Betting On Your Batteries: Tips for Starting Diesel Engines in Sub-zero Temperatures

Tip # 1:  To avoid risk of explosion, DO NOT attempt to jump start a battery in below freezing temperatures.

Tip # 2:   Increase your chances of engine start up by warming your battery above freezing before use.

Tip # 3:  Pre-heat your engine block using various methods before relying on your battery to start the engine sub-zero temperatures.

Tip # 4:  Keep your battery maintained to prolong its use and preserve its starting capacity

Operating heavy machinery in sssssssusususussssssssssub-zero temperatures calls for special preparations.  As long as you can start the machine, you’re generally good to go– put on some warm clothes and get on out there, right?  This weekend I was reminded the hard way that it’s not that simple.

It’s Sunday morning and I’m stuck with a rented excavator that won’t start.  I’ve taken the battery out and am now trying to warm it.  With half the day gone by, my progress level is equal to the temperature outside: zero. The battery is still on the charger… I’ll write while I wait…    Hopefully by the time I finish this article things will have turned out for the better…

This weekend I decided to rent an excavator to get ahead on a road building project.  I’m carving out about a thousand-foot stretch along the treeline of one of my fields.  “An excavator???- But it’s freezing cold out there,” was the first remark from the guy working the rental shop.  “Yea, you’re right,” I told him.  I had also been telling myself I might be crazy all along.  But a respected contractor told me once that winter can be one of the best times to dig on a building project.  The frost cuts down on the muddymess and traction for your machinery can be superior.  I had also confirmed that the ground was soft under the 8-inches of fluffy snow we just had.  I hand-dug a few test holes.  Despite deep frost above ground, the soil below was still as soft as warm butter!


Operating heavy machinery in winter is doable. Erosion protection will be needed once the ground thaws in the spring.

  All I had do was get the thing started.  Sunday morning I mounted the machine dressed like a north pole explorer.  I turned on the glow plugs, and cranked it over.  Nothing short of a sputter.   I repeated about six times, but all it would give me was one or two pitiful cranks,


and it was a lost cause.  After cursing to high heck I quieted down.  I was the source of my own stupidity.  It was 5 below that morning, and I knew I should’ve brought that battery inside the house for the night, but I didn’t.  Of course the thing won’t start!  It didn’t matter what kind of engineering was under the hood of that machine; there was a diesel engine inside that had not been plugged in despite temperatures dropping to below five degrees that night.  It didn’t have a block heater, so all bets were on the battery for a successful start-up. 

First tip for betting on your starter battery is to put safety first:

Jump starting a battery in below freezing temperatures (vs. jump starting a warm battery) greatly increases your chances of having the battery explode.  Do not attempt to jump start or charge a battery in sub-zero temperatures.  When batteries are at a low state of charge, the liquid electrolyte inside can freeze.  There is a chance the battery can explode when current is passed through frozen electrolyte.  There is also a chance that frozen electrolyte can crack the battery casing causing highly flammable gases to escape which can be ignited from sparks upon charging.  More information on battery charging safety can be found here.

How can you tell if the battery is frozen?  In most cases you can’t, which is why it is safer to avoid the risk of explosion by assuming that the battery should not be jump started or charged outside when temps fall below freezing.  Sub-zero temperatures greatly increase the likelihood of a discharged battery being frozen, making conditions especially dangerous.  Warm the battery first by taking it inside and allowing it to acclimate to room temperature.  This might sound like ridiculous advice if you don’t have time for this, but think of it this way:  you might not have time to do much of anything ever again if a battery explodes in your face.

Second tip:  a warm battery will have much more cranking capacity than a cold one.

If you anticipate attempting to start a diesel engine (or any engine for that matter with a battery powered starter) in sub-zero temps, take the battery off the equipment at least six hours prior to using it, and keep it in a warm place.  This will greatly improve your chances of cranking the engine over.  If you are not using the equipment routinely throughout the winter, keep the battery stored in a basement or elsewhere where it’s warm.  This will greatly lengthen the life span of the battery.  It’s also a foolproof way of remembering to keep the battery warm when it comes time to starting a diesel engine in unique circumstances.


Battery blankets are a simple solution for keeping batteries warm in between regular winter uses. Image from

In cases where you need to rely on the battery routinely for starting tractors or other machinery throughout the winter, battery blankets can be used.  These are heating pads that you wrap around the battery.  They are powered by a conventional 120vac circuit, and you can plug them in along with an engine block heater and have both on a timer (more about this below)

Third tip:  Warm the engine before start-up.  There are generally three ways to do this:

1.  Heat the engine coolant

2.  Heat the crankcase oil

3.  Heat the metal of the engine block itself

The general idea with warming the engine is that it is very tough for a battery to energize a starter that is responsible for moving cold, unlubricated engine parts.  It is much easier for a battery to power the starter system when the engine is pre-heated, meaning parts will be quicker to become lubricated, and will be much more likely to move.

1.  Most “block heaters” consist of an electric heating element, similar to the type you’ll find in a domestic hot-water heater, built into the engine block to warm the coolant in the internal channels of the engine.  If you have this type of block heater, plug it in!  Aside from extreme temperatures (sub-zero and below) there is usually no need to keep a block heater plugged in all night long- 3-6 hours prior to anticipated engine start up is usually all that is needed.  Efficiency Vermont is giving free timers to farm operators on a first come first serve basis through its Vermont Engine Block Heater Timer Program.  If the engine has a block heater, use it.

2.  Less common are mechanisms to heat the crankcase oil, but consider this: warm oil flows freely, while oil at sub-zero temps definetly does not!  Preheating the crankcase oil provides superior lubrication for engine components that are trying to move for the first time on a cold morning.  Various electric heating pads can be siliconed or affixed to the underside of the crankcase to warm the oil overnight.


Oil pan heaters are affixed to the bottoms or sides of oil crankcases. Image from

3.  Warming the metal of the engine itself is achieved indirectly by heating coolant and crankcase oil.  You can boost the effectiveness of preheating engine components by keeping your equipment in a shed or garage while it is plugged in.  This cuts down on wind that steals heat that you are trying to save.  In turn you save energy costs.

Forth tip:  Keep the battery maintained.  Remove all dirt from the battery surface- this can cause your battery to leak charge over time.  Prove it yourself- test with a voltage meter from the positive terminal to a spot on the top of the battery casing.  If the meter shows voltage, you have a battery that is discharging electricity while it is just sitting there with a dirty surface.  Corrosion at the terminals can cause similar problems.  Make sure all connections and cables are free of corrosion at all times.

It is especially important in cold weather to keep your battery at full charge.  Batteries used for starting internal combustion engines are designed to provide a great amount of energy in a short period of time.  However, unlike deep cycle (e.g., for solar applications) or other types of batteries, starter batteries are not meant to be discharged for extended periods of time.  Failing to recharge a starter battery spells quick ruin for it.  An important battery maintenance tool to have is a good charger.  If the charger will be used outside in various temperatures, it is worth paying for a good one with a temperature sensing feature.


Typical battery charger. This one shown is temperature compensated to ensure optimum charge voltage according to ambient temperature. Image from

There are a plethora of great resources out there detailing battery maintenance.  It is the kind of thing where, for a very small cost of keeping your battery maintained, you will save a lot of money by prolonging the life of your batteries and avoiding the time and hassle from unexpected failed starts.

I ended up getting lucky this weekend.  I brought the dead excavator battery inside, warmed it up for an hour, then put it on the charger for another three.  The weather was no warmer when I attempted again that afternoon to turn the engine over, yet with a warm, charged battery it fired right up!  Wish I could say the same for my fingers and toes, but the job got done.


What are your favorite methods for battery care and engine start-up when it’s five below?


About Ben Waterman

Ben writes about land access, tenure, and stewardship issues that are relevant to new farmers in Vermont. He coordinates the Land Access Program at UVM Center for Sustainable Agriculture:
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