hi Experts,

I've recently bought a 2007 S600 95k miles, so it's my first post. It's also a post about a problem :-( engine coolant leak (not IC leak) on both sides on back of the engine. When I pressurize the radiator, it drips behind steering rack (between the steering rack and the cross-member which is further to the back). Both sides, more on the driver. The distance between the leaking points is the same as the width of the engine oil pan. Needs to top up the radiator tank every about 500 miles.

I've suspected the turbo leak at first, removed air filter box etc and ignition cassette on one side to have a better look. Used a mirror on the other. Both sides appear slightly wet, but hard to see the actual leak. Everything in front of the steering rack appears dry under the car (the plastic shields removed of course) So some questions:

1) Is there anything else except the turbo cooling pipes which could cause a leak at the back?

2) Assuming those are turbo pipes, do they always leak at the turbo only or sometimes at the block? (I would expect the top tubes to leak first due to being "return side" with hotter coolant)

3) Can the seals/gaskets be replaced without engine removal?
- top looks fairly easy if I only do it at the turbo, bending the pipe slightly without removal on the other (block) side. Is it how it's done? Can it be done without disturbing oil pipes?
- both top and bottom are slightly wet - does it make sense to fix the top and check for leaks, hoping the bottom does not leak but was getting wet from the top?
- can the bottom be done without engine removal?

4) Assuming engine out - how many hours (or dollars) is to do a complete engine-our replacement of all turbo coolant and oil feed seals? (may as well do oil with engine out as well)

I can do any work from the top, but I don't have a proper hoist so it's hard to do much on the ramps/on a jack, so I would need to give it to a mechanic to take the engine out etc

any help appreciated, thanks!

I had a very similar leak that drove me nuts. It leaked slowly out of the back of the engine on both sides and down the back of the heads and bellhousing. After days of searching it ended up being the thermostat housing in the front (top) of the engine. It would leak down the valley pan in the center of the engine and then drip down the back on both sides. I replaced the gaskets and orings on the thermostat housing and all was well. Try looking to see if you see any coolant running down the center valley of the engine from the front.

Thanks! I will also check the thermostat, but meanwhile I have removed half of the stuff from the engine bay and I can clearly see a big leak on the upper coolant pipe of the driver side turbo. Interestingly, there are multiple crossmembers under the engine which catch the leaking coolant and distribute it to leak on both sides of the car, so it looks like both sides are leaking :-). Dealer wants $6300 to fix (engine out), so I'm going to try to do it myself (top only). Thanks!

of course I will have to bend the metal coolant pipes (it's impossible to access the other ends without engine removal), which requires unbolting and lifting out the intercooler pipes, which is a lot of gymnastics by itself (the bottom bolts of the intercooler pipes mounting brackets have a terrible access without engine removal). Mercedes has installed plenty of invisible razor blades in those tight spaces (to protect from unauthorized access? :-), so I've also just bought another pack of band aids to catch the leaking blood and a second pair of mechanic gloves.

hi, here is an update. I did change the top turbo seals myself, not very complicated but very time consuming. Requires removal of ignition cassettes and many other parts, project lasted several days. No leaks 4 months later. Considering the coolant direction (from bottom to top) bottom seals will last much longer so I don't feel bad about not changing them. But if you get the same problem and if you find a mechanic who can do the top seals for less than $1000 just save yourself time and let him do it. I could not find one - independent shops just did not want to touch the car or like the dealer wanted to do the complete engine-out job. Passenger (USA) side is much much easier. I changed both sides, it is hard to say which one is leaking - there is enough parts below to spread the leak to appear on both sides even if only one is leaking. In any case it makes sense to change both as they will have similar life span. You will also need to change the seals in turbo oil pipes as they use the same mounting. Use brass equipment (I'm using Parker Seal) to remove/install/clear the coolant seals to avoid scratches and leaks. I also did not drain coolant completely, just disconnected a pipe near radiator top and siphoned coolant out to the turbo level. Also I know now where the burnt m275 engines come from - the fuel line (driver side) just slides on without any fastener and probably slides out by itself sometimes causing fuel spill and fire - I've fastened it properly to avoid future problems.

thanks for the info. glad you got it sorted.

hi, glad you got it fixed, but have a question. it's very interesting what you said about the engine fuel line just going into the hose with no clamp. i think i located the fuel line. it is covered by a metal sheath on the rear top of the engine and has a bolt on connection to the middle top of the engine. when i follow it down the firewall i see a clamp like connection in the firewall that appears to loosely attach to a thin pipe that attaches to a hose. the clamp is now around the thin pipe and the thicker rubber hose is under the firewall clamp. i'm assuming that the hose should be pulled up into the firewall clamp and re tightened. am i correct and is an additional clamp required under the firewall clamp to secure the hose to the pipe? i think that you've really hit on a fire problem here and i would really like to repair it properly. any info would be greatly appreciated so i can do this job properly. actual pictures of the hose and connection would be great. anyone?
thanks

Fuel line in front of the black filter housing



Thanks for the kind words - here is the photo. The rubber hose which is sideways in front of the black filter housing is not secured to the metal pipe by Mercedes - slides out very easily. You can see 2 non-standard, shiny clamps which I have added to secure it. There could be other weak spots too, but this one is the most obvious and on the top of a potentially hot engine. Hope this helps.

And right above a very hot turbocharger.

thanks. i haven't looked at that hose so i'm really happy you posted a picture. what are your thoughts on the hose i posted about with metal sheath that goes from the rear center of the engine down the firewall? i assume that is another fuel line and has a similar problem. am i correct? thanks for continued great info.
the best, harv

That's an evap line, right? Or pcv? There's no liquid fuel there, just a tiny amount of vapor. Careful that you don't crack the plastic hose by overtightening those clamps!

The one with the sheath is the pressure line from the pump. That's the one to worry about if there's an unsecured connection. Most cars this era will have small sections of plastic lines thermoformed onto the metal hardlines somewhere in the sytem though. These types of connections do not need clamps, in fact clamps could damage the plastic hose. If you're talking about a rubber line then that's a different story.

thanks zeph. after conferring with a mechanic friend he confirmed everything you said. also we established that the fuel line on the firewall doesn't go into a hose, it goes into a rubber grommet that the fire wall clamp is supposed to attache to. i did notice that the evap line rubber hose is hard. do you think it needs to be replaced, or is it okay for what it's use is?
the best and thanks for clearing this up.

fuel vapor hoses tend to be stiffer than regular rubber (like vacuum or heater hoses), so I wouldn't worry about it.

thank you.

okay, the high pressure fuel line with the metal braiding attaches the a 3/8" metal line that goes from the back middle of engine down the firewall. there is another 3/8" metal line coming from the driver's side fender wall to the back of the engine in very close proximity to the 3/8" engine fuel line at the fire wall. probably 1/2", or less between these 2 lines. these two lines run down the engine side of the firewall and attach to a clamp. under the clamp is a rubber line separator that prevents these two metal lines from vibrating together. anyone know the part # for this rubber line separator? i've searched for 3 days and can't even find a picture of it let alone a part#. the dealer is clueless.
thanks

That's a tough one. I don't know but I have a few on the ABC limes that I would like to replace (they got fluid on them when I had a leak and swelled/aren't in good shape).

okay got the part# 000 987 77 70. this is the rubber hose connector i was looking for. piece of rubber that has two holes that have a slit on one end to push over the fuel lines. dealer says they come in 1 meter lengths that you cut to size. the actual part is about 1" in length. dealer wants $102 for the 1 meter length. found on line for $51 plus shipping. dealer says the part has to be shipped from germany. don't know if online is 1 meter, or 1". i assume 1 meter. i think i'm going to get some hose and split one side and push on each fuel line. should have the same effect i believe. we'll see.
just wanted to update.

Interesting. Rubber hose is probably a much firmer rubber than those factory isolators, but yes, it should more or less have the same effect. Your best bet would probably be to make sure it's vacuum tubing, or other non-reinforced hose if possible. Some of that stuff is pretty soft.

Tkwilliams01 - bending coolant lines is not a problem at all. I was also afraid of that at first, thinking that maybe I will need to loosen something on the other (totally unreachable) end in order to move them. Turns out the lines are made of quite a soft metal and you just move/bend them around a little as needed.

Good luck with your project! Let us know how it went

BTW, my S600 is still running without any leaks

Does anyone knows the name of these line or part number and the o-ring inside of it. The dealer is unable to determine which lines are they are badly leaking and the o-ring inside of it is broken and need to be replaced but i dont know the name or part number to buy it. i need help . thank you all for your help.
The car is a 2007 S class v12 but my engine is from a 2006 model




.

Literally the exact same thing happened to me. Tightened up that rubber hose hopefully that solves it.