Care And Maintenance
Coolant
Coolant Thermostat
Oil Cooler
Oil Thermostat
Protective Radiator Screen
Radiator
Radiator Fan
Radiator Fan Switch

The engine cooling system on modern sportsbikes is designed to maintain the coolant temperature between 86°C and 100°C (187°F to 212°F), and most produce their maximum power between 92°C and 96°C (198°F to 205°F). The thermostat controls the lower end of that bracket and the upper margin is defined by the cooling system's ability to shed heat.

A bike radiator installed in a buggy often doesn’t have the capacity to keep the engine temperature as low as 96°C (205°F). This is due in part to the engine having to work a lot harder in the buggy and also because the engine runs at higher, and more constantly higher revs. 

The boiling point of water actually increases when put under pressure, and a radiator cap increases the boiling point of the coolant in the same way a pressure cooker increases the boiling temperature of chicken stock.

The radiator cap is actually a pressure release valve, which on cars, is usually set at 15 PSI. Every pound of cap pressure increases the boiling point of the coolant by 1.6°C (35°F).

Stant make racing radiator caps up to 24 PSI in both car and bike sizes. The filler neck doesn’t necessarily have to be mounted to the radiator, in fact, most bikes’ fillers are mounted in a frame spar. These odd-shaped items may not lend themselves to being fitted in your buggy, but as long as you can fit some sort of device with a filler at the highest point in the system, then all will be well. Some cars have remote plastic expansion bottles that include a filler cap. The other alternative is to install an in-line filler neck in a hose at the top of the system. If that route is chosen, then don’t forget to mount an overflow or catch bottle too, otherwise the expensive coolant that expands when the engine is hot will be lost. When a catch bottle is fitted, the coolant will be drawn back into the radiator as it cools.

Coolant

There is another tool for reducing operating temperatures, which is both easy to use and relatively inexpensive. Filling your radiator with a 50/50 mixture of glycol/water will raise the un-pressurised boiling point of the coolant from 100°C to 106°C (212°F to 223°F). By increasing the ratio of the mixture to 70/30, the un-pressurised boiling point will rise a further 7°C to 113°C (35°F to 235°F).

Most automotive parts stores and garages sell ready mixed anti-boil and anti-freeze mixtures, but read the accompanying label to establish the strength of the mixture. It may be more beneficial to buy the full strength coolant additive and mix it with water to your own preferred ratio. Also check to see if the coolant additive is suitable for aluminium engines and radiators.

Coolant Thermostat

Removing the thermostat so the engine will run cooler is a myth. All that happens is the engine takes considerably longer to warm up, and in the mean time, if the engine is pushed hard, the wear on internal components will be increased.

Similarly, fitting a massive radiator in the attempt to keep the engine cool can also cause problems. The radiator’s capacity of cool liquid may prevent the engine from attaining its correct operating temperature with the same wear consequences.
 

Radiator

The size of the radiator has to be carefully balanced with the engine’s output, though radiator placement within the chassis will also influence the final size. An overhead radiator fitted behind the driver is the best position for both airflow and protection from debris.
Typically, a 400mm x 300mm (16” x 12”) overhead radiator with a 38mm (1½”) core fitted behind the driver works very well and is the best location for both airflow and protection from debris.

If ordering a custom radiator, don't forget to request threaded bosses to suit your water temperature sender, fan switch and drain cock.
 

Radiator Fan

The fan should be mounted behind the radiator to minimise the build-up of muck on the blades. If muck is allowed to collect on the fan blades, imbalance may occur which could prevent the fan from operating.
The fan can either be mounted to a 3mm (1/8”) aluminium shroud behind the radiator, or mounted directly to the radiator using a special plastic tie kit. The ties pass through the radiator fins and are secured by plastic toggles on the front side.
If you ever need to replace any of the fan ties, you may be in for a nasty shock when you go to pay for them! 

A cheap, and equally effective solution, is to use eight ordinary zip ties. Cut the zip lock heads off four of the zip ties. Make four plastic washers by cutting small discs from the side of a polyethylene bottle or jar and punching a hole in the centre of each of them.

Hold the fan in position against the radiator. Thread four zip ties through some small washers and then through the fan mounting holes and gently through the radiator fins.

Place one of the plastic washers over the end of each of the zip ties followed by the zip lock heads and snug them down firmly. Trim off any surplus zip ties that extend past the zip lock heads.
 

Radiator Fan Switch

The radiator fan switch should not be omitted or overlooked. Under normal conditions, the fan should remain idle, only turning on when the temperature rises significantly. Typically, this may be during, or slightly after, a dual with another competitor or a passing manoeuvre. If the engine remains within the correct operating temps only with the aid of the fan, then it can be assumed the radiator is too small. There is then the significant danger that there is no back up for that passing manoeuvre.

Davies Craig produces a thermatic fan switch that is adjustable from 80°C to 115°C (176°F to 279°F). This mechanical switch is located next to the radiator and a copper probe is mounted inside the radiator hose to detect the cooling system temperature.

After a hard race, the engine will be at its maximum temperature, and if the engine and its electrical system are shut down while in the pits, heat soak could result in isolated areas of the engine rising to higher than normal temperatures. This could result in damage to the cylinder bores, pistons and head.

To prevent this damaging form of heat soak, the radiator fan switch should be wired live and not through the ignition switch. Thereby the fan will be free to continue running after the engine is shut off, for as long as necessary. Just remember to switch the engine off with the kill switch and not the battery isolator switch!
 

Oil Cooler

Sportsbikes also make use of external oil coolers to help maintain optimal engine temperature, and as with the case of the coolant radiators, it may be necessary to upgrade the oil cooler to a larger capacity when the engine’s installed in a buggy.

The older Suzukis were air/oil cooled, that is to say, their primary method of cooling was by oil cooler, but the engine itself was lightly finned to present a larger surface area to passing cool air. These “toasters” can suffer very badly when installed in a buggy, because the engine is tucked behind the driver and out of the air stream.
I’ve seen attempts to duct air directly onto the engine, but usually, muck from the front tyres and those of buggies in front, gets directed through the vents and splattered all over the engine cases. This results in an insulating layer building up on the engine, making cooling even more difficult. In such cases, a larger capacity oil cooler is mandatory. Typically, a 400mm x 250mm (16” x 10”) single pass cooler with a capacity of around 375cc will drop oil temperatures by as much as 20°C -25°C (68°F -77°F).
 

Oil Thermostat

An oil thermostat should also be installed to bypass the cooler until the desired temperature is reached. There are several styles of thermostat; a sandwich plate installs between the engine case and the filter, and an in-line thermostat installs in the line between the filter and the cooler. Both types will open when the oil temperature exceeds 82°C (180°F), allowing 95% flow through the cooler. At temperatures below 82°C (180°F) the valve opens, permitting 90% of the oil to bypass the cooler. The remaining 10% of the oil flows through the cooler, maintaining constant system pressure, preventing air pockets and eliminating cold oil shock. Try and keep all external lines as short as possible and secure them to the chassis at regular intervals. Ultimately, the oil cooler should maintain the oil temperature below 93°C (200°F).

If there isn’t room to install a sandwich plate between the engine and filter, then a take-off plate can be fitted to the engine in place of the filter, which is connected by hoses to a remote filter head. The remote head can be mounted in a convenient location out of harm’s way.
A neat way to keep the engine compartment clean looking is to install a combined remote filter head and thermostat.

Prolonged use of engines in conditions that oil cannot reach optimum working temperatures will cause sludge formation and crankcase oil dilution, which can lead to excessive wear especially in the cylinder bores. Thermostats combat this by regulating oil flow to accelerate warm up. This in turn reduces drag, helping to yield optimum engine efficiency and performance.

Aftermarket thermostats often facilitate the mounting of oil pressure and temperature switches, which may be handy if you have had to modify the sump to reduce overall height.  

If considering making the sump shallower, give some thought to adding “wings” to it to increase the oil capacity. It doesn’t do any harm to TIG weld some 4mm thick fins in a staggered, inverted “V” pattern to the sump of any engine to catch air passing underneath the engine.
If designed thoughtfully, the fins can also make a level base for setting the engine on the workshop floor.
 

Care And Maintenance

Occasionally flush the radiator fins clean by very gently directing a hose into the radiator from the back, to force the debris back out the way it entered.

In the event of a blown head gasket, aluminium radiators should always be checked for damage. Air pumped by the pistons into the radiator can expand the coolant tubes thus blocking external airflow through the fins. Radiators thus damaged should be very carefully inspected, and if necessary, replaced or else engine overheating will most likely occur.