Diesel / Alaska winter
Keeping a diesel running through an Alaska winter
Two things stop a diesel at forty below: fuel that gels and oil that’s too thick to crank. AMSOIL says its Diesel Cold Flow lowers diesel fuel’s cold filter-plugging point by up to 40°F, but it has to go in before the fuel reaches its cloud point. For oil, run the lightest grade your owner’s manual allows; AMSOIL’s 0W-40 Max-Duty is its coldest-starting diesel grade.
From AMSOIL product pages, checked October 10, 2026 · Fredric Riech · Independent AMSOIL Dealer · Wasilla, Alaska since 2013
Why does diesel fuel gel?
Diesel fuel carries wax. AMSOIL explains it this way: as the temperature drops, the wax starts to crystallize. The temperature where crystals first form is the cloud point, near 32°F for most fuels and as warm as 40°F for low-quality fuels. As it keeps getting colder, the crystals clog the fuel filter and starve the engine; that temperature is the cold filter-plugging point, or CFPP. In Alaska we spend a lot of the winter below both.
#1, #2, and winter blends
Cutting #2 diesel with #1 is the traditional fix. AMSOIL notes the trade-off: #1 diesel has better low-temperature operability, but its energy content is about 95 percent of #2’s, so a heavier #1 blend gives up some energy per gallon. What your station sells changes through the season, so ask what is in the tank, especially before a trip from the Mat-Su up to the Interior.
Where AMSOIL Diesel Cold Flow fits
AMSOIL makes two fuel additives with cold-flow protection. Here is what AMSOIL says about each:
| Product | What AMSOIL says it does | How to use it |
|---|---|---|
| AMSOIL Diesel Cold Flow | Lowers cold filter-plugging point by up to 40°F (22°C) in ULSD; wax anti-settling; inhibits fuel-filter icing; safe in all diesel fuels, including biodiesel; alcohol-free | Add before filling, above the cloud point. Won’t reverse gel. Don’t store below 0°F (−18°C) |
| AMSOIL Diesel 4-IN-1 | Combines Diesel Injector Clean, Diesel Cold Flow, and Diesel Cetane Boost; lowers CFPP by up to 40°F (22°C); raises cetane up to 4 points | One ounce treats up to 2.5 gallons of fuel |
The rule that matters most: treat before the cold, not after the truck quits. AMSOIL says Diesel Cold Flow has to go in above the cloud point and will not reverse gel or wax crystals once formed. Shop Diesel Cold Flow or Diesel 4-IN-1.
Which Max-Duty oil for an Alaska winter?
Start with your owner’s manual: it lists the viscosities your engine allows by temperature. If it lists 0W-40, AMSOIL says its 0W-40 Signature Series Max-Duty Synthetic Diesel Oil delivers 4X better cold-temperature performance than SAE 15W-40 oil in the ASTM D5293 cold-cranking viscosity test. AMSOIL makes Max-Duty in other grades for engines whose manuals call for them. See the full lineup on AMSOIL diesel oil.
Plug-ins, block heaters, and idling
This part is experience, not product claims. Most diesels that live outside up here wear a cord through the grille. A block heater, and on a lot of trucks an oil-pan pad and a battery blanket, are what make a cold start an easy one. Plug in on a timer so the engine is warm when you leave, not all night. Long idling to warm up a cab is hard on a diesel and counts against you on oil life; see the next section.
Idling, plowing, and severe service
AMSOIL defines severe service for diesels as extensive idling, daily trips under 10 miles, or frequent dusty driving. Plenty of Alaska pickups hit the first two all winter: remote starts, job-site idling, short runs into town. Plowing and heavy towing add load at low road speed. If that is you, follow your engine maker’s severe-duty schedule and AMSOIL’s severe-service interval for your oil, and keep a log of miles and hours.
Stock up before freeze-up
Fuel additives have shipping limits. AMSOIL says fuel additives can’t go by air freight or parcel post, so off-road-system orders need ground or special arrangements through USPS or Carlile. AMSOIL also says not to store Diesel Cold Flow below 0°F (−18°C), so keep the bottles in a heated space, not behind the seat. Shipping, pickup, and AMSOIL’s Alaska freight surcharge are on buying AMSOIL in Alaska.
More cold-weather reading
Engine oil viscosity for the cold is covered in the Alaska oil viscosity guide and on the Alaska page. Questions about your truck? Call or email me in Wasilla.
Alaska winter diesel, answered
At what temperature does diesel fuel gel?
It depends on the fuel. AMSOIL says wax in diesel starts to crystallize at the cloud point, which is near 32°F for most fuels and as warm as 40°F for low-quality fuels. The fuel filter plugs at a lower temperature, the cold filter-plugging point (CFPP). #1 diesel and winter blends have better low-temperature operability than straight #2.
Can AMSOIL Diesel Cold Flow un-gel fuel?
No. AMSOIL says Diesel Cold Flow must be added at temperatures above the fuel’s cloud point and will not reverse gel or wax crystals once they have formed. Treat the fuel before the cold, not after the truck quits.
Do I need Diesel Cold Flow if I already buy winter-blend fuel?
Not always. AMSOIL says Diesel Cold Flow is safe for all diesel fuels, including biodiesel, and that it minimizes the need to blend #2 with #1 fuel. If your fuel supplier’s blend and your trips keep you out of trouble, you may not need it; for deep cold, long cold soaks, or fuel you are not sure about, it is cheap insurance.
0W-40 or 5W-40 for a diesel pickup in Fairbanks?
Use what your owner’s manual allows for the temperatures you see. If the manual lists 0W-40, that is the cold-start choice: AMSOIL says its 0W-40 Signature Series Max-Duty Synthetic Diesel Oil delivers 4X better cold-temperature performance than SAE 15W-40 oil in the ASTM D5293 cold-cranking viscosity test. The AMSOIL vehicle lookup lists the grades for your engine.
Does idling count as severe service?
Yes, by AMSOIL’s definition. AMSOIL defines severe service for diesels as extensive idling, daily trips under 10 miles, or frequent dusty driving. Remote-start and job-site idling add up fast in an Alaska winter.
How often should I change oil if I plow?
Plowing is hard work at low road speed. Use your engine manufacturer’s severe-duty schedule, and if your use fits AMSOIL’s severe-service definition, use AMSOIL’s severe-service interval for your oil. Write the hours and miles down.