LandSeaAir

2008 C300 4Matic recently noticed burning oil smell coming from the left passenger side of engine. Changed the oil in the summer, wondering if maybe drips of oil have been building up in the under carriage tray if I didn't tighten the plug enough. Although I have only noticed this smell recently. I also noticed it starts very quickly after only a couple minutes of running and the engine wasn't even fully warm yet, making me think the oil is dripping on something that gets hot quickly perhaps the exhaust. Any idea what this could be at 53,000 miles, I hope nothing serious, although the smell is quite strong.

Carsy

There is nothing like a through inspection with a strong torch from above & below.

How is your oil level? Is it falling?

Glyn M Ruck

Check your cambox covers for leaks & especially the cam bore blankers & covers on the back of the heads. These sometimes leak onto the manifolds/exhausts on the M272. Those two round rubber plugs being the most common. Easy fix.

LandSeaAir

Once again Glyn I think you hit the nail on the head. Before I started this thread I took off my air box and looked around with a flashlight I noticed this had fresh oil around it so I took a picture of it to post here. At first I didn't think it was the culprit because I smelt right around it and got no burning oil smell, but it makes total sense that it is dripping onto the exhaust. I also noticed the plug had a bit of wiggle room and moved a little if I stuck my finger nail in between it and the engine. Seal must have failed. Once again thanks Glyn!

It looks like its held on with some sort of rivet? I figure I'll get the part and if I can't do it properly I'll have my mechanic do it. Don't want to risk improperly installing something that hold the whole pressure of the engine oil.

There is no burning smell coming from the driver side so I am assuming all is okay there, but maybe I should replace that one too as preventative maintenance?

As far as the bigger black plugs, are those a lot less likely to fail? Are they worth replacing?

Thanks again.

Carsy

No worries mate !!

Glyn M Ruck

I would only touch what is leaking. It's mainly the little round jobs that give trouble. Don't disturb things unnecessarily. I think you will need a gasket for the bigger breather plug on that side because you will disturb it. Some use gasket & some sealant.

LandSeaAir

Hahaha, thank you for the response as well Carsy

Gavin Baker

Im not seeing any leaking fluid, but the smell is definitely coming out of the left side near the back of the block. Im not 100% sure thats the smell, but it sounds about right.

I may not be able to get to mercedes today, is this issue going to cause any problems if i still drive the car?

Glyn M Ruck

No Just watch it. If this is the problem make sure they use the new redesigned plugs.

Some more info.

https://mbworld.org/forums/clk-class...et-sealer.html

Glyn M Ruck

Bulletin:

Oil Seepage From Back of Cylinder Heads on Mercedes M272/273 Engines


This bulletin affects all Mercedes vehicles equipped with M272/273 engines built up to June 2008 production date.



If you receive customer reports of oil seeping from Mercedes vehicles equipped with M272/273 engines, the cause could be the round plastic expansion plugs on the back of the cylinder heads (Figure 1). To resolve, perform the following.

Note: As of June 2008 production, new improved plugs were phased into production.

There are two different size plugs as listed below:
• p/n - A000 998 55 90 – 2 small expansion plugs
• p/n - A000 998 56 90 – 1 large expansion plug (engines without vacuum pump)

Remove the existing plugs, clean the opening and install new plugs (Figure 2). Note: The plug opening should free of grease or oil. No sealer should be used in the installation of the new plugs.

Gavin Baker

Can you see this same issue with mine? Im new to MB. Thank you!

samaritrey

On your second picture there is something down below the small plug

Gavin Baker

Yeah i notice after i replaced the plugs that a small amount of smoke is coming from that area. The smell i was having on the left side is now gone, but a oil smell remains near that oil stain on the right where it is smoking. Could that have come from the plugs i replaced, or do you think i still need to have it checked? Suggestions are greatly appreciated as you have helped me get this far!

Gavin Baker

Basically do you think its the oil spot smoking, or should i have it checked for worse things. OBDII port throws no codes, car drives fine, all fluids are good to go....

Glyn M Ruck

You have a leaking expansion plug on the RH bank looking from the front. The likely cause of smoke.

Gavin Baker

Thats not the same as the Cam plugs I just did?

Glyn M Ruck

Yes probably. Did you clean up after the replacement or is it the residual oil burning off? Did you fit the new part numbers?

If it's not leaking expansion plugs or cambox gaskets then check the transmission cooler line unions at the transmission housing. They also leak onto the exhaust.

LandSeaAir

I'm guessing this is the transmission fluid, not the engine oil that would leak from here?

Now I am getting a different smell from under my car, it's more of a burning plastic smell. I am wondering if its possibly the transmission fluid producing this smell.

At the same time it seems coinciendental to have both at the same time.

I hate all these burning smells from my car!!

Glyn M Ruck

Indeed - That leak would be transmission fluid. Sometimes just nipping up the retaining bolt fixes it. At other times you need a new O ring. Remember there are 2 cooler pipes. I'm showing one as an example.

LandSeaAir

A while back I replaced one of the small rubber plugs, however the oil burning is back, this time if I have the hood open I see white smoke coming up.

I put my finger underneath the bigger rubber cover with the hose coming out of it and there was oil there.

Anyone know what the part number is for this? What should I use for sealant or a gasket? I'm hoping I can just undo the screws, peel it off and put the new one on with a gasket or sealant.

Also, what does this piece do? What is that hose carrying and where is it going? Are these covers and plugs holding the engine oil pressure?

Glyn M Ruck

It is the breather/full load oil separator. I recommend a light coating of Yamabond 5 or 6 on reassembly to ensure no leak.



260 A 272 010 04 31 COVER [010]
001
265 N 000000 0001478 SCREW
COVER AT CYLINDER HEAD
M6X25 004
250 A 273 010 01 62 OIL DRIP PAN
FULL-LOAD SEPARATION 001
255 N 000000 0003495 SCREW
CENTRIFUGE TO CAMSHAFT
6X30 LH 001
270 A 272 016 01 34 SEPARATOR 001
275 N 910143 3006001 SCREW
PARTIAL-LOAD SEPARATION
M6X16 003
300 A 272 018 13 82 HOSE
PART-LOAD BREATHING 001
310 A 009 997 05 72 HOSE FITTING
PART-LOAD BREATHING 003

LandSeaAir

Thanks Glyn, I just ordered the part as well as Yamabond. I wasn't sure whether 5 or 6b would be better, but ultimately went with 5.

Glyn M Ruck

5 will be fine!

LoveMy2008MB

I am taking in my car for this tomorrow. Is it still safe to drive like this. Any worry of fire with this or is it just an annoying smell?

IGB

I hope I am not intruding here or hijacking this thread but I do have a related question regarding the one item that is circled in the picture above that I cannot find much info on it... We discussed the two smaller Expansion Plugs... We also discussed the "Breather" (also called the "Oil Separator")... Which leaves us with the Vacuum Pump (the larger circle that is on the left side of the picture).

The Part Number for a 2008 C300 is as follows: 2722300565 - Vacuum Pump

And here is a link to the Blow Up Chart as well as the list of associated part numbers.

I am getting a small oil leak (similar to those from the Cam Plug and/or the breather) from under that part.

I have contacted one parts source who indicated that the O-Ring (the part labeled as # 15 in the above chart is not sold separately. It only comes with the Pump...

Question is: what is the likelihood that replacing the O-Ring (assuming it is available on its own) will resolve the issue, or are these pumps prone to failure which results in an oil leak?

Thanks in advance for any information anyone can provide.