We froze a RAM to -40° for science

OE-Level Testing

In this video, we take a 2024 RAM 2500 into a state-of-the-art climate chamber to test its cold-starting limits all the way down to -40°F. We detail the severe strain that sub-zero temperatures place on a diesel engine, from thickening oil and frozen batteries to dropping compression temperatures, and outlines the necessary steps to prevent catastrophic engine wear. Finally, we reveal our solution for extreme-cold starts: the scalable-wattage, Triple Heat Capable Banks Monster-Ram, designed to maximize manifold air temperature and replace the factory grid heater that is prone to engine-killing failure.

Gear Featured in this Cold Start Test

Want to bulletproof your own 6.7L Cummins against extreme cold and grid heater bolt failure? Here is the exact patent-pending intake system the engineering team tested at sub-zero tests.

Choose your Monster-Ram based on year range. See bankspower.com for 2007-2024 RAM chassis cab applications. 

2019-2024 RAM 6.7L
2013-2018 RAM 6.7L
2007-2012 RAM 6.7L

New heater upgrade kits.

Triple Heater Upgrade Kit (2250 Watts total)
Dual Heater Upgrade Kit (1500 Watts total)750W and 1500W Billet Heater Upgrade Kits

Key Takeaways

• The Four Startup Factors: A successful diesel start relies on ambient temperature, coolant temperature, heat of compression, and manifold air temperature.

• The Stock Heater Flaw: The factory grid heater used in ’07-’24 RAMs features a bolt that is notorious for melting, falling into the intake manifold, and destroying the engine.

• Block Heaters Are Essential: Attempting to start your RAM without a block heater at temperatures of -20°F or below will drastically increase internal wear and can cause micro-cracking of the cylinder walls.

• Double Pre-Heat Your Intake: Utilizing two manual pre-heat cycles (rather than a single remote "couch start") significantly boosts manifold air temperatures, which can make or break a sub-zero start.

• Battery Voltage plummets in the Cold: At -40°F, the resting voltage of a healthy battery can drop from 12.6V to 11.4V, causing cranking voltage to fall so low (6.4V) that the engine's computer completely shuts down.

• The Monster-Ram Upgrade: Banks Power's new Triple Heat Capable Monster-Ram provides up to 2,250 watts of scalable intake air heat, safeguarding your engine and ensuring reliable combustion in extreme climates.

Video Transcript: We Froze Our RAM To -40° For Science

We spent almost $50,000 last summer, renting the same climate chamber that Tesla and GM use for sub zero temperature testing. Why? To find out what’s actually required to start a RAM in sub zero temps.

We found that there are four temperatures that ultimately determine whether or not your engine fires:

• Ambient Temperature – You have no control over this; it's determined by God.

• Coolant Temperature – Warmer engines start easier—You control this.

• Heat of Compression – The heat generated as the piston rises on the compression stroke. This is determined by battery condition, cranking RPM, and the engine’s health.

• Manifold Air Temperature – This is where Banks comes in, with scalable-wattage heaters that raise manifold air temperature.

Since you’re not God, let’s start with something you can influence—coolant temperature. Your truck was manufactured with the block heater already in it. Sub-zero starts, without block heat, as recommended by RAM, will ultimately kill your engine. And a hell of a lot of you are unaware of the damage you’re causing on every sub zero start.

I’m Gale Banks. In the fall of 2024, we invented a completely new version of our Monster-Ram. It improves throttle response, fuel economy, and prevents grid heater bolt failure which can kill your $30,000 Cummins. And, this all-new design improves cold starts in sub-zero temperatures. We called it, our “Banks Dual Heat Capable—Monster-Ram.”

Naturally, we wanted to validate its sub zero start capabilities. But as you know, Southern California isn’t known for its cold weather. So, we found a climate chamber, big enough to drive our ‘24 RAM into—and then we froze it, all the way down to -40°.

Let’s start with the basics—Here’s Erik to explain why starting a Diesel in sub-zero temperatures is so difficult.

A Diesel engine doesn’t use spark plugs. It relies on compression heat to ignite the fuel. That works great when everything is warm. But when temperatures drop—especially below 0° Fahrenheit—things that make a Diesel efficient, start working against it.

At sub zero temperatures battery voltage drops, oil thickens, and the cranking power requirement increases. You get slower cranking speed, and that means lower compression temperature and that’s a problem—because without enough heat, diesel fuel doesn’t ignite properly. What you get is unstable combustion or no combustion at all.

That’s why cold start systems exist—things like grid heaters to heat the manifold air and block heaters to heat the coolant. Their job is simple: raise manifold air temperature and coolant temperatures so the engine can actually light off.

But there’s a problem. Unfortunately the stock Cummins intake air grid heater assembly, used in all 07-24 RAMs, has a fatal flaw. This bolt, which supplies voltage to the grid heater assembly, is notorious for melting off, rolling down your intake manifold, through the intake valves, and destroying them, along with the piston, and cylinder wall and head.

Personally, I’ve seen 5th Gen RAMs with failed grid heater bolts, some with as few as 34,000 miles on the clock—right here–in our shop, in sunny Southern California! That’s because the grid heater turns on at any temperature below 66° Fahrenheit or 19° Celsius. And, the colder it gets, or the higher the altitude, the longer the heater circuit is active—to a maximum of 75 seconds. And know this, there’s not a state in the union where 66 degrees doesn’t happen.

This grid heater is from a ‘19 RAM in the Phoenix area. The bolt was days away from falling into the manifold and killing the engine. Now let’s talk about what sub-zero starts do to your engine. Because even if it does start when it’s freezing, you might be doing damage.

My first consideration is—Oil viscosity. At room temperature, your oil flows like… oil. At -20, -30, -40? It starts to behave more like molasses in January… or worse. Here’s Gale and the team at AMSOIL to show you.

That thick oil that you’ve just seen has to be pumped through the engine immediately at startup. If the oil can’t flow adequately, you’re starving critical components of lubrication, right when they need it the most. That’s why choosing the correct oil is so important.

Here’s another challenge you’re facing—Diesel fuel gelling. Diesel fuel gelling occurs at sub zero temperatures when naturally occurring paraffin wax—a component of Diesel that provides lubricity and energy density—turns into solid crystals. The crystals grow, clump together, and turn the fuel into a thick, waxy substance that restricts or completely blocks fuel flow.

There’s two popular types of fuel station Diesel—#2 is standard Diesel, containing higher levels of heavier hydrocarbons, including more paraffin wax. And #1, Winter Diesel, which has little to no paraffin wax. With #1 Diesel, you give up the higher energy density and the higher lubricity of #2 Diesel to avoid gelling in sub-zero temps.

Fuel gelling is so detrimental that Cummins has incorporated a heating element and temperature sensor into the engine-mounted fuel filter housing. The heater is not computer controlled. It only operates when the key is on and the fuel temperature is below 45°F or 7°C. Once activated, the heater stays on until the fuel temp reaches 75°F or 24°C.

The third thing you’re fighting on a sub zero start—is battery voltage. Sub-zero temps slow electro-chemical reactions inside a battery. For example, with the truck off, the batteries’ resting 12.6 volts on a summer day drops all the way to 11.4 volts at -40°. Coupled with increased engine cranking demand due to thickened oil, the voltage can drop so fast when cranking that the entire electrical system struggles to stay online. A common battery rating is cold cranking amps or CCA, which is tested at 0°F. The problem is, they don’t rate the cold cranking amps where we’re goin’.

And what happens the moment you start cranking?—Accelerated Wear! At sub-zero temp, metal components contract at different rates, altering internal clearances, increasing friction and wear. At the same time, poor lubrication during startup puts rotating components, like bearings, and reciprocating components like pistons, at significant risk. Thick, cold oil flows poorly, delaying formation of its hydrodynamic film and leading to metal-to-metal contact. At startup, the oil pump has to draw the oil up through the pickup-tube, feeding it to the oil passages in the block and throughout the entire engine.

With oil this cold, it’s like trying to suck a Dairy Queen Blizzard through a straw.

If the engine starts, combustion introduces rapid heating, creating steep temperature gradients across the cylinder walls. Picture this—the engine has been sitting all night—and let’s say it's cold soaked to -20°F—and you didn’t connect the block heater. You manage to fire it up—but know this, the owners manual tells you the block heater is mandatory at this temperature, and here’s one of the reasons why. During combustion, the temps inside the cylinder are going to be 300°F or greater while the outside of the cylinder facing the water jacket is still -20°F. So you have a thermal war going on across a relatively thin cylinder wall. Naturally, it’s going to be damaging. In extreme cases, such as no block heat, this can lead to micro-cracking of the inner cylinder wall surface.

Speaking of cylinder damage, starting at sub zero temps without block heat, can also result in incomplete combustion which can be spotted by black smoke, or a mixture of black and white smoke. Pure white smoke occurs when fuel is being injected but not lighting off at all. This unburned fuel can make its way past the rings, strip away the protective oil film, and end up in the oil pan—and just between us, Diesel sucks as a lubricant. So, if you see white smoke, I would not continue trying to start without changing something.

Starting your engine in sub zero temps is shortening its life—especially if there’s no block heat! The best way to avoid damage is by keeping the engine warm while it’s not running.

Now, let’s talk… block heater.

A block heater warms your block by heating the coolant and everything that the coolant touches, thus heating the cylinder head fire deck, and the cylinder walls. Now, your oil isn’t heated directly like the coolant, but the block heater pre-heats the oil passages and jump starts the engine oil warming process.

The RAM owner’s manual actually gives you guidance on block heater usage. You’ll find the owners manual—in your glovebox. For ambient temperatures below 0°F or -18°C, engine block heater usage is recommended. For ambient temperatures below -20°F or -29°C, engine block heater usage is—required. And I want to say something—the guys at RAM know what the hell they’re talking about.

Block heat helps, but the final factor concerning sub zero starts is manifold air temperature. Our original Banks single heat Monster-Ram replaced the failure-prone factory grid heater with a single 750W coil heater threaded into the casting. While the vast majority of RAMs cold started flawlessly with the 750W coil heater, we heard from a few customers in places like Canada and Alaska telling us: “Hey, the Monster-Ram works great… until it gets really really cold.”

So, back in November of ‘24, Gale began designing a Dual Heat Capable Monster-Ram, which would deliver 1500 watts of intake air heat. Once the design was finished, we started looking for a climate chamber where we could create extreme cold—on demand. In April of ‘25 we were ready for the climate chamber. We decided to work with Thermal Dynamics in Rancho Cucamonga, California, who just happened to have a multi-million-dollar facility used by the OEMs for extreme temperature testing.

And here’s the key: the Thermal Dynamics Climate chamber is very accurately controlled, eliminating guessing. So when we say -20, -30, or -40… that’s real, calibrated temperature, measured to within a half a degree.

Before we get to the testing, let’s talk about the victim. We used a 2024 RAM 2500 Tradesman 4x4. Stock with the exception of new Interstate AGM batteries, which came highly recommended by our friends up North. For lubrication, we used AMSOIL Signature Series 5W-40 100% Synthetic Max-Duty Diesel Oil, which is RAM’s recommended viscosity for sub-zero temps. For fuel, we used #1 winter Diesel—which is hard to get in Southern California, by the way. We had to sneak in a 50 gallon drum from Arizona. We replaced the fuel water separator, and we ran AMSOIL Cold Flow fuel additive to further prevent fuel gelling.

We wanted to give the truck every realistic advantage—without adding external aids that would mask the performance of the Monster-Ram’s heating system. So, no battery blankets. No oil pan heaters. Because we were trying to isolate one variable: manifold air temperature.

Then we instrumented—everything.

• Temperature sensors

• Pressure sensors

• Battery voltage

• Amperage

• Cranking RPM

• Fuel rail pressure

We recorded everything at 25 samples per second, with all this real-time data feeding two iDash Data Pros mounted in a Stealth Pod on the A-pillar.

And here’s the thing—We didn’t even start testing unless the truck had been cold-soaked for a minimum of 12 hours—and all temperatures were within a half of a degree of our target. This cold soak isn’t your iPhone, for example saying, “It might have hit -30° for a few hours last night.” But what you fail to realize is that -30 was the low and then it started to warm up as morning approached. If we set the climate chamber to -30 it’s not getting any warmer until we change the target temperature or we generate chamber heat by starting the engine. So, the truck is absolutely at -30 when we test.

And, you only get one test per day. Once you add heat to the chamber, you’re done. Now you have to wait until everything returns to the target temperature, which takes at least another 12 hours. So every successful start? Well, that was a $7,000 day. We’d leave the truck in the cell to chill overnight, just to do it all over again.

Now let’s talk about the actual testing.

Despite RAM’s recommendations, we tested with and without block heat below -20°F. If you think block heat doesn’t matter, it does. Lack of block heat will absolutely damage your engine. So whatever you do, try to never ever start without block heat at -20°F and below.

However, we did follow RAM’s recommended procedure for pre-heating intake manifold air—including two pre-heat cycles. This is achieved by leaving your foot off the brake pedal each time you press the engine start-stop button or rotate the key into the ignition position. The second pre-heat is achieved by going back to the off position, waiting 5 seconds, then back to the ignition position with your foot off the brake.

Each time you do this, the engine control module energizes the intake air heater circuit for a set amount of time based on manifold air temp and altitude. As Gale explained earlier, the time increases as manifold air temperature drops and/or altitude increases. Since the manifold air temperature was warmed from the first pre-heat cycle, the second pre-heat cycle may be shorter due to the warmer air already present in the manifold.

Here’s something most people don’t know. If you only do—one pre-heat—like a remote start with your key fob—or as I like to call it, a “couch start,” you’re only getting about half of the peak manifold air temperature improvement compared to two pre-heats—and two pre-heats are a big deal when it comes to sub zero starts. So yes—it’s inconvenient. You have to go outside and freeze your ass off, but it makes a massive difference.

We currently offer two Monster-Ram heating configurations. The standard Monster-Ram comes with a single coil heater threaded into the casting at 750 watts. Or, you can add a second heater totaling 1,500 watts. We wanted to test how these two configurations would perform with and without block heat.

But as you’ll recall, there’s more at play than just heating the intake air. We needed to know what happens to the engine coolant temperature, as well as battery voltage, before and during cranking. And, we wanted to know the cranking RPM.

Before we got into cold start testing, we needed to baseline the truck’s starting capabilities with a Monster-Ram, where the ambient temp was above 66°F. Remember, all Monster-Rams for the 6.7 Cummins include a 750w coil heater. We didn’t want to turn on the heater circuit which would have happened at 66°F or below. So, our baseline test was performed on a typical 75° California day. We measured a resting voltage of 12.6 volts, a cranking voltage of 10.8 volts, and a cranking speed of 154 RPM.

Our first test series in the climate chamber was performed without a block heater. A single coil heater at 750 watts without block heat started the engine down to 0°F or -18°C. And, of course, with no block heat, the coolant temp was the same as the ambient temp thanks to the cold soak. Resting voltage dropped to 12.2 volts, cranking voltage dropped to 10.7 volts, and the cranking RPM dropped to 128.

You can see there was some degradation to the resting and cranking voltage, and the cranking RPM. But remember the batteries are rated down to 0°F. So, as far as batteries are concerned, we’re just about to enter no man’s land.

Looking at the Monster-Ram 1500 watt configuration, we were able to start the engine down to -20°F or -29°C. The resting voltage fell to 11.6 volts, the cranking voltage fell to 9.3 volts, and the cranking RPM fell all the way to 82…

Well, welcome to battery no man’s land. At -20°F, we lost one volt before Erik even got in the truck and a volt and a half while cranking. But the interesting story with this -20 test is just how much the second pre-heat cycle helped the manifold air temp.

This graph makes it easy to see. Along the X axis is time in seconds. Along the Y axis is engine RPM on the left, with voltage and manifold air temp on the right. The red line is heater circuit voltage. You can see our two pre-heat cycles, here and here. The purple line is the manifold air temp. The first pre-heat was 30 seconds, which brought the manifold air temp above 0°F. At 0°F manifold air temp, the ECM reduced the heater on-time to 15 seconds. Even with the shorter on-time, look how the second preheat pushes up the manifold temp to damn near 16°F. Now take a look at the blue line, engine RPM. You can see the engine cranked for 8 seconds reaching 82 RPM– and at 82 RPM, the engine just barely fired, even with intake heat.

To show you what I mean, let’s compare the 154 cranking RPM on a warm day with the 82 cranking RPM at -20°F. At 154 RPM, the piston travels 2.09 feet per second. At 82 cranking RPM, piston speed falls to 1.11 feet per second. That’s a 47% loss in piston speed. On the compression stroke, you need the piston to come up rapidly to help create the necessary heat to reach the kindling temperature and ignite the Diesel fuel. But you’ve lost 47% of the piston speed. Chances are without our 1500 watts of intake heat and two pre-heats, it would never have fired at 82 RPM.

Now let’s see how the engine cranks at -30°. With no block heat, at -30°F or -34°C, the resting voltage fell to 11.5 volts and the cranking voltage fell all the way to 7.9 volts.

Do you hear that starter fighting for its life? It only managed to spin the engine to 73 RPM—less than half the RPM of a warm day start and far too slow to light it off.

Now, let’s see what happened with the block heater on! With the truck cold soaked to -20°F or -29°C, and the block heater on, the coolant temperature rose to 32°F or 0°C. That’s 52 Fahrenheit degrees or 29 celsius warmer than the climate chamber. Remember, without block heat the coolant would have been at -20°F. The resting voltage dropped to 11.8 volts, the cranking voltage dropped to 9.9 volts, and the cranking speed dropped to 96 RPM, which was 58 RPM less than our 75 degree warm day start.

Now that we knew what a Monster-Ram with a single 750w heater could do in combination with block heat, we threaded in a second coil heater, totalling 1500 watts. The additional intake heat allowed us to start the engine down to -30°F or -34°C. We measured a coolant temperature of 20°F or -7°C, a resting voltage that dropped to 11.7 volts, cranking voltage that dropped to 8.7 volts, and a cranking RPM of 89—pretty slow—but she fired.

Having a block heater helps by warming the coolant, but we’re still fighting frozen batteries and cold oil. Resting voltage fell by a volt, cranking voltage dropped by over 2 volts, and compared to our 75 degree warm day start, we lost 65 RPM while cranking!

So far, we’ve started all the way down to -30°F or -34°C, and that’s damn cold! But, with that success under our belt, and a climate chamber that would go to -40°F or -40°C, I said to the guys, “Button up your union suits, we’re going for -40!” And oh by the way, -40 is where the Fahrenheit and celsius scales meet.

Even with block heat warming the coolant to 9°F or -13°C, the batteries’ resting voltage dropped even further to 11.4v. And when we tried to crank, the voltage dropped all the way to 6.4v, the lights went out, and the ECM left the building. In other words, 6.4v isn’t enough to keep the ECM alive. And—no ECM—no start!

This is no longer a manifold air temperature problem. It’s a frozen battery problem. The key takeaway here is cranking RPM is now zero.

I want to point out something important about these tests. Everything was optimal in our ‘24 RAM. Everything was as good as it could get! Fresh engine, new batteries, and the right fluids with clean filters. Chances are good your truck won’t have all these advantages.

While I can’t give you a fresh engine, or new batteries, or the right fluids with clean filters, I can give you more manifold air temperature. So my suggestion is to ensure your sub zero cold start performance by adding a heater. The more wattage, the better.

If we started the engine with 750 watts, I suggest you go with 1500. If you’re a guy who vacations in cold country, 1500 watts is great insurance.

If we started the engine with 1500, I recommend you go with our new triple-heat kit which comes with two additional coil heaters, totalling 2250 watts. Yes, that’s right, I’m announcing our new Triple Heat Capable Monster-Ram! It resets the bar on sub zero cold start manifold air temp—and our new triple heat kit is available—now!

If you live where temps require our new 2250 watt triple heat kit, I strongly recommend using a block heater. I swear somewhere in the bible, maybe Cumminthians 6 point 7 it says thou shall use block heat below -20. ‘Cause if you don’t, you can expect to damage your rod and main bearings, piston, rings and cylinder walls. Your engine’s going to wear out before it’s time.

Simply put, cold weather stacks the deck against a Diesel. Compression temperature drops. And without heat, you get no combustion. Your engine is virtually a block of ice and heating your intake is your only salvation.

Remember, ambient temp is up to God. Coolant temp is up to you. Compression temp is up to the battery and your engine’s condition.

That’s why we focused on intake heat and we did it by producing the most accurate and repeatable test data possible. We didn’t guess. We didn’t simulate. And, we sure as hell didn’t copy. We put a truck in a cold cell and tested it—over and over.

We’ve pioneered a patent-pending intake system that gives you control over intake heat with scalable wattage, and eliminates the failure-prone factory grid heater. And for you guys with our original single-heat Monster-Ram, we have a direct bolt-on solution for you, too. You can add 750 watts with our single billet heater kit, totalling 1500. Or add 1500 with our dual billet heater kit, totalling 2250 watts.

The new Triple Heat Capable Banks Monster-Ram is available at bankspower.com or at any of our hundreds of authorized installers.