Coolant Leak Back of Engine - PeachParts Mercedes-Benz Forum

desert240d · #1 06-27-2010, 08:41 PM

Flushed the cooling system first with straight water several times, then used Shout mixed with water to de-oil. Rinsed thoroughly and then did citric acid flush. I started the ’81 240D/manual trans. and let run for 10 minutes, shut off and took a quick shower. I came back out, and went for a short drive first stopping to put a few gallons of diesel in the tank. I left the car running and went to pay. When I returned to the car a fellow motorist spotted some green liquid pouring from the bottom of the 240D. I was less than a mile from home so watching the temp. gauge carefully, I limped her home and shut her down. I watched with a puzzled look on my face as a greenish liquid continued to pour from the back of the engine where the transmission mounts. I cracked the radiator cap and stood back as steam and pressure poured from it. I went to church and let the car cool. When I returned, I pulled the engine block drain plug, radiator drain plug and flushed the system through the upper radiator hose until the water ran clear. Replaced drain plugs, and now when I pour any water through the upper radiator hose, it leaks out from the back of the engine. I pulled a small metal cover plate held by two 10mm bolts on the front of the tranny and had my wife pour a small amount of water into hose. The water almost immediately comes out where the cover plate attaches. I know this is a long post, but I wanted to be as thorough as possible. Any suggestions are much appreciated.

leathermang · #2 06-27-2010, 09:18 PM

Clean the area and take pictures of it leaking...

charmalu · #3 06-27-2010, 09:27 PM

If the OM616 is like the OM617, there is a freeze plug on the back end of the block. sounds like it rusted through and needs to be replaced.

Might be able to replace it w/o pulling the engine.

drop the transmission, remove the clutch, flywheel and adaptor plate.
drain coolant. tap edge of freeze plug (closing cover in MB lingo) with a chisle.
It will turn on it`s longitudal axis. careful you don`t knock it into the waterjacket. grab it with a pair of vice gripe, and pull it out.
clean the inner edge of the hole. coat it with a sealant or MB sealant glue part # 002 989 94 71
fit new plug in with a mandrel or something suitable to drive it in.

replace all parts removed, fill with coolant, and look for leaks, or which ever order you want.

Charlie

leathermang · #4 06-27-2010, 09:44 PM

I think pulling the trans is a little premature...
what if this is just a head gasket leak and is running down behind something ?
Clean everything nearby, cause it to leak again and take picture of it...

charmalu · #5 06-27-2010, 10:06 PM

Iam betting on the freeze plug

.

I would rather drop the trans than pull a head. but you could be right, we`ll see.

Charlie

desert240d · #6 06-27-2010, 10:40 PM

Thanks for the responses. The area is pretty clean perhaps from all the coolant/fresh water that has passed over it. I will take some pictures tomorrow when I have better light and post. While underneath the car with a flashlight, I had my wife pour a small amount (pint) of water through the upper radiator hose. It took about 15 seconds for it to find its way out the back of the engine.

leathermang · #7 06-27-2010, 11:38 PM

I am just saying you do not want to ' correct' the wrong hole... and then have to do another one...
and I have seen misleading situations where something is following a path down from somewhere it did not look like it was coming from....
of course we do not have pictures of this situation so we can only speculate... but think we should be conservative in our speculating .....

Cr from Texas · #8 06-28-2010, 12:08 PM

I've found that I can slide in a small digital camera and snap a view of a lot of places that I can't get a line of vision. The camera has become one of the best tools in my tool box!

ftwchopper · #9 06-28-2010, 01:56 PM

After reading so many horror stories of leaks after coolant flushes it almost makes me want to just leave it alone and just change the coolant every couple years.

4x4_Welder · #10 06-28-2010, 02:16 PM

Seems a lot of people are having issues after the FSM citric acid flush procedure- Maybe it would be better to use an off-the-shelf citric acid based flush, like Prestone's Super Flush.

ah-kay · #11 06-28-2010, 02:53 PM

'Flushing' by definition is open ended way of washing something, so there is no pressure. I would be very surprised that flushing would cause any problem, with water or otherwise. There will be much more pressure created in a closed system when the engine is hot and water pump is running. As it is evidented that MBZ calls for a 20lbs or 14 lbs radiator cap.

IMHO, it is unlikely the flushing would have caused the leak. I think a freeze plug was corroded and it just bursted after you pressurized the system again. It may just be a coincident, an accident waiting to be happened whether you had flushed it or not. The freeze plug just happens to be between the engine and the tranny. I have seen it happened before in a Corrolla, $500 to pull the tranny to fix it, 99.9% labor, 0.01 parts.

It is unlikely to be a head cylinder gasket as the OP says water leaks out when 1 pint of water is poured in. If the gasket is so bad then water will squirt out when engine is running or something even worst. You may be lucky that it is a hose clamp but I doubt it. If 1 freeze plug is gone then the others will not be far off. I always change my coolant every 2/3 years as there is rust inhibitor in the coolant, as well as raising the boiling pt and lowering the freezing pt.

charmalu · #12 06-28-2010, 04:18 PM

DESERTDOG240d, this line makes me think it is the freeze plug.

While underneath the car with a flashlight, I had my wife pour a small amount (pint) of water through the upper radiator hose. It took about 15 seconds for it to find its way out the back of the engine. {quote}

the head gasket is exposed all the way around the back of the head. so if it is leaking I would think you would see the water trickling down the back side.

was this with the engine running, or not?

I agree with AH-KAY that the Citric acid did not make the engine leak. there was a problem already there, and it just let you know where it was.
Better to find out now than on a road trip some where.

Charlie

TnBob · #13 06-28-2010, 04:19 PM

How many miles on your 240D ?

Other than this issue does she seem to run well ?

Answers there might allow for some 'creative' responses.

4x4_Welder · #14 06-28-2010, 05:01 PM

I may have an answer for why this is causing so many failures-
At the time the Mercedes citric acid flush was developed, most citric acid was produced from citrus fruit. Now, most citric acid is derived from phosphoric acid, and does behave differently when exposed to iron oxide, as well as frequently being of a stronger concentration. Most casting core plugs are galvanized steel. Over time, that coating gets worn away leaving the steel exposed, and the steel rusts. Citric acid eats rust, but phosphoric acid is much more aggressive, and those core plugs are very thin when new.
Now, in a newer engine, this would not be a big deal since the zinc coating would protect the steel. In a 30year old car, though, the zinc is gone and some of the steel is as well, so the stronger acid solution eats through what's left and you suddenly have leaking core plugs.
Again, I have to say that some FSM procedures are only intended to work up to the end of the warranty period, and should not be trusted past that. This, I believe, is a prime example of that.

Having said all this, replace all your core plugs. If one was thin enough to be eaten through, then the rest can't be far behind and it's better to do them in your driveway on your terms than pay someone when they fail on the road.

DeliveryValve · #15 06-28-2010, 06:32 PM

I agree with Charlie's assessment.

If any part of the head (rear heater hose, head gasket, cracked head, etc) is leaking, it will leak down and around the tranny, not out of it.

The rear Freeze Plug is most likely cause.. See pic of it's location courtesy of member oel_brenner.

.