Reading up on fogging my 496HO motor, I've read those who say just to spray fogging oil directly into the throttle body and some who say that's crazy because it'll mess up the sensors.

The mechanic that just winterized my boat just sprayed fogging oil into the throttle body to fog it saying that's how he's always done it for EFI motors and there have been no issues.

So who's right? Any real bad fogging experiences?

We have never sprayed fog into a dry intake, just wet intakes like carbed motors. Thats the way Mercury taught us to do it so thats the way its been done for years. Dry intake meaning anything with fuel injectors in the intake runners, wet meaning anything with a throttle body or carb. Everybody does it different so I cant say if he'swrong or right. You'll get hundreds of different responces on whats right or wrong.Good luck.

My mechanic said and did the same thing with my HO's. No issues over the years except I did have an IAC valve go bad. Who knows if it was related. It was the middle of summer when that happened.

But, I will be going with 2 cycle oil in the separator for my 525's.

I've heard of guys putting ATF in the fuel filter and running the engine to winterize. Not sure if this is ideal either.

I have always been told not to spray a dry EFI throttle body. You are leaving an oil film on the sensors and and throttle body. I have read that the correct method is pull the fuel seperator and drain off half and fill with two stroke oil and run the engine for a few minutes.

thats the way i was told to do it so thats the way i do did.

+1

John has been a mechanic/friend of mine for years, and his word/advice has never let me down.

Pull the fuel/water separator. Why half-ass it?

*Also, replace your fuel/water separator in the spring.*

According to the MerCruiser Operation and Maintenance Manual for MX 6.2 MPI's (fuel injected) they recommend mixing 5 gallons of fuel, 2 quarts of TC-W3 outboard oil, and 5 ounces of Fuel System Treatment (802875A1) together. I cut the recipe in half and mix in a 3 gallon fuel tank. Connect this tank to the fuel inlet and run at 1300 rpm for 5 minutes. 2-1/2 gallons of fuel is PLENTY to fog two engines.

I too have heard it is a no-no to fog thru the throttle body due to possible sensor damage(?)...

My mechanic runs the efi motors on a mixture like 4mulafastech talks about, not sure it is the exact formula of things or not though. I have always heard no fogging efi thru throttlebody also?