Skip to Content

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

Coolant System

If your bike is designed to have coolant then you can bet if you ride without coolant you’ll damage the engine. Your cooling system works by pumping cold liquid around the engine where heat is transferred to the liquid. The hot liquid is then moved to the radiator where incoming ambient air cools the rad, some bikes may also employ an electric fan to aid cooling for slower-paced trail riding.

Your bike’s coolant system is pressurized to about 15psi, pressurized liquid has a higher boiling temperature (126°c) and a higher boiling point is always helpful.

Coolant system components

Your bike’s coolant system consists of various components, all with an important function, they are as follows:

  • Radiator and expansion tank (some) – the rad is critical, it’s tasked with aiding the transfer of coolant heat to the air
  • Rad cap – cap obviously allows access but it also regulates coolant system levels by working in tandem with the expansion tank.
  • Fan and fan switch – fan and switch helps cool the rad when the ambient air isn’t sufficient
  • Coolant temperature sensor – temp sensor is used to aid bike performance in fuel injected bikes and fan activation
  • Hose pipes – can’t route coolant around the bike engine with hosepipes
  • Thermostat – helps engines warm up quickly, which improves performance and fuel efficiency
  • Water pump – pump keeps the fluid moving around the system
  • Frost plugs – plugs are caps designed to be pushed from the engine’s coolant passageways in a bid to prevent damage caused by frozen coolant
  • Coolant – critical for the health of the whole system
Coolant system

Coolant system components

1 Overheating

Your bike engine produces a ton of heat as it runs, some air-cooled bikes are designed to run without coolant but their engines have been specially designed. Their surface areas are increased by adding fins to the cylinder head and the increased surface area increases its ability to radiate heat from the engine. Critical for engine health.

Air cooled engine

An engine designed to run coolant, however, doesn’t employ these cooling fins and so relies on the coolant to help dissipate all that heat.

Running the bike without coolant won’t kill the engine immediately but likely will after less than twenty minutes riding depending on ambient temperatures. You already know that coolant has a high boiling point and obviously using coolant in your bike will reduce the chances of it overheating.

That said, even with coolant overheating can still happen, here are the most common causes:

  • Low coolant level
  • Old coolant
  • Faulty rad cap
  • Air locked coolant system
  • Blocked rad (mud etc)
  • Faulty thermostat
  • Faulty fan
  • Faulty fan switch
  • Blow head gasket
Head gasket

Riding without coolant risks blowing the head gasket or much worse, seizing the engine.

2 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 if you know what I mean.

3 Corrosion

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. When corrosion gets into the system it happily starts to eat your motor from the inside and usually goes undetected until it’s too late.

Coolant is specially formulated to prevent corrosion of the coolant system. Rust inhibitors in the coolant won’t allow corrosion to take hold.

ATV rad without coolant

However, do make sure your coolant is compatible with your engine materials. Alloy is treated differently to cast metals.

4 Lubrication

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

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


The thermostat (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.

ATV thermostat

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.

5 Metal Erosion

Metal erosion is a silent killer, topping up old coolant with straight water may prevent overheating but it may be masking a more serious issue. Old coolant is acidic, and the acid 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 until it’s too late. 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 may find the following posts useful:

Coolant in cylinder

Coolant in oil