Fuel problem ?

[GeoffV]

A week ago my engine started to play up -running rough and losing full revs. (D1-30F)

Today, it was the same when running so I decided to change the fuel filters as they were due anyway to be done this month.

The primary is a Racor 500fg copy. Starting the process by draining the glass bowl and it was real slow to come out. The colour was light brown and not the usual pale straw colour (I use white road diesel) and it was slow to move around the catch vessel. It was very clear no contamination but much less viscosity than I have ever seen before. Clearly, this is affecting the running of the engine and I have 75 litres of this in the tank.

At temps around 3 to 4 degrees this morning I would not expect it to be waxing so, any ideas?

[tiger79]

It was very clear no contamination but much less viscosity than I have ever seen before.

Did you mean "much more viscosity"?

[Yngmar]

If it was 3-4°C in the morning, it probably was colder in the night, meaning the fuel in the tank, which has significant thermal mass would still be colder than ambient temperature.

Here's some photos so you can compare what it looks like when diesel starts to crystallize: https://dozr.com/blog/diesel-gelling

If the fuel in the tank has turned to gel, the lift pump will not be able to move it, and fuel won't flow from tank through filters into engine, creating a vacuum, which could result in the engine hunting for fuel and running as you describe. You can easily rule this out by pulling the hose off your Facor (engine side) and sticking it into a small can of pre-warmed (room temperature), clean diesel. It'll empty fast with the return line not going in the can too, but you'll probably find the engine runs fine from that.

Winter diesel sold in cold climate areas has additives to lower the point at which the diesel gets goopy. You can probably also find additive to pour into your existing fuel store.

[diverphil]

it does sound like fuel starvation or contaminated fuel, but as you use white derv from garage then it shouldn't be waxing up, road derv has had additive for winter in it all year, they don't change the mix anymore and haven't for many years over here (uk). also, the return to the tank is a lot more than the fuel used by the engine and would warm the fuel in the tank. it's been many years since I've had to go out to a truck with waxed fuel filters.
hope you find whats got into it
phil

[marioxp]

Partially blocked exhaust, maybe?

[GeoffV]

I am on the south coast of England so certainly didn't expect gelling but definitely have higher viscosity in the diesel out of the Racor and slightly darker colour. Filter looks clean after 1 year.

Thanks for all the replies.

Water egress from the exhaust is the same as ever but have planned to check the exhaust elbow in January after 6 years of use. However, I do run the engine at over 2000rpm nearly all the time apart from leaving the berth bit and return in the marina.

Have just found this on the Marine 16 website as I use their diesel fuel complete:

Modern diesel is highly unstable, it’s been refined to within an inch of it’s life to remove the sulphur and now it has 7% plant oil along with animal and cooking fats. It degrades very quickly producing sludge that ends upon the bottom of your tank. The stability improver and antioxidant we blend into Marine 16 Diesel Fuel Complete (DFC) helps slow some of the degradation, but it cannot be fully prevented or reversed, would you get a blackened banana in the fruit bowl and try and recover it? No? you can’t, it’s same with diesel, it just doesn’t go as black.

This is something I need to check this weekend drawing a sample from the bottom of tank.

[tiger79]

This is something I need to check this weekend drawing a sample from the bottom of tank.

That's a good idea.  My boat is marina-based and stays in the water all winter.  In the new year, after the boat has been stationary for a few months, I suck about a litre of fuel from the bottom of the tank into a clear plastic water bottle, then let it settle for 24 hours.  It's a good way of checking for fuel bug, etc.  I use Marine 16 too, and haven't had any problems yet.

[Salty]

Last Saturday I met up with a friend onboard his boat in Beaumaris North Wales where it has been ashore now for the winter since early in September. He had been onboard since the previous morning and had stayed onboard overnight to Saturday. When I arrived he said that he had not been able to get his diesel heater running. At first he had suspected that having separated part of the fuel supply line to the heater, that the line needed to be refilled. We took a few minutes to do that, and then operated the start control for the heater. It ran for a short while during which time the fan had started to increase speed, and then it shut down. It did this several times over a period of more than an hour, re-setting itself each time before eventually running up and continuing to run through until we decided that the heater was now running fine. After leaving I continued to think about why the heater had initially been reluctant to run for more than a few seconds at a time, but had noticed that run times on each occasion had been marginally longer each time the heater had fired up. At the time, It hadn’t crossed our minds that that the problem might have been down to fuel temperature, but outside temperatures overnight had been below freezing that night and for several days prior to the weekend. With the boat being out of the water since early September, the fuel within the diesel tank would have been exposed to much lower temperatures than a boat left in the water such that I had started to wonder if fuel temperature was the reason. Each time that the heater had fired up, it had added a little heat into the boat, and no doubt also to the temperature of the fuel within the fuel tank.  Yngmar’s posted website reference I think has confirmed that fuel temperature most likely was the problem. Thanks Yngmar.