Testing the Mudiro M-5S Ultra Diesel Heater in a Frozen School Bus ❄️🔥

A brutally honest review from inside a steel popsicle.

Last winter, Kim and I converted most of our school bus with no heat.

Not “low heat.”

Not “inefficient heat.”

I mean zero, as in:

“Congratulations, you now live inside a walk-in refrigerator.”

By February, my hands had reached a level of cold normally reserved for arctic researchers and people grabbing metal tools without gloves.

So when Mudiro emailed me and asked if I wanted to test their new suitcase-style portable diesel heater, I had to laugh.

Had they been watching my footage?

Did someone leak the fact that I almost froze to my floor pan doing wiring?

But honestly… I knew exactly where I should test this thing.

And it wasn’t in a shop.

It wasn’t on a bench.

It wasn’t next to a well-behaved space heater.

It was inside my steel-walled bus — the closest thing you can get to a cryogenic test chamber without NASA clearance.

This is my full review.

No fluff.

Lots of data.

And a little humor so you don’t feel your fingers freezing off in sympathy.

The Setup: Preparing the Bus for a Cold-Start Torture Test

The day before the storm, I installed the heater inside the bus.

No permanent mounting.

No fancy duckwork.

Just

• Set the unit on the bus floor

• Route the exhaust through an old blinker hole

• Clamp it down so it doesn’t hop back in

• And let the temperature plummet overnight

I wanted a real cold start — the kind where your diesel fuel second-guesses its career choices.

When I came outside in the morning, it was 18.7°F in the bus.

My slippers instantly regretted coming along.

This is the kind of cold where your breath fogs, your tools glare at you for touching them, and the floor starts making little “help me” noises.

Perfect.

Cold Start Performance: Does It Even Want to Live?

I hit the power button, expecting some drama.

Maybe a cough.

Maybe a puff of diesel fog.

Maybe the heater whispering, “Sir… please… no.”

Instead?

It fired immediately.

No smoke.

No rich diesel smell.

No hesitation.

Considering the combustion chamber was basically the same temperature as my frozen soul — that’s impressive.

Heat Output: Can It Warm a Bus or Just My Feelings?

The walls and ceiling of my bus are bare steel right now.

Zero insulation.

No reflectix.

No spray foam.

Just cold.

So when I set the heater to max and put a thermometer inside, I had modest expectations.

After one hour?

18.7°F → 45°F

Look — 45°F is still cold.

But “cold enough to die” and “cold enough to work” are two very different temperatures.

If 18°F is an iceberg, 45°F is a slightly judgmental spring day.

It was enough to work, film, and regain feeling in my fingers.

Controls, App, and Altitude Wizardry

The built-in display is shockingly good:

• Burner temperature

• Fan speed

• Voltage

• Set point

• Altitude

• Power level

• Carbon monoxide alarm status

Oh — and yes, this heater has automatic altitude adjustment.

Because if you’re heating your van on Mount Everest, you deserve that kind of support.

But the standout is the WiFi app.

It is genuinely one of the best apps I’ve seen on any diesel heater:

• Beautiful interface

• Real-time data

• Easy to adjust

• Reliable connection

• Looks like it was actually designed by a human

No sarcasm here. It’s great.

CO Testing: Why Is This Exhaust… Not Trying to Kill Me?

I bought a CO detector just for this test because I wanted to confirm the built-in sensor was accurate.

Here’s what threw me:

I could not measure a single bit of CO coming out of the exhaust.

Not at low power.

Not at high power.

Not at point-blank range.

To see if the detector was broken (which seemed likely), I mounted it behind my old pickup truck and did a cold start.

Immediately:

BEEP BEEP BEEP BEEP

Ah yes. There it is.
So no — the detector wasn’t broken.

The heater was just burning incredibly clean.

Will your mileage vary?

Sure.

But this unit impressed me.

Power Draw: Good News for Battery Users

Using both a clamp meter and BMS data, I saw:

3.8–4.4 amps on high

Consistent.

Predictable.

Nothing weird.

This heater won’t destroy your battery bank.

At least not any faster than you will by filming cinematic B-roll in 18°F weather.

Fuel Consumption: The Hard Numbers

I ran a controlled 30-minute test:

• Starting fuel weight: 775 g

• Ending fuel weight: 587.6 g

• Total used: 187.4 g in 30 minutes

Which works out to:

• 0.44 liters/hour

• 0.116 gallons/hour

• 10.56 liters per 24 hours

• 2.79 gallons per 24 hours

On full power.

No cycling.

No breaks.

That’s normal, respectable, and sustainable.

Tear Down: What’s Actually Inside This Thing?

Once you open the case, you’ll find:

• A familiar 8 kW heater core

• Clean wiring

• An accessible inline fuse

• Remote-mountable display

• Metal shell

• Good airflow

• A burn chamber that stayed spotless even after 10+ hours of running

Casting quality is okay — not perfect — but the internal components are arranged better than many heaters I’ve tested.

My only nitpick is the heat exchanger lacking fins at the very end.

Could squeeze out a bit more efficiency with those.

But overall?

Solid engineering.

Would I Use This as a Permanent Heater?

Honestly?

Probably not.

Not because it’s bad — it’s actually shockingly good — but because

• The exhaust gets very hot

• Routing it inside a finished space makes me nervous

• A floor-penetrating exhaust is safer long term

• Permanent heaters are designed for… well, permanence

But as a temporary heater, a construction heater, or a portable heating solution?

It’s fantastic.

And I’ll be using it all winter.

Full Transparency

Mudiro sent me this heater to test.

They did not pay me,

they do not approve my videos,

and they do not control my findings.

Everything here is my honest experience after running the heater for several days, 4–8 hours at a time.

Mudiro Heater Links + Discounts

If you want to check it out yourself, here are the links and codes:

Mudiro M-5S EVO-H (18% off)

https://www.amazon.com/dp/B0FL7VSRP9

Code: 8KIL5F8O

Valid: Oct 31 – Dec 31, 2025

Mudiro M-5S Ultra (15% off)

https://www.amazon.com/dp/B0FN7CFQCN

Code: VFNEZKS5

Valid: Oct 31 – Dec 31, 2025

Using the links supports the channel, and it means I get to keep doing ridiculous winter tests so you don’t have to.

Final Thoughts

If you’re dealing with a project vehicle, workshop, van, or—like me—a giant unfinished bus in the dead of winter… this heater isn’t just useful.

It’s sanity-preserving.

It made the difference between “I can’t feel my hands” and “Hey, I can actually work today.”

And in my world?

That’s priceless.