Just want to get a bit of a poll here on who does what when they pressure wash their engine. With an aluminum head on the OM60X series engines, do you wait for the engine to cool down before hitting it at the car wash so as not to induce any cracks in the head prematurely or do you just let 'er rip?

Also, anyone happen to have a Becker 1492 head unit laying around and don't want an arm and a leg for it?

Thanks, for the comments about pressure washing, I'd like to take care of mine soon but I know that having the engine at operating temp helps to loosen things up too.

I don't have an aluminum head on my Merc, but I do have other cars with aluminum heads, and have never had trouble pressure washing the engine compartment.

Just steer clear of electrical connections and the intake system. Water in those can be, well, bad. I also never wash down a hot engine. Mildly warm, by all means. If the motor is cold, I fire it up and let it run for a couple of minutes, then give it another couple of minutes off to let the exhaust manifold/s cool down. Once upon a time a cast manifold on my Chevy cracked as soon as i hit it with cold water from the pressure washer. I'm sure it was going to crack anyway, but I'm reasonably confident I sped up the process when I shot cold water on it while it was still blistering hot.

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'77 300D Euro Delivery
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404 Milanbraun Metallic / 134 Dattel MB-Tex

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My '77 300D progress thread

I would let the engine cool off... spraying a hot injection pump is not a wise idea

I have several vehicles and never did I have any problems,,,,Common sense needs to prevail here.I always wait till the engine compartment is cool.

I would first spray on some Gunk or similar crud loosener, let it sit awhile, and then apply the water. "Warm" is OK, "hot" less so. Also don't use the high-pressure water close to seals and gaskets and such, as it could penetrate and do bad things. Don't let the car sit afterwards, drive it so that the water blows off or evaporates.

Jeremy

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Our all-Diesel family
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"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I don't use a pressure washer under the hood. Just doesn't seem like a good idea to spray water at several thousand psi in the general direction of components that were never designed to withstand it. A pressure washer will cut your skin right open so it will have no problem pushing water past seals, gaskets, etc. My preference is to spray a good degreaser on a warm engine and let it sit. Very dirty parts get the degreaser scrubbed in with a toothbrush, old paintbrush, etc. Let soak for a few minutes and then hose off with warm or better hot water. Hot water works much better than cold for this.

Regarding the not spraying the IP with cold water. I feel this is a myth. Ever see a diesel 4X4 go splashing into the water? How about a military vehicle going for a swim? They keep going don't they? Never heard of an IP quitting from this treatment so why would washing it hurt any?

RT

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I wouldn't use a home pressure washer. But the ones at drive in car washes aren't nearly as high pressure as those gasoline powered home units.

I can't get to one of those washes without heating the engine up to temp. What I do is a little risky but not as much. I don't shoot it full blast at first.

I try to just sort of "Mist" the engine... just sort of hit it with a few drops at a time, and take the worst of the heat out that way. After 30 seconds of just sort of gently swiping things without just dumping water on it wholesale, I'm able to hit everything except the exhaust without steaming... and then I just gentle-swipe the exhaust until it quits boiling and then have at it.

May regret this when I crack something.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

I washed my engine once with a garden hose. Tracking down the knocked off vac lines was a real PITA. I can't imagine how not fun pressure washing would be.

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1984 300TD

Isn't the pressure on pressure washers adjustable? I've seen them use those in used car lots. I assume that's why they are usually so clean in the engine compartments.

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OBK #55

1998 Lincoln Continental - Sold
Max 1984 300TD 285,000 miles - Sold
The Dee8gonator 1987 560SEC 196,000 miles - Sold
Orgasmatron - 2006 CLS500 90,000 miles
2002 C320 Wagon 122,000 miles
2016 AMG GTS 12,000 miles

The max pressure on the washer I used was set at 1500psi. Other than knocking loose the wire to the pressure switch on the a/c receiver/dryer, all seems to be okay.

I went through the Detroit Diesel apprentice program in '81 and '82 with a GM Diesel outfit in Seattle; a two year deal. Whenever over the road trucks came to the shop for ANY sort of service; from mild to major overhaul, the engine and drivetrain components always received a MAJOR cleaning before and after the work was performed. Now, in that shop that routinely had anywhere from thirty trucks in the shop on a given day, the pressure washer system was plumbed-in from the shop's live steam heat system - true steam cleaning at around 2800psi. No question about it, it was a matter of course that every engine was douched that way. The pressure wand was simply stuck down into a 55 gallon drum and ran ALL day long and into the night (a 24 hour shop). The 55 gallon drum would just stay full of scalding hot water and run over onto the pavement outside the shop. That is, until one day, the guy who ran the dyno shed somehow knocked the drum over with a forklift and sent another tech to the hospital with third degree burns on his feet and lower legs. OSHA stepped-in at that point and the pressure wand had to have a 'dead-man' trigger on it after that. It's pretty common sense not to hit carburetors, distributrors, the alternator and so on. My original question really had more to do with the danger of cracking an aluminum head. What prompted that was a memory of a neighbor who owned an Alfa Romeo GTV-6. He thought you were supposed to pressure wash the engine with it still running and so, cracked a head right where a spark plug boss happened to be. Even a Heli-coil wouldn't save it.

I don't know if there's any truth to the adage I once heard; that a clean engine runs clean?

I routinely wash the engine bay at the car wash, though I don't do it when the engine's really hot. Also, I avoid the IP, but not assiduously because I don't think I could damage it with my .44 mag.

What is the "IP"?

Injection Pump.

Clean with Simple Green Extreme, don't bother with the pressure washer. The stuff works.

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Gone to the dark side

- Jeff