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I have a Conquest 23 with twin Merc 135 Optimax's. I bought the boat a year ago and am doing the yearly service. I can find no fuel filters between the fuel tank and the motors, tho the motors have internal replaceable spin-on fuel filter canisters. My local Merc dealer says I need external filters. The boat is almost 10 years old and seems to be functioning fine without them. The Conquest has little room to install them, all the fuel lines are under small hatches in the engine well. Do I need to install external filters? Are the Optimax filters enough?

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You can get these type. You cut the hose and insert them with a clamp on each end. They are made by Sierra or Mallory. You need to know your hose size. They are plastic or others have a glass where you see the filter inside. The glass ones can be cleaned or the filter replaced. Easy to install, do not take up much room and I have 2 on my boat in the fuel hose.

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Rusty -

Many boaters in the States use a fuel/water separator in addition to the fuel filter under the engine cover. With the introduction of blended fuel; 90% gas, 10% ethanol, the need for this filter is increased.

A typical filter with bracket looks like this:
[img]http://www.go2marine.com/go2_structure/8/5/4/4/85448F-f.jpg[/img]

There is one version that adds a clear bowl and drain below the filter that looks like this:
[img]http://www.starmarinedepot.com/smd/images/prodimages/racor/pr1415_L.jpg[/img]

The key is to get a filter that has a 10 micron cartridge.

I found another Conquest 23 owner (bmotril) and he has a photo on his webpage. I think his boat is a 2000.

Here is his page, scroll down 2 or 3 screens and see the photo of his compartment. Hope this helps.
Bill's Conquest 23 page

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You need filters like the one listed above. One for each motor.

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I guess my question was more of an Optimax one, do they need external filters or are the internal ones sufficient if you change them yearly. One filter was pretty rusted on the inside, so perhaps that answers the question. The boat was imported from Florida to Western Australia by a Bogan (classless Aussie idiot) a few years ago and who knows the last time the filters were changed. (I'm an American living out here: good ocean, wide open spaces, strange culture).

Looking at Biil23's photos is helpful, but it looks like his external filters are screwed into his fresh water tank. It's convenient but I don't like the idea of drilling holes into a tank. I can install one filter on the starboard side of that compartment, but the resevoir for the trim tabs is on the port side and leaves no room. I'm looking at mounting them on the inside of the transom under the round hatches, but there's little room to work, and it'll be hard to remove the filters for replacement.

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My Optimax is run with a Racor Fuel/Water filter. With the ethanol in the gas my bowl does gather water, better there than in the engines filter which is a pain in the a.. to change on the water. I experienced water in the engines filter last season the engine alarms and goes to idle,thereafter an oil filter wrench and extra filter is kept onboard although if inverted the filter will drain and work.

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Rusty -

I would advise installing filters given the potential costs for not installing them. In my book, all filters are on my annual maintenance list.

Do you use the boat year round? While I familiar with Sydney weather (sister lives there) not sure of Perth.

What is the marine fuel quality like? Do the fuel dock pumps have filtering systems?

One "idea" is to install a long piece of "starboard" like material to the location you cite with a good adhesive and then screw the filters into the starboard. This way there are no holes in that water tank wall area.

The filter should be installed to hand tightness so a wrench should not be necessary. :o

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Phil, As you suggested I was thinking about mounting a dummy bulkhead infront of the water tank and screwing the filters into that, or make a 90 degree L bracket of aluminum and bolting it to the underside of the deck.

The fuel here is a lot better than in the US, regular unleaded is 92, premium is 98, and they haven't added ethanol...yet. I remember how ethanol in the gas messed up my 2 stroke Bultaco dirt bike back in California, it made gum in the carby. I keep the boat on a trailer and don't fill on the water. The down side is gas here (called petrol) is A$1.45/ litre, or about U$6 a gallon. The Conquest has a 100 gallon tank...ouch. However I've determined my 2 Opti 135's on the 23-footer get about the same mileage as the single old-style throttle-bodied Merc on my previous boat, a 19' Haines Signature.

I don't use the boat much in winter, but the summers here are 6 months long, Nov thru April. In winter I store with the fuel tank full and add Mercury fuel stabilizer.

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Don`t know why you would need one filter for each motor. Their are two exit ports on each filter. There are two inlet ports on each filter. Simply plug one inlet port with the supplied plug, and run the hose from the tank to the filter housing, and run two hoses off the two exit ports, one two each motor, with a priming bulb to each motor. Buy a stainless housing, about $40, it won`t corrode like the aluminum ones.

rich

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I wonder if the single filter can handle the flow rate of 2 engines at full throttle. If I'm installing one I might as well install 2, that way if one plugs up I can still get home on the other engine. If you're gonna go to all the expense and hassle to run two engines you might as well have all the redundancy you can afford. Good idea about the stainless fittings, I'll see if I can get them here in Oz, otherwise I'll have to mail order from West Marine.

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One filter can certainly feed two engines. I used one filter to feed two thirsty inline 6 cylinder Mercurys with never any problems, and I used to run them wide open often. If one plugs, the other will too, as they are both fed from the same tank. BTW if a filter plugs, becuase of water, simply unscrew the filter, dump it overboard, re screw it on, and away you go. I have done this. If a filter plugs becuase of sediment, you have left it on way too long, and you will be forewarned, by the engine coughing at high speed, but will run at low speed. If you have two identical # of gallon fuel tanks, you can run two complete separate fuel systems , one to each engine, but I`ve never seen this done. If you didn`t moniter the fuel amount perfectly, you could be in trouble and in danger of running one tank dry, and only being able to run one engine.

rich

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OK, I'll give it a go.

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Rusty, Obviously the fittings should all be stainless, but You can also buy the filter housing in stainless, not that uncommon. I`m sure you can find one Downunder.
rich

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I was told by a Mercury engineer that their Water Separating Fuel filter can handle a maximum fuel flow of 60 GPH. That should be enough for most twin engine conditions. I assume all of the Mercury knock-off filters would be similar.

I have also heard that Opti's should not be run with an external fuel filter, which is probably why BW did not install one in the factory rigging. Combined with the filter on the engine, they can create too much resitriction in fuel flow. Check with Mercury, as your dealer may not be correct, or conversely, maybe the thinking has changed.

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Interesting everone's take on things. I emailed Mercury and will post their answer. Thanks everyone.

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Thank you for the recent inquiry regarding your 1999 Mercury 135hp Optimax engine, serial number 0G871213. We appreciate the opportunity to respond to your question.

The water separating fuel filters that are on the engine are sufficient. However, you are able to add an inline filter if you choose. You just need to make sure that you do not create a fuel restriction that will cause poor running conditions.

We hope this information was helpful. Should you have any other questions or concerns, feel free to contact our office at 920-929-5040 between the hours of 7:30am and 4:30pm, Monday though Friday, CST.

Sincerely,

Mercury Outboard Customer Service


So I guess I'll just keep her the way she is, if it aint broke, don't fix it.

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Rusty -

I have read the above advice on Opti's before. Concerning Verado motors, Mercury does not recommend additional filters. It affects the fuel lift pump.

If you forgo the water separator filter, I would add a fuel treatment with each fill up to help with condensation. In the US, one example is Stabil Website I am not sure what products are available down under.

Love the photo on your page, post MORE !! Winter is coming here! :o