Marvel Mystery Oil fogging

I suggest you follow the manual.

Really been meaning to start a thread about this very question, not sure what the manual says however have always been told exactly what Brian said, don't fog the intake on EFI.
Recently a very trusted mechanic told me it is not a problem and via intake ensures valves are treated as well. So there lies the question, with EFI is it really bad to fog via the intake and why??

I will add however, just winterized mine last weekend and stuck with my usual EFI procedure, fogged via the spark plug hole using a spray.

I don't agree with your mechanic, the issue is just as simple as sensors don't want to be bathed in an oily mist. Once coated with oil there is nothing to clean them off, no heat, no combustion, no fuel to wash them. And on the issue of getting valves coated, I'm pretty convinced that fogging cylinders and spinning the engine over gets enough oil on valves to take care of them. It's really the mating surfaces that you care about.

Gary S wrote: It can be done,just does not seem worth the effort,but then again I never have had my intake covers off to see how it would be done on the PCM .I just pull the plugs instead. Here's Sea Foams method

Right, so they are just saying to direct the spray to the throttle plate, beyond the MAF sensor to keep it clean. I guess that's an option if someone really really really doesn't want to pull spark plugs.

I do think that sometimes people mistake the fogging purpose. While it's good to coat all metal surfaces, it's really mating surfaces that are critical. Cylinder walls and rings, valve seats and valves, are the critical points. If the inside of the intake manifold stays dry it's not like it's going to rust away on you and cause problems.

63 Skier wrote: Right, so they are just saying to direct the spray to the throttle plate, beyond the MAF sensor to keep it clean. I guess that's an option if someone really really really doesn't want to pull spark plugs. I do think that sometimes people mistake the fogging purpose. While it's good to coat all metal surfaces, it's really mating surfaces that are critical. Cylinder walls and rings, valve seats and valves, are the critical points. If the inside of the intake manifold stays dry it's not like it's going to rust away on you and cause problems.

Yep most marine FI engines run a MAP (Manifold Absolute Pressure) sensor not a MAF airflow sensor. The MAP sensor is in the inlet manifold downstream of throttle plates. I would play safe and just remove plugs like David indicated.

63 Skier wrote: Mark, do you change your fuel filter every year? I haven't been, was wondering what interval GT-40 people are using.

The manual I thinks states annual. I have a extra inline filter between pump and low pressure pump that I change every year, The FCC filter I then replace every 100 hours.