PeachParts Mercedes-Benz Forum - View Single Post

JimSmith · #7 03-12-2002, 01:57 PM

Midas,

Congratulations on your successful repair! The engine should be starting better and with less cranking now.

As for the oil leak, it is highly unlikely black oil is coming out of the injector bore. It is more likely you have oil leaking into the area, and like you saw on the fuel pump, it is filling the recesses in the area. When you start the car it runs a little rough and you are likely seeing some spatter from the puddles being shaken.

The most probable source is, as TXBill noted, the valve cover gasket. This gasket sits under the aluminum cover on the engine that has the cap you pour oil into, as well as where the throttle linkage is supported. The cover is called the valve cover, and is an aluminum casting that mounts onto the cylinder head, an iron casting on your car. The aluminum valve cover should be shiny metallic silver when clean, while the cylinder head only has "as-cast" surfaces visible in the assembled state. The "as-cast" cylinder head is a rough, kind of motled gray color. The gasket is black rubber, and follows that winding pattern around the injectors you noted and seals between the aluminum cover and the cylinder head.

The valve cover is held on, and the gasket compressed to make a seal, by fasteners kind of evenly spaced around the perimeter of the cover. The fasteners consist of nuts and washers that screw onto studs that stick out of the head. If you elect to tighten these nuts, be careful not to just tighten one, or tighten them too much.

If you have a torque wrench, you can check just how tight the nuts are and use it to make them all the same while ensuring you do not snap one of the studs off by tightening it too much. I am not able to check the torque values at the moment, but the nuts are about 13mm or so they are pretty robust. If you have no torque wrench, which I assume is the case, to this with the smaller size wratchet wrench (3/8" vs. 1/2") with the long extension bar you should have in your kit from Sears. It is harder to break a fastener with a smaller wrench as you get a lower mechanical advantage. I have done these particular fasteners a hundred times without a torque wrench, so you do not need to expect you will break a fastener if you do not have one. Pay attention to how the tightening force feels as it turns the nut, as compressing the gasket feels different than stretching the stud.

You should start in one location and check how tight the first nut is by turning the nut in the tightening direction until it turns just slightly. Then pick a nut that is nearly diagonally opposed to the first one and check to see it is about the same tightness. Then repeat this process until you have checked all of the fasteners.

If the first one seems too tight, you can loosen it and then snug it back up, then repeat this on all the fasteners in the pattern noted above. Once they are all snug you can tighten them one increment of tightness at a time in the same pattern. An increment of tightness that is used sometimes is a flat of the nut, meaning you turn the nut about a sixth of a turn with each increment.

If the rubber gasket is worn out (rubber loses its elasticity and becomes brittle with exposure to heat and pressure, so it is not unusual for this gasket to become too stiff or hard to effectively seal after a few years - I usually change the gasket when I adjust the valves which is typically a 15,000 mile to 20,000 mile interval, and can be one to two years in time) tightening the fasteners will not help much as the pressure distribution on the gasket between the fasteners will be very irregular and range too far to provide an effective seal between the fasteners.

Overtightening the fasteners to compensate for this can crack the gasket under the fasteners and make the leak worse. If you are leaking in the vicinity of one of the fasteners, and they are all pretty tight, I would suspect the gasket is shot. Replacing the gasket is another do it your self job, which might be combined with a valve adjustment or lash measurement. If you get convinced you need a new gasket and want to check valve lash (gap between the rocker arm and camshaft lobe of each valve), ask for instructions.

There are some other possibilities, before you change the gasket though. On my cars the oil fill cap and the rubber hose that connects to a pipe nipple on the top of the valve cover have leaked, and these can make a real mess. I have also spilled a little oil in the filling process that has run down to the injector area. And, remember how dirty everything was before, and how great a solvent Diesel fuel and new oil can be. If fuel was leaking in the area, it would quickly pick up the color of the grime on the adjacent surfaces as it tricked over them, and look like black liquid pretty quickly. It will still smell like Diesel though, so dab a paper towel into the puddle and smell it to help identify what it is.

As for the oil in the air filter, it is normal for these cars (and most other cars) to generate a higher pressure inside the engine spaces that are lubricated by the engine oil than in the air intake. Too keep this pressure differential reasonable, it is vented to the intake manifold. On my 1982 240D this vent line comes off the top of the valve cover and runs down under the air filter housing to an liquid/vapor separator. The liquid is supposed to run back to the crankcase, while the vapors are supposed to go to the intake via two lines on the discharge of the separator. I have read on other posts this feature is inside the 300D Turbo air cleaner housing. It is possible the drain line is clogged or the separator is not able to do its job because it is full of crud, and the oil droplets that are suspended in the vapor are being carried into the air cleaner area, rather than being collected and drained into the crankcase. This should be correctable by cleaning these parts, but I do not know anything about these parts on a 300D Turbo as they are not the same as my 240D. Someone else on this board will have to pipe in here to provide more explicit data.

There is another potential, and that is the source of the overpressure in the engine internals, combustion product blowby (meaning the high pressure of the combustion process is leaking past the piston rings and into the crankcase) is increasing due to either sticking rings or cylinder bore wear. One way to check this is to carefully loosen and remove the oil fill cap with the engine running.

If a lot of gasses/smoke are blowing out the openning, it is an indication you have higher blow by than is normal. Remember, there will almost always be some blow by, and there will be some oil being flung around by the camshafts. When you put the cap back on you will be able to feel if there is a lot of blow by how much force it takes to push the cap back in place. There should be no difficulty getting it back into position.

Midas, do a few of these checks and report back so we can try to figure out what is causing the oil leak, and the source of the oil in the air cleaner housing.

Glad the pump changeout was a success, and you will soon have another task completed! Good Luck, Jim