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Can I Wash My Engine?

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I'm curious if anyone has any tips on washing the engine bay on my 2006 GS300. I know that every time I did it on my old Mercedes, some wiring harness would get water in it and it would backfire and miss until it dried out. Can I expect the same on my Lexus? Or is it OK to gently wash it? Any advice would be greatly appreciated.

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I have lightly power washed the engines of our past and current LS400's probably a hundred times over the past 16 years -- about once every 1 or 2 months -- and have never had a problem with it affecting the performance of the cars. Of course, the engine covers on my current LS and on more recent Lexus cars means that you really can't see the engine anyway -- the covers make it pretty hard to spray water on critical electrical parts.

I suspect the key to washing the engine compartment is the word "lightly" -- I rarely spend more than two minutes total on both the soap and rinse settings and keep the spray nozzle at least a couple of feet away from anything I am washing in the engine compartment. I doubt if I am getting any more water on the engine than by driving in a heavy rain storm.

If you frequent the various Mercedes forums, you might have seen comments about how the insulation on Mercedes wiring harnesses completely disintegrates after a relatively short time -- as has happened on a friend's E320 which is having all sorts of odd electrical problems. Toyota/Lexus products do not seem to have this problem so I doubt if you have to worry.

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I concur with LS400.

I have mine done by my detailer twice a year (October and May).

Do not use engine degreasers as these will deteriorate, harder, make brittle and dramatically short live the plastic and rubber gromets, hoses, wire covers, belts, etc.

More importantly, do not use a high pressure washer, use gently water pressure and try to keep the flow of water off vital electronics.


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  • 4 weeks later...

Here's a system that works for me:

As required by your level of compulsiveness, but at least twice a year... and before visiting the car wash:

Start car and allow engine to warm up... not hot just warm.

With sprayer set to 'mist' or 'spray', spray entire engine compartment with 409.

Allow to stand for five minutes.

Using garden hose and spray nozzle, rinse using the medium spray setting. This works best if you use hot water. (The drain bib on the hot water heater will usually fit a garden hose.)

If areas of grease are built up and don't wash off, wet a shop rag with carb cleaner (B-12 Chemtool) or use the B-12 from a spray can and wipe off the build up. A parts cleaning brush (looks like a big watercolor brush with shorter bristles) will help get to hard to reach spots.


Use shop rag to dry up trapped water and flat surfaces to prevent spotting... or, use compressed air at about 60 psi to blow water off the motor. Be careful not to allow the air blow on or toward connectors/seals, etc.

Restart engine an allow to idle for ten minutes.

This has worked well on my '87 Mazda B2000 and '95 V6 Camry. Neither is 'concours' but they are clean and present a well-kept appearance. Guaranteed to get a comment from any service personnel. I intend to continue same routine with my newly acquired '01 RX 300.



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