Fuel Issues

This page is under construction:

Priming, Old boats, Spare filter elements, Easy Pour Spouts, Spin-on cross reference, comparison of Turbine and Spin-on filters, extra fuel, Vacuum gauges and leaks, gas boats, custom priming system, Chinese "knock-offs", fuel polishing systems, Misc, check lists, fuel return line issues, metric threads, lost deck fill caps, general supply issues, rebuilding, resources, vacuum pumps, spin-on filter issues, measuring fuel tank levels, bill of materials, where to buy and pricing.

What does a "proper fuel system" look like. Dual Turbine Racors with Vacuum gauges, hydraulic fittings and Racor Check Valves and shutoff valves leading to each engine and near the filters. Twin engine installations should have COMPLETELY duplicate and INDEPENDENT components, especially dangerous are single distribution manifolds that feed into both engines and generators(bad...). Be sure to read the Racor FAQ contains vital background information.

Seaboard Marine Tutorial  This is a reasonable presentation of fuel systems. Note that the picture: "A simple and low restriction manifold" is an example of what NOT to do. The single manifold running both engines and generator, if it develops an air leak, will take down all engines and the gen sets at the SAME TIME. And don't tell me it can't happen. It did on a 75' fancy yacht in the dark, inside the boat basin at Bodega Bay, with the wind blowing 35 knots and this after we had been running without problems for 1000 miles. Don't ask what happened next, cause we didn't hit anything. But, we did end up against the seawall, no damage. Try that sometime for excitement.

Is there a lesson in the story? If you have such a system be sure to inspect that the filters are full, before entering harbor or crossing a bar; every single time.

PassageMaker Magazine Article


Search String for Google: marine diesel fuel issues

What to beware of with old boats.

Vacuum leaks, leaking seals on the internal check valves of Turbine Filter bodies, buildup of gunk that will clog filters in rough seas. Most boats do not have access plates to allow cleaning up the gunk in the bottom of the tank(s). If the check valve(ball) or o-ring degrades the check valve won't seal and fuel may siphon back into the tank. Then the engine may not start, or worse quit after a few minutes, just as you are getting across the harbor.

Racor sells an external check valve 17780F-f  RK 30770 3/8" NPT($40-55) which can be added ahead of the filter. The internal check valves should be replaced on Turbine and Spin-on Racors at least every 10 years, 5 would be better. See rebuilding for instructions.

Fuel issues are divided into several categories

Extra fuel for priming.

Carry a one to five gallon jug with no more than two gallons of diesel for priming. Yellow (diesel) jugs are hard to find. Use a Red(gas) one if you have to and mark it diesel with black marker. The cheapest are at WalMart.

Gas or Diesel jugs from: WalMart, Home Depot, Lowes, Target, Sears, Ace Hardware, Kmart, Harbor Freight, auto supply places including NAPA. Water jugs can be used in an emergency, but for Diesel ONLY. Jugs for water are not usable for long term storage of diesel.

Easy Pour Spouts to replace hard to use ones.

Spare filter elements.

Turbine (paper) filter elements can be obtained at most fuel docks.

Turbine Filters: It MAY be possible to substitute a smaller turbine paper element in a larger unit, if nothing else is available(see Turbine notes). If you do the smaller unit will have to be lodged in place such that it will cover the holes that feed the engine. I have not tried this, yet! The smaller filter will NOT last as long, you have been warned.  There are 4 holes in the 900/1000 units spaced close together. They are about 2 1/2" and 3 1/2" down from the top of the return tube. A substitute filter must cover these holes if the fuel is to be filtered. A tie-wrap could be used to lodge the small filter at the proper level to cover the holes. A 500 can be used in the 900/1000 units. A 900 can be used in the 1000 units.

If you are tempted to use "bigger is better" filter systems, note this: the "clean pressure drop" is 15 times as high between the Racor 500FG and the 75/1000FGX unit. The table for this is in Parker 95191975, page 28.

Racor metal canister filters(spin-on), AND their equivalents, are hard to come by and should be ordered weeks in advance. In an emergency see the Cross Reference List.

Comparison of Canister(Spin-On) and Turbine filter systems

Canisters cost 3-4 times that of the Turbine paper filters and harder to find in stock(extra shipping costs).

Spin-ons allow air into fuel system.

Messier to replace.

Can't be visually inspected to see how clogged they are, the Turbine units can be pulled out to inspect.

Requires tools to take off and remove bowls. Note: the 400-600(4.5") series Racor's can't use the commonly stocked filter wrenches. The Filter Pliers listed, will fit at least 4.5". The common wrenches(3.5") will fit the 200 and smaller Racors. Sometimes due to age and corrosion may require a workbench environment to remove the bowl.

Oil Filter Pliers: AutoZone 25320, Amazon Tekton 5866, 5867. Harbor Freight Pittsburg 61477. Home Depot Tekton 5866, 5867. Sears 20520. OReilly 4561.

Vacuum gauges and air leaks.

Vacuum gauges can be used in the vent port on Spin-on filter heads which will measure the vacuum of the filter and all of the fuel line back to the tank. The same result can be gotten on Turbine units placing the gauge in the "T" handle or the outlet of the Racor Turbine. Proboat Magazine Article

For more precise measurements a second gauge can be inserted before the filter and the difference in vacuum will be the actual vacuum of the filter element, alone. This second gauge could be placed in a Spin-on at the unused inlet. In the turbine units it could be placed in the heater port(if not in use).

Racor Vacuum gauge Notice the extra red needle that stays at the last highest level reached. With "T" handle.

Racor Vacuum Indicator This unit comes with fittings for the Spin-On filter heads vent plug(3/8-24 UNF) or with a 1/8" NPT.


Murphy Can have wired alarm set using the built in contacts.

Compound Pressure Gauges Article

Warning: vacuum gauges are nearly worthless if the fuel system is gravity fed. In that case you need combination pressure/vacuum gauges. More on this later...

Special problems with gasoline powered boats.

Most twin engine gas boats do not have any way to transfer fuel from one tank to the other and generally have two tanks, one for each engine. If one engine fails to run you may not have access to the fuel in the non running engine's tank. The "thig-a-majig" below can solve this problem. I carry the adapter fittings to attach to the canister heads that the gas (or diesel) engines use.

WARNING about Gasoline

A quarter cup of gasoline mixed with air is equivalent to a half stick of dynamite if ignited. Be very carefully if using any of these tricks with gasoline.

Custom Priming System

This custom built thig-a-majig can be used to prime filters or transfer fuel(gas or diesel). The entire kit weighs about two pounds and can be taken as carry-on luggage on the airplanes(new, unused). The "thingy" screws into the top of the Racor 500, 750, 900, 1000, replacing the "T" handle and the little electric pump will then pull  filtered fuel out of the tank into the filter housing completing the priming process. Or the fuel can be dumped into a jug or even a paper cup to be then dumped into another filter housing.

The Priming System (above) can be used with a 5 gallon jug to provide emergency diesel(only) fuel. It only requires a shut off valve and reversing the fuel pump. The Turbine filter units have a check valve, which if it is working, will prevent fuel from flowing back into the contaminated main tank. If there is a shut off valve leading to the main tank, it can be shut off, but only while you have the jug hooked up and in use. If the filter is completely plugged fuel will be drawn from the jug, in any event, simply because the vacuum to it will be lower.

Depending on the engine you may also have to provide for the fuel returning from the engine. This kind of priming is for Diesel only, as gasoline is not done this way and is extremely dangerous.

I haven't said anything about putting a hose down the fill pipe since many boats don't have fills that run straight down and may be impossible to get a hose down to the fuel, even if you have a hose to try this with.

Here is another trick for priming filters. If the filter body is connected with hoses that can be moved around, in other words the filter body can be taken loose from the wall and lowered until it is below the level of the fuel in the tank then it may be possible to fill the filter by gravity feed. Or, if the feed line from the tank can be removed and lowered until gravity causes the fuel to flow you can get diesel to fill the filter with. If gravity won't work and you have anything including a pump bulb from the outboard to start a siphon, you can get priming fluid that way.

One more trick for twin engine boats with Racor 200/400 Spin-on filters. If the priming pump on one of the units will not pump. You may be able to get fuel to prime that filter from the other unit. Open the drain of the working(pump) and use the pump to force pressurized fuel out the drain and into a container.

Chinese "knock-off's"

Racor 500 and 1000 fuel filters. Less expensive, use different port threads. Parts not interchangeable and may NOT be available, except filter elements. The 1000 units are available in a Dual setup. Easy to find on Ebay. This is NOT a recommendation. There are a lot of look-alike racor filters listed on Ebay and Amazon. They are mostly not real Racor.

Fuel Polishing Systems

KTI Systems  Deluxe systems with many control, including remote, and priming features.

Racor turbines don't have a gasket under the lid pressing on the return tube to prevent unfiltered fuel from entering the return tube.

Simply polishing the fuel will not clean up the gunk stuck on the bottom of the tank. Tanks that have been agitated may have most of the gunk suspended in the fuel where the filters can remove it. But, this may result in the engine shutting down without much warning.


Fuel should return into the original tank. If fuel in tank tends to get hot it may require a fuel cooler.
Fuel returning to the tank should enter near the bottom as splashing on the surface introduces air into the fuel.
Fuel polishing systems can be so vigorous that air and water may be dispersed to the point where the air or water will actually go thru the fuel filters and enter the engine. Lowers engine efficiency and in the case of electronically injected engines, do actual damage.
Fuel pumps should be after the filter as water should be removed first or it will be broken up into fine particles that the filter may not catch.
The more valves, fittings, and sealant you have in the system, the more chances of air leaks(vacuum).

If you can shut off the fuel line leading to the filter and have a vacuum gauge on the filter, you can run a test for vacuum leak. Run the engine until the vacuum reads about 10hg. Shut off the engine... see how long the vacuum holds. It should take at least 5 minutes, more is better.
Another test you can try is to shut off the fuel line and wait for the engine to quit, note the vacuum gauge when it quits as this tells you you much vacuum your engine fuel pump can manage. Test both engines and note this for future reference.

Use of pipe fittings instead of hydraulic to plumb the filter housings, generally results in loose fittings and may lead to air leaks.

Old Racors, New Racors and Filters    More A tie-wrap can be used to hold a new Racor Turbine filter element in place if the spacer is not available to use in an old style Racor body.
Bubbles in Bowl

A Check List

Pictures of all filter housings with ports visible in pictures, and any manifolds.

Pictures of return line(s) from engines and any other key components of fuel system. Including vent lines.

List of fuel tanks, sizes and locations.

Fuel tank feed system: draw from top, draw from bottom?

Is there a crossover system between tanks and are the valves open/shut?

How is the fuel level measured and is the system working. Dip stick, electric gauge, sight gauge?

Amount of fuel in tanks.

Relation of fuel filters to the level of the fuel in the tanks?

Fuel Return Line Issues

Using the return line is quite problematic as there is such a wide variety of tubing and fitting sizes and types.

If you can disconnect the return line from a main engine or gen set it can be used to supply fuel for priming or possibly even to run another engine(slowly) directly.

Ports with Metric Threads

The real Racor spin-on filters are available with metric threads. It is not likely that these metric threads will be encountered in U.S. built boats, but maybe in foreign built ones. The 200 series could have 14 mm x 1.5 and the 400-600 series may have 16 mm x 1.5.  1/4" NPT will fit the 14 loosely. 3/8" NPT may fit the 16 loosely. You are not likely to see any 600 series filters on boats, they lack a priming pump (and check valve ?). The 400 series have a priming pump that has not always worked properly.

Note: that the spin-on heads(120,200, 400) have a check valve built-in.

Lost Deck Fill Caps

Expandable Rubber Plugs, McMaster Carr   Most likely trade sizes from 9-10.

Also Home Depot, Lowes, Auto supply stores

Trawler Forum Discussion

Measuring Fuel Tank Levels

The unused inlet port of the 120/400/600 series could be used to hook a hose up and see the fuel tank level. This won't work on the 200 series as there is no unused inlet port. It also won't work on the Turbine units.

Depending on the setup of the fuel return line, you might be able to hook up to it and use it.

Any of these methods requires siphoning enough fuel to get the transparent fuel hose filled up and then see where the fuel level settles out at. This is a bit tricky. Needs more explanation. It is hard to see a practical use for this trick, but... since if you have bought the tubing and fittings in the bill of materials you may have the wherewithal to employ these tricks.

General Supply Issues

The one thing you can be sure of is that if you need any of these things it will be on Friday evening at 5 pm, just before a 3 day holiday. You had thought of that?


Compass Marine Tutorial of Racor 500(similar for 900,1000)


Racor manuals:

Mobile Fuel Filtration  Installation Diagram, Parts layouts, cross reference lists.

Parker Catalog(fittings)

Vacuum Gauges & Indicators Testing, instructions, usage, installation.

Racor Check Valve Instruction Manual


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