Cooling system service

[Erik Marquez]

This preventative Maintenance "fix" is applicable and recommended for all year and model year DRZ 400

Use of a service manual is recommended. NOTE Technical papers found here and the factory service manual are not a replacement for common sense, general mechanical aptitude and at least some motorcycle specific maintenance experience.

The basic procedure described below will guide you through a drain, flush, change and filling your coolant system. It is recommend the use of low or non silicate coolant. Aluminum motorcycle motors are filled with aluminum and others bits of metal. They are susceptible to corrosion like any other internal combustion engine, thus requiring a quality coolant with corrosion inhibitor. Additionally there are packages of additives used in some automotive coolants called silicates. Silicates are abrasive in nature, and should be avoided in motorcycle coolant. In practicality, a very low silicate coolant is often “approved” for use in motorcycles. So when choosing a coolant, if it says silicate free, and aluminum safe you’re good to go. If you see low silicate and motorcycle safe, you’re still ok.
The premix available for motorcycles is a good choice. Maxima, Honda, Silkolene, Engine Ice and many others market premixed coolant..If you mix your own go 50/50 with distilled water.

Basic Step by Step How to

1: Remove small screw securing radiator cap and remove radiator cap... drain coolant;

2: Drain the coolant using the drain on the water pump cover (10mm hex head)NOTE small aluminum washer may stick to the cover, remove it and safeguard.

You can pull the lower hose and drain faster, but it will make a mess. If you spill coolant remember it is poisonous to animals, clean up and dispose of the spilled coolant..
Lower hose

CAUTION with the radiator cap removed, and the cooling system vented, coolant will shoot out of the drain several feet. Be ready for it or the mess if the stream misses the bucket.
3: Lean bike over to each side to move a bit of the trapped coolant to the right side drain.
If you desire to flush the system, do so now, run clean fresh water through the system from radiator fill neck, let water drain…
4: Replace hose if removed
5: Replace drain plug with sealing washer, go easy on tightening, just snug it up.
If you have a need to further flush the system do to contaminates like oil from a bad head gasket, fill the system with distilled water, follow the rest of these instructions, drain again and flush as above. Repeat until the water comes out clean at the first drain step. Remember, you have lower boil over and freeze points with plain water, and no wear or corrosion protection. Replace the flush water with the proper mix of the correct coolant immediately after your done flushing the system.
6: Look at the water neck, top front of head; there will be a hex head cap screw with a Phillips slotted head. That is an air purge. Open it a few turns; it does not need to come all the way out. The shaft is slotted so air can bleed past. 

(NOTE, some DRZ models have a water neck with no bleeder screw, if the neck points straight up  you will not have the bleeder screw nor a thermostat 

7:       Open the air bleed screw on top of the left radiator

8: Fill the right radiator with coolant, air will come out past the air bleed screws on the water neck and left radiator, once coolant comes out the water neck bleed screw snug up the screw.
9: Keep filling radiator slowly, as air gurgles out add more coolant. As soon as coolant comes out of the left radiator air bleed screw, and the right radiator is topped off snug the left radiator bleed screw down..

Once the right radiator is topped off. Lean the bike over far left and far right, more air will come up to the radiator fill neck. Top off one more time.
10: Replace radiator cap (replacing the screw is your choice, I’ve never seen a cap come loose by itself) Start bike. Let it come up to operating temp, just a few minutes sitting still in a garage or drive way will do this, stay with the bike, it can overheat quickly, more so if there is a large air bubble trapped in the coolant system.
10: Let the motor cool down, open radiator cap and top off.

 

I prefer to put about 1” of coolant in the coolant overflow bottle. This step is not in a manual. But recommended anyway. What it does, is give you a before operations visual check to indicate if you radiators are full. If the bottle is empty, you know your system sucked up some coolant as the system cooled down. . And you need to check levels in the radiator itself. If the bottle has its normal 1” or so of coolant, you know you’re good. Bulb syringe or the like works well to push some coolant in to the overflow hose down to the tank. This is not a replacement for normal maintenance checks, just a good simply before operations check.


11: Check coolant level in bottle after ever cool down period for a few rides,

bottle with 1" of coolant) Very common for trapped air to purge while riding the first few days. If you find coolant has been sucked from the bottle to the air bleed, No worries, top off the radiator, add another few ounce to the bottle, go ride.

Optional Higher Pressure Radiator Cap



This is the OEM 1.1bar cap
An option to increase boil over protection for the DRZ is to install a higher pressure radiator cap. The DRZ, all models comes with a 1.1bar =16psi cap, you can source a 1.6bar=23psi cap from your local auto parts store, as it's the same as used on many foreign cars at a fraction of the cost of a motorcycle OEM part. Kawasaki uses the 1.6bar cap on applications in their line up. PN 49086-1073

STANT also makes a 1.6BAR cap that fits; Stant 10362 from the "Racing" division.

Lastly there are several aftermarket vendors that sell "High Pressure Caps" that fit..

If you choose to use a 1.6 cap, just remember, the motor is still getting HOT all you are doing is delaying boil over a bit. Sometimes that’s all it takes to get through that technical section, up and over that hill climb.. And you can dial it back some and let the motor cool. The higher pressure cap is not a fix all for an overheating motor.