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  • How to Winterize a Diesel Engine

How to Winterize a Diesel Engine

Top 5 “check, add, and replace” suggestions to ensure your rig is ready for winter’s deep freeze.

Dec 18, 2020
Photographers: Courtesy Of Truck Trends, Hot Shot’s Secret
Although there are a few states that have experienced cold temperatures and, in a few instances, snow, since October, we're now in the heart of winter, the season that officially runs from December to March but often lingers until as late as May.
In traditionally cold areas, the air is chilly for weeks at a time, and "nice" 40-degree days typically are followed by weeks of subzero degrees and blizzards. On a people level, these climates and conditions are not for the faint of heart, and they require preparation to ensure we're able to make it to springtime.
Cold can wreak havoc on mechanical things with the same vengeance it has on living creatures. For diesel engines, new, and especially older oil burners using glow plugs, measures must be taken when winter sets in, to protect powerplants and ensure rigs remain reliable until climates get warmer.
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If you're in an area that experiences severe cold (below 0 degrees Fahrenheit), or even for trucks that are driven regularly in "warmer" 30-degree temperatures, here's a quick list of five simple things to note, check, or do to maintain your rig's engine and ensure it starts and runs when and as you need it to, every time.

Battery Check

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The lower the ambient temperature is or gets, the fewer electrons a battery generates, and thus it is unable to produce sufficient current to start an engine. The loss can be as much as 20 percent in 32-degree weather. If engine cranking is slow or seems labored, have a technician (or DIY if you have the equipment) perform a battery load test to determine its true condition (a voltage gauge/meter won't tell you everything). In the strong likelihood that you need to replace the battery, consider also adding a battery warmer to keep the new cell heated while your truck is parked (similar to a block heater). Fresh batteries and accessories like warmers bring confidence that an engine starts and runs every time during the winter months.

Glow Plugs

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If it's not the battery, it's the glow plugs, again, especially with older Cummins, Duramax, or Power Stroke engines. Glow plugs can heat each cylinder's combustion chamber to almost 1,900 degrees Fahrenheit, and somewhat "warm up" a cold engine before it is started. Glow plugs are tested using a specific testing device, which doesn't require removing the plugs to complete the procedure. That's the easy way. For OG traditionalists, or those who want to save $200 by not buying the tool, use a multimeter to check plugs' resistance (from connector to the body). Place one point on the battery's positive post and the other on the plug's body. Make a note of the reading, which should be between .6- and 2 ohms. After checking all of the plugs, remove those with readings greater than 2 ohms. Always install factory-manufactured or endorsed glow plugs if possible.

Fuel Filters and Additives

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Diesel fuel arguably suffers the most in cold-weather conditions. Paraffin in the fuel freezes easily, creating waxlike gel that can block almost everything in the system—especially filters. Excessive moisture (water) also creates problems by freezing in the lines and filters. Isopropyl is diesel fuel's cold-weather friend. It absorbs water and reduces fuel's freezing point, but more important, it completely dissolves in diesel so there is no contamination. Fuel should be treated with additives such as Hot Shot's Secret Diesel Winter Anti-Gel that protect fuel systems against freezing water and wax buildup. Installing a clean fuel filter at the start of winter will also help ensure a diesel engine survives winter's cold.


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Oil—more specifically its thickness/viscosity—is one of the main things to be mindful of when cold weather sets in. The 15W-40 crude that most engines use typically thickens in cold temperatures, and this increased viscosity can lead to starting difficulty and insufficient lubrication of bearings and other engine internals. In cold weather, "thin" is what's happening when it comes to the primary engine lubricant. Switching to 5W-40 provides better flow and protection, and it also thickens enough to increase oil pressure. Diesels used in subzero cold will probably fare very well with ultra-thin 0W-40. Using thinner oil will also help take some of the stress off a diesel truck's battery, starter, and fuel system.

Block Heater

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Arguably the best cold-weather accessory a diesel pickup can have, 110-volt block heaters do exactly that: keep the engine block (and coolant) warm when a diesel truck is parked—typically overnight. Stock and aftermarket heaters help make cold starts much easier and only require a good extension cord to use.
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