Fuel additives

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  • #83981
    jltaylor
    Participant

      This is the first winter with our 421B. The POH recommends adding alcohol, and says not to use prist for some reason. What do most of you do in the winter months? Do you use alcohol? Do some of you use low flow prist?
      We are based in Great Falls, Montana, so it seems we are in very cold temps most of the year at the flight levels – 20 to 25,000 ft? — anyone out there who has experienced fuel icing problems?

      #97376
      pmcnamee
      Participant

        We learned the hard way about fuel icing. Twice had to declare emergencies and go in to Reno when operating 1980 C-414A non-stop Palm Springs to Seattle.

        Winter operations. Warm fuel from fuel farm in Southern California. The warmer the fuel the more water moisture suspended in fuel.
        At normal cruise altitude FL220, 2 hours into flight both engines started slightly surging and fuel flows decrease along with EGT’s, got worst until could no longer hold altitude. Declared Emergency and start down. Of course, as you get into warmer air ice in the distributor (spider) valve thaws and engine starts run normally. Land and get alcohol or Low-Flo Prist.

        In the early ’80’s Cessna came out with a Service Letter suggesting the use of Low-Flo Prist. In 1981 Cessna added oil heated fuel distributor valves and the problems went away. Tip tank airplanes are more susceptible because less fuel cools faster at Altitude.

        1980 C-340A Fuel valve froze in the Aux tank position. Had to shoot an at minimums approach to Penticton, Canada with less than 5 gallons of fuel in aux. Would have been unable to fly a go-around without fuel starvation on that engine.

        If flight is planned to be at altitude long enough to take fuel temperature below freezing we always add additive IAW Cessna recommendation. This is really scary the first time it happens to you.

        Keep’em Flying

        Pat

        #97381

        Hey guys not to sound stupid, but where would a guy pick up these additives?
        I plan to fly from okla, to fla,at altitude. Though it is not as cold as up north I would
        believe the temps at 24000 would be in the minus temps. I made a trip 2 weeks ago
        and got to enjoy the pilots window on the shady side ice up on the inside,don,t want
        to fight frozen fuel lines ,or ice elsewhere in the system.

        gthornton

        #97382
        #97385

        . Thanks Rich for the info. Question, How much of this product is required for approx 2hanks again gthornton38 gals. ? What is
        the best way to formulate it in the fuel tanks.? Thanks gthornton

        #97386

        Rich that was 238 gals. g.t.

        #97387

        Looks like 16 oz to 100 gl, but… I’ve never felt the need to use prist or alcohol, so I’m no “expert”. I limit myself to 18,000 in spite of my airplane’s 28.2K service ceiling 🙂

        Here’s another link:

        http://www.pristaerospace.com/hi-flash/use/index.html

        #97397

        I may be doing something wrong with this, but I go to my local wal-mart or other flavor and pick up the pure stuff. It’s cheap and readily available.

        #97398

        So another dumb question – does this seem to only be an issue at the high altitudes, ie a problem with both temp and altitude? I’ve flown the 310 at -40C temps (Canada in January, was -20C on the ground) without any issues. But maybe I was just lucky. Of course, the fuel also came from a very cold fuel farm.

        #97399
        quote ZARMSTRONG:

        I may be doing something wrong with this, but I go to my local wal-mart or other flavor and pick up the pure stuff. It’s cheap and readily available.

        My book “recommends” no water dilution for the windshield alcohol system, although I’ve been known to use the 70% stuff from local stores. Right, it’s inexpensive and available. Just for “grins”, a couple of winters ago, I put a qt. of 70% isopropyl in a glass mason jar and put it in the chest freezer with a thermometer. At 0 deg F, the next morning, I found no ice crystals in the clear liquid. I don’t feel bad about using the 70% in the windshield tank, but I’d hold out for the 99% or pure for fuel tanks. I’ve not found 99% at local stores. FWIW.

        Here’s another:

        http://www.cqconcepts.com/chem_isopropylalcohol.php

        #97400
        quote TDUPUIS:

        So another dumb question – does this seem to only be an issue at the high altitudes, ie a problem with both temp and altitude? I’ve flown the 310 at -40C temps (Canada in January, was -20C on the ground) without any issues. But maybe I was just lucky. Of course, the fuel also came from a very cold fuel farm.

        I think the cold fuel farm helps, Ted. I’ve been lucky too, never had a problem. Yet.

        I do recall, as a kid, having a pair of pliers handy in my Dad’s Aztec. In case of frozen fuel selectors flying Lock Haven to Burlington, VT, during the winter months. 🙂

        I started looking at iso alcohol and Prist a couple of years ago when the frozen selector issue came up on one of the Comanche forums. Leaking fuel caps and obvious water in drained fuel samples was the main culprit, but it was pointed out that avgas can hold invisible water that will, under the right conditions, form ice crystals capable of clogging filters, screens, spiders, selectors, etc. I don’t want to see “cloudy” fuel when checking sumps.

        #97401

        That’s interesting, Rich. In 1,000 hours in my Aztec, including crappy winter weather, I never had a frozen fuel selector issue. I also flew the plane a good bit, so it never sat long before getting fresh fuel..

        My wife said they never used alcohol in the 310 or 340 out in Montana, but I don’t want to find out the hard way that we should be doing it. We will go to 15k in the winter sometimes.

        #97405
        quote TDUPUIS:

        That’s interesting, Rich. In 1,000 hours in my Aztec, including crappy winter weather, I never had a frozen fuel selector issue. I also flew the plane a good bit, so it never sat long before getting fresh fuel..

        My wife said they never used alcohol in the 310 or 340 out in Montana, but I don’t want to find out the hard way that we should be doing it. We will go to 15k in the winter sometimes.

        Don’t remember that we ever had to actually use the pliers. Seems that Dad was advised to be prepared by someone at the factory or one of his instructors. The early 60’s was a long time ago 😯 FWIW, I always have the Leatherman on my belt when I go flying.

        As I’ve said, I have not felt the need to use either alcohol or prist. Nor did my AP/IA, when he owned a Part 135 co. flying 320’s, 310’s, 340’s and Navajos around the Inter-Mountain West.

        My 310 is inside an un-heated t-hangar. I keep the tanks full. I’ll keep checking my drained fuel for any contamination, including “cloudy” fuel. I want my drained 100LL to look like Yukon Jack Permafrost schnapps … blue and crystal clear 😀

        #97407
        pmcnamee
        Participant

          Don’t make the mistake thinking that you will see the water during preflight. This water is suspended in all aviation fuels. The amount is a function of temperature, as is specific gravity. It’s not a matter of if you get it, it’s a matter of when you’ll get it. Think about it like you do with Carb. Heat in a carburetor. If you fly long enough above the Freezing Level the fuel will cool below freezing, the water particles will freeze and plug something up.

          Our airplanes do not have fuel temperature gauges that are required for the FAR25 airplanes. You either protect the fuel with additives or install the heated fuel manifold (spider valve) heated oil mod. That will not keep the fuel selector valves from freezing.

          I don’t have access to Cessna Service Letters at the moment, but maybe someone can pull it up and post it here.

          Keep’em Flying

          Pat

          #97408

          Right, Pat, I’ll likely not see suspended moisture. But… Since my airplane is stored at ambient temp, should I drain cloudy fuel on a cold, frosty morning, the flight will be cancelled. For suspended ice crystals. Best I can do.

          Should I ever have occasion to buy fuel in Phoenix, in January, coming home to sub-zero temps, I’ll ask for prist, like a corporate jet jock. 8)

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