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 "Fogging" a 1999 MerCruiser MPI
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RO# 2904

Posted - Oct 07 2020 :  12:24:14  Show Profile  Reply with Quote
My last boat was carbureted, so it was easy to spray fogging oil into the carb when winterizing.

I now have a 1999 MPI engine so I know I can't do that. I've seen articles talking about using a separate tank of gas with an oil mix in it.

What do you good folks suggest?

Bill W.
1999 Formula 260ss - "Bare Necessity 2"

Homeport: Ripley, OH


RO# 5015

Posted - Oct 07 2020 :  14:12:32  Show Profile  Reply with Quote
I am in same boat going from a carb engine to a MPI.

Yes they talk about a separate small gas tank with a mix of gas, TCW-3 oil and gas stabilizer.

But your engine still sucks in air, not sure why you cannot spray in fogging oil there.

Or pull plugs and spray in fogging oil there.

I will probably just get stabilizer into the gas tank and call it a day.

Unsure how much emissions stuff is on your engine but that may be a consideration for not using fogging oil down the air intake.

Homeport: Hyde Park, NY Go to Top of Page


RO# 2124

Posted - Oct 07 2020 :  14:28:43  Show Profile  Reply with Quote
Since I have my MPI engine, I do not fog, I am worried about clogging the injectors.
If it's important to you, pull the plugs, spray the cylinders and turn the engine to coat the full range of the cylinder.
OR, you can winterize as late as possible and fire it up as early as possible to minimize the time the engine has sat.

I wonder what others will say about this.

Favorite Quote: Don't sweat the petty things...AND...Don't pet the sweaty things!! - Steven Tyler

Homeport: Hudson River Go to Top of Page


RO# 5508

Posted - Oct 07 2020 :  14:30:11  Show Profile  Reply with Quote
You donít really need a tank. If I recall, you can fill the water separating fuel filter up with the mixture described above, shut off ( or disconnect ) the main fuel line, and run the motor from the cocktail in the filter., With the computer in charge, I donít believe you can stall it out like you do with a mixture ( or spray). I canít remember if I read about this method in a service manual, or in a gvp post on boatfix but thatís how I used to do it.

After a year or two, I decided it was not worth the effort. Instead, after changing the oil, I run the motor for a few seconds to coat everything with fresh oil, and call it a season. Hopefully this decision hasnít shortened my motors lifespan.

Edited by - alk on Oct 07 2020 14:40:45

Homeport: PA Go to Top of Page


RO# 27559

Posted - Oct 07 2020 :  16:59:47  Show Profile  Reply with Quote
I do it every year. I use a separate outboard fuel tank and made the end fit to my fuel shut offs. you mix. 2.5 gallons of gas with 32 Oz of 2 stroke oil and 2.5 oz. of fuel stabilizer. Run it for 10 min. I have inboards so I Run like 5 gallons of Pink Anti freeze at the end into strainer then shut it down.

Homeport: Hauppauge,New york Go to Top of Page


RO# 1159

Posted - Oct 07 2020 :  18:29:52  Show Profile  Reply with Quote
Walshie - If you are referring to actual spray fogging , that probably would not affect the injectors since they are fed fuel separately from the air supply.
But I believe fogging an MPI engine is not recommended due to need to keep the various sensors clean as possible.

Bones's system using TCW3 & stabilizer sounds safe as the TCW3 will be more easily washed off with gas than the sticky fogging spray we used on carb engines.

Stabilizing the fuel in the tank and running it through the system on the last ride,- yes,definitely . Don't just dump stabilizer in an already stored boat tank as it won't mix very well, though agitating it in a portable tank of gas then pouring it in will help.. And I am a big believer with E10 especially it is important to have that added to the gas when it is most fresh when 1st pumped in and not potentially deteriorated. That's why I most always pump in stabilized Valv-Tect marine gas, then add a little extra Valv-tect( just because I don't like to mix stabilizer additives) at last fill before winter layup.


Homeport: The Vineyard Go to Top of Page


RO# 10314

Posted - Oct 09 2020 :  14:00:46  Show Profile  Reply with Quote
The question of whether to fog or not, I think depends on your storage conditions. If the boat is stored outside in a damp climate like here in Long Island fogging is definitely advised, but if you are storing in a dry climate the chance of condensation on intake and exhaust valves is less. If the boat is stored inside in a dry building same thing.
If I open the cover up during a span of cool damp weather the whole engine is wet with condensation. Very common on fall/spring days when the day is a bit humid and then temps drop at night and moisture condenses on all the cold cast iron.

1988 Four Winns 200 Horizon 4.3 OMC Cobra
1998 Jeep Grand Cherokee 4.0 Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi Quadradrive II

Homeport: Long Island NY Go to Top of Page


RO# 3002

Posted - Oct 11 2020 :  10:23:12  Show Profile  Reply with Quote
There is Merc service bulletin #2001-15 which is "New Gasoline EFI/MPI Engine Fogging Procedure".

The bulletin indicates that it is for all Merc EFI/MPI engines produced in Stillwater and NOT carbureted or high performance engines.

The fogging mixture is 5 gal. regular unleaded 87 (90 RON) gasoline,
64 oz. of Merc/Quicksilver Premium Plus 2 cycle TCW3 Outboard oil
5 oz. of Merc/Quicksilver Fuel System Treatment & Stabilizer (or 1 oz. of Merc/Quicksilver Fuel System Treatment & Stabilizer CONCENTRATE)

Procedure: Disconnect & plug boats fuel line from the water separating filter inlet.
Connect remote fuel tank to the inlet of the water separating filter inlet.

IMPROTANT: Make sure you have adequate water source to run the engine if the boat is not in the water.

Cool Fuel model engines: Start & run the engine at 1300 RPM's for 5 minutes.
VST engine models: Start & run engine at 1300 RPM's for 10 minutes.

After specified running time is complete, slowly return the engine RPM's to idle & shut off the engine.

For my 8.1L Merc engine, I modified the procedure and mixed a proportionally smaller quantity of the fogging mixture ingredients in a 1 gallon gas can. (1/2 gal gas, 6.4 oz. TCW3 oil, 0.5 oz. fuel system treatment). Prior to performing the fogging procedure, I have added fuel stabilizer to the fuel in the boats gas tank. Spin off the currently installed water separating fuel filter and dumped the gas out. Fill the water separating fuel filter with the fogging mixture & reinstall. Run the engine for 5 minutes at 1300 RPM's. Shut off the engine. Remove the water separating fuel filter, throw it away, fill a NEW water separating fuel filter with the fogging mixture and install the new filter. Run the engine for 5 minutes and shut off.

Any remaining fogging mixture in the 1 gallon gas can is put in the lawn mowers, chain saws & weed eaters.

Homeport: Lake Anna, VA Go to Top of Page


RO# 2904

Posted - Oct 12 2020 :  12:16:28  Show Profile  Reply with Quote
Thank you all for your input.

I just finished winterizing mine and decided this year to not worry about fogging. I was thinking about pulling the plugs and spraying directly into the cylinder but haven't decided yet.

I'm one of those that fills the fuel tank (I know there's different thoughts on this) so I add stabilizer first and then filled the tank. I then warmed the engine and changed the oil, warmed it again to make sure the thermostat is open and removed the drain plugs on the engine to get out as much water as possible and then ran 4 gallons of the pink stuff through the engine.

Bill W.
1999 Formula 260ss - "Bare Necessity 2"

Homeport: Ripley, OH Go to Top of Page


RO# 5508

Posted - Oct 12 2020 :  16:01:29  Show Profile  Reply with Quote
Fill the fuel tank? Now youíve done it - (:

I used to fill my tank to the top in the Fall; then came ethanol. Now I do everything I can, including running the risk of running out of gas on my last trip, and siphoning from the tank, to have it bone dry before layup. Like you said, there are different thoughts on this - and probably no right answer.

Assuming you have an outdrive, you changed that fluid, right? And have the drive positioned so as it isnít holding or will not take on any water? My only winterizing fail was a cracked outdrive case. Still not really sure how it happened - but it had a crack with a leak in the spring.

Homeport: PA Go to Top of Page


RO# 2904

Posted - Oct 14 2020 :  13:35:20  Show Profile  Reply with Quote
Yep, the gear lube is changed and I always store it in a down position to avoid leaving the bellows stretched. I'm fortunate to have the boat stored in my pole barn so I don't have to worry about water.

Bill W.
1999 Formula 260ss - "Bare Necessity 2"

Edited by - BillWilliams on Oct 14 2020 13:36:05

Homeport: Ripley, OH Go to Top of Page
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