Fuel filters

[Thats Good]

I bought a used 200 merc efi i need to get a owners manual dont have one yet anyways i have an external fuel filter water separator and i know theres one inside on front side of engine, so do i need the external one or is the one on the engine sufficent, also how often do you change it or is there a way to know when it needs to be replaced thanks in advance

[jethro1]

You may get some varying answers on this subject. I have a 175 EFI with an engine mounted fuel filter but also have a Racor boat mounted filter. That is the way the boat came from the factory but I am glad it has the Racor. The Racor filter has more capacity and is also cheaper than the Merc engine mounted filter. Additionally, it lets you see if there is any water in the water separating chamber which the engine mounted filter does not have.

I installed a vacuum gauge just downstream fromt the Racor filter. As the filter loads up with debris the vacuum will increase. Once it gets to 7 or 8 inches of mercury (the metal not the manufacturer) I change the Racor. Some change them yearly but I don't change mine anywhere nearly that often since the gauge tells me I don't need to.

[76GMC1500]

The filter in the engine is only for particles, the Racor filters remove some water. I would strongly suggest having water seperating filters in any boat and have them mounted low in the boat where the water will collect.

[Mumblerone]

RACOR - Marine Gasoline

[seahorse]

jethro1 - 4/5/2006 11:17 PM

I installed a vacuum gauge just downstream fromt the Racor filter. As the filter loads up with debris the vacuum will increase. Once it gets to 7 or 8 inches of mercury (the metal not the manufacturer) I change the Racor.

Jethro1,

You may want to change the filter a bit more often. Both Yamaha and Johnson-Evinrude state that there should never be more than 6" or 4" of mercury vacuum in any of their respective fuel systems. I believe Merc says never more than 3-4" of vacuum.

[jethro1]

Seahorse, thanks for the info. I have never seen any advice from an engine maker on this subject. The Merc service manual that I have for my particular motor does not say squat, other than to address anti-siphon valves being a protential problem. I got my initial guidance from Racor literature, but it was just that, initial and general guidance.

Even pulling 8 inches of mercury, the output of the diaphram pump is to spec but I could see where if the vacuum gets high and the pump gets weak there might be a fuel flow problem. I respect and trust your advice. Based on that I will adjust my fuel filter change schedule to a more frequent basis.

[seahorse]

Some years back there was a fuel filter test in Trailer Boats, I think. If I can find a back issue, they stated the manufacture's fuel vacuum recommendations.

Also, in a higher vacuum situation during the summer heat, the fuel will boil at a lot lower temperature and cause vaporlocking and other drivability problems. Now with the Ethanol being added to gasoline, that alcohol boils at a lower temp than gas and can add aggrevation to the situation.