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Old 06-05-2020, 20:43   #1
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Diesel filler cap lock

There has been a bit of diesel thieving in my area, and I came across a filler cap with a key lock. Wonít work for me as I know if I donít loose the keys, the saltwater over the deck will ruin the thing anyway.
Got me thinking that I could just put a shut off valve inside the boat to prevent any syphon hose getting to my tank.
Would be easy to do as I have plenty of access

Other advantages are no salt water or dirt will get in when I donít tighten the filler cap again.

Can even do it on the fresh water too
Iíld attach the filler cap key to the shut off valve so as to remember to open before filling up, but not a biggie anyway

Any reason why I canít do it?
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Old 06-05-2020, 21:48   #2
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Re: Diesel filler cap lock

Sounds like a good idea... but you're adding another point of potential failure into the system. I personally like the filler cap with lock key idea. Make a few duplicates and you won't have to worry about the key. Spray it with something against rusting and you're good to go.

Just my $0.02
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Old 07-05-2020, 05:18   #3
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Re: Diesel filler cap lock

Quote:
Originally Posted by Markhunter1097 View Post
There has been a bit of diesel thieving in my area, and I came across a filler cap with a key lock. Wonít work for me as I know if I donít loose the keys, the saltwater over the deck will ruin the thing anyway.
Got me thinking that I could just put a shut off valve inside the boat to prevent any syphon hose getting to my tank.
Would be easy to do as I have plenty of access

Other advantages are no salt water or dirt will get in when I donít tighten the filler cap again.

Can even do it on the fresh water too
Iíld attach the filler cap key to the shut off valve so as to remember to open before filling up, but not a biggie anyway

Any reason why I canít do it?
Wouldn't an internal valve in the fill line just trap dirt and water above the valve until the next time you had to open it to refill, at which point it would be deposited into the tank?
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Old 07-05-2020, 05:56   #4
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Re: Diesel filler cap lock

In the 70s, there was a gas shortage in the US. Everyone thought there would be a rash of people running around w/siphon hoses/gas cans to steal fuel, so they some bought locking gas caps for their automobiles.
When it was "over" (many years later), never saw/heard of anyone attempting to steal gas (not everyone had locking gas caps either). The locking caps were a pita.


Mark,
By even putting in a valve, you make be over thinking the possibility of siphoning/extracting the fuel out of your boat. To extract fuel out of bilge tanks, one would need a very long hose and probably an electric pump to lift it up to deck level. Not saying desperate people couldn't do it, just seems like a lot of work for 10 gallons or so.
Would be less work to put up a motion detecting camera/game camera to catch a possible thief. Maybe the marina already has cameras up (since they are now everywhere).
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Old 07-05-2020, 06:02   #5
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Re: Diesel filler cap lock

Quote:
Originally Posted by Markhunter1097 View Post
There has been a bit of diesel thieving in my area, and I came across a filler cap with a key lock. Wonít work for me as I know if I donít loose the keys, the saltwater over the deck will ruin the thing anyway.
Got me thinking that I could just put a shut off valve inside the boat to prevent any syphon hose getting to my tank.
Would be easy to do as I have plenty of access

Other advantages are no salt water or dirt will get in when I donít tighten the filler cap again.

Can even do it on the fresh water too
Iíld attach the filler cap key to the shut off valve so as to remember to open before filling up, but not a biggie anyway

Any reason why I canít do it?

This is common

Large yachts may have several tanks and a single fuel fill

Fuel is directed thru a manifold into tanks with shut off valves

Make sure your valve is fuel resistant . Correct ID
so you donít reduce fuel flow
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Old 07-05-2020, 10:36   #6
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Re: Diesel filler cap lock

Quote:
Originally Posted by Markhunter1097 View Post
There has been a bit of diesel thieving in my area, and I came across a filler cap with a key lock. Wonít work for me as I know if I donít loose the keys, the saltwater over the deck will ruin the thing anyway.
Got me thinking that I could just put a shut off valve inside the boat to prevent any syphon hose getting to my tank.
Would be easy to do as I have plenty of access

Other advantages are no salt water or dirt will get in when I donít tighten the filler cap again.

Can even do it on the fresh water too
Iíld attach the filler cap key to the shut off valve so as to remember to open before filling up, but not a biggie anyway

Any reason why I canít do it?
A ball valve sounds like a great idea.
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Old 07-05-2020, 10:52   #7
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Re: Diesel filler cap lock

We installed a ball valve directly under the deck of each our two fuel fills- mainly as a hedge against water getting into the tank. [Not that we don't trust a single o-ring in a removable cap with our entire fuel supply... But I like redundancy, and ice in winter can play all sorts of games...]

The tops of the closed balls are within ~4 inches of the deck fill, so it is easy to mop out anything that accumulated there before opening the valve.

No issues [and no accumulations in several years.... yet...]

Access to work the valves is reasonable, and could be augmented with a simple push/pull extension if needed.

Go for it- with fuel/hydraulic rated valves.

Cheers! * Bill
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Old 07-05-2020, 11:15   #8
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Re: Diesel filler cap lock

Since you proposed an in-line valve on the fuel fill line you must have access to at least a section of it. How about installing the simple anti-siphon arrangement used on most cars? It consists of an L or U elbow in the line so that any siphon line will stop at that point, preventing it from reaching the fuel.
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Old 07-05-2020, 12:51   #9
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Re: Diesel filler cap lock

Quote:
Originally Posted by thunderhoof View Post
Since you proposed an in-line valve on the fuel fill line you must have access to at least a section of it. How about installing the simple anti-siphon arrangement used on most cars? It consists of an L or U elbow in the line so that any siphon line will stop at that point, preventing it from reaching the fuel.
The problem that I see with that solution is that if you ever need to have your fuel polished the fuel polishing company will not be able to get the hose down into your tank. might be the same problem if your ball valve is too small also.

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Old 07-05-2020, 13:04   #10
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Re: Diesel filler cap lock

Swap the deck fill cap for one that says "WASTE" and for extra fun, put the one marked "DIESEL" on the waste tank. Whoever siphons that deserves what he gets.


You would, of course, have to be *very* careful when filling or pumping out your own boat.
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Old 07-05-2020, 16:14   #11
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Re: Diesel filler cap lock

Great idea
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Old 07-05-2020, 17:15   #12
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Re: Diesel filler cap lock

There is an anti siphon spring available, it’s a cone shaped spring that merely is placed in the fill hose and stops a siphon hose. It was very popular back in the day.
Here it is on Amazon, probably cheaper other places, but it stops a siphon hose, but has no effect other wise
https://www.amazon.com/Stanco-GBB-01...8896851&sr=8-7
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Old 07-05-2020, 17:26   #13
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Re: Diesel filler cap lock

Many years ago a coworker had a problem with someone siphoning gas from his pickup. Tried as he might, could not catch the culprit.

Took the fill off the filler and routed the line to a 5-gal jerry can full of a gas/molasses mix. Couple days later can was empty. Few days later a neighbor's new car seized.

Never had a problem again.
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Old 08-05-2020, 07:17   #14
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Re: Diesel filler cap lock

sorry for unrelated question:

Can you siphon a full tank of diesel with a long hose and pump? Can you extract all the deposits at bottom of tank by doing that?
Would that work?
Thanks
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Old 08-05-2020, 07:22   #15
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Re: Diesel filler cap lock

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Originally Posted by ferrailleur View Post
sorry for unrelated question:

Can you siphon a full tank of diesel with a long hose and pump? Can you extract all the deposits at bottom of tank by doing that?
Would that work?
Thanks
You can get some of the deposits but not many, a pro who show up with a pressure washer and a huge filter that often uses paper towels as a filter media and can recirculate the fuel while the high pressure wand stirs up the deposits and if it’s recirculated enough times he can get most.
Ones I have seen have different “tools” one is what looks like a metal ball on the end of the wand, it’s full of holes that spray fuel in different directions, it seemed to work best when I have seen it used.
However if you can get into you tanks and to all areas and aren’t blocked by baffles, you can get them cleaner than any other method.
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