MAN Secondary Fuel Filter

[BobFino]

Hello, I have a question on the engine secondary filter on the MAN 900's. It reads on the filter to open the fuel tank prior to removing the cap, is that as simple as taking off the fuel fill cap? The second question I have is the red fuel prime. On the Volvo Penta Diesels I had the primer had a bleeder on it to open until all air is out and you get a steady stream of fuel. I don't see a bleeder on this primer, is there a bleeder valve or just pump away until the filter is full? On the Racors I add fuel before closing up the canister to eliminate the air. I attached a couple pictures. Thank you.

 

[carterchapman]

Hi Bob,

My "MAN man" did not open the fuel cap before he changed the two final filters - the "on engine" filters (I refer to the Mann & Hummel filter with the plastic bowl and sensor as the secondary filter). However, he did open the drain valve and fully drain the two final filters prior to removing them.

They just did a lot of pumping with the primer pump - I didn't see them use a bleeder. It took a lot of cranking to get them rumming again afterwards...

I use 10 micron racors on the primaries...

 

[bmac]

I never noticed that on top of the filters before. My actual practice is to close the tank valves before doing any fuel filter maintenance and then reopening them before trying to go through the start sequence. One thing you should know; recharging the fuel system following fuel filter maintenance on these engines is a two man job. Just using the primer pump alone won't do it. My practice is to put the engine switch to "On" so that I can see fuel pressure on the MMDS screen. I have someone in the ER using the primer pump and once I see pressure starting to build I'll crank the engines over for 15-20 seconds. We continue to repeat this until there is sufficient pressure for the engines to kick over and run. You will be able to see significant, sustainable increases in fuel pressure as you repeat this process. This can take 3, 4, 5 or more iterations of pumping and cranking before the engines turn over. Also, I agree with Carter on draining the system through the Man & Hummell filter drain valve. By doing so you avoid a big mess.

 

[tc410]

I agree and confirm with bmac and Carter above. I’ll just add a little flavor to this as well. I think what you are reading on top of your filter housing may pertain for truck/commercial equipment use where there could be back pressure causing fuel to burp out when you loosen the cap.

Furthermore, I totally agree that these engines require lots of priming and cranking to get them fired up. Make sure your batteries have a really good charge. Going into the diagnostic menu on the MMDS will show you the pressure counts as they build up. Your arm will ache for hours if you’re the one in the ER pumping the primers...

 

[carterchapman]

I think the reason for draining is so no "unfiltered" fuel can get in the system. Other threads talk about "prefilling" fuel filters, but with some of the tiny passages in our electronic injectors, "cleanliness is next to Godliness" - at least with fuel...

 

[tc410]

Thank you, Carter. I can’t understand for the life of me why some folks like to take a shortcut with filling the filters from what they insist is a “clean” can of fuel - especially when manufacturers put priming pumps on for just this purpose. It makes no sense in the grand scheme of servicing the most expensive 2 items on our boats (both engines). It takes something as small as talcum powder to plug an injector, so apparently these guys have very good eyesight to be able to confirm their fuel is clean.

 

[carterchapman]

Thank you, Carter. I can’t understand for the life of me why some folks like to take a shortcut with filling the filters from what they insist is a “clean” can of fuel - especially when manufacturers put priming pumps on for just this purpose. It makes no sense in the grand scheme of servicing the most expensive 2 items on our boats (both engines). It takes something as small as talcum powder to plug an injector, so apparently these guys have very good eyesight to be able to confirm their fuel is clean.

My "MAN man" told me we have some passages in our injectors that are the size of a human hair...

As our generators return almost 30 GPH per hour, I have switched to using 10 micron filters on the genny Racor. Easy to change, and the genny works like a fuel polisher. I cycle sides on the genny feed and return each outing....

 

[BobFino]

Thank you all for all the in-sight and advice on these filters. Be safe during these crazy times.

 

[bmac]

I think the reason for draining is so no "unfiltered" fuel can get in the system. Other threads talk about "prefilling" fuel filters, but with some of the tiny passages in our electronic injectors, "cleanliness is next to Godliness" - at least with fuel...

That's exactly right Carter. In addition, the high pressure fuel pump on these engines is an engineering marvel. IIRC, each engine essentially has a Bosch V4 direct gear driven pump where the "pistons" don't have rings, they are virtually zero clearance devices. Fuel cleanliness is essential in these (or any other) high performance engines.

 

[cod]

Hmmm...... Develop 1 or 2 gallon fuel jug with 2 micron attached filter, shut-off valve, 3 ft. Hose, and battery operated pump.

“Call Starkist! We’ll feed the tuna mayonnaise!”

 

[tc410]

Hmmm...... Develop 1 or 2 gallon fuel jug with 2 micron attached filter, shut-off valve, 3 ft. Hose, and battery operated pump.

Or just use the built in primers that are already there?

 

[cod]

Or just use the built in primers that are already there?

And have your arm ache for hours as you stated along with lots of cranking

“Furthermore, I totally agree that these engines require lots of priming and cranking to get them fired up. Make sure your batteries have a really good charge. Going into the diagnostic menu on the MMDS will show you the pressure counts as they build up. Your arm will ache for hours if you’re the one in the ER pumping the primers”