I recently bought a 2010 C300. The last issue I am dealing with is smoke on the rear passenger side of the engine compartment. It was a known issue when I bought the car. They thought it was leaking at the back of the engine on the drivers side, dripping down and onto the exhaust on the right side.

I verified that it is in fact the vacuum pump. The other 3 possibilities (cam plugs or PCV valve) seem fine for now.


I have two questions:

1) It runs and drives beautifully. Is it safe to drive in the short term? I have read of people that have put up with this leak and smoke for a year or more. I won't be able to fix this for 3 or 4 weeks. Is it safe to drive in the meantime? Smoke I can deal with. Is there any real chance of fire?

2) From videos, it is pretty straightforward, but space is tight and a bit of a pain to get the pump off. At a minimum I am replacing the o-ring. What is the expected life of the vacuum pump itself? At 115K should I go ahead and replace it, or is it something that should not really wear out? It isn't cheap, but I would rather not wrestle it out twice if it is going to go soon. I don't notice it leaking from the pump itself, but it is hard to see the underside. It definitely is wet where I would expect it to come from the o-ring

 

Im assuming you have the M272 engine. I have this engine and the vacuum pump is on the drivers side.

If there is oil leaking from the passenger side then its probably coming from the crankcase oil separator cover. Unless im not understanding the issue.

heres a thread on the subject: https://mbworld.org/forums/c-class-w...ine-bay-2.html

 

I saw that thread earlier and the clear pictures of the rear of the engine were very helpful. The mine is definitely leaking from the vacuum pump on the driver side, but the path of the leak takes it to the exhaust on the passenger side. That caused minor confusion at first as to where the oil was coming from. I actually bought the cam plugs and the oil separator cover just in case since they were not expensive. I won't change those until they leak. I'll save them for the future.

That thread mostly describes fixing a leak in the pump itself, and shows taking off the back cover with the 6 T torx bolts. My problem is the o-ring where it mates to the head and is held on by 3 E10 torx bolts.

My question is which approach makes the most sense in this case:
1) Pull off the pump, replace the leaking o-ring and reinstall.
2) Pull off the pump, replace the leaking o-ring and also remove the back of the pump, and also replace its gasket as a precaution even though it is not leaking yet. That gasket is what was leaking in the other thread.and also gets stiff over time.
3) If the pump itself will wear out over time, at 115K miles should I just replace the entire pump? The pump isn't cheap, but I'd do it if that made the most sense.

My other question is how safe it is to drive with oil dripping on the exhaust and smoking. Is there any real danger of fire?

 

I would go with option 2. Mine is at 179k miles and definitely original vacuum pump on it. And my car was definitely not maintained too well before I picked it up unfortunately.

As for the oil on the exhaust, there is a *very* minor risk of it catching fire, but I’ve quite literally never known anyone who had it happen to them, or known anyone who knew someone that had it happen to them either. I think you’d be just fine. Hell, my old Subaru had the oil filter literally shoved in between two exhaust pipes formed around it.

 

In my opinion what makes the most sense is to replace the failed gasket and reinstall the vacuum pump, if in fact its just the gasket. I say this because removing/installing the pump does not seem that big of a job. If it were a big job that I absolutely would only want to do once then id replace everything while in there. But its up to you.

A new OE Pierburg vacuum pump isnt that much, $138.99 at FCP.

A new Genuine Mercedes gasket is $3.09.

If after replacing the gasket the leak turns out to be the vacuum pump itself then go ahead and replace it.

 

From the videos I have seen, it is absolutely trivial in theory, if you could access the back of the engine. The problem is that there is limited clearance and its very difficult to get a socket on it.

The history of this car is that I bought it knowing it had a small evap leak and it had this oil leak. Somebody had been trying to get it to pass smog and could not figure it out. I can tell they tried a bunch of the easy and obvious things. It had a new aftermarket gas cap. It had a new, non-Mercedes purge valve. It had a new line from the vacuum pump to the purge valve. I tracked the actual problem down to a leak in the fuel pump seal. You were an enormous help, telling me about the extended emissions warranty, and Mercedes fixed the fuel pump, and it passed smog. I replaced the gas cap and purge valve with mercedes parts, because I did not trust the cheap aftermarket parts the previous owner tried.

I just poked an endoscope behind the vacuum pump and saw a little orange on the bottom rear of the vacuum pump. That concerns me, because one video I saw showed somebody smearing some kind of orange gasket sealer on the mating surface of the back plate of the vacuum pump, but I don't think you are supposed to do that. Based on what else they did, I'm afraid they may have either tried to reseal the back plate or just smeared some gasket sealer on the outside. It is not super easy to get your finger or a rag underneath to the bottom of the o-ring where it is definitely leaking, so they may have thought (or just hoped) that it was the more accessible back plate that was leaking.

I definitely need to pull the pump no matter what, just to replace the O-ring. I'll check its condition, see what, if anything, they did to it, and go from there.

Thanks again.

 

I just removed the vacuum pump. Top two bolts were easy. Bottom bolt underneath was a royal pain. I'm 6'4", so it is enough trouble just bending over that very low hood, then I have big hands and there is just no room back there. I took off the MAF, which helped a little with visibility, if nothing else (plus it is very easy). It would have been nice to remove the water hose through the firewall (to the heater core?), but that looked like more trouble than it was worth. I cut up my hand against it (through fairly thick rubber gloves. I was able to get a very small socket wrench on it to break it, but I could not hold it well enough to use the ratchey, nor get my fingers on it to spin it. I finally got a tiny ratcheting 5/16 box wrench and was able to hold it with my finger and use the ratchet, a couple clicks at a time until it was out enough to spin a socket with my fingers. That part would have been much, much easier with smaller hands

I'm both appalled and not surprised by what I found. The previous owner must have also found it difficult to remove and also must have thought the pump back was leaking and not the o-ring, so they slathered on an orange gasket sealer on the outside of the back of the pump. I'm going under the immediate assumption that it is the o-ring and they at least didn't hurt anything. It got dark and rainy, so I will reinstall it tomorrow. I don't think there is any reason to do anything to it before I install it, it just looks a little weird.


Rear of brake vacuum pump. Orange gasket sealer smeared on the bottom edge.

Front side of the pump, where it inserts into the head. You can see how much orange goop they smeared on.

 

When I replaced the crankcase breather cover I found a 5/16 offset box end wrench worked the best to remove/install the bolts back there. I still managed to drop a bolt but luckily I had the undertray removed and it fell down to the ground so it was easy to find. Reinstalling the bolts i went around tightening each one a little more at a time to hopefully have it seated properly.