TWL: Need clarification on bleeding air from fuel lines
Well, I'm a little confused. I am getting ready to change my fuel filters
for the first time. I'm clear on everything except the necessity to bleed
air from the primary filters. (Just so we're clear here, I am using PRIMARY
in the same way that the Lehman Ford manual and Nigel Caulder book does, to
mean the fuel/water separator filter, in my case, Fram, but often Racor,
that is between the fuel tank and the engine, which has its own SECONDARY
CAV or Bosch dual filters after the lift pump.)
Now, every maintenance guide I have read has stressed how important it is
to get air out of fuel lines after the filters are changed, and doesn't
really make a distinction between primary and secondary filters. But the
instruction manual that comes with the Fram filter says it isn't necessary
to bleed the filter if it's on the suction side of the pump. Yet
intuitively it seems like air could easily be sucked into the system if
there is big pocket of air in the filter housing. I suppose I could install
a manual or electric pump, but is this really necessary, since it seems
like the boat has gotten along fine for decades without them? I'm not even
sure how I could build enough pressure before the filter to bleed air at
this point.
Is it even necessary to fill the filter housing "cup" with fuel before
dropping the new filter in? Do I just not have to worry about suction side
air?
Another small issue: I've read that Caulder thinks that filling filter
housings with fuel to reduce time to bleed is a really bad idea since it
can introduce impurities that the filters don't have a chance to screen. Is
this being overly obsessive, or is it good advice? Thanks for any insights...
Richard
49' Marine Trader Pilothouse (1978)
Twin Lehman 120's
SF Bay, CA
At 06:24 PM 2/10/02, you wrote:
Another small issue: I've read that Caulder thinks that filling filter
housings with fuel to reduce time to bleed is a really bad idea since it
can introduce impurities that the filters don't have a chance to screen.
Is this being overly obsessive, or is it good advice? Thanks for any
insights...
If you put the fuel in the Racor after the filter is in place it should get
the impurities.
You can bleed the system and ANY air pockets of air, before you try to
start the engine or you can wait to see if the engine will do the job.
After a few attempts at this sort of thing, you will figure out just how
much bleeding is required to get going. Most folks will do no more than
necessary, especially if bleeding while in a rolling seaway.
I have used the Cat priming pump, to boost fuel pressure during the start.
There is nothing in any manuals that suggests this is ok. But it works like
gangbusters. It might work on other engines.
Capt. Mike Maurice
Near Portland Oregon.
If you have Ford-Lehman engines, bleeding the primary filter isn't as
much as a problem as with other engines, since the Lehman will pump air
out of the system (if your batteries will keep cranking long enough).
Whether I'm changing the primary or secondary filter (and no matter how
you define it, that includes both filters in the line), I fill up the
bowl from a tin can of diesel fuel before finally closing the filter. On
the Racors, that's fairly easily done just before screwing the top back
on. On the engine mounted filters (after the pump), I keep the highest
screws on the top plate off and the lowest screws loose, then use a
turkey baster or syringe to add fuel to the filter bowl through the
highest screw until it starts to seep out of the loosened lower screw,
tighten the lower screw and add a few more cc's until you can see a
little fuel in the top hole. Voila! No, or darned little, air in the
lines!
Keep a disposable diaper (or disposable mattress pad) under the filters
just in case you spill a few drops!
Richard Morrison wrote:
Well, I'm a little confused. I am getting ready to change my fuel filters
for the first time. I'm clear on everything except the necessity to bleed
air from the primary filters.
--
Bob McLeran mailto://rmcleran@ix.netcom.com
M/V "Sanderling" Docked at Point Patience Marina
Hailing port: Wianno MA Solomons, MD
Hampton 35 Trawler