2026-04-30 · By the Auto Trends technicians
Northern Colorado winter is bimodal: most days are mild (40s and sunny), but the cold snaps are real cold — single digits and below for several days at a time, sometimes -20°F at night in the foothills or up by Wellington and Cheyenne. That’s cold enough to do real damage to a poorly-prepared vehicle.
Diesel trucks have an extra problem: untreated #2 diesel starts gelling at around 15°F and is fully gelled by 0°F. A gelled fuel filter means a no-start, period. Gas trucks have less to worry about with fuel, but cold-weather electrical and oil issues affect everything.
This post is the winter prep we do on customer trucks every fall. It’s not exhaustive — a heavy-duty work truck doing daily mountain runs needs more than this — but it covers the basics that prevent the common cold-weather problems we see.
A battery at 100% capacity at 80°F has 65% capacity at 0°F and about 40% capacity at -20°F. A battery that’s already weak from age is going to be useless on a cold morning.
What we do: load-test the battery (a 30-second test under engine-cranking load) and measure cold-cranking amps. If the battery is below 70% of its rated CCA, it’s a replace. We use AGM batteries with at least 800 CCA for diesel trucks, 750 CCA for V8 gas trucks, and 600 CCA for everything else.
Cost: $30 for the test (free as part of any maintenance visit). Battery replacement runs $180–$340 depending on truck.
Every modern diesel comes with a factory block heater — but most owners don’t use it because the cord is buried behind the bumper. Pulling the cord out and routing it to an accessible spot takes us 15 minutes and dramatically improves cold-start behavior.
For gas trucks that live in unheated garages or sit overnight in cold temperatures regularly, an oil-pan heater (like the Kat’s brand) is a $60 part that significantly reduces cold-start engine wear.
Plug the heater in for 3–4 hours before start on a day below 10°F. The truck will start instantly, fuel economy will be better for the first 10 miles, and engine wear is reduced.
Most pumps in Colorado switch to “winter blend” diesel (#1 + #2 mix, sometimes with anti-gel additive) starting in October. But the timing varies by station and there’s no guarantee.
What we recommend: add a quality anti-gel additive (Howes Diesel Treat, Power Service Diesel Fuel Supplement, or Stanadyne Performance Formula) at every fill-up from late October through March. Anti-gel additive is cheap insurance — about $0.20 per gallon — and it works.
If you’re heading up into the foothills or to Wyoming where temperatures get colder, also consider running 50/50 #1 and #2 diesel in your tank. Most truck stops in colder regions sell pure #1 — you can always find some at the Loaf ‘n Jug north of Fort Collins or any Pilot/Flying J.
What to do if you do gel up: change the fuel filter (frozen wax accumulates here first), warm the truck in a heated garage if possible, add anti-gel + #1 mix to the tank. If the truck is bad enough to need a tow, call us — we can usually get a gelled truck back running same-day.
Glow plugs are the diesel cold-start helper — they pre-warm the cylinders. Failed glow plugs make cold starts harder (sometimes impossible at very cold temps). Most modern diesels will throw a code (P0671, P0672, etc.) when a glow plug fails, but some don’t.
What we do during winterization: scan for glow-plug-related codes, measure the resistance of each glow plug, and replace any that are out of spec. A typical glow plug job runs $300–$700 depending on engine.
For gas trucks, spark plugs that are at the end of their life make cold-starts longer and rougher. If you’re approaching the spark plug replacement interval (typically 60,000–100,000 miles depending on engine), winter is a good time to replace.
The coolant in your truck should be a 50/50 antifreeze/water mix that’s good to about -34°F. If the system has been topped off with water (some shops do this lazily), the freeze point may be much higher. We test with a refractometer to verify the actual freeze point and confirm the coolant is the correct chemistry for your engine (OAT vs HOAT vs IAT — these matter).
If the coolant is more than 5 years old or 100,000 miles, schedule a flush before deep winter. Old coolant loses its corrosion inhibitors and can cause water-pump and head-gasket damage.
Aggressive all-season tires (Falken Wildpeak A/T3W, BFGoodrich KO2, Toyo Open Country A/T) are usually adequate for most Northern Colorado winter driving. Dedicated snow tires (Blizzak DM-V2, Michelin X-Ice) make a real difference if you commute over Cameron Pass, Berthoud Pass, or up to ski areas regularly.
The minimum: tread depth above 6/32″. Below that, hydroplaning and snow traction degrade rapidly. We measure tread depth as part of every multi-point inspection.
If you bring your truck in for a winterization service, here’s what we do: load-test battery + measure CCA, scan for glow plug codes (diesel), verify cold-start operation, test coolant freeze point and chemistry, inspect belts and hoses for cold-weather cracking, check tire tread + pressure, top off washer fluid with -25°F formula, route block heater cord to an accessible location, and add anti-gel to the diesel tank if applicable.
Total time: about 90 minutes. We always provide a written report with photos. If we find anything that needs work, we quote in writing — no surprises.
Mid-October is the sweet spot in Northern Colorado. Get it done before the first cold snap (usually late October to mid-November). Procrastinate past Thanksgiving and you’re playing chicken with the weather.
Below 20°F overnight, plug it in. Below 10°F, plugging it in is essential for diesels — your starter and battery will thank you, and your fuel economy on the first 10 miles will be noticeably better.
Belt-and-suspenders, yes — especially if you’re heading to colder regions (foothills, Wyoming). The anti-gel costs almost nothing per gallon and works as additional insurance against fuel quality variations between stations.
First, check that the block heater is plugged in (sounds dumb, but it happens). Second, check the fuel filter for ice / wax. Third, check battery voltage with a meter — anything below 12.0V resting is too low for a diesel. If those three are OK and it still won’t start, call us. We have ways to get a stuck diesel running and we have a tow service partner if needed.
Standard winterization (everything in this post) starts around $189. Add-ons like glow plug replacement, battery replacement, or coolant flush are quoted separately based on what’s needed. Most customers spend $189–$350 total for a comprehensive prep.
If your vehicle is showing the symptoms in this post, the next step is a real diagnosis. Bring it in or book online.
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