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Author Topic:   In-Line Fuel Filter - additional required for 2008?
Pilot posted 03-02-2008 08:01 AM ET (US)   Profile for Pilot   Send Email to Pilot  
I was planning on adding an in-line fuel filter (Racor) - then I read the owners manual and it said:

"Mercury already provides the appropriate level of filtration to protect the engine from debris. The addition of another in-line filter to the system will create a possible flow restriction that can starve the engine(s) of fuel."

"As a precaution, it is advisable to carry extra on-engine filters in case filter plugging from debris in the fuel tank becomes a problem during boating."

Should I stil add an In-Line filter?


Marlin posted 03-02-2008 08:19 AM ET (US)     Profile for Marlin  Send Email to Marlin     
Richard, my manual says the same thing, yet my 160 Dauntless came from the factory with an additional inline filter. I assume that the manual is referring to the shot-glass-sized filter that's under the cowling of my 115 4-stroke. While it may be adequate "to protect the engine from debris", it would seem wholly inadequate to protect from any significant amount of water in the fuel.

I'd add the additional filter.


glen e posted 03-02-2008 08:32 AM ET (US)     Profile for glen e  Send Email to glen e     
Add [an additional fuel filter external to the engine] if you want, but do it right. [Mercury] has no problem if you add one as long as it does not put additional drag on the fuel flow. See the shop manual for details. If you install [an additional fuel filter incorrectly] and it burns out a fuel pump. [Mercury] will not warranty it. Use 3/8-inch fuel line and keep the elbows to a minimum.
jollyrog305 posted 03-02-2008 09:27 AM ET (US)     Profile for jollyrog305    
I just carry extra filters - they are easy to drain and/or replace if needed. They are not that expensive ($42 each for the 250's) I also treat every other fill-up.
jimh posted 03-02-2008 10:58 AM ET (US)     Profile for jimh  Send Email to jimh     
A large capacity RACOR filter will give you excellent performance. The RACOR is a 10-micron filter. The suction drop across the RACOR is minimal, and it should not be a problem with most engines. You did not mention the horsepower of your engine. The greater the horsepower the more fuel flow, and thus the greater potential for a problem.

As Glen recommends, using 3/8-inch ID fuel hose is a good idea if adding any extra plumbing to a fuel system.

I have a RACOR with the clear bowl. This option is legal for outboard boats, and I think it is a nice feature. You can see what the filter has blocked, and you can also draw off the residue if you suspect anything is amiss.

This article reviews several brands of filters:

Screen Test
by Bill Grannis

Pilot posted 03-02-2008 12:34 PM ET (US)     Profile for Pilot  Send Email to Pilot     
The motor is a 90 HP EFI (current that comes with the 2008 Montauk).

I think I will go ahead with the RACOR. I was also looking at the Clear bowl bottoms as well . . . to be able to see water and drain off.

When you mention to be sure to use 3/8" line . . . I was assuming that's what's used now correct?? I don't have the boat here to look at.


dbrown posted 03-02-2008 02:25 PM ET (US)     Profile for dbrown    
I use the spin-on "oil filter type" fuel/water separating filter on my 90 HP FOURSTROKE and have had no problems. I did use 3/8" fuel line from the tank to the engine...
GreatBayNH posted 03-02-2008 03:47 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
My manual says the same thing. I think it's CYA on Mercury Marine's part.

I'm installing one and these are my reasons why.

a) Boston Whaler dealers have installed additional water seperator/fuel filtration on Montauk 170s with factory 90HP Mecury four cycle EFI engines. Do they know something I don't? I would hope so since I don't know much.

b) If you want to install a fuel flow meter in the future you will need a fuel filter before the fuel flow sensor and the primer bulb.

My 2 cents.


Lars Simonsen posted 03-02-2008 03:55 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
I have a 135 Optimax, and was warned by two different Mercury Master Mechanics that having an inline filter could cause the the fuel pump to fail (due to the increased vacuum). I therefore removed my inline filter. There's a reason the manual says not to use an inline filter, and not heeding the warning could cause an expensive problem for your motor. In my opinion, having two filters is overkill, anyway, so the possibility of damaging an expensive part on my motor isn't worth the risk.
glen e posted 03-02-2008 04:17 PM ET (US)     Profile for glen e  Send Email to glen e     
[The two Master Mercury Mechanics cited above] are wrong. My information comes straight from the VP of corporate service at Mercury. Call them and ask. Here is the email from the VP:

I asked if it was ok; he said:

"The key is 'properly installed. If any engine failure results from the installation of a Racor filter, we will void the warranty. A simple test to confirm if the filter is adding too much restriction is to install a vacuum gauge and measure the fuel system vacuum. The acceptable values for various elevations are listed in the Service Manual."
bigjohn1 posted 03-02-2008 04:43 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Pilot - the existing fuel line on your boat is already 3/8" so there is nothing additional you'll need to buy other than the filter kit itself. You can easily mount it under the RPS on the starboard side directly above where the fuel line comes up from the floor. Its a no-brainer install, 10-15 minutes and you're done. Your engine will run fine with the filter and will not burn up, not to worry.
jimh posted 03-02-2008 04:58 PM ET (US)     Profile for jimh  Send Email to jimh     
The larger RACOR units are rated for 60-gallons-per-hour (GPH) flow. If you have a 90-HP four-cycle motor you probably won't be using more than 6-GPH, so you have more or less a TEN TIMES safety factor.

Maximum flow rate = 60-GPH
Clean pressure drop = 0.6-PSI

Check those specifications against the parameters allowed by your engine manufacturer and your current fuel system vacuum pressure.

By the way, my 1992 (or 16-year-old) old fashioned two-stroke engine has a fuel supply vacuum pressure sensor which signals an alarm if the fuel system vacuum pressure exceeds the tolerance specified. If your 2008 outboard motor manufacturer stand stands ready to void your warranty on this point, don't you think they should have provided you with a sensor and an alarm?

glen e posted 03-02-2008 05:12 PM ET (US)     Profile for glen e  Send Email to glen e     
Jim writes:
"If your 2008 outboard motor manufacturer stand stands ready to void your warranty on this point, don't you think they should have provided you with a sensor and an alarm?"

That's absolutley rediculous. They never said if something fails in the fuel system and you did not mess with it, you would have a problem so they are supposed to put an alarm so when you goof up the addition, it'll tell you about it. Your [anti-Mercury] bias is showing again.

jimh posted 03-02-2008 05:24 PM ET (US)     Profile for jimh  Send Email to jimh     
Glen--It is not a bias against Mercury. I didn't even mention them. It is a bias about poor design. Imagine if you had a car and there was no way to check the oil level, yet the manufacturer was going to void the warranty if your car ran low on oil. Is that a good design?

If an engine has a critical problem with fuel system vacuum, it should monitor the fuel system vacuum and sound an alarm. Why is that different than any other parameter. If an engine overheats it sounds an alarm. It's the same basis.

My motor has a fuel system vacuum sensor located right at the inlet to the fuel pump on the power head. If there is a fuel system problem it sounds an alarm and lights up an indicator lamp. If your engine does not provide that please do not attribute the difference to some sort of preternatural bias on my part for or against a particular brand. I like good design, that's all.

If fuel system vacuum is to be monitored with a pressure gauge, there ought to be one on the initial installation. Now in these cases of a total factory pre-rig you are getting into an area of customer modification. I can see that would be a sticky point in a warranty. But if this fuel pressure vacuum is really a big concern, stick on a sensor and monitor it yourself. You could rig one up for about $100.

glen e posted 03-02-2008 05:39 PM ET (US)     Profile for glen e  Send Email to glen e     
Mercury feels the the system is fine as it comes from the factory, their filter is 2-micron. But then a customer like here wants to add a extra filter. Mercury says "ok, but do it right." Where's the problem? If it blows up because you did not follow their directions and specifications for the fuel system after the install, it's your fault, plain and simple. I see no need for additional indicators and safeguards FROM THEM, because you wanted something they did not supply or think you need.

Putting one on yourself is another matter altogether. And, yes, you did not say "Mercury" but that's who you were talikng about as no other brand has been mentioned in this thread.

glen e posted 03-02-2008 06:03 PM ET (US)     Profile for glen e  Send Email to glen e     
My Verado technicans tell me if the fuel is restricted you will get a lift pump alarm but it will not tell you it's the new filter you added. This would go for OptiMax motors with SmartCraft, too.
jollyrog305 posted 03-02-2008 06:45 PM ET (US)     Profile for jollyrog305    
So why put a 10 micron filter on if the factory supplies a 2 micron? The only reason(s) I see would be the larger capacity, easily check for water (although it not that difficult to access the factory one), or if you wanted to "pre-filter". Am I missing something???
glen e posted 03-02-2008 07:31 PM ET (US)     Profile for glen e  Send Email to glen e     
No, you are not. The 2-micron is a good filter, but if you want another one, Mercury asks you to do it the right way. The only downside of a 2-micron filter is you need to replace it if it gets clogged. That has never happened to me in 2,000 hours of runing OptiMax and Verado motors.
aubv posted 03-02-2008 07:35 PM ET (US)     Profile for aubv  Send Email to aubv     
Let's not forget that Mercury engines also have water sensors for the fuel system SmartCraft gauges.

I had a discussion with the dealer when we bought a 225 Optimax in 2002. I asked that they install a water separator and the answer was, Mercury does not recommend it.

I had the same discussion with the Marina that now does the service on the motor when ethanol was introduced two years ago as many boaters where having problems, including a number or Yamaha motors that burned up fuel pumps as the fuels pumps are fuel cooled and the introduction of ethanol was "cleaning" the inside of fuel tanks and clogging filters. Anyway, the same response not needed nor recommended.


Casco Bay Outrage posted 03-02-2008 07:37 PM ET (US)     Profile for Casco Bay Outrage  Send Email to Casco Bay Outrage     
Glen -

With all due respect, why be such a hard ass? This is a new owner asking a simple question.

Take your pissing contest with Jim to the META forum!

My apologies to you Pilot. Some people just derail conversations and need a good smack. Keep the questions coming.


glen e posted 03-02-2008 07:40 PM ET (US)     Profile for glen e  Send Email to glen e     
I answered the OP's queestion--it's ok to do it.
Lars Simonsen posted 03-02-2008 07:43 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Glen E- I wasn't disputing your post (honestly, I didn't read it until after I finished my post). Proper installation is certainly a valid exception to the "rule." My boat is garaged, and I've never had any appreciable amount of water in my filters when I changed them. Having a second filter just adds another maintenance item to the boat. I'll continue to change the under-cowling filter once a season, or so, and not worry about having to monitor/maintain a second filter. Once I got the advice from two mechanics that I trust 100%, I felt the only wise choice was to listen to their advice and remove the inline filter. My optimax has run flawlessly for several years, and I hope to keep it that way for a couple more years.
jimh posted 03-02-2008 07:49 PM ET (US)     Profile for jimh  Send Email to jimh     
"...if the fuel is restricted you will get a lift pump alarm...

It sounds like the Mercury already has the fuel vacuum sensor or something similar to detect a problem in the fuel system.

With the sophistication and cost of modern outboards, it is surprising that the manufacturers don't have more stringent controls on proper installation in order to certify the engine for warranty. You might recall that a (now out of business) boating magazine blew up one modern engine during a test period, only to reluctantly later admit that there was a problem in the fuel system on the boat they'd rigged it on which was the likely cause of the problem. So rigging is a factor.

But, again, a 60-GPH 10-micron filter properly installed upstream on a 90-HP engine that maybe is going to draw 6-GPH won't be likely to increase the fuel system vacuum more to greater than the specified maximum.

By the way, what is the specified maximum fuel system vacuum on this motor? It seems like we are making a big issue out of a pressure reading which no one has bothered to even specify.

It is typical on larger engines to have a vacuum gauge installed across the fuel filter as a way of measuring how dirty the filter has become. As the filter element blocks out more contaminants, the suction pressure across the filter increases. That's how you know when it is time to change the filter.

glen e posted 03-02-2008 08:30 PM ET (US)     Profile for glen e  Send Email to glen e     
Lars - I understand and I'm sure you will have no problems whatsoever....I have run 8 merc outboards (2 sets of optis and 2 verados) and never had any filters upstream of the engine filter. Many techs are just old school and especailly some of the master guys, they get so full of knowledge that stop checking for changes in philosophy or procedure as they been at it a long time.

This "OK to add a filter" is relatively recent change for Merc - as was explained to us in the june 06 tech session we had with the verado powerhead designers in Bimini. Up until then they had said "no" so that's where many techs got it from. But with the advent of many triple engone boats in SKA and tourney guys that went thru a lot of gas, they rethought it and said "OK, do it right". What they really want is a fuel pump in the tank (like many cars)pushing gas instead of their engine having to suck it uphill in many cases, but that requires a total mfr agreement which they cannot get.

So there are still many out there that think it's verboten but they are not up to date. Any customer can call merc at 920-929-5000 and ask, They will tell you they'd rather not have you do it as the 2 mic filter is enuf and safe, but if you press them - like my email from merc above, they will tell you it's ok as long as you do it right. Virtually every boatbilder in S fla that I know installs racors with verados when they build them.

GreatBayNH posted 03-06-2008 05:24 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
Again, if you want to install a fuel flow sensor you'll need a filter before the sensor but before the primer bulb(engine). That may be a can o' worms as well with Merc. I'm installing a fuel flow sensor so I'm forced to install a filter before it. I'm going with OEM Mercury water seperator/fuel filter just to keep on the up and up.

GreatBayNH posted 03-06-2008 05:43 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
I really should have just said "you'll need a filter before the sensor" period. My bad.
Liteamorn posted 03-06-2008 07:50 PM ET (US)     Profile for Liteamorn  Send Email to Liteamorn     
My 150 hp Optimax (2005) already has a water separating spin on fuel filter mounted on the engine, it is wired to an alarm if it detects water. My manual also warns about adding filters. I think a second water separating filter is overkill so I'm leaving mine as is.
lakeman posted 03-08-2008 07:59 AM ET (US)     Profile for lakeman  Send Email to lakeman     
With the introduction of ethanol in my local gas chain, I was wondering what to do about it, potential water in my tank. The boat and it's opti 135 does not get used enough now days to use or replace 60 gallons of gas on a regular basis.
I know the regular filter may have been very good in the pre ethanol days but now I'm looking at alternatives. I wonder if anyone knows about a system like racor that just separates the water with out the filtration.
jimh posted 03-08-2008 03:14 PM ET (US)     Profile for jimh  Send Email to jimh     
I am a curious person, so you must indulge me and explain how fuel from a boat's tank containing an agitated mixture of gasoline and water could be separated without using a filtration process.
lakeman posted 03-09-2008 01:59 PM ET (US)     Profile for lakeman  Send Email to lakeman     
I thought that the filter was for filtering out dirt and other stuff not good for the carbs or dfi injectors. Water which is in the gas tank would fall out into a catch basin as it passed through a filter like housing ie: Racor filter. I also assume that the filter would be the real culprit in restricting fuel flow and as it got dirty. I also doubt that the filter catches the water and as it passes through the filter and since water is heaver than gas or in my case no filter it would fall out into a sump of some kind.
Dam, I hope that makes since in a 2 minute reply.
GreatBayNH posted 03-09-2008 06:29 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
I am a curious person, so you must indulge me and explain what dfi injectors are.
sosmerc posted 03-09-2008 08:57 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
Guess I might as well chime in with my .02 worth. I am well aware of Merc's recommendation to not add additional filters in the boat in order to reduce the possiblity of added restrictions.
however, IF PROPERLY INSTALLED, I see no problem with a quality water seperator/filter such as the RACOR 320R. I put one in my 18 Ventura and have had a number of years of trouble-free use with my 1998 Optimax 135.
The Optimax engines DO NOT have any kind of sensor to detect "restriction" nor do they have any sensor for detecting whether or not the engine is developing sufficient fuel pressure. So YES, it is important to use 3/8's line and fittings etc. I like the ability to get a quick check of the fuel quality by simply opening the tap at the base of the filter. I do not depend upon "appearance" through the site bowl though, because if the bowl were completely full of water you might not be able to tell whether it was fuel or water from just looking.
With Verados you DO NOT have a fuel primer this can present some issues when changing a filter when it comes to "priming" the system. I would sugguest filling the filter with fuel before re-installing...and then you may still have to fill the engine mounted filter as well to give the lift pump on the engine a chance to get things going.
I also have a FloScan in my boat and any sudden changes in fuel flow can indicate either restrictions or leaks. My older Optimax is not SmartCraft compatible so the FloScan was the only way to get this data. I look forward to the day when I will have a SmartCraft engine on the boat so that I can compare the FloScan to the fuel flow info provided by the engine itself.
Feejer posted 03-10-2008 05:56 AM ET (US)     Profile for Feejer  Send Email to Feejer     
My local BW dealer sends ALL's of their new boats out with a fuel / water separator on. They have been doing this for many years and have never had a fuel flow problem.
lakeman posted 03-10-2008 10:50 AM ET (US)     Profile for lakeman  Send Email to lakeman     
Many newer engines Optimax(dfi engines) etc use injectors to put the fuel in the combustion chamber. Now I'm not a willing to pay to go to Mercury's school of mechanics so I cannot qualify so to go beyond that, I'm a loser a knowledge of modern engines.
All I really would like to do is, possibly find just a water separator, the filter on my optimax is fine for most issues but with using ethanol fuel which may add more water to the gas tank, I would like to have a water separator that I could visally check now and again.
GreatBayNH posted 03-11-2008 07:24 PM ET (US)     Profile for GreatBayNH  Send Email to GreatBayNH     
No need to go into further detail. Direct Fuel Injection is all I needed to know.
Speedo66 posted 03-20-2008 10:45 AM ET (US)     Profile for Speedo66  Send Email to Speedo66     
My owners manual from a Mercury 2004 60HP Bigfoot on a BW 150 Sport recommended installing a fuel-water filter, which I did.

This is an injected engine and I've had no problems. The engine came with 3 separate fuel filters in the engine from the factory.

I origonally installed a Sierra head unit, but changed to Racor spin on filters, model 5510 10 micron, when I discovered they would fit. Cheap way to get into Racors at $9.50 a pop.


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