Or put another way… what’s the best way to clean the engine compartment in a vehicle?
While at the car wash (the kind with a wand that can spray high/low pressure water or soap), I have always been tempted to pop the hood and spray soapy water on an around the engine, followed by a rinse w/ water. But if the engine is hot - which it would be, since I drove to the car wash - I’ve heard there is risk of cracking the block due to thermal shock. Is there any truth to this? If there is, what’s the best way to clean the engine & engine compartment?
That might not be your only issue, either. Water getting into electrical components and the like can sometimes cause issues, especially if you are using a high-pressure hose. Maybe you will get lucky, maybe not. The really safe way is to just wipe down the plastics and hoses under the hood with some detailing spray or protectants and leave it at that. Some people use plastic bags or aluminum foil to protect computers and electrical components and then spray the engine compartment down.
Here’s a video from a serious detailer about how he does it:
Unless you have a car that was built in 1965 I wouldn’t. Too many electronic components under the hood that are only designed to work dry. Just the cost to replace the computer can be considerable. Why take the chance?
The “right” way includes capturing all the greasy wash water and running it through an EPA-approved decontamination process. Which is not what happens at any coin-op car wash.
If you’re OK ignoring that issue, then the thing to do is buy a spray can of engine compartment degreaser at the auto parts store. Drive to the coin op car wash so the engine is nice and warm. Spray the gunky parts of the engine compartment thoroughly with the spray can. Let it soak a few minutes per the can’s instructions. Use the hand-wand on the high pressure setting with soap to thoroughly spray the gunky areas. Try to avoid directly blasting the boxes holding the computers, but getting them wet with overspray and splash is just fine. After you’ve knocked off all the gunk, switch to rinse water & spray the same areas the same way again.
If you care enough about cars to care how gunky it is under the hood, you probably care enough to notice if the lid to the box with your main engine computer is missing, cracked, or unlatched. If so, fix that before washing the engine compartment.
Is it possible you could harm something under there with truly reckless malicious spraying? Sure. It’s also possible you’ll crash driving home from the car wash. And about equally likely. Relax.
It really depends on how hot the engine, how cold the water, and how much/how fast the water. In most cases I think it’s pretty unlikely.
What I would worry about more than that is the possibility of water getting into some electrical or electronic component or connection. This is quite a bit more likely, and is something I’ve seen and had to fix. Said fix isn’t cheap because there’s no simple way to tell where water got to and where it didn’t get to. This doesn’t follow a consistent pattern from case to case. It’s generally unique in its (vital) particulars, and can be tedious and time-consuming (read: expensive) to track down. I strongly suggest taking pains to avoid it rather than outright doing it.
The safer way to clean a dirty engine is with solvents such as carb cleaner and brake cleaner. More expensive than soap and water, but generally quite a bit more effective. And a lot less expensive than rectifying a one-of-a-kind problem in the engine’s electronic control system.
One engine bay washing school of thought is to disconnect the battery beforehand and then let it dry thoroughly before reconnecting. That should theoretically reduce the risk of anything electronic being damaged, although you still want to cover the alternator and distributor (if you’ve got one.) That obviously wouldn’t work at a you-spray-it car wash though!
underhood is considered a wet zone, and all electrical connectors should be double-sealed. Otherwise no car would be able to drive through even a puddle.
to the OP, the things to avoid are blasting the alternator or focusing a high-pressure stream at electrical connectors. I think it’s unlikely you’re going to crack anything on the engine. Otherwise (like said above) you couldn’t drive a car with a hot engine through a puddle.
Underhood electrical connectors are well-sealed, but the seals aren’t foolproof. While some rain or groundwater will come through the grill or splash up from the road, some underhood connectors won’t be in the path and thus are never tested, but could easily be wetted by washing. Applying a pressurized spray of water to the engine and environs is pressing one’s luck. If water is introduced somewhere under pressure it may be trapped and not evaporate. This can lead to the scenario I described above.
What are the benefits of a water-washed engine that justify the risk of water ingress where it’s not desired?
You do drive your car in the rain don’t you?
:rolleyes:
I’m gonna have to disagree with Gary T here.
Every used car on every used car lot in the United States has had the engine cleaned and detailed using a water spray and cleaner usually a high pressure spray.
I can guarantee you that if a significant percentage of these cars experienced electrical failures afterwards this practice would stop right away.
Yes if you put the high pressure nozzle right next to a connector the spray can overcome the seal, so don’t do that. Hold the spray a foot or two away and you won’t have that problem.
It ain’t rocket surgery.
To the OP. No you won’t crack the block cleaning the engine.
Go to the auto parts store get a can of engine cleaner. I like Gunk EB-1 myself.
Drive the car till the engine is hot shut it off and spray the engine with cleaner. Let it set a bit and then rinse off.
Don’t direct high pressure stream at any electrical connectors and don’t forget to wash off the fenders and windshield when you are done.
Not many distributors around anymore but if anyone found out that I could not dry one, the coil, and keep heavy spray away from computer stuff on today’s car, I would lose my man card.
If all you know is how to open the hood & check levels, then just do that.
Want to do more, then learn. It’s an $30,000.00 investment, or more.
Ask most any mechanic which engine he likes to work on? Pretty clean or 1½" of caked dirt & grease.
Oh, I agree. they’re not foolproof but you just have to avoid concentrating a blast of water from a pressure-washer onto it. The typical “spray it yourself” quarter car washes use an air compressor to apply about 130 psi to the spray, so they’re not really pressure washers. an actual pressure washer has a hydraulic pump which can raise it to 1000+ psi. You DON’T want to use one of those on your engine.
I had a car that leaked oil like a collander, and the entire engine and everything around it was encased in congealed old oil. Various mechanics told me I had to get the engine steam-cleaned before they could ever hope to figure out where all the oil was leaking from.
So there’s one reason for getting your engine steam-cleaned.
I tried using a can of engine cleaner that I purchased from O’Reilly’s. I don’t know if my engine was too hot or what the problem was but something started a fire and I ended up having to replace a large portion of hoses and wires.
I was going to say this. Car lots clean the engine on every car and there should be no problem.
There is, however, the odd car that needs extra precautions. Mazda Miatas (and maybe other Mazda, I dunno) used to have spark plugs on top of the engine with a cheap rubber boot. Washing the engine will cause water to get into those boots and get the plugs wet, causing the car to run like crap. Blowing compressed air into the plug wells to dry out the water usually fixes it. This was still true a few years ago, but I’m not sure if the latest Miatas are the same.
I watched a video on YouTube a few days ago, a guy took a small block powered Jaguar through a car wash on at least 3 different occasions to cool the engine, they had overheating problems. The engine also had a big blower poking through the hood. They finally gave up and removed the hood to keep the engine cool. No apparent damage to the engine occurred. The car was later used in two other episodes.
So engine washing is for car obsessives and people with an engine problem that makes it unusually dirty.
I’m not a young man and I live in Southern California where cars are a necessity. I have never, ever heard someone talk about washing an engine before this thread.
Answer to the OP: don’t bother washing the engine.
