I do not wash the engine bay when it is hot or the engine is running but that is just how I do it. The myth that keeping the engine running is going to make everything OK is a joke...due to I get customers who washed off their engines and the next day it would not fire up.

The other reason I prefer NOT to have the engine running is due to the type of degreaser being used..and IF the car is in the sun and the paint is HOT....the blow back that will occur due to the fan turning and blowing crap over the top of your car...if you do it this way...I would advise you that you make a conscience effort to constantly rinse the rest of the car down during this process...or you might just REGRET doing this.

I do use a pressure washer but I often times let the customer know they the engine had been neglected for so long that the chances that I blow paint off is HIGHLY likely. I do not do it at a car wash due to I can do it at my shop and I have a way to make sure the run-off does not get into the creeks and storm drain system. I like doing it at my shop due to I can raise the front end and get under it.

I prefer to use my wand I have that allows me to connect it to my air line and siphon the solution out of a container and slowly under low pressure and soak the engine and let it sit.

I lay a very large piece of thick plastic down...pull the car onto it...I raise the edges so it creates a containment area like a pool. When I am done. I use my sump pump and pump out the crappy water into a container. Then I take that crap to a self serve car wash...or I put it out on an other aluminum tray I have and allow the water to evaporate off and scrape up the sludge and give it to my guy who picks up my waste oil.

I do agree..when you are done...like Alan stated...things can rust due to no longer having grease and oil on the parts. Simply degreasing down your engine can then cause you to have to really go in and get it clean so you can begin to apply a paint on parts needed if that is a concern for you. I can not tell you on how many rusted oil pans I have seen due to no one taking the time to protect parts.

DUB

 

I just put some DAWN in the pool and let it sit for a few hours - running the pump helps...

Then sometimes you have to put it on it's side to get the water out of the corners...