Pre Heating

[LToxvard]

Starting to get some really cold days in Colorado, and would like some cold weather advise, geared toward the 0-300, as when to pre heat and when it is safe to fly, as far as engine longevity. I have a rule to pre-heat at 40 degrees or bellow and I install the oil pan cooler block in the cowling bellow 20 degrees. I know when I rented various aircraft they really didn't want you to do pattern work in the single digits. Thoughts?

[hilltop170]

You're on the right track, if you use 100W straight oil, pre-heating at 40°F is probably prudent. I use 15w-50 in the winter in Alaska and pre-heat and tape-over the lower oil tank inlet below 30°F. Cold starts are about the worst thing you can do to the engine in the winter so more pre-heat is better than less. Engine fires due to overpriming a cold engine are more common with insufficient pre-heat. Keeping the engine warm while flying is not that much of a prolem.

When its cold and you're concerned about keeping the engine warm, you really should always keep rpm in the green even on descents and in the pattern. Some say that it is not possible to descend or make an approach and keep the engine warm at the same time. Nothing says you can't start your descent earlier and leave the power at cruise rpm during the descent or lower full flaps on downwind which will then require power (rpm in the green) to be held all the way to the ground. The engine will be just fine at any ambient temp down to -20°F as long as you keep rpm in the green. Colder than that keep rpm high up in the green and use full rich and carb heat if necessary to enrich the mixture further in very cold temps especially when close to sea level. Density altitudes can be thousands of feet below sea level in -30° to -40°temps requiring much richer mixtures than normal. The airplane can be safely operated in those conditions when operated properly but it is much more risky below -20°F.

My personal cutoff is -20°F not only because of the problems caused by colder temps on the airplane but because if you have to make an emergency landing, if you as much as sprain your ankle it could be fatal. You only have minutes to put your survival gear to work and survive. You do require every occupant to dress appropriate to the conditions and carry survival gear for all occupants appropriate for the conditions to be encountered don't you?

[rusbac]

Another cold related question:

I almost never find water when I sump my tanks, but what would happen to that water when the temps get well below freezing?
Does the water turn to ice? Does water ice float or sink in avgas? Does it have the ability to clog a fuel line?

[bagarre]

Another cold related question:

I almost never find water when I sump my tanks, but what would happen to that water when the temps get well below freezing?
Does the water turn to ice? Does water ice float or sink in avgas? Does it have the ability to clog a fuel line?

In my 6 years with 81D, I rarely had water in any of the sumps.
Water is heavier than fuel so it sinks to the lowest point it can find. Thats why sumps are at the lowest points. The fuel selector has a plug that's supposed to be removed at each annual to drain any water/crud that might settle there.

I don't know if ice floats in fuel but my guess is no. Would be a neat experiment to drop an ice cube in a bucket of 100LL tho.

Water will freeze in fuel which could block a line. If there is enough water, it can freeze and split a fuel line or crack your fuel valve body. I've never heard of that happening in an airplane but I've replaced plenty of copper pipe in our old home to freezing water and I've seen it crack an engine block (used water vs anti-freeze)

[hilltop170]

Well, here is the answer to the age-old question I just heard for the first time this morning, "Does ice sink in 100LL?". Yes. Immediately without hesitation.

Ice cube in 100LL

If you are concerned about ice crystals in the gas, you can safely use isopropyl alcohol to help remove them. If the gas tanks are not completely full, condensation can form on the inside forming what I assume looks like hoar frost although I have never seen it. Then as the gas sloshes in the tank and washes it off, it is now mixed into the cold fuel as ice crystals. I have heard these loose crystals can migrate to the fuel outlet strainer and possibly plug it off, again I have never heard a first-hand story of that happening. Always leaving the tanks completely full will help reduce the potential but unless your plane is level when it is filled as when on floats, there will always be some room at the top that is not completely full so there is no perfect answer other than heated storage. But again, flying in Alaska winters for 33years, I have never had a problem with ice in the gas tanks causing problems. As sneaky as gasoline is in finding ways to leak out of anything, I can't help but think it would find a path thru loose ice crystals around the fuel outlet strainer no matter how much ice there was. Maybe someone else has had trouble with it but not me and my plane never spent one night in a warm hangar in 23 years in Alaska.

Isopropyl alcohol

Isopropyl alcohol

[c170b53]

Hummm... that canning jar's contents looks suspiciously like UV Vodka.

[hilltop170]

Nope, it's pure 100LL, the previous contents of un-taxed water removal solution from the back woods of West Virginia have already been consumed.

[Ryan Smith]

I rarely get water in the fuel in 56D, but when I was preflighting on a chilly morning (high teens) last week, I was almost hoping there would be a little bit of water in the fuel, because I hypothesized that I wouldn't get anything out of the sumps.

If It weren't dangerous to try, I'd almost be interested in dumping a little water in the tank of an abandoned airplane and then try to sump it after it has been below freezing for several days just to see if it would freeze over the sump.

[rusbac]

Ryan, I had the same thought when I was pre-flighting this week. If the water is sitting at the sump when it froze (and now we know, ice doesn't float), I wondered if I'd get any gas out of the sump.

Sigh - I really just need a hangar!

I rarely get water in the fuel in 56D, but when I was preflighting on a chilly morning (high teens) last week, I was almost hoping there would be a little bit of water in the fuel, because I hypothesized that I wouldn't get anything out of the sumps.

If It weren't dangerous to try, I'd almost be interested in dumping a little water in the tank of an abandoned airplane and then try to sump it after it has been below freezing for several days just to see if it would freeze over the sump.

[LToxvard]

Good stuff, one time years ago I was preflighting a Cherokee 180 on a very cold morning and noticed the bottom of my fuel sample looked extremely cloudy, after a closer look it was definitely ice. The water had crystallized to almost the same consistency of snow. It all drained out fine, but I filled the cup about four times per side until I was comfortable it was completely removed.

[Bruce Fenstermacher]

Christine,

My plane has lived at least the 50 years outside. My partner has owned all or part of it since 1968. To say he's flown the plane a little in the cold freezing weather in PA would be an understatement. He doesn't bother to sump any sumps when it's freezing. Reason is the water would be frozen, if there was any, and wouldn't come out. He does not want the sump to get stuck open.

[hilltop170]

It's easy to tell when water has frozen in your tanks. The water will freeze in the drain valves as well and they will not move. I have had that happen. Don't force them or you might rip out the o-ring. At least you know the water isn't going anywhere. When it warms up they work again normally.

[pdb]

I check the sumps every flight. If the quick drain is frozen stuck, I stop right there and try some isopropyl. Like Richard says, if you to try to bust it loose, you will likely just bust it. My plane is always outside and I do experience water in the fuel from time to time and have had things freeze up.

If the isopropyl doesn't work, it goes into the hangar until things thaw enough to clear the blockage. I don't think any good comes from flying with either water or ice in the fuel system.

[170C]

All I can say is you guys flying in sub zero temps must have a better heater than I do, be nuts , have on a lot of warm clothes or just be TOUGH I can manage to stay pretty comfortable at +25 with lots of clothes (makes fastening seat belt difficult). Not sure what survival items would be recommended in TN.
I have a 1500 watt electric heater and duct work to force air up under my cowling opening on the bottom, a moving blanket over the engine and cooling inles and a towel stuffed in the oil cooler hole. Although leaving the heater on over night doesn't help any more than turning it on for several hours, its more convenient. Everything feels nice and warm when the oat is in the low 20's, but it still takes a while for the oil temp to show on the gauge. I suppose when I don't fly, and the heat is on, and I turn the heat off that as the engine cools, it draws cool, moisture laden air into it innards, but I don't know how to avoid that in a non heated hangar.

[GAHorn]

FAA and Cessna state that only ISOPROPYL alcohol is allowed in aircraft fuel for ANTI-icing purposes (not DE-icing, and not more than 1% by volume, and is best ALREADY MIXED during fueling...not simply added to frozen fuel.. NEVER ETHANOL.)

This is NOT your medicine-chest rubbing alcohol (which contains water and sometimes glycerine as well) but is only pure "anhydrous" which means DRY, PURE, Isopropyl.

HEET (brand) is NOT ISOPROPYL. It is methanol and other "secret ingredients". It is unapproved for aircraft use.