Tiny air leak

I had the Webasto serviced n October, and it ran fine until the filter was filled with air and stop the Webasto from firing.* So I filled the filter back up and it ran fine for about a week.* Filled it again and it did the same thing.* Bought a new filter and the same thing.* Then we had the discussion about RPM surges and FF and/or Rick mentioned a clear in*line filter to see the air bubbles.***

I can see the air*bubbles in the clear filter.* The air is not continuous but is spurts. There will be no air for periods of time, 60+ seconds, and then tiny Campaign air bubbles for 5 seconds or so.* Then no bubbles for*60+ seconds of so and then air again.* The air leak is not enough to shut the Webasto down, but it will fill the big filter with air over a period of time.

I have replaced the old valves with new ball valves, tighten up fitting with Lok Tite and the air leak is still there.* About 1/3 of what it was when I first noticed it.*With the electric fuel pump I have back flowed/flushed to make sure the lines and intake are clear several times and there seem to be no blockage.*

Any suggestions how to find this tiny air leak? ******


-- Edited by Phil Fill on Monday 27th of December 2010 10:51:53 PM

Get a can and gravity pressurize the feed line.

An outboard tank with squeeze pump will speed the process.

Wipe everything clean & wait for a drip to show up.

-- Edited by FF on Tuesday 28th of December 2010 06:15:30 AM

FF wrote:

Get a can and gravity pressurize the feed line.

An outboard tank with squeeze pump will speed the process.

Wipe everything clean & wait for a drip to show up.

-- Edited by FF on Tuesday 28th of December 2010 06:15:30 AM

Click to expand...

On pickup trucks I have pressurized the fuel tank (thru the fill pipe) and that always finds the tiny leaks.
All you need is a couple of psi and the leaks will usually show up.



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jleonard wrote:
On pickup trucks I have pressurized the fuel tank (thru the fill pipe) and that always finds the tiny leaks.
All you need is a couple of psi and the leaks will usually show up.

Click to expand...

Man, that is scary. Putting air pressure on a tank full of fuel can go horrible wrong in a heartbeat.

Disconnnect the fuel line at the tank and install a fitting that will allow you to put a length of clear tubing long enought to reach about 10 feet above the suspect components then fill it with fuel to some convenient level. It will act as a sight glass and show if you are losing fuel from a leak, and it will provide about .4 psig per foot of height.

If something fails you will only lose a tiny amount of fuel instead of creating a FAE device.

With the fuel pump I can back flow and pressurize the line, which I have done, but*maybe not long enough.* I was thinking of gooping up the out side of the fitting will Loc Tite? Maybe white primer paint?* I will try to pressurize the lines again as the new ball valves should hold pressure better.


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Since the period of time is 60+ seconds, I would think its the valves/fitting at the tank, which I have taken a part and Loc Tite.* Do you think the 60 seconds is an indication of where the leak close to the filter, 1 ft. *or at the tank about 3 ft a way?* *I am beginning to think its the pick up tube that is a threaded pipe inside the tank that is loose?* I will work on it again to night.* **


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which loctite are you using?
Steve W

"Man, that is scary. Putting air pressure on a tank full of fuel can go horrible wrong in a heartbeat"

Not really , my son has a tool made specifically for this...snap on most likely. He had done this many times. It is a regular procedure.
We are only talking 2 or 3 psi tops.

*"*I am beginning to think its the pick up tube that is a threaded pipe inside the tank that is loose?*"

There is a wicking type of loctite (I forget the number) that you can add to a fitting, as long as it's* clean that is.
We use Loctite 242 at work on threads prior to assembly. We assemble thousands of fittings every day and they don't leak with this loctite.*

-- Edited by jleonard on Tuesday 28th of December 2010 09:47:21 AM

P/F, You have air is getting into the line, not fuel leaking out. If your system is pump-fed, then the culprit is*on the suction side of the pump, or the pump itself. If it's gravity-fed, then I'm stumped. Let us know what it turns out to be.

First, what is a Webasto? Sounds like you are talking about a diesel engine. If so here are a few pointers.

Start at the last thing someone touched. The fuel filter gasket could be wrong. I have also seen someone install a gasket without taking the old one out. If the filter is the type that bolts on don't forget there should be a seal on the bolt. If you were to call me out for a service call I would have brought a new fuel filter and seals. After you got done arguing about how its a new filter and there was nothing wrong with it I would explain that the filter is cheaper then my hourly rate and a good place to start, replace the filter and there would be a good chance it might be fixed.

Second; A suction leak can be hard to find. Sometimes pressurizing the system will not find the leak because the air pressure pushes the leak closed. Look close at the suction side of the system for cracks in hoses and lines and wrong size hose clamps.

Check the engine oil. If it making its own oil or it smells like diesel the lift pump or even the injection pump could have a seal out.

Last, if we are not talking about a diesel engine disregard everything*I wrote.

cd30ketch,

It's a diesel furnace. But as you pointed out it could be the filter itself, a seal improperly seated or damaged or missing around a securing bolt.

P/F,* if it's a leak, try cleaning everything as clean as you can, the dust suspect areas with talcum powder.* You will quickly see staining from a leak, and it's easy to clean up afterwords..................Arctic Traveller

A Webasto is a diesel hot water boiler to provide heat.* Is sort of like a RV hot water heater.* The Webasto has its own internal pump.**The air leak was noticed*when the Webasto was serviced as it was making an odd noise, it was installed and about a week later the Webasto quite burning/firing as the filter was filled with air.* So I filled the filter up with diesel, fire right up and quite about a week later because the filter was filled with air again.* *I bought/changed the filter still had air in it, and I installed the in line clear so I could see the air.* So its not the filter.* *


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Last night it would take 60+ seconds with no air then a surge of air for 1 to 2 seconds.* So last night I gooped up the fitting with Loc Tite red.* This morning I applied a coat of Pre Kote primer and this evening another coat over the Loc Tite. **The air leak is still there.*Tomorrow will put one more coat of Pre Kote.*


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I am beginning to think the leak is in the pick up tube in the tank.* So plan B is to retro fit an old 1000 Racor filter that I have that has a big canister and every week or two fill it back up with fuel and/or* Plan C is to pressurize the line with the electric fuel pump used to prime the lines and polish the fuel.* If I slightly pressurize the lines the air leak goes away. The pump would be powered by the Webasto when it turns on the pump will be turned on.* However, before I jury rig it I would like to find the small air leak.******


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