Yesterday was a perfect winter flying day in New England, 20F, sunny, dead calm, fresh carpet of snow to ogle.

Alas, while pre-flighting my 170 i couldn't push in one of my fuel sumps. The sump would spin freely but wouldn't push in easily. I pulled out my trusty space heater and aimed it at the fuel sump for a while. Sure enough after a few minutes the sump moved freely and a bit of water came out into the GATS jar. I sumped it a few more times and got some ice crystals out of the sump, and eventually only fuel. Since I'm located on the paranoid end of the spectrum I reasoned that there might be more ice within my fuel tank and I pushed the plane back into the hangar, kicked some snow banks, and went home.

Today it's 50 degrees (and Low IFR) I plan to go to the hangar after work and sump fuel until I'm "confident" that there is no water left in the system.

I can't be the first person to have encountered frozen water in my fuel system.

Question #1 What do i do about it?

Question #2 Since the sumped fuel was clear. Should I have just gone flying?

Any water at the low point of the fuel system or was it all in the tanks

As far as I can tell it was all from the left wing sump. I have a belly sump and of course the gascolator. Did not get any water out of them.

I left my plan out in a heavy rain before i flew last. I thought I got all the water out before flying... guess not.

I'm not sure where Charlestown is but being from a northerly latitude myself I would hazard a guess that many airplanes fly around all winter with some ice frozen in the bottom of the fuel tanks, any ice downstream of that could lead to an "operational issue" !!

It sounds like you chose to go with a cautionary approach, good call I'd say.

You did the right thing. Never force a drain open in freezing conditions it always wrecks the seal and leaks immediately if there is any ice.

According to Cessna it is OK to use Isopropyl alcohol to deal with the ice crystals that form inside the tank. No more than 1% of volume.

This is not to remove any quantity of water, just a means to not have issues with ice crystals building up in the fuel system.

And yes once all fuel drains clean you can go fly.

ALL fuel contains SOME water. As fuel cools, some of that water "condenses", and if it's cold, freezes into crystals you described. In this case, you're probably right that what you found was rain water, likely leaked in via a fuel filler, or??

I'd get some 90 + % Isopropyl Alcohol (NOT Methyl Alcohol) and pour it into that wing tank, then slosh it around some by rocking the wing.

What little water is left in there will be absorbed by the Isopropyl, which will also prevent it from freezing again. Which will allow you to drain it. Isopropyl Alcohol is approved for use in aircraft engines, though I've forgotten the specific amount.

I've used red can HEET, which is high percentage isopropyl, in my fuel tanks in freezing weather for decades. One of the small red bottles in each fuel tank of a 170 should be fine.

Again, don't use the yellow bottle HEET, only the red bottle.

Thanks for the intel on adding ethanol to the fuel. If I get into a situation where I need to leave it outside for another thaw freeze cycle I’ll add some.

Got the plane thawed out. Sumped a gallon of fuel from it (and a teaspoon of water). Went for a rip.

Thanks again everyone!!

SmokeyTheBear wrote:Thanks for the intel on adding ethanol to the fuel. If I get into a situation where I need to leave it outside for another thaw freeze cycle I’ll add some.

Got the plane thawed out. Sumped a gallon of fuel from it (and a teaspoon of water). Went for a rip.

Thanks again everyone!!

NO, definitely NOT ethanol. That is specifically prohibited for use in aircraft fuels.

The ONLY type of alcohol that's approved in aircraft fuels is ISOPROPYL alcohol.

SAFETY WARNING attention: NO ETHANOL

Guess that moonshine is going to go to waste….

Isopropyl. RED HEET. Got it!

SmokeyTheBear wrote:Guess that moonshine is going to go to waste….

Isopropyl. RED HEET. Got it!

I don't think it needs to be a specific brand name that you will simple pay more for. A basic isopropyl in a small quantity will do the job just as well.