Diesel fuel additive

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Oct 3, 2005
112
Catalina 30 Downtown//Shoreline Marina, Long Beach
What additive do you recommend for an M25 diesel and how much per fill?
Thanks.
 
Jan 6, 2010
1,520
AA,
I recommend...........NONE. Over time microbes which live in diesel fuel mate, breed and party in you fuel over time. Add condensation in your tank and they are happy buggers.

If you use an additive, some types can actually kill these bugs. The problem is that they die & settle to the bottom of your fuel tank. This is the grey sludge you may see on your pick up tube screen. This can clog the flow at the worst possible time(especially during high throttle) at your filters & screen clogging can cause your engine to quit.

There are several schools of thought on this. You can find pros & cons for additives. My suggestion after research would be to clean you tank first if your having problems, especially if your fuel sits at half tank or lower for extended times. Hopefully have a primary 10 micron filter & secondary 2 micron filter.

I had these problems with clogging and after doing a thorough cleaning, I looked for a gas station that had good filtered fuel. My exxon station has fuel the color of water almost aviation fuel grade. Also i use my boat but keep the fuel around 3/4's full.

Another method people swear by is buying an in-line magnet piece found on the internet. The claims are it doesn't kill the microbes, but makes them sterile and they don't reproduce. Because your system constantly recirculates your fuel from tank to engine back to tank, back to engine, the bugs over time will be burned in your cylinders, not die & settle to the bottom as sludge.

I'm sure some folks will disagree with me but since doing the above on my boat, I no longer have any problems.

Hope this helps,
CR
 
Aug 25, 2010
62
Catalina 30 Seabrook, TX
Are you experiencing engine problems? Why do you think you need an additive? I have the same motor in my 1984 C-30,(original motor) and with regular service and occasional cleaning of the injectors (min. expense) my motor works great.
 
Feb 26, 2004
23,101
Catalina 34 224 Maple Bay, BC, Canada
This is the grey sludge you may see on your pick up tube screen. This can clog the flow at the worst possible time(especially during high throttle) at your filters & screen clogging can cause your engine to quit.

Take that screen out if you have one. Catalina stopped putting them in about the early 90s because of just this problem.

http://c34.org/bbs/index.php/topic,5078.0.html has helpful hints for the M25 engines.
 
Oct 3, 2005
112
Catalina 30 Downtown//Shoreline Marina, Long Beach
No problem...yet! Engine's only two years old. I'm just fishing for useful info since this M25 is my first inboard diesel; been an outboard dude up until now.
 

Tom J

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Sep 30, 2008
2,325
Catalina 310 Quincy, MA
I suggest using a good biocide occassionally to kill all those bugs that live in diesel fuel. Yes, they fall to the bottom of the tank, but otherwise, they reproduce and clog everything in sight!
Yes, try to keep the tank as full as possible. As far as the performance additives goes, the best thing you can do for your diesel is to run it at full throttle once in a while for 5 minutes or so.
 
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