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Fogging a fuel injected engine 350 Mag MPI

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Old 10-18-2010, 06:03 PM
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Default Fogging a fuel injected engine 350 Mag MPI

I read about people fogging an engine for the winter by slowly pouring down down the carb, but why cant a FI engine be fogged the same way? The engine I want to fog is a 350 MPI MAG.
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Old 10-18-2010, 06:06 PM
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Fogging is not recommended for Fuel Injected engines. You can actually cause more problems than you'll prevent by doing it. We only fog older carburated I/O's and outboards.
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Old 10-18-2010, 06:14 PM
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Is it because oil can accumulate in the intake manifold?
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Old 10-18-2010, 06:31 PM
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Fogging prevents rust build up on your valves and seats..per merc manual all you have to do is remove the fuel filter and dump out a few ounces of fuel and replace the fuel with two stroke oil..this supposedly lubes the fuel injectors,valves and seats.. i do both,i run the boats i work on in a antifreeze bath good for -*50 below and while doing so i fog the engines weather its efi or its a carb..
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Old 10-18-2010, 06:37 PM
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Thats what i read also...
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Old 10-18-2010, 08:17 PM
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from 1995 to 2001 350 mag mpi,from 2001 til now 496 HO always fog with mercury spray can in the throttle body never got a problem.
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Old 10-18-2010, 10:39 PM
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Merc has a process explained in the manual where you mix the 2 stroke and stabilizer in a small fuel tank then hook it direct to the water seperating fuel filter and fog it that way. They say to run on the mix for 5 minutes @ 1300 rpm.

I always fogged the carb 500's, but since the 525 EFI's and the marina guys saying they just stabilize the fuel and run long enough to get it thru on the EFI motors, I've come up with a different deal. For the past 3 seasons I have added the fuel stabilizer, then added Lucas fuel additive, take one last run and shut it down and load it the trailer. Run the anti-freeze thru later and it's done. Works for me, fires right up in the spring and runs like a champ.

I assume the 2 stroke in the filter would achieve the same result as the Merc method. I just wonder how long you would need to run it to get the oil thru.


Actually a question here, how long would you need to run it to get the 2 stroke thru if you did the filter method?

Last edited by RaggedEdge; 10-18-2010 at 10:43 PM.
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Old 10-18-2010, 10:42 PM
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At our shop we fog all injected motors and never ounce had any issues at all.
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Old 10-19-2010, 06:51 AM
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I just winterized my new motors(efi whipples) that Eddie Young built. I added Marine Stabil to my fuel, fired up the engines on water so that I could change the oil. Drained the block. Removed the fuel filters and added 5 oz. of Marvel Mystery Oil. I connected my antifreeze mixture. Fired the boat back up. It started to smoke just as I ran out of 5 gallons of antifreeze. Perfect. Probably 30-45 seconds.
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Old 10-19-2010, 06:52 AM
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OK, I'm going to correct myself and admit that there is a way to fog a FI engine - and several of you have noted it. I'm not in a salt water environment where fogging to prevent corrosion is a big issue, so going through the pain of opening a fuel line to introduce the fuel / oil mixture is something we've decided not to do. BTW, how many times can you break open a fuel line and not have it leak. Hmmmm. Anybody smell (literally) a liability issue for a marina here?

On the other hand, can anybody name the upstream sensor that doesn't like dirt / crud / oil getting coated on it - and is critical to your engine's proper operation? With carburated engines, you just introduce fogging oil right through the carb throat(s) for a bit and you're done. Do that through a FI motor and guess what gets crudded up over time? Food for through.
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