What micron Diesel Fuel Filters should I use?
One question that comes up all the time is what micron size of marine diesel engine fuel filters should I use? The short answer is almost always use a 10 or a 30 micron fuel filter for marine diesel engines. Most diesel engines can run on a 10 micron fuel filter. But many can not run on a 30 micron fuel filter. These are the two most common micron filter sizes used, a 10 micron, and a 30 micron.Why do some Diesel Engines use a 10, and others use a 30 micron filter?
More and more diesel engines are using what is called a common rail fuel delivery system. This fuel delivery system is delivered by a high pressure fuel pump. This fuel pump pressurizes the fuel to over 1,500 psi. The fuel travels into a pipe the length of the engine cylinders. This pipe has the largest diameter in the fuel system. This large pipe then has smaller feeder pipes coming off of it to feed each solenoid valve in a form of direct injection.Common Rail Diesel Engines
The large pipe in this system is called the common rail, as all solenoid valves are feed by this single pipe that has smaller pipes coming off of it. This is why it is called a common rail system. Since the fuel is being fed at high pressure to a smaller solenoid valve the fuel needs to be filtered better than a low pressure diesel engine which is sending fuel through a fuel injector or pump nozzles. If a fuel filter micron size is too big the fuel system can clog.When do you use 10 micron diesel fuel filters?
You use 10 micron diesel fuel filters on a common rail diesel engine. These engines always use a 10 micron fuel filter. And if ever in doubt always consult your owners manual for the engine you are replacing the fuel filters on. If you use a micron filter with a higher number than 10 on a common rail diesel engine you run the risk of causing the fuel to get clogged while going into the solenoid valve. At such a high pressure the opening is smaller which means clogs are easier to occur. Parker Racor 10 micron fuel filters will have blue lettering for quick identification. See the picture below.
When do you use 30 micron diesel fuel filters?
If your diesel engine runs off of a low pressure pump which feeds injectors or pump nozzels you can use a 30 micron fuel filter as the opening into the injectors is larger. Being larger it is then fed by lower pressure. This allows less filtration to be needed. Now low pressure engines with injectors can use a 10 micron filter but a 30 is better so that you do not strain the low pressure fuel pump. Low pressure fueled diesel engines are far more forgiving. They are also usually smaller engines without as much demand for high output. Such as inboard diesel engines on small sailboats. Or on small to medium sized diesel generators. Parker Racor 30 micron diesel fuel filters have red lettering on top for quick identification.
Cummins Onan 11.5 MDK Diesel Engine Generator
A very common low pressure fueled diesel engine is the Cummins Onan 11.5 MDK BM-4564F these diesel generators are installed on a myriad of boats throughout the world. They are reliable compact, and relatively easy to work on. These diesel engines take 30 micron fuel filters as they are fed by low pressure fuel pumps that send fuel to the unit injectors. These diesel engines generally use Racor Model 500MA diesel fuel filter/water separators. And the replacement fuel filters are replacement element 2010 Series in 30 micron. The gallery below shows the racor fuel filter / water separator housing stickers. Along with the fuel filters used in these housings in 30 micron. 30 micron fuel filters will have red lettering, while 10 micron will have blue lettering on top.
Cummins QSC 550 is a common rail diesel engine
An example of a common rail marine diesel engine is the Cummins QSC 550. These engines are very popular in many inboard diesel engine boats 40 to 50 feet. Since they are common rail diesel engines they use 10 micron fuel filters. These fuel filters are usually used on these engines in a Racor Model 75900MAX Diesel Fuel Filter/Water Separator which uses replacement element 2040 series diesel engine fuel filters. Below is a gallery showing the stickers on the racor fuel / water filter separators.
Racor Model 75900MAX Diesel Fuel Filter/Water Separator
With a Racor Model 75900MAX Diesel Fuel Filter/Water Separator each engine has two Racor fuel filters / water separators. What you do is run off of one fuel filter / water separator at a time. This way if you have a fuel issue you can easily and quickly switch to the other fuel filter by turning the handle. So if one filter gets clogged, or if one fuel water separator gets full of water you can quickly switch to the other side by turning the lever. The lever has an arrow pointing away from the yellow handle. If the arrow is up all filters are off. Arrow down all filters are on. Arrow to the left is left filter. And arrow to the right is right filter.Which position to have the Racor selector?
You should always run off of one filter at a time in this sytem. Running both filters on with the arrow down has absolutly no benifit to you at all. You will only use more filters faster. And will not have a emergency filter to switch over to if the filters get clogged or water over takes the fuel water separator. So with the Racor Diesel Fuel Filter/Water Separators run off of one side at a time. On the duel fuel filter / water separator run the engine always off just the left or right filter. I recommend always running off the left filter as its easier to remember that is the first filter to be used as we read left to right. This way when you are on the right filter you know they need to be changed next time you are in port.
