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Old 13-05-2015, 11:36   #1
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Causes of Recurring Vapor Lock

I have a Yanmar 1GM10 with a recurring vapor lock problem. I can bleed out and the engine will perform fine for around a half an hour. Or, if I turn of the engine after motoring out of the harbor -maybe 20-30 minutes-, then restart I will have difficulty with restart or else the engine will quickly lose power and die.

Is it possible that a fuel pump shaft seal, or gasket, or check valve, etc. needs replaced because it is introducing air into the system?

Once I tried to drain the fuel bowl and noticed an actual vacuum had developed indicated by a suction I could hear and feel with my finger. I changed the fuel filter and did not have any problems for quite some time. I don't notice the same symptoms now, but it could indicate some is wrong or got damaged by the clogged filter.

I my background and training, vapor lock is often associated with high local temperatures near a fuel system component, altitude, and fuel system assembly issues. I am a novice to diesel mechanics, and this is what looks like possibly a two stage fuel pump (low pressure delivery, followed by a high pressure injection pump). I think air is being introduced on the engine side of the system, but it still could be around the fuel filter or other connections.

Has anyone had a recurring vapor lock issue with a Yanmar or similar fuel system?

The engine likes to run around 1800 RPM. Beyond 2000 RPM it eventually loses power, and sometimes dies. The boat is a Hunter 27, if that helps.

Thx for reading.
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Old 13-05-2015, 12:03   #2
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Re: Causes of Recurring Vapor Lock

Possible clogged pickup tube in the tank?
Are your tank vents working? Sometimes little bees block them near the hull exit.
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Old 13-05-2015, 12:12   #3
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Re: Causes of Recurring Vapor Lock

You're not really going to vapor lock a diesel. What you have either sounds like very dirty fuel clogging filters or a clogged tank vent, or even a severely restricted pickup tube.


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Old 13-05-2015, 12:16   #4
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Re: Causes of Recurring Vapor Lock

I had friends with a similar problem, they tried to find it forever. Turned out to be a very tiny air leak in the fuel piping... more likely to be the above things though.
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Old 13-05-2015, 15:01   #5
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Re: Causes of Recurring Vapor Lock

Vapor lock: Only with those pesky explosive gasoline engines.


Diesels have their own unique maintenance hell, they don't do vapor locks.
If there's suction when you open things up, odds are there is a blockage forming and after your "half hour" there's so much suction that it prevents your engine from sucking any more of the fuel.


Same as an outboard engine, when the vent is still closed on the fuel tank.


I'd check for blockages, closed vents, kinked lines, clogged filters, anything along that kind of good stuff first. Sometimes bugs form mud nests in the diesel tank vent, if this is just the start of your season, that's one to check first.
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Old 13-05-2015, 16:29   #6
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Re: Causes of Recurring Vapor Lock

It would need to be going into melt down to have a vapor lock, there is no place for it to get vapor lock, forget that idea.
The vac you feel/felt in the system is not that uncommon and if you have some, it will pull in air from all kinds of places. Your problem sounds like air in the system.
Put a piece of clear hose in the system as close to the engine as possible and play with stuff, looking for air bubbles, valves, connections etc..
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Old 13-05-2015, 16:39   #7
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Re: Causes of Recurring Vapor Lock

If he's got an air leak (as opposed to a suction blockage) there's another easy way to locate it. If you feel lucky, play an unlit propane torch around and see if the engine changes rpm's at some location. That's from the propane being sucked in, instead of air. Or, spray water from a mist bottle on the suspected joints and bits. Again, when the water mist is sucked in...that engine's going to sing a different tune.


Takes a lot of patience, but if nothing changes, all you have to do is wipe down the engine and not reassemble any bits. Collateral damage is a clean shiny engine.(G)


Some folks would use WD40 instead, the diesel will just think that's more fuel, and you can still wipe it clean and shiny. As long as you've got the spare WD-40 around.
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Old 13-05-2015, 16:42   #8
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Re: Causes of Recurring Vapor Lock

Probably an air leak. But how many hours are on the engine?

An electric fuel pump would likely cure this.
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Old 13-05-2015, 16:44   #9
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Re: Causes of Recurring Vapor Lock

It is possible your fuel lift pump has an issue.


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Old 13-05-2015, 16:45   #10
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Re: Causes of Recurring Vapor Lock

Quote:
Originally Posted by hellosailor View Post
If he's got an air leak (as opposed to a suction blockage) there's another easy way to locate it. If you feel lucky, play an unlit propane torch around and see if the engine changes rpm's at some location. That's from the propane being sucked in, instead of air. Or, spray water from a mist bottle on the suspected joints and bits. Again, when the water mist is sucked in...that engine's going to sing a different tune.


Takes a lot of patience, but if nothing changes, all you have to do is wipe down the engine and not reassemble any bits. Collateral damage is a clean shiny engine.(G)


Some folks would use WD40 instead, the diesel will just think that's more fuel, and you can still wipe it clean and shiny. As long as you've got the spare WD-40 around.

Didn't they cause the very first nuke plant meltdown with that plan? Brown's Valley or something?
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Old 13-05-2015, 17:06   #11
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Re: Causes of Recurring Vapor Lock

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Originally Posted by hellosailor View Post
...play an unlit propane torch around and see if the engine changes rpm's at some location. That's from the propane being sucked in...
That is highly unsafe.

Propane will accumulate in the bilge until some spark sets it off.
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Old 13-05-2015, 17:07   #12
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Re: Causes of Recurring Vapor Lock

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Originally Posted by DH777 View Post
I have a Yanmar 1GM10 .......

The engine likes to run around 1800 RPM. Beyond 2000 RPM it eventually loses power, and sometimes dies. The boat is a Hunter 27, if that helps.

Thx for reading.
I suspect you have had this problem for some time and is now getting worse.

This engine should be able to exceed 3600 rpm under no load and fully loaded, somewhere between 3400 and 3600 depending on prop and hull fouling etc. Note redline is 3600.

All good advice by others above.

To repeat, air getting into fuel supply line or crud blocking fuel supply line.
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Old 13-05-2015, 17:13   #13
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Re: Causes of Recurring Vapor Lock

If the engine runs for awhile then loses power and dies but after sitting for awhile can be restarted there is likely a blockage somewhere. The fuel filters are the prime suspects, clogged intake, tank vent, etc. are next. If the engine cannot be restarted without bleeding the system, there is likely an air leak somewhere.
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Old 13-05-2015, 17:35   #14
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Re: Causes of Recurring Vapor Lock

I have seen a fuel line partially blocked at a 90 deg. elbow on top of the tank. Engine would run for a few minutes and die and after 20 minutes or so would start up again for a few minutes.

Edit: I forgot to mention that a vacuum gauge with a tell tale needle at the output of the primary filter can tell you a lot in these kinds of situations.
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Old 13-05-2015, 20:44   #15
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Causes of Recurring Vapor Lock

I had similar with a Vp KAD 32 compressor( super charged) turbo diesel, which had a high volume lift pump, the clean racon primary filter would show air after a high rev run but it would not occur running on low revs, after replacing all the original copper fuel line and brass compression fittings with rubber which made no difference, it turner out to be a wire gauze filter at the pick up in the fuel tank that was fizzing the fuel
My advise would be to direct feed from a fuel container with new clean fuel, straight to the lift pump them work backwards to the tank until you find out which filter,pipe or fitting is introducing the air or restricting supply
Hope this helps


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