I'm wondering if someone with technical knowledge on this engine can help me with an oil leak.

About a month ago, I noticed a puddle under my car. Turned out to be a failed vacuum booster pump. Fixed that (thank you Aman, you're a lifesaver), and it went away. Checked under the car daily, and it was perfectly dry for a month. Then I stopped looking underneath, another month passes until this week (including a week where my car was parked while I was out of town), and holy @#%*!! there's a giant puddle (guessing 0.1L or so) on the floor. I checked the pump and it's almost completely dry - maybe half a drop, but I suspect that's residue from my original pump job. When I replaced the pump last time, I also replaced 2 of 3 gaskets (one that seals the pump to the engine block, and the tiny O-ring that fits into the spindle that goes into the engine block). I didn't do the one that holds the pump halves together. The leak is definitely not there (that's where my 1st pump failed), so I know what it looks like, and this is not it.

Now everyday I have a small amount (5mL or so) coming out onto the garage floor. Here's the kicker. The oil on the floor is normally black and obviously used. Worried about the oil level, I added 0.1L of new oil to the engine (no spills), then drove around town and parked it back in the garage. Today the leak looks like brand new oil.

I have had the cam sensors replaced several years back, so I took a look and they're perfectly dry. So is the engine up top, under the cover.

Not sure what the dealer does, but I have never opened the drain plug under the car. I do my oil changes out the top.

I also looked in my coolant. I see a few tiny tiny metallic flakes, but these bits have been in here for years and don't seem to do anything to be honest. There is also no oil in the coolant tank. I'm guessing the oil should be non-miscible in this coolant (the coolant is water-based, right?).

The oil filter canister is also perfectly dry.

Any idea where I should look, or if there are other known leak points for the M271?

 

Well I would check the drain plug and the bottom of the engine first and work my way up.

 

Get under the car and look. The underbody panels only leak oil off the edges, so it can fool you as to where the leak is coming from.

Are you monitoring the oil level in dyno mode? Likely you've got more than 100ml of oil leaked as it tends to collect in the underbody panels.

 

your rear main seal on the back of the engine could be leaking
only way to repair this is to drop the trans and replace the seal

another leaking spot is the valve cover gasket...but isnt major

 

Crawled under the car and looked today. Drain plug looks OK (and perfectly untouched as it should be). Bottom of the oil pan is slicked with oil. Gave it a good wipe and tried to see what else was wet. Didn't find anything above the pan wet (though I didn't get a super good look).

Aman, thanks for the tip. I just realized the panels are all completely solid with 1 pea-sized hole in each one, so anything that leaks anywhere over a given panel is only going to drip onto the floor where the hole is.

Sammy, where is the valve cover gasket located?

 

Slammer, please don't depend on Sammy for any reliable information. Disregard everything he says - known troll whose favorite thing to do is spread misinformation around the forum.

The valve cover gasket is the top of the engine.. you take it off to, say, replace the timing chain on an M271. In every car I've known/had, an oil leak from the valve cover gasket was more of a weep and since it had to run down the engine it never really made it to the floor. I really doubt that's your issue. I've also never heard of the M271 having a rear main seal problem, but again, Sammy only posts things to be annoying.

The first suspects you've already ruled out - the oil filter canister and drain plug on the pan. Can you get the car up on a lift? Like someone else suggested, are you monitoring oil level in dyno mode?

 

Lilbenz, thanks for the info. After wiping the car dry the other day, I'll be monitoring the garage floor. This might actually just be just a crapload of residue from the leaking oil pump that I fixed.

Aman, I'm down to 4.2L in dyno mode. Yeah it's a bit low, but car seems to be holding up okay. Oil change due in a month or so anyways. Just hoping I can pinpoint and fix this problem (if there is one) before I start dripping brand new fresh oil.

 

Leave the lower panels off and monitor. Put down a large piece of cardboard if you're worried about your garage floor.

Leaks can be hard to find. This weekend I had to find an oil leak on my GF's Volvo. Turned out to be the nylon drain plug crush washer was cracked by the speedy lube place she used. Looking under the car I thought it was a couple other places that were weeping oil cause the drain plug looked dry. After letting it sit for awhile without the splash shield it was evident the drain plug was the culprit, it was leaking out a crack in the bottom of the crush washer and thus very little oil build up in that area.

4.2L is low, was that after sitting for awhile on a level surface? It should be ~5.5L when full.

 

is their something wrong with u?

 

There is nothing wrong with me except for the fact that on every thread where someone legitimately needs help you come along and string car-related words together in an effort to intentionally mislead people. No one will hold being clueless about cars against you. We're all here to learn. But your posts pollute the forum and are counterproductive and unhelpful.

 

To be fair, slammer has been txting me about the oil leak he cannot find so I had considered it might be a rear main seal as well since he's checked everything else - yet looking under the car it'd be obvious where the leak was if this was the case.

Slammer, if you still cannot find it txt me this Sat and I'll come by and crawl under the car to take a look. Maybe a second set of eyes will find it.

 

Obviously you are not familiar with his posting habits.

Slammer, hope you get it figured out soon. All the places and panels can be deceiving, but at the amount you're losing it shouldn't be impossible to find upon closer inspection.

 

No love for Sammy?
No one wants to buy his car?

 

Thanks for the help guys. Garage floor has been perfectly dry for the last 5 days, and so is the bottom of my car (the parts I can see at least). Still keeping my eye on it.

Aman, thanks for your offer. Always greatly appreciated. If I do need you to swing by, beer's on me.

 

lol watch if im right i swear about his car watch man

as for my car i have the money to fix my car... its just i work until 5pm everyday

 

I had similar issue--turned out to be rear crank shaft seal, transmission had to come out to fix it. Luckily, it was part of the balance shaft sprocket repair and it's all covered (by MB) even though I'm long out of warranty.

Here's the oil leak thread: https://mbworld.org/forums/c-class-w...any-ideas.html

Hope your issue is solved for good!

 

Those engines are totally different. Again, a rear main seal leak on an M271 is basically unheard of on this forum and should not be suspect number 1.

Slammer, maybe it was leftover from the oil pump change. An oil leak like you described shouldn't just suddenly stop happening. Hopefully all's clear now. Keep us posted.

 

x2

Definitely monitor oil level in dyno mode.

 

Any updates on this? I had a very slow leak that looked like rear main seal (came from the square plugs at the bottom of the bell housing), and has almost stopped since I changed oil from 5w-40 to 0w-40 a year ago.

Thanks. John

 

You probably want to check out Slammer111's thread here,.... you M271 is likely at the beginning stage for that rear plastic piece,....

https://mbworld.org/forums/c-class-w...ml#post6404779

 

Thanks for the heads up on the rear coolant pipe ... I already replaced the head breather pipe several months ago (o-ring was leaking), so I will watch for this one in the rear as well.

You are mentioning coolant though -- my leak is oil.

Thanks. John

 

Any luck on this one? I have a weird leak too, but mine is the vacuum pump refusing to seal with the engine. I really cannot figure out why.

 

My "rear main seal lieak" has stopped for the time being ... during the last oil change several months back I could not see any traces of oil coming from the bell housing anymore.

There was another oil seepage coming from around the oil filter housing, though. I puled off the air filter housing to investigate, and it turned out that the top oil breather hose (from valve cover to MAF tube) was on backwards. The two end of the hose are different diameter, the top connector is slightly bigger than the bottom connector, so when installed backwards the top is very tight and the bottom is jiggly loose, allowing the oil vapor to seep out of the hose connection and down the MAF pipe and muffler, and eventually dripping down the side of the block and onto the engine cover. The last person outside of me to touch my car was the local MB dealership 4 years ago ... very surprised ... I hope they did not intentionally reverse the pipe to get some extra "fix oil leak' business. Anyway, I cleaned up the oil and mounted the pipe on correctly, and it's been dry ever since.

 

Hiyall, Did you find the leak yet? Here is the long shot.... Our cars have Hyd Oil filled eng mounts , when mounts rubber get old and brittle it breaks down and cracks, and small amount of oil slowly leaks out , once its all gone - oil leaks stops, the mount then collapses and you can scratch you head all day to find this leak, and you may not notice driving the car any different. Just a thought . How many miles on the car?
I just replaced both of mine eng mounts and found one collapsed . Good luck

 

Unfortunately the car is still leaking away, between the bell housing and the engine. Sammydragon may be correct this time in that it might actually be the rear main seal.

To clarify, my car had the leaking vacuum pump back then, which has finally been fixed. However, the rear main seal seems to have also gone these last few weeks. One leak after another.

Anyone have directions on the procedure for this, for the M271 engine?