Unusable Fuel ??

cooker · Post by **cooker** » Sat Mar 10, 2012 6:21 pm

We have the M-4 in the hangar for some service and i went to change the fuel drains in the main wing tanks. The bottom cowl was off so i disconnected the fuel line at the fire wall, installed a short hose and let both tanks drain via gravity, i took the right drain out and was happy that there was only a cup or so of fuel that I collected in a coffee can. The left side however was a different story however as it filled the can made a puddle on the floor and soaked my arm before i could get the drain back in and find another can. Anyone else done the mad dash for another can lately ?????

I estimate there was 1.5 - 2 gallons left in the left tank which seems like a lot of unusable fuel and also seems weird that the right would drain essentially dry not the left?

The M-4 is on floats and sitting level on a concrete floor, and not tail low. I looked at the fuel lines and they don't show any signs of concern?

Is this normal?? why would one tank drain completely and the other still have fuel??

Mr. Ed · Post by **Mr. Ed** » Sat Mar 10, 2012 6:56 pm

I just replaced my left tank drain valve. I drained the tank through the Curtis drain down by the left step. Then used the sump cup to drain the remaing fuel from the tank. I only got five sump cups full before it was empty.

maules.com · Post by **maules.com** » Sun Mar 11, 2012 12:12 am

Cooker, is'nt your M4 a modified M4-210C which had the Continental IO360 which utilized a header tank ?

cooker · Post by **cooker** » Sun Mar 11, 2012 9:43 am

Hi Jeremy, its a modified 220C

Wings and fuselage are original Maule i believe even the wing extensions came from maule, the only big modifications are the engine (now lyc 540) and the floats.... i have started some posts in the past asking about the header tanks in general as at one time i was curious if one would have any benefits in this application as currently the biggest worry i have is not being able to deliver the 25gph required at takeoff. so far we have had no issues and i should probably not worry but complacency gets people into trouble as well i guess.

The tanks apear to be original maule. I did let some fuel out of the belly drains but was tricked into thinking the left was dry as the drain was starting to girgal ... i am still curious as to why one tank would drain completely through the firewall fitting via gravity and the other would hold 1.5 - 2 gal of "unusable" fuel

Thanks again Jeremy

maules.com · Post by **maules.com** » Sun Mar 11, 2012 10:04 am

It is possible that the tank vent lines are blocked and not letting all the fuel out if not enough air can get in.
If you were draining the fuel beyond the fuel selector valve, was the selector on both.
Draining of tanks is usually done at the step drains.
You probably still have the pancake style fuel tanks and if on floats when draining, the plane would be at a different attitude than as a taildragger, but nevertheless, there will always be some undrainable fuel except if you remove the plugs at the bottom rear of the tanks.

cooker · Post by **cooker** » Sun Mar 11, 2012 1:45 pm

I don't have a both setting just left, right, and off.

I retried the experiment today. Started by letting the fuel drain via gravity from the fire wall fitting and was only able to drain 18.5 gal. another +/-1.5 gal was then available from the step drain and only a few cups came from the tank drain.

I guess it is likely to do with the pluming and possibly an air lock that won't let the left tank completely drain through the firewall fitting ... my theory is that once the front port has no fuel the system is far less efficient.... there are quite a few ups and downs along the fuel journey from the rear fitting .....rear tank fitting, down to step drain, up to the tee above the selector valve, down through the selector and finally to the firewall....

Anyway looks like only 18.5 usable in that tank i guess ?????
Some day when i am feeling sporty we'll run it dry in the air and see how much is remaining

maules.com · Post by **maules.com** » Sun Mar 11, 2012 2:20 pm

Try raising the tail until the wing bottom is parallel to floor and drain . I would advise changing the selector to Left Right Both and Off ASAP for safety.
In the case of a skid or crosswind takeoff or landing, it is too easy to unport the fuel line pickups when below half fuel. Use Both in the above cases.

cooker · Post by **cooker** » Sun Mar 11, 2012 8:35 pm

Who makes the Right, Left, Both selector? Where does one get a "both" selector quickly? and finally is it direct replacement or should we be prepared to make a bracket and make pluming changes??

Geesh i feel like i am taking advantage of all your knowledge

maules.com · Post by **maules.com** » Sun Mar 11, 2012 11:27 pm

Direct replacement already on TC. Maule has them, or you could ask them about the Andair fuel selector used nowadays.

maules.com · Post by **maules.com** » Mon Mar 12, 2012 7:42 pm

Take a look above fuel selector behind left kick panel and see if there is a header tank there even though it was an M4-220.

cooker · Post by **cooker** » Tue Mar 13, 2012 4:29 pm

No header tank, the front and back supply lines tee into the top of the selector

i have a "both" selector on order from Maule. It should provide a better degree of safety than just the "one tank at a time" method ........ I'm still having trouble talking myself out of the idea that a header tank would be benificial even with a carb to ensure uninterupted fuel supply but i guess it could add some problems as well and I don't think were gonna start into that at the moment.

maules.com · Post by **maules.com** » Tue Mar 13, 2012 6:13 pm

Well, no leakage there, and no header tank so still wondering where the 1.5 gals comes from.
Are your Aux tanks empty? Fuel can be leaking through the fuel transfer pump into the Main tank on the left wing but the right transfer pump could be not leaking.

cooker · Post by **cooker** » Tue Mar 13, 2012 8:19 pm

i don't have aux tanks in the wings, just 20 gal in the floats which is transfured to the right main via electric pump.

One thing that i have not checked is the fuel cap vent. I don't have the curved pipe vented tank caps but rather a spring loaded cap vent. If the cap is corroded or gummed up it may be possible there is some vaccum in the tank i suppose

the firewall fitting is significantly higher than the step drain and on the seccond try after the fuel quit running at the firewall i did manage to drain all but a few cups of fuel from the step drain with a little patients watching it girgle and squirt ... girgle and squirt ..... girgle and squirt .... not sure why i didn't think of the vent eirlier, i guess i didn't have much time to play with it.

I won't be home for a couple weeks but when i get there i will try again with the tank cap off .....

maules.com · Post by **maules.com** » Tue Mar 13, 2012 8:31 pm

If the original system only had the curved pipe fuel cap vents, probably best to go back to them as the later pressure valve caps do not pass much air.
How was your fuel pressure at climb?
If you have the vent pipes which exit the wing underside near the wingstrut attach point, there is an anti siphon hole in the back side. Remove the fuel cap and try blowing through the vent line into the tank.
If you cannot, then push a length of .032 or .040 safety wire through it almost to the tank, then blow into the tank to blow debri (mud daubers) back out the line.
Hopefully the experimental builder has not put a one way anti siphon valve in the line.

cooker · Post by **cooker** » Tue Mar 13, 2012 8:45 pm

with a full main tank we are seeing 4-5psi at the carb, below half tanks we have noted fuel pressure as low as 2.5 - 3 lbs at the carb. There is an engine driven fuel pump and lycoming min i believe is less than 1 lb ..... i agree with your comment suggesting pressure valve caps are limitting airflow

Unusable Fuel ??

Unusable Fuel ??

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