Possible early signs of blow by? - PeachParts Mercedes-Benz Forum

bob_98sr5 · #1 07-03-2009, 02:11 AM

Hi folks, this is for my 87 300D turbo:

I have three small oil leaks which I believe to be early signs of blow by. The first leak is coming from the top of the valve cover at the breather tube. The 2nd one is at the rearmost valve cover bolt on the passenger side (near trans dipstick). The last one seems to be either from the front most driver's side valve cover bolt and/or from the first intake valve. I believe its the former and its leaking down on top of the intake valve.

I checked the oil to make sure I didn't overfill and/or the effects of the very warm summer heat (over 96 the past week). It was nearly perfect after 30 minutes of driving, a touch below the max line on the dipstick. Nevertheless, I vac extracted just a little w/ my Mityvac fluid evacuator to pull the oil level down just a hair.

So is this the early signs of blow by? If yes, I have plenty of reading to do. If no, can anyone throw up some recommendations what it might be?

Bob

TylerH860 · #2 07-03-2009, 02:12 AM

Since there's nothing you can do about blowby, I wouldn't worry about it. The breather line is likely due to age, along with the others.

BodhiBenz1987 · #3 07-03-2009, 02:28 AM

Did you check for blowby at idle? I.e., take the oil filler cap off while running, rest it on the opening and see if it dances. If it sits perfectly still, I wouldn't even begin worrying about blowby. The breather hose I would think it more likely due to wear on the hose. If it's leaking around the valve cover, it could be a worn valve cover gasket or maybe an improperly torqued down valve cover.

If it's coming from around the intake, that might be due to a tired intake gasket and a lot of gunk in your intake due to EGR. Unplug EGR, clean intake out, replace gaskets.

But as far as blowby, I'd start with the basic blowby test. And, like Tyler said, even if you have some blowby, not much you can do about it ... just drive it and enjoy it as long as it starts/runs OK. Lots of high-mileage MBs have some blowby (and some have a lot!).

pawoSD · #4 07-03-2009, 02:28 AM

Blowby is nothing to worry about. My engine has had a good amount of it since I bought the car....6 years and 75,000 miles ago....and it still starts fine in the extreme cold. Just keep on maintaining and enjoying it....proper oil change intervals with a good oil will minimize the increase of blowby and timing chain wear.

kerry · #5 07-03-2009, 08:38 AM

In my opinion, oil leaks are symptoms of oil leaks. Blowby is sucked into the intake system so unless your PCV system is plugged, it's not going to cause gases/oil to escape elsewhere. Replace the old hard PCV hose if it's leaking, repair other leaky gaskets and blow off the blowby.

If, on the other hand, you're curious about blowby, purchase the MB measuring tool and measure it, or use the garbage bag measuring system described and pictured on an old thread here somewhere.

Simpler=Better · #6 07-03-2009, 12:26 PM

Next oil change use mobil delvac diesel oil, it really does help.

pawoSD · #7 07-03-2009, 12:45 PM

Quote:

Originally Posted by Simpler=Better

Next oil change use mobil delvac diesel oil, it really does help.

If by helping you mean help drain your wallet.

Changing it hot and often is better than using the "finest oils"

Oracle12345 · #8 07-03-2009, 01:07 PM

Quote:

Originally Posted by TylerH860

Since there's nothing you can do about blowby, I wouldn't worry about it. The breather line is likely due to age, along with the others.

exactly. all engines have blowby and is perfectly normal, hence why engines have pcv systems .

bob_98sr5 · #9 07-03-2009, 01:19 PM

guys,

thanks for the answers. I'll perform the cap off test and see what happens. im also going to crank down the valve cover bolts just a tad bit more in those 2 leaky places.

what puzzles me is that I've changed the valve cover gasket, the breather tube, and disconnected the EGR as well within the last year per many people's advice. nevertheless, ill continue to monitor it.

thanks, gents.

bob

Simpler=Better · #10 07-03-2009, 01:36 PM

Expensive? Delvac here is $10/jug while super tech is $9.50/jug....seems pretty simple to me

BodhiBenz1987 · #11 07-03-2009, 04:25 PM

Quote:

Originally Posted by bob_98sr5

guys,

thanks for the answers. I'll perform the cap off test and see what happens. im also going to crank down the valve cover bolts just a tad bit more in those 2 leaky places.

what puzzles me is that I've changed the valve cover gasket, the breather tube, and disconnected the EGR as well within the last year per many people's advice. nevertheless, ill continue to monitor it.

thanks, gents.

bob

Bob, just a shot in the dark, but is there a chance something is blocking your breather tube? That might cause the normal blowby gasses to try to escape elsewhere. Maybe check the other end of the tube to make sure there isn't an obstruction.
Even if you had noticeable blowby, I don't think the valve cover should leak. My 240D has quite a bit of blowby at 360k miles, approaching air-cannon status, but since I replaced the valve cover gasket and tightened the hose clamp, I haven't noticed much leakage, if any.
I would also make sure that the oil isn't coming out of the intake where it connects to the engine. Mine is leaking there, and I could see how it would look like it's coming from the valve cover. A new gasket (and the little gasket for the crossover pipe) isn't too expensive.