The short answer
Ford's 2026 Super Duty manual says the engine block heater is most effective below 0°F and shouldn't run more than three hours at a time, and that diesel exhaust fluid may freeze below 12°F (the truck has a heater, but a truck parked for days in the cold can have a frozen tank). Ram's 2026 heavy-duty handbook recommends 5W-40 synthetic oil in the 6.7L Cummins below 0°F, and a diesel fuel treatment against gelling if No. 1 or climatized fuel isn't available when you operate below 20°F in sustained arctic conditions.
Neither manual wants alcohol-based additives, and both cap biodiesel blends: Ford at B20 and Ram at B20 for pickups (B5 otherwise).
Block heater
Ford: the block heater warms the engine coolant, plugs into a grounded 110-volt outlet, is most effective below 0°F, and shouldn't run for more than three hours. Check that it works before winter, and unplug the cord from the outlet and the truck before you start. On Ram heavy-duty stickers in our stock, the $245 Cold Weather Group lists an engine block heater and a winter front grille cover; see Cummins vs. HEMI.
Diesel exhaust fluid (DEF)
Ford says DEF may freeze below 12°F. The truck's preheating system lets it operate below that, but if the truck sits for an extended period below 12°F, the tank can freeze. If it's frozen, the gauge may not register a refill until it thaws. Ford recommends filling before or after a drive of more than 20 minutes and warns that overfilling a tank that then freezes can cause damage the warranty won't cover. Ram specifies API-certified DEF meeting ISO 22241.
Fuel and gelling
Ram: No. 2 diesel (ASTM D-975 Grade S15) works for most year-round service; if climatized or No. 1 ULSD isn't available and you're operating below 20°F in sustained arctic conditions, use Mopar Premium Diesel Fuel Treatment or an equivalent to avoid gelling. Ford: use Motorcraft anti-gel and performance improver or an equivalent if fuel gels; don't use alcohol-based additives; if you get cold-weather gelling or frequent LOW FUEL PRESSURE messages on biodiesel, try another brand or a lower biodiesel blend. Drain the fuel-water separator when the truck tells you to.
Winter oil grade
Ram's 6.7L Cummins: 10W-30 above 0°F; 5W-40 synthetic below 0°F, meeting MS-10902 and API CK-4. Ford also recommends 5W-40 when running more than 5% biodiesel. Follow the grade in your own manual.
Checklist
Before the first cold snap
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Service in Barron
Swant Graber Motors (Chevrolet, Ram, Dodge), 1690 E Division Ave, Barron, 715-537-5657. Service hours: Monday–Friday, 8:00 a.m.–5:00 p.m. (no Saturday service). Service loaners are available; ask the service department when you book. You don't have to use a dealer to keep your warranty; keep receipts wherever the work is done. Swant Graber Ford, 1697 E Division Ave, Barron, 715-537-9500.
Questions
At what temperature does DEF freeze?
Ford's 2026 Super Duty manual says diesel exhaust fluid may freeze below 12°F. The truck has a heater for operation, but a parked truck's tank can freeze.
How long should I plug in a diesel block heater?
Ford's 2026 Super Duty manual says not to run the engine block heater for more than three hours, and that it's most effective below 0°F.
What oil should a Cummins use in winter?
Ram's 2026 heavy-duty handbook recommends 5W-40 synthetic below 0°F and 10W-30 above 0°F, meeting MS-10902 and API CK-4.
Can I use alcohol to keep diesel from gelling?
No. Ford says not to use alcohol-based additives; use an anti-gel additive approved for diesel instead.
Next steps at Swant Graber
Swant Graber Motors (Chevrolet, Ram, Dodge): 1690 E Division Ave, Barron, WI 54812, 715-537-5657. Swant Graber Ford: 1697 E Division Ave, 715-537-9500. Search new or used inventory, or see shop near you for model-by-model answers.
