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Pressure washing engine

Pressure washing engine

Pressure washing engine

So my truck is a “ leaker”. It’s had its share of oil, anti freeze, and power steering leaks over its 400k mile journey. Enough that our severe winters with heavy salt have had little effect under the body and frame. It is a slimy mess under the hood.

Since we are car guys, we got talking about pressure washing under the hood. Some of the local detail shops don’t do this any more as they have had problems with the newer cars electrical systems after pressure washing under the hood.

I regularly wash the under hood of my Fiberglas 41 Willys with 6-71 blower. It leaks oils occasionally and I drive it a lot so it can get messy in a day or two. My el Camino is bone dry but gathers dust and grit like a magnet so it gets washed under the hood weekly.

So far I’ve never had any problems with either car.

Back to my truck. It’s a diesel so add a little diesel fuel too. It has a computer for all the truck plus the fuel injection is computer controlled.

What’s the general opinion of pressure washing cars and trucks under the hood?


RE: Pressure washing engine

The seals on the electronics are raintight when new, but probably not resistant to pressure washing.

I'd foam her up with Gumout Engine Wash or similar, and rinse very, very gently, but thoroughly, ON A WARM DAY or in a heated garage, and not turn the key until everything was demonstrably dry.

Mike Halloran
Pembroke Pines, FL, USA

RE: Pressure washing engine

If you mean washing with high pressure as a lot of those washers nowadays can do (50 bar or more) it is not such a good idea. Part of the cleaning process then is taking soluble dirt in solution in the water that flows away and part is using the impact of the waterjet to break free dirt and deposits that you want cleaned off the engine. The impact of a waterjet may be too much for certain seals (that are designed to be tight in a rainy and splashwater environment, but not necessarily capable of dealing with high pressure cleaners).

A safer way to clean is to first spray the parts to be cleaned with a water soluble solvent that is capable to emulsify hydrocarbon residues from engine oil and diesel fuel, then let it soak in for a while and then just rinse with low water pressure - the water then will run off as a "milky" fluid because it has formed a emulsion with the oil and fuel stuff you wanted to get rid off.

High pressure cleaners can be very useful, but keep them away from electronics and also from your tires - they are capable of making miniature holes in them if used from too short a distance too long.

RE: Pressure washing engine

Pressure washers are also bad news on radiators and air conditioner condenser coils . They will bend the fins in a new York heartbeat.

You are judged not by what you know, but by what you can do.

RE: Pressure washing engine

If I was to wash an engine etc in a driving vehicle my optimum method would be first run it until up to full operating temperature, and plastic bag or otherwise seal the electronic stuff.

Then spray on of the Gunk like detergent products, and use a parts cleaning brush accessible problem areas.

Finally, After letting it sit a bit, rinse low/no pressure water.

Pretty much what it says on the Gunk EB can I think, and quite unlike what is shown on the official Gunk videi

RE: Pressure washing engine

I would avoid the Gunk. I have found that the petroleum distillate in such products tends to degrade plastics such as connectors and wiring. Not immediately, but over time and temperature.

Keep the pressure washer nozzle a couple feet back from the engine. If you get it closer to clean a grimy spot on the block, move it straight in to the spot so you avoid high pressure on possible sensitive items.

RE: Pressure washing engine

Suggested detergents? Simple Green or some such?

Really heavy grease deposits seem to only come off with the use of solvents, but a lot of the time deposits like that are best just left alone, especially if they're not in a particularly visible place. The countershaft sprocket cover on a motorcycle engine and the surrounding area get really nasty (chain lube + dirt) ... but the only time I ever clean behind there is if it all has to come apart for some reason. Otherwise I leave it alone.

RE: Pressure washing engine

I wash them regularly with high pressure, the trick to preventing issues is to keep the wand moving decently quickly and hit areas multiple times from multiple angles. While youre washing its also a good idea to blast out boxed sections of frame to prevent rotting from the inside out and also brake components to clean out the dust, particularly in drums.

Up north many folks still prescribe to redneck undercoating - spraying the underside of vehicles with used motor oil from a garden sprayer to prevent rust. The first step in most maintenance projects on those vehicles is pressure washing.

RE: Pressure washing engine

I have found that "Shout" laundry pre-treat works great cold and no petroleum products.
I just rinse with a garden hose and a spray head.
It de-greases bearings too.
I get it by the gallon at Sam's Club.

RE: Pressure washing engine

We had more problems steam cleaning or water blasting engines with distributors, exposed coils and carburettors than modern engines. Always had to clean out the dist, run up, then clean again. Use a small unit, 1,000psi is ok, those 3,000psi ones are the ones that cause the problems...and just use some common sense on where you hit. Adjust to fan for a start, on jet it's going to do damage.

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