap it and put in a plug to seal the leak entirely.

Thanks in advance,

Paul

meltedpanda · #2 05-14-2009, 09:47 AM

wow , news to me, I will follow as I have never heard of this before.
MBDoc - do you know?

ptspringer · #3 05-15-2009, 03:55 PM

would a picture help? It's on the drivers side rear of the block. Untapped hole.

ptspringer · #4 05-19-2009, 12:33 AM

OK,

I've attached a photo. The clean stuff on the right is where the rebuilt transmission bolts on. The hole is 9 mm in diameter and I can stick a 10 cm rod clear in. There is nothing blocking it at all. Oil comes out, but not under pressure - just an annoying leak - when the car is hot and cooling down. I've plugged it with a tapered rod.

What is this hole for? Is it associated at all with the rear seal which may have been damaged in the transmission overhaul - and if so, under warranty.

Gurunutkins · #5 05-19-2009, 01:18 AM

if its on the left bank (from the drivers seat) there is a drainage hole from the valley between the v's of the 2 banks that drains out about half way up the block right back near the transmission. There is no seal between the top of the engine and the v of the 2 banks so they put in a small drainage hole to drain anything that dripped into the v from the rocker covers, or intake plenum. The picture is very close up so its hard to see properly where its situated on the engine. Is it definitely just oil or an oil/gas mix?

Graham · #6 05-19-2009, 09:35 AM

Quote:

Originally Posted by ptspringer

OK,

I've attached a photo. The clean stuff on the right is where the rebuilt transmission bolts on. The hole is 9 mm in diameter and I can stick a 10 cm rod clear in. There is nothing blocking it at all. Oil comes out, but not under pressure - just an annoying leak - when the car is hot and cooling down. I've plugged it with a tapered rod.

What is this hole for? Is it associated at all with the rear seal which may have been damaged in the transmission overhaul - and if so, under warranty.

If, as Guru suggested, it is a drain hole, perhaps you could push a flexible wire in and see how far it goes. It does seem possible that it is a drain hole from between the V-s and that the oil you see if from a valve cover leak. But perhaps it could also be a drain for any leaks from the rear seal?

I have same car, but perhaps someone has a spare engine that would be easier to check?

By the way - I had a leak from the grating in front of the transmission too - Had the transmission resealed for C$700 and no more leaks.

Whenever I find where oil is dripping from, it never helps find where it is REALLY coming from!

ptspringer · #7 05-19-2009, 10:58 AM

Undercar photography is hard.

If it does go to the V, and I stick a flexible wire through it, will I be bale to see the other end under the plenum?

The leak is mostly oil - but does smell of gas some, but only like that of used oil.

Sorry about the close up picture. There is no way to zoom back. I'd say that the hole is about 3/4" forward rear of the block , maybe 1/3 of the way up the block. right above the drivers side exhaust.

I plugged the hole - I want to see if this makes oil come out the tranny bell housing, to exclude the possibility of a bad rear crankshaft seal.

Paul

Chas H · #8 05-19-2009, 12:04 PM

That is a drain hole for the valley. If it smells of fuel you may have a leak up on top of the engine. I sure wouldn't plug it.

meltedpanda · #9 05-19-2009, 01:16 PM

I am 99% certian I do not have that hole on mine (72) but currious enough now that I may just have to get under and look

ptspringer · #10 05-19-2009, 01:33 PM

Has anybody had a rear crankshaft seal leak, & if so, does the oil come out the bell housing grate or though a drain hole?

I think I'll pour some water down into the V and see if it comes out that hole.

What besides the valve covers will leak oil on the upper engine?

Thanks,
Paul

Gurunutkins · #11 05-19-2009, 03:06 PM

try the hot water through the plenum, you will be surprised at how much crud comes out. if your rear seal is leaking it generally comes out of the bottom grating (its just black for a rear seal or red for a tranny front seal). generally if you are seeing a bigger leak the problems are from the crank vent pipe on the right side bank valve cover to the air filter leaking down into the filter othen into the cavity or if the pipe is loose (which most are) then just leaking. could be a valve cover seal leaking but they generally leak on the down side not the up side. The worst case is that you have a leaky injector pipe etc thats washing crud down thew drain hole, that can get explosive quickly. the valley is all enclosed by the block sides, transmission and front timing cover, hence the drain hole. (have a look at my picture in this link and you will see what I mean (no the hole is not shown its at the other end Timing Chain Replacement on My 560SL )
cheers
barri

Graham · #12 05-19-2009, 07:41 PM

I sent a copy of the picture to a guy who really knows these cars. He confirms that it is a drain from the V of the block. He suggested that it could be oil or coolant. If its oil he would suspect the v/cover gaskets.

But as has been suggested, I would also double check all the fuel hose clamps and hoses. I once had one rubber hose develop a crack that was almost all the way through. - This was caused by a HT plug lead running near it arcing across - The rubber was burned - a very dangerous situation!

Also check the valve cover vent hoses - they usually are oily.

ptspringer · #13 05-19-2009, 09:44 PM

Thank you all!

Sounds like an oil leak on the topside into the valley. I'm pretty sure that it isn't coolant (which is sweet and green), or fuel.

I've recently replaced all the hoses on the injectors and smell no fuel when I drive.

It was so pleasant today, with the drain hole plugged, not finding an annoying little puddle under my car, nor any smell from oil dripping on the hot exhaust.

I'll trace the possible leaks (valve cover gasket, vent line into air cleaner, fuel). I know the valve cover gaskets are not dry, but figured they would leak downhill & cause smoke on the exhaust manifold.

Glad to know that tranny & rear seal are OK.

Paul

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