Why Is My Diesel Hard to Start When the Weather Gets Colder?

Cold weather can make existing diesel problems much easier to notice.

The weather cools down, you turn the key, and suddenly your diesel does not start quite as easily as it did during the summer.

Maybe it cranks longer. Maybe it starts rough. Maybe you need to try twice. Cold weather can make existing diesel problems much easier to notice. A diesel that struggles to start when temperatures drop may have a problem with the battery, starting system, fuel system, glow plugs, intake heater, or another engine component.

Diesel engines use compression to create the heat needed for combustion. When the engine and outside air are cold, creating enough heat becomes more difficult. That is why diesel engines use systems designed to help with cold starts. Depending on the vehicle, that may include glow plugs or an intake-air heater.

Diesel engines require significant power to crank. Many diesel trucks use two batteries because of the amount of electrical power needed to start the engine. Cold weather reduces battery performance, which means a battery that worked adequately during warmer weather may struggle once temperatures drop. Symptoms can include:

Slow cranking
Clicking
Intermittent starting
Lights dimming while starting
Needing a jump start

On dual-battery systems, both batteries should generally be tested. One weak battery can affect the entire system.

Many diesel engines use glow plugs to help warm the combustion chamber before startup. If one or more glow plugs are not operating correctly, you may notice:

Longer cranking
Rough running immediately after startup
White smoke
Hard starting when cold
A glow-plug or check-engine warning

A vehicle may start normally during warm weather and show symptoms only after temperatures drop.

Some diesel engines use an intake-air heater instead of traditional glow plugs. The purpose is similar: help warm the incoming air so combustion can occur more easily when the engine is cold. A problem with the heater, wiring, relay, or control system can lead to difficult cold starts.

Your diesel engine depends on the correct amount of clean fuel being delivered at the proper pressure. Problems with fuel filters, injectors, fuel pressure, or air entering the fuel system may become more noticeable during cold starts. If the truck starts poorly year-round but gets significantly worse when temperatures fall, the fuel system may need to be tested.

If the starter is worn or unable to crank the engine fast enough, the engine may struggle to start. Cold weather increases the workload. What sounded like a slightly slow starter in August may become a no-start problem in December.

Diesel engines rely heavily on compression. If an engine has internal wear or compression concerns, cold starting may become increasingly difficult. This is less common than some electrical or fuel-related problems, but it is one reason proper diagnosis is important.

If your diesel is equipped with a block heater, using it during colder temperatures can help warm the engine before startup.

This can make starting easier and help the engine reach operating temperature sooner. Follow the recommendations for your particular vehicle and engine.

If your diesel is already taking longer to start, fall is a good time to have it checked. Testing may include: