91 300E Oil leak & stuck drain plug
 

Hi

Leak near rear of motor center of vehicle, can't pin point, not sure if seal around oil pan or? So looking for likely suspects in that area.

Also the drain plug is stuck, very stuck. So most likely will need to replace pan, anyone have any idea what is entailed here?

Do I have to remove engine? Or can it be accessed otherwise?

Thanks in Advance.

Nv Joe

Besides the pan gasket and rear main seal, a very common oil leak on an M103 that usually shows up as oil at the back/center of the pan is the oil level sender. It's a unit that bolts (2 bolts) into the oil pan just above and behind the oil drain plug on the drivers side. It uses an O-ring for a gasket. But, It's not just that o-ring that can leak. Where the wire plugs into it there is another small o-ring which I think just keeps water and dirt from the contacts but they sometimes develop leaks through the plastic casting of the electrical components. Oil senders are generally about $50 online.

When they leak the oil film is very thin from the unit but it gathers at the back of the pan. You'll be able to feel oil around and under it with your fingers. Clean it off good with brake kleener (careful of your eyes spraying under the car) and see if it quickly returns after a short drive. If you can trace a leak to the sender, replacing it (or the o-ring) is very easy but will require the oil to be drained. Which could be a problem if you can't get the drain plug out. The drain plugs are pretty accessible, if it's rounded, maybe just a big honkin' pair of vise grips clamped super tight could coax it?

I've never done it but I think oil pan removal is bit of a pain on these. I believe you can just raise the engine a few inches, with a hoist, or a jack from underneath or maybe a top engine support would work if it has a few inches of lifting capability. you'd need to undo the motor mounts, probably the exhaust at the manifolds and bracket at the trans as well as the trans mount. Careful of the shift linkage I suppose. Somebody who's done it would have to chime in to verify all that or give further advice on this procedure.

What's the problem with the plug? Is it buggered up, rusted?
I Think I'd give my best shot at liberating that plug before I'd replace the pan because of it. Maybe even drilling it out and using a big easy out.

I did not remove the exhaust pipes or the transmission mount when I redid the gasket on my oil pan. Just unbolt the motor mounts and jack it up using a 2x4 to make sure the pan is not dented. Just watch the hoses that attach to the radiator (can't remember if I removed the air intake assembly or not...), but it should give you enough space.

It is tricky to get out...so be prepared. It might be easier unbolting all of the other stuff, but it is not 100% necessary.

You can usually get a small set of these at autozone (or wherever):

http://www.irwin.com/irwin/consumer/jhtml/browse.jhtml?catId=IrwinCat100511

Put the size you need on a breaker bar, and unless it's welded into the pan, you'll get it out.

And yes, there are kits to repair oil pan threads should everything strip out.

Thanks, I will definitely look around there as it seems like it could be the oil sender as the pressure drops to zero at idle, but when on accelerator it's all the way pinned.

Yes the plug is "buggered" up, started drilling on it for an easy out, and stopped as that just didn't seem the way to go just yet.

Tried those, not Irwin but another brand from Harbor Freight, no luck, not because they don't work, the plug is made of aluminum and just shreds. Any other thoughts or am I doing something wrong?

Thanks

are you saying that little round gasket around the sending unit could be the problem? Can't pull the sending unit off, but it does seem to have a tiny leak.

I will get a photo for examination and feedback.

Thanks

Photos of Oil Sender Unit
 

So here is the actual oil sender, under the electronics cap, there is some oil leaking out., I'm not sure if it leaks more under pressure, but barely anything came out all afternoon under the the thing. So I guess the leak is more towards the front of the engine or it is leaking out of here and blowing back as this leak does have a bunch of blow back under the car.

Also, anyone know how the electrical cover comes off? It was not just removing itself easily, and the wire is pretty fragile near the cap, so I don't want to snap that and really FUBAR it.

Thanks,

J

That is the Engine oil LEVEL sensor, not the pressure sensor that operates your instrument panel oil PRESSURE gauge. The oil LEVEL sensor will operate a warning light if your oil LEVEL [quantity] drops too low in the pan. If your oil PRESSURE is actually dropping to 0 [zero] at a warm[or cold] idle you have other issues.

But, to answer your question, if you have oil leaking out of your oil level sensor connector, then you will need to replace the entire lever sensor and any related gaskets, or seals [o-rings].

I would recommend repairing your oil drain plug, and installing some 20/50 oil and a new oil filter, and see what that does for your oil PRESSURE before you replace a oil level sensor on a engine that may have serious internal issues.

Best to replace the oil level sensor after draining the engine oil. Under normal circumstances there isn't any pressure in the oil pan so the oil level sensor O-ring isn't apt to leak. Check that the oil level sensor mounting bolts are torqued properly.

I don't recall the oil pan drain plug being aluminum. Have you tried using a small pipe wrench to remove it? I would only remove the oil pan itself as a last resort ... that could introduce another set of problems.

Don't drill unless you plan on removing the pan, because you'll never be able to get all the shavings out, and since it's aluminum, you can't just use a magnet to trap them.

The extractors from Harbor Freight WILL shred things, because they aren't made with anything close to the same quality steel and have nowhere near the hardness. The Irwins will not shred anything, they will only bite deeper into the bolt.

If you're using HF tools, you're only making things harder on yourself.

For the plug, I would take the car on a freeway run for 15 minutes or so and get everything good and hot. That should improve the chances of getting the old plug out. When you get it out, use a 1/2' 6 point socket from now on and you won't ever have that problem again. 1/2" is 12.7mm and fits the thing perfectly.

I've already attempted that, heated it with torch too...
Not sure anything short of dynamite gets this plug out.
I don't know how it got stuck. It will be the last time I take it to anyone to change oil.