Question:
I have a 2003 Westfield Megabusa with a 99 Hayabusa and it has your SBD dry sump pack. The oil temperature gauge never seems to get much above 65-70C on a trackday after circulating for 15-20 minutes. I suspected that the gauge wasn’t reading correctly, but I’ve tested it static and the reading on the pipe at the oil cooler is the same as on the VDO gauge, around 65C according to the temp sensor for my multimeter.

The oil system takes just over 6 litres and there isn’t a thermostat. I have an oil cooler with core dimensions of 360W x 193H x 50D, which to me looks very large for a 1300cc bike engine. The previous owner replaced the oil cooler, and decided to fit a bigger one on the “bigger must be better” principle!

I’m under the impression that the oil temperature should be around 100-110C when working hard. If so, what setup would you recommend in conjunction with the dry sump kit?

Answer:
If your engine is running the oil temperature you are seeing, this will be a first. Suzuki bike engines were originally air cooled, then oil cooled and then finally water cooled, but when they produced the water cooled version, it was effectively only added on top of the oil cooling design, which instead of virtually same amount of heat transferred into the oil system as in to the water system, hence the reason for running a very large oil cooler. Keeping the oil temperature under control helps to keeps the water temperature under control as well, due to heat transfer within the engine.

You have to remember that the oil temperature you are seeing is after it has been cooled, before it re-enters the engine and therefore it would be lower than if you measured the oil temperature within a wet sump for example. Normally cars such as sportscar and single seaters have space to mount the radiators and oil coolers on separate sides so they both get clean air flow and would be able to achieve efficient cooling. Normally on cars such as the Westfield, this is very difficult to achieve because all the air flow has to go through the nose cone and therefore either the oil system or water system will have an advantage. Obviously we don’t know your installation and how you have fitted the radiator and oil cooler, but if they are both achieving good efficiency, it is some that I am sure others including us would like to know how you have done it.

Since we don’t know how your installation is done, we can only give some basic advice. The Hayabusa itself is effectively a road bike engine, which has reasonably large clearances so it can be driven quite hard when not up to optimum temperature, otherwise they would be engine failures on the road bikes. As the temperatures rise the engine case expands, the clearances increase and the oil pressure will drop. When you get up to what would be called optimum oil temperature, when the oil is at its most efficient, the crank cases are potentially larger than would be optimal so we quite often like to see the engines running at a minimum of 60-degC and 80-100-degC, even though the oils can work at 120-degC the slightly lower temperature help to keep the bearing clearances tighter. Remember that the oil temperatures you are seeing, if correct, are after cooling.

Fitting thermostatic controls adds weight and complexity and not something that we try to do. Fitting a smaller oil cooler means you limit your cooling capacity and if you want to slightly increase the oil temperature, the common practice in all motorsport is to blank off parts of the oil cooler effectively reducing its size, you then have the ability to increase or decrease its efficiency very quickly. I would also check the oil temperature with a laser temperature gun directed at the oil in the tank from the filler cap just for piece of mind.