And possibly have a good snicker at my expense...

Yesterday, after completing the somewhat disagreeable task of changing the gasket on the upper timing cover of my '92 300SE (M104 motor), I decided to change the oil. Changing the gasket was particularly disagreeable because of the carelessness of the previous owner/mechanic that did the head gasket job on the car before I bought it.

I have one of those vacuum-extraction devices for changing the oil through the dipstick. I've modified mine by machining a plug which fits the top of the dipstick tube, sealing with an o-ring. This gives me a larger diameter orifice to pull the oil through. The extractor came with a small hdpe (high-density polyethylene) tube that fit down the dipstick - but that took forever to pull the oil.

I'd already started the motor and determined everything to be in working order, both lubrication and coolant-wise.

The extractor works good, but it doesn't like changing hot or even warm oil. The heat causes the plastic tank to soften to the point where the vacuum pulls the sides of the tank in towards the end of the extraction process. That causes the scale on the side of the tank to improperly indicate the true extracted volume.

I further modified the tank to allow me to use air-pressure to reverse the extraction process and use the hose to transfer the oil back to the now-empty bottles used to provide the new oil.

When the extractor was sucking nothing but air, I - and I still don't know why - decided to use air pressure to re-shape the tank back to the right dimensions so I could read the volume of oil extracted. Nevermind that when I return the oil to the bottles, I'll know how much was extracted....

I turn the pressure down on the compressor - way, way down. So low that I can hold my finger over the end of the air gun and stop the flow. I have one of those great (but not OSHA-spec) air guns with no bypass holes on the tip.

So, I press the tip of the air gun to the hole in the fitting on the end of the tube and apply some air pressure. I hold it for like maybe 5 seconds and I start to hear gurgling from the tank.

And then it happens... oil starts coming out of the tank around the shaft of the handle. I release the air gun, but it's too late. There's sufficient air space in the tank to the point where it takes too long for the pressure to drop via the air escaping through the now open hose. The stupid tank (sitting the floor next to the even dumber idiot with the air gun in his hand) has turned in to an oil geyser!!!

The extractor is nothing more than a large-capacity, heavy-duty hand-pump garden sprayers you see at your local home center. It says it will handle about 8 quarts of oil. The pump mechanism is modified by capping the end with a pvc fitting, to which is attached a hose and a one-way valve. This valve is located high up in the tank, secured to the pump mechanism via a zip-tie. Apparently, the tank had collapsed to the point where the oil had covered this valve (a bad thing). I'm guessing the valve failed, allowing the oil back into the tube, and out through the pump.

It belched about a quart of oil out the top - splashing onto me, the car (with the hood up means also all over the external fans and fan grille) and the floor of my once-clean garage.

Fortunately, the tank was sitting partially on some cardboard I had on the floor to catch the drips from the previously mentioned leaky gasket. I quickly grabbed the tank and moved it to the center of the cardboard to reduce the mess.

How an otherwise intelligent individual can be so completely STUPID is beyond me. At least the car's not a diesel... I'd never get the ink-black stain out otherwise.

I've now got to make sure that I got all of the oil off the car - especially around the fan resistors.