DRZ400 Radiator Fan Install

I've never found the DRZ400 to overheat when there is plenty of air movement past the radiators, however when riding tight, steep, slow going tracks when air movement past the radiators is reduced and either/both the engine is working hard or ambient temperatures are high, the DRZ400 can overheat and boil the radiators.

A hot day on a slow going tight track with lots of muddy sections that gave the engine a workout. The result was overheating four times on a short 7km track.

On the trip from the photo above I wasted a lot of time sitting and letting the bike cool on four occasions. Aside from the fact waiting around is no fun, it's just no good for any engine to repeatedly overheat. The solution was to install a radiator fan. Although the DRZ400S and DRZ400SM both have fan kits that I could have installed on the DRZ400E, I opted to go for the Trail Tech fan kit as I liked the extra functionality of the programmable relay that allows you to set the temperature that the fan will kick in.

The Trail Tech fan kit has all the items needed for a fan install on a DRZ400. The only major thing to note is that the DRZ400 bikes I ride are fitted with Safari 28 litre tanks and the fan had to (a) clear the tank when it is sitting in place and (b) allow me to access the bolts that secure the tank to the frame. The fan is mounted here in just the right spot, any higher and it would hit the tank, any lower and I would not be able to access the tank bolts to secure/remove the tank.

View this DRZ400 Fan

Important Note When Fitting the DRZ400 Fan Temperature Sensor

Trail Tech doesn’t make a radiator fan kit specifically for the DRZ400 so the only option is the Trail Tech universal fan kit. The radiator fin sensor that comes with the universal fan kit is too wide for the DRZ400 radiator columns and will require filing down to fit.

Alternatively, the fan temperature gauge/relay uses the standard Trail Tech plug sockets which allows you to plug in any Trail Tech temperature sensor. This gives you three options:

1 - the 19 mm radiator hose sensor

2 - the top of the radiator bleeder screw sensor

3 - flush mounting the provided fan kit temp sensor to the top of the radiator with high temp epoxy (in the above image).

Tank mounted in position: it is hard to see here but the fan protrudes out into the tank's bolt access cavity, has full clearance, but cannot be mounted any higher or it would make contact with the tank.

Tank mounted in position: here you can see there is access to the tank mounting bolt. Good skills at Milton Bradley's game of Operation helps to guide the bolt in, but it is achievable to guide the bolt in without major grief.

The Trail Tech digital gauge mounted next to the ignition. This is easily programmable to kick the fan into life at a temperature you specify. It also has programmable backlight and also acts as a volt meter; a very cool little gadget!

Testing the Fan on the DRZ400

Stationary idling will see the DRZ400 coolant temperatures eventually rise over 100 degrees Celsius to the point of boiling. Three initial tests were of the bike stationary and idling with fan set to kick in at temperatures of 70, 80 and 90 degrees Celsius.

In all three tests the fan kicked in when it should have and immediately stopped the temperature from rising. Ambient temperatures of 17 to 22 degrees Celsius saw the repeat cycle of the fan turning on when it hit the target temp, the temperature dropping, the fan turning off, then kicking back in again when the temperature rose and hit the target temp.

Summary: the fan operates perfectly in these stationary idling test scenarios.

This graph shows the rising temperatures of both the left and right radiators with the fan set to turn on at 90 degrees Celsius. It is easy to see the curve deviation of the left radiator (left radiator mean= 58.5 and right radiator mean=43.7) as a result of the thermostat. It is worth noting that thermostats are normally only fitted to the DRZ400S and DRZ400SM, not to the DRZ400E. I have fitted thermostats to all my DRZ400E bikes to maintain higher oil temperatures when riding in low ambient temperatures. Once the temperature nears 70 degrees the deviation lessens however once the temperature reaches 90 degrees the difference is only 3 degrees between the left and right radiator.

The three photos below are from an install on a DRZ400, using 4mm threaded rod to secure the fan, with a 28 litre Safari tank. The placement of the fan is detailed to allow the tank to be fitted without interference, and still allow access to the tank mounting bolts.

View this DRZ400 Fan

Placement of the fan is 5mm with the ruler sitting hard against the top of the fan housing (below the protruding lip) to the end of the radiator cores where it meets the top tank.

Author of this article: RMOTO