6BTA fuel filter change out vacuum pressure

[Steve Woodward]

I’ve got a pair of 6BTA’s each with SMX Double Double fuel filters plus the stock on engine fuel filter. I’ve had the system for about 6 years. I happened to read an article about fuel systems having too much pressure drop. The Cummins specs for my engines refer to a max dirty pressure drop of 4”hg. That seems very low. I don’t think my filter pressure drop is that low with clean filters. The gauges don’t go into the red until 10”. What is the appropriate change out vacuum pressure? 

Topic

[Bill Desmarais]

Quantum Double/Double between the twin fuel tanks and the QSB 5.9 480.

From launch of boat after repower with the QSB.

Clean tanks 

 

[Rob Schepis]

So after 400+ hours you’re at 5″Hg total between the two filters?  If that’s the case you have VERY clean tanks.

Can’t be sure as to 3/8″ or 1/2″ looking at that pic.  Assuming you used fuel rated hose it will have markings.

[Steve Woodward]

Thank you Rob!

I did not understand the gauge readings reflected the total pressure drop back to the tank! I thought they read the PD across their individual filters. That is a huge clarification! I will change out the 19513 mud filters and record what that does. Then I will change out the 1000 filters and record those results. <br /><br />Another thing this conversation tells me is the importance of knowing my baseline clean PD.

I last changed the filters out in 2020 and the motors have about 4-500 more hours since then.

The pic I am referring to is the one in the original post. I don’t remember seeing any markings on the hoses and I don’t recall the fitting sizes I used when I installed the Double Double and priming system 6 years ago. My recollection is using the fittings Sbmar sent. Do you have a guess as to the hose size? 

[Rob Schepis]

As to your concerns with Cummins specs, yes to my knowledge  you are interpreting them correctly and your concerns are valid.

Keeping it below 8″ would be the total. 

So how many running hours are on the gauges in your picture in your original post?

Your have a gauge on both filters so the 1st gauge on the 19513 is reading that filter plus any restrictions back to the tank.  The 2nd gauge is reading the 1000 plus the 19513 plus any restrictions back to the tank.  So if you change out just the 19513 both gauges will come down.  That’s one way to do it since the 19513 is doing the “dirty work” and then go from there if the 1000 needs changing too in order to bring you back down close to your starting base number.

There was no pic attached to your last post.

[Steve Woodward]

BTW

I think my fuel lines are 1/2” but I suppose they could be 3/8”. I did the install a while ago. The boat is a 2000 Bayliner 47. I’m not at the boat presently. Any guesses on what the line size is based on the pic?

[Steve Woodward]

Thanks Rob!

As I recall the clean pressure drop is around 1-2” per filter. I might be mistaken. <br /><br />

Is 8” the total for both filters or for each filter? If it’s the total, I’m at that now. <br /><br />

It is odd that the Cummins specs are so low at 2.5” clean and 4” dirty. (Specs in pic below) Those amounts seem low and spread seems like nothing. Am I not interpreting the specs correctly?

[Rob Schepis]

What is your inherent restriction with new clean filters?  Depending on this baseline, if you are looking for a number I’d keep it under 8″Hg.  If your baseline is basically zero I’d say the 5-7″Hg range is your change out time.  Here’s an article covering fuel supply restriction: https://www.sbmar.com/articles/understanding-fuel-line-sizes-vs-fuel-supply-restriction/

[Steve Woodward]

Can anyone from Sbmar help to clarify?

At what pressure drop should I change out my fuel filters?

[Richard Dodson]

Filters

FWIW, I change mine if they get into the yellow or annually before I winterize.

[Author]

Replies