Why aren't you supposed to spray hot engines?

[wschrade]

Good morning,

One thing I've seen repeatedly is to not spray down the engine compartments while the engines are "hot".

Why is this? Is this bad for the engines or the hull materials?

And how long should I let the engines cool off before spraying in there?

 

[Julian]

It isn't a great idea to super cool hot metals....you want to wait for them to cool off if your purpose is to rinse them (what are you rinsing them of???)

 

[Babin Farms]

If you cool down metal too fast it can change the hardness or even crack, plus it will shrink it at a faster/different pace than other items that it's mated to causing leaks and all sorts of problems. It's best to let things cool down normally and then do a rinse down or whatever your plans are.

 

[wschrade]

So how long is long enough to let them cool before rinsing them off? 10 minutes?

 

[Babin Farms]

When you can rest your hand on the entire engine without pulling away What's the reason for wanting to rinse them so quickly?

 

[1WetBoat]

For me its usually the trip from the ramp to my driveway, engines are cool to the touch. Its about 10 miles and about 20 min trip.
If you wanted to speed it up, open the hatch and let them cool off. However, not sure why you would be in a hurry to rinse them off before the engines cool down. Unless you don't have access to wash them down at home/storage facility and can only do it at the ramp for example.

 

[FSH 210 Sport]

So how long is long enough to let them cool before rinsing them off? 10 minutes?

No.

Wash your engines Cee Ell Oh Dee ( COLD). Differential contraction rates of material can cause all sorts of issues as @Babin Farms states. I wash my engines cold then start and run them on the hose until they are at operating temp then leave the hatch open to all the compartment to dry fully.

 

[wschrade]

When you can rest your hand on the entire engine without pulling away What's the reason for wanting to rinse them so quickly?

Well, I keep the boat in the boatel at the marina, and usually have the dam waiting on me while I handle cleaning up the boat. I suppose we should take two cars when headed out. Glad I now understand the why... Thanks all.

 

[zipper]

Are you in salt water? https://jetboaters.net/threads/engine-anti-rust-spray.16950/#post-291819

You might not need to wash it down as much if you have a thin film of protection from salt corrosion.

 

[Robconn]

Spraying a hot engine with water may create thermal shock which leads to metal fatigue and cracking over time. However this mainly depends on how cold the water is, how much volume of water and how hot the engine is. To be safe, I would atleast wait ten minutes after shut office until you can tolerate touching the engine without losing your fingerprints.

 

[Dixemon]

Paint failure, steam entering electrical connections, forced material thermal cycling...ect... Yep not a good idea. Also not a good idea to rinse them and close the hatch. Fsh 210 has the right idea with the above post.

 

[Mac’nCheese]

I guess this leads to the next question: Are you getting enough water/salt water/debris in your engine bay to require hosing it down??? If so, that doesn't sound right at all. I had my AR195 for 2.5 years (fairly heavy use), and the engine bay still looked new when I sold it. I maybe cleaned the engine bay once per year.

Next time you have the engine bay clean, I'd hose it down with the Yamaha Silicone Spray (it's what Yamaha recommends). It'll prevent corrosion in salty air environments, and keeps the engine bay looking pretty nice.

If you're talking about the rinse out/clean out port for the cooling cavities, that's a bit of a different story. Since the engines use raw water intake to cool the engines, those internal cooling passages are really the only parts of the engine that are exposed to salt water. I'd use that cleanout port every single time you have it in salt water. Just be sure to read the manual on the procedure, you don't want the hose running when the engine is off, but you also don't want to run the engines for more than 10-15 seconds without water running through the cooling lines!