M20K Fuel Measurement

[dtoelke]

Before anybody asks, yes I have looked through the old threads dealing with this topic and I could not find what I was looking for.  So, two questions...

 

1) At what fuel fill level has the 36 useful gallons been met on each side?  Should it be even with the backflow valve, or higher, or lower?

 

2) Would any 231 or 252 owners out there happen to have a calibrated dipstick and be willing to share their measurements?

 

Any help would be greatly appreciated.  Thanks!

 

[peter]

SN 25-0446 and earlier have 72 gallons useable. 25-0447 and later have 75.6.

 

I realize the following doesn't directly answer your question, but it might be helpful anyway.

 

We drained the fuel and refilled our 82 M20k several years ago - our serial number is above 25-0447.  For our aircraft when the fuel is at the bottom of the filler neck we have 34 gallons of useable fuel. From there, fueling slowly and "burping" the wing while fuel rises above the base of the filler neck will allow us to add the remaining 3.8 gallons to get to "full full", which corresponds to fuel starting to spill out onto the wing.

 

When we drained and refilled we found that the wing site gauges were pretty accurate throughout the fill range. The right gauge was correct at all value and left indicator under read the actual fuel by 2-3 gallons for all partial loads below 25 gallons. Above 25 gallons it was correct.  Both wing gauges showed empty (no longer moving when sloshing the wing) when there was 5 gallons fuel remaining in the tank.  The panel gauges were wrong everywhere bat at E.  The tanks are truly empty the instant the needle aligns with the red mark (and not below the mark like in a car).

 

Our low fuel lights came on at 4 gallons left and 5 gallons right.

 

Hope this helps.

 

Peter

82 M20k 231

[dtoelke]

Thanks Peter, that's some good information.  Hopefully somebody with a S/N less than 25-0447 will chime in (mine is a '79) as well.

[Houman]

Not really directly related to this post and not wanting to hijack it, but I have a problem with my right fuel sender, I have a M20K Rocket with a serial lower than 25-0446, and when both tanks are full to the wing overspill level, my panel gauges are at Full on the left tank, but at 27 Gallon (3 rd making on the gauge ) on the right tank. I know that it must be the sender or the gauge the problem and looking to get it fixed at the next annual.

 

So that being said, I'm also very interested in a measuring stick, what I find difficult is that with the claps at the tank opening, it is almost impossible to see visually how much fuel is in the tank unless it is full...

[schule]

The wing sight gauges are most accurate on the ground. The cockpit gauges are only most accurate in a level attitude equivalent to flight. And I believe only guage required to be correct is the cockpit gauge when on E in flight.

Although close from wing to wing and 231 to 231, they may not be exactly the same measurements, especially if the fill site has a slight left/right or fore/aft slope. Would be terrible to get someone else's measurements and run yourself out of gas thinking you have enough.

Might be worth it to make your own specific to your aircraft by draining the tanks, adding in the requisite unusable, and then adding a few gallons at a time.

[dtoelke]

Good point.  How do you drain the tanks completely (including the reserve)?