Riding Motorcycle Without Coolant (Horrifying)

Coolant does more than protect in high and low temperatures, it protects from some deadly silent engine killers that most riders don’t even know about.

Top 5 reasons you should always use coolant in your motorcycle, include:

  1. Protects from overheating
  2. Protects from frost
  3. Protects from corrosion
  4. Lubricates
  5. Metal erosion protection

In this post, you’ll learn why you should never use straight water in your motorcycle’s coolant system.

Coolant System

Your cooling system works by pumping cold liquid around the engine through passageways, engine heat is transferred to the liquid. The hot liquid is then moved to the radiator where incoming ambient air rushing through the rad (or radiator fan) cools it, and the cycle begins again.

The coolant in the system is pressurized to about 15psi, pressurized liquid has a higher boiling temperature (126c) and a higher boiling point is always helpful.

Your bike’s coolant system consists of a radiator, expansion tank (some), rad cap, fan, hose pipes, thermostat, temperature sensor, switch, water-pump frost plugs, and coolant.


Your coolant system is a mix of various components made from various materials – rubber, silicone, aluminum, cast metal, steel, plastic, graphite, paper and are all susceptible to some form of degradation.

Using straight water in your system will simply create rust, which will begin by eating the softer components like gaskets and pump seals first.

This of course won’t happen right away it may take several months for the first signs of trouble. But when corrosion gets into the system and starts to eat your motor from the inside, and usually goes undetected.

The first great reason to use coolant – it’s specially formulated to prevent corrosion of the coolant system. Rust inhibitors in the coolant won’t allow corrosion to take hold. However, do make sure your coolant is compatible with your engine materials.

Alloy is treated differently to cast metals.


Moving parts need lubrication and not just the metal components. The rubber and silicone seals, hoses, and gaskets need to be conditioned. Lubrication helps message them and keep them vibrant.

The metal moving components need love too, your thermostat, rad cap, and water pump.


The stat divides the coolant system in two, the rad side and the engine side. An engine isn’t at optimum performance until it’s at operating temperatures, the quicker that happens the better.

Its purpose is to close and prevent the coolant flow when the engine is stone cold and open when the coolant reaches the desired temperature.
The action is automatic.

Rad Cap

It’s not just a cap, it must act as a valve to control the pressure inside the coolant circuit. As liquid heats, it expands, your rad cap allows for this by opening an internal passageway and allowing the excess liquid flow to an expansion tank.

As the liquid inside the system cools it contracts and creates a vacuum, the cap allows for this too, by opening a valve and allowing expansion tank liquid to flow back to the rad.

Water Pump

Is tasked with moving coolant around the system, without the pump your bike would quickly overheat.

Pumps are pretty durable but do wear out, a common failure is a leaking pump seal. Keeping all these components, metal, rubber, silicone lubed extends their life.

Metal Erosion

This one is a real silent killer, topping up old coolant with straight water may prevent overheating bot it may be masking a more serious issue.

Old coolant is acidic, which attacks the softer metals of your engine. Pitting and eroding the metal away. It’s a silent killer because most riders aren’t aware of it.

You can check for this condition by using a Dvom voltmeter, acidic coolant creates voltage.

  1. Set Dvom to 20 volts dc
  2. Ground your negative test lead
  3. Place tip of positive probe into coolant
  4. Reading of 1 volt indicates acidic coolant and your engine is under attack – change coolant asap


You already know that coolant has a high boiling point and obviously using coolant in your bike will reduce the chances of it overheating in traffic.

Frost Protection

Coolant contains anti-freezing agents, so coolant is antifreeze and vice versa. The problem with straight water in the system overwinter is the risk of freezing solid, and freezing water as you know expands and can do some horrible damage.

And although most don’t ride their bikes in the ice and snow, it could still freeze up solid in the garage.

If you’re storing your bike over winter, and the system is filled with straight water, go ahead and replace with coolant or drain it down.

Only one thing worse than seeing frost plugs pushed out – not seeing frost plugs pushed out.

You may find the following posts useful:

Coolant in cylinder

Coolant in oil

John Cunningham

John Cunningham is a certified mechanic and writer on ATVFixed.com. I’ve been a mechanic for over twenty-five years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of ATV ownership, from maintenance & repair to troubleshooting.

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