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Old 11-16-2016, 08:50 PM   #1
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Fuel Filter Question

O.K, let's say your tooling along and your fuel filter gets clogged. Engine stops. So you change the filter, fill it up with diesel before screwing it back on. Doesn't the engine suck all the fuel out of the feed line before it stops running? So after replacing the fuel filter will the engine suck fuel back up the feed line to the engine, or would one have to manually pump at the engine cracking each injector to get fuel back to each injector? Just bought a 1984 34 Mainship and want to be prepared for what ever gremlins may happen. So... i.e... what is the procedure to replace a clogged fuel filter.
Thanks in advance.
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Old 11-16-2016, 09:04 PM   #2
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Yes to all, you will have to bleed out the air. Buy a fuel filter vacuum gage it will give you a warning that the filter element is getting dirty.
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Old 11-16-2016, 09:14 PM   #3
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Yes , you'll probably need to reprime the system. I installed a quick disconnect into the filter cap. Hook up a priming pump and problem solved.
Some guys have small electric pumps permently plumbed in for the same situation.
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Old 11-16-2016, 09:57 PM   #4
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Try it dockside. Repriming is a good skill to know.

Turn fuel valve off at filter supply. Let engine run in neutral at 1000rpm til it dies. Open fuel valve and see what it takes to get it restarted. That will simulate a clogged filter.

Harder challenge is an air loading. Like what happens when you run out of fuel. Supply is not restricted, it is just air. Crack loose cap on racor and let engine run til it dies. The refill filter, pump primer, open bleed screws on secondary and inj pump. bleed it and get it going.

Good to know what it takes to get going again if things go badly on the fuel side.
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Old 11-17-2016, 05:54 AM   #5
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Try it dockside. Repriming is a good skill to know.

Excellent!

Ken, FWIW, when we change filter during normal service, we have to reprime... but generally not all the way to the injectors.

After a stoppage like you describe, I'd most likely to have to crack the injectors, too.

But learning your engine at the dock is MUCH better than learning in rough seas!



I've seen vacuum gauges for primary fuel filters (e.g., Racors) but I've not ever noticed anything like that for spin-on secondary fuel filters.

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Old 11-17-2016, 06:58 AM   #6
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As I will change my filter for the first time next spring I also have a question. My filter is higher than my engine pump. By this I mean that the fuel line is going down from the filter to the pump. Also its model is a spin on cartridge with clear bowl below for water. Logically, as it is higher than pump, air won't go down the line when removing the filter. So changing the filter than filling it till fuel leaks by the bleed screw at the top of the filter head should be enough and I should not need to bleed the whole fuel system. Am I right to think so?
Ski you know my engine setup is a bit particular so I would like to avoid screwing up everything
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Old 11-17-2016, 07:20 AM   #7
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Greetings,
We still don't know WHAT engine Mr. KM has in his vessel. Filter change procedure may be slightly different depending on the engine. Yes, it's all basically the same but with subtle differences I suspect.
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Old 11-17-2016, 07:40 AM   #8
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O.K, let's say your tooling along and your fuel filter gets clogged. Engine stops. .
Prevention is the key.

Insure your tanks are clean while at the dock. Several TF members have posted on this action, particularly Flywright and Alaska Seaduction. PM them for tips.

As suggested, get vacuum gauges installed. Generally, you should never see vacuum with our low HP small fuel flow engines. And bleeding the engine should not be required if changing the primary only. If you do see vacuum increasing, something is probably haywire. Don't wait, find the problem while at the dock.

Learn how to bleed your system while at the dock. Change your filters before they become clogged, both primary and on engine.

Only fill up at reputable high volume fuel stations.

Did I mention prevention is important?
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Old 11-17-2016, 07:54 AM   #9
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The likelyhood of the filter getting completely clogged so fast that you get no warning before shut down is slim.

In most cases you can tell something is wrong by the way the engine is running.

And no, the engine will not necessarily suck the lines dry with a clogged filter. With a clogged filter there can still be fuel in the lines but the pump just can't move it do to the high vacuum created by the clogged filter.

Pull the clogged filter out, replace it with a clean one, and off you go.
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Old 11-17-2016, 09:11 AM   #10
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If you are paying the slightest attention to the sound of your engine(s) and to the rpm gauges you will catch a clogged fuel filter long before it shuts the engine down.

I and many others have installed in line electric fuel pumps which can serve as a priming pump.

If you do a lot of cruising a duel Racor system is ideal, allowing you to switch filters underway without any hesitation.
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Old 11-17-2016, 10:39 AM   #11
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Not sure if this has been mentioned before, but the p/o of my boat painted the heads of all the bleed screws so they're easy to identify.
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Old 11-17-2016, 11:40 AM   #12
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Not sure if this has been mentioned before, but the p/o of my boat painted the heads of all the bleed screws so they're easy to identify.
Now THAT is a good idea. I have to go back to the manual to remember which two bolt heads to crack on my injector pump.

FWIW, my engine manual says you only need to crack 2-3 injectors, no need to do all six of them. I tried it and it worked. Still makes me nervous though.
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Old 11-17-2016, 12:57 PM   #13
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What Bill said,

Usually not necessary to bleed all injectors just the furthest one from the pump. A clogged filter will often show up as reduced power but run fine at low power because some fuel is getting through. Unusual to suddenly shut down without notice.
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Old 11-17-2016, 01:28 PM   #14
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Bleeding issue depends on the engine make. Detroit non issue.
Ideal setup is 2 primary filters with valves so 1 filter can be changed while running.
On my boat one filter is new and waiting, the other carries the fuel load. My vacuum gauge shows Zero when the filter is new. I change at 7", but I use 2 micron primaries. A 30 micron would probably change at 2 or 3.
Also an aux electric fuel pump will make bleeding easier. Mounted between the vacuum gauge and the lift pump. The lift pump will pull thru the aux pump ok. And should your lift pump fail the aux pump can take over. One like the picture is less than $20 inc shipping on ebay.
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Old 11-17-2016, 06:59 PM   #15
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I've done this a couple of times, which I'm not proud to admit, by sucking the mud off the bottom of the tank.

In my experience the fuel lines will not go dry and require a complete prime. What happens instead is that the fluid remains in the line between the Racor and engine when a vacuum is pulled, starving the engine of fuel. There is no air available, so no air is introduced into the line. After changing the Racor filter some extra cranking will be required, but I have not had to crack open fittings and bleed manually. This is with a Perkins T6.3544.
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Old 11-17-2016, 07:22 PM   #16
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Originally Posted by Lou_tribal View Post
As I will change my filter for the first time next spring I also have a question. My filter is higher than my engine pump. By this I mean that the fuel line is going down from the filter to the pump. Also its model is a spin on cartridge with clear bowl below for water. Logically, as it is higher than pump, air won't go down the line when removing the filter. So changing the filter than filling it till fuel leaks by the bleed screw at the top of the filter head should be enough and I should not need to bleed the whole fuel system. Am I right to think so?
Ski you know my engine setup is a bit particular so I would like to avoid screwing up everything
Yes Lou you are correct. It depends a bit on the engines as some are more susceptible to air locks than others but as a general rule if you just prime your filter after changing it you should be fine. That's how I do ours (6BTA) and generally have no problems,

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Old 11-17-2016, 09:13 PM   #17
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Quote:
Originally Posted by Ski in NC View Post
Try it dockside. Repriming is a good skill to know.

Turn fuel valve off at filter supply. Let engine run in neutral at 1000rpm til it dies. Open fuel valve and see what it takes to get it restarted. That will simulate a clogged filter.

Harder challenge is an air loading. Like what happens when you run out of fuel. Supply is not restricted, it is just air. Crack loose cap on racor and let engine run til it dies. The refill filter, pump primer, open bleed screws on secondary and inj pump. bleed it and get it going.

Good to know what it takes to get going again if things go badly on the fuel side.
Ski,

Wonderful advice.
I wish I would have thought of it. But weirdly, any significant problems in getting the Lehman restarted always seemed to occur at dock.

Also, in spite of all of my fuel shenanigans, I've never had to crack open injector tubes. But I think that's a function of the SP135 and injector pump.

Richard
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Old 11-17-2016, 09:27 PM   #18
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Bleeding issue depends on the engine make. Detroit non issue.
Ideal setup is 2 primary filters with valves so 1 filter can be changed while running.
On my boat one filter is new and waiting, the other carries the fuel load. My vacuum gauge shows Zero when the filter is new. I change at 7", but I use 2 micron primaries. A 30 micron would probably change at 2 or 3.
Also an aux electric fuel pump will make bleeding easier. Mounted between the vacuum gauge and the lift pump. The lift pump will pull thru the aux pump ok. And should your lift pump fail the aux pump can take over. One like the picture is less than $20 inc shipping on ebay.
Yes. This is also exactly what I did. However I was leary of putting pump in line, making the lift pump suck harder, so I made a loop/bypass.

Think main line from fuel tank to Racors, with a loop between Racors and Fuel Tank, as I wanted to prime Racors also, as needed.


I put the extra valves, V2, V3 in because I did not want to introduce another source of air/leaks if not needed.

But I have also run the eingine with both valves open and it runs fine.
However, if priming, with only valve 2 open, the fuel just makes a little loop and primes nothing, therefore V1 must be closed for priming.

Best mod I ever made, as it makes life much easier and faster.

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Old 11-17-2016, 09:51 PM   #19
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See Picture of what I describe above
Red handle is main gravity line from tank.
blue handle valves are bypass, both are usually closed, only open when priming and then Red is closed.
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Old 11-18-2016, 05:43 AM   #20
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See Picture of what I describe above
Red handle is main gravity line from tank.
blue handle valves are bypass, both are usually closed, only open when priming and then Red is closed.
IMHO this is the textbook and correct way to install an auxiliary fuel pump or squeeze bulb primer. Good job.
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