I had a similar issue. Unfortunately, I do not have a good suggestion, just a story about how it worked out for me.
My
trawler carries 400 gallons and the
Perkins 4.236 85hp burns under 1-1/2 gph. I've had her for almost 25-years and last time I filled up was about 20-years ago - she's been sitting for years as a pied a Terre in SF. We aew getting ready to retire and
cruise her, so it's time for a sorely needed
refit. Last year, I decided to bring her from SF to Ensenda for a total
refit which is underway.
I had about 150-200 gallons of roughly 20-year old
fuel aboard. I can tell you diesel definitely has a shelf life - one side smelled more like linseed
oil than diesel. I've used the same
mechanic for well over 20-years and trust him. He strongly advised disposing of the
fuel....... until he found out the
price, which would have been at least $4000. I needed about 120 gallons to make the 500 nms run to Ensenada and part of the refit was planned to
repair or replace the fuel
tanks, so didn't want excess fuel aboard.
We decided to triple dose with Stanadyne (find it at Diamond Diesel in Oakland) which was also recommended by a friend who works for Deere
Marine Propulsion. My understanding is its a fuel conditioner that helps keep asphaltines from precipitating out. I also added 80-gallons of fresh diesel.
I did about 20-hours of local sea trials and the
engine ran fine so made the decision to just go for it. Ran about 75
engine hours straight through to Ensenada. The pressure on racors came up a bit and the clear bowls were dark as night from old tarnished fuel. I ran mostly on the tank that didn't smell as bad though.
I ended up replacing both fuel
tanks so tried to unload the old fuel - 250 gallons, or over $1000 worth of fuel. Tried giving it away to the local
fishing fleet. When they saw the fuel in a Mason jar, even they wouldn't take it. But my old
Perkins ran fine with it. Doubt a newer Tier 3 (common rail) engine would.