How do I service the cooling system?

Warning

You are working with anti-freeze/coolant, which is caustic. You should try to keep it away from any painted surface, and clean it off if you spill any. Likewise, if any comes into contact with your skin, clean it immediately. If discomfort persists, seek medical attention. It will also kill animals if they drink it, so don't leave any on the ground, and dispose of it at a recycling center.

How do I check the coolant level?

Your coolant tank will have two marks on it - a low or cold level, and a high or hot level. Overflow tank, behind left quarter (side) panel

When the bike is cold (has not been run) the coolant level should be no lower than the low/cold level. When the bike is hot (just been shut off after a significant ride) the coolant level should be no higher than the high/hot level. This is a normal operating range - coolant level will fluctuate as it expands & contracts.

If you need to add coolant, add a 50/50 mixture to the plastic coolant reservoir. Make sure the coolant that you use states that it is "safe for aluminum engines." There are two types of anti-freeze: ethylene glycol and propylene glycol. One is green and the other orange. You shouldn't mix them when topping off. They are not compatible. If you're not sure which kind you have, and you can't tell what color it is, it's probably time to change the coolant and start over. Brand doesn't matter. It also doesn't matter if it states that it's for cars or motorcycles. If you're really concerned, you can always see what the manual has to say.

Fluid levels should always be checked with the bike straight up, resting on its tires, unless the manual states to do so on the centerstand. The slight elevation a centerstand or swingarm stand gives may give you an erroneous reading. When in doubt, follow the manual, then check the other way to see if there's any difference.

One variation to this method is if you have let all the coolant run out of the overflow tank, or otherwise suspect that there is air in your radiator. Adding coolant to the reservoir isn't helpful if the radiator isn't full, or has air in it. If this happens, add coolant at the top of the radiator on a bike that is absolutely cold. The radiator cap is located behind the right side of the front fairing.

Fill that up first, and then add to the overflow until the coolant is at the proper line (most likely 'low'). You will then have to purge the air from the system (see below). If you check your system regularly, this should not happen.

How do I change the coolant?

There are 2 coolant drain plugs. First, open the filler cap, then remove the first one, which is on the water pump, below and behind the gearshift lever; it is a 10mm bolt (as opposed to the 8mm mounting bolts).

Watch out, as the water comes out with quite a bit of pressure; it goes straight out the side and will land a foot or two(!) from the bike. Then drain the coolant in the block; the plug is on the front, between and slightly under the pipes.

The expansion tank is probably most easily drained by taking it off and pouring it out. If you want to be sure to get all coolant out, you should probably flush once with water as well.

If you're changing coolant types (say from ethylene glycol to propylene glycol, which is less toxic), flush the coolant system completely by filling it with water, running the engine for a minute, draining the water, and repeating until the water comes out clear. It should only take one or two flushes to completely clean out the system. For a coolant system flush, any kind of clean water can be used, but for the final water/coolant mixture, distilled water must be used. The flush water isn't in the system long enough to cause problems if it's not distilled. Most coolant comes premixed these days -- check the label on the coolant bottle to be sure, and only use distilled water if it's not already mixed, and you have to mix it yourself.

You can't fill it at the expansion tank. Just fill at the filler cap at the radiator. Fill slowly; this will make purging the air bubbles from the cooling system (see below) easier. Fill the radiator to the top.

Purging the air from your cooling system

Traditional method

After you refill the cooling system through the radiator, you're going to need to get all the air out of the system. Like the brakes, the cooling system doesn't work well with any air in it.

There are two methods for accomplishing this. The traditional one involves putting the bike on the centerstand and leaving the radiator cap off. Start the engine and run it until the air bubbles stop coming up. You first have to get it warm enough for the thermostat to open, and it takes another few minutes of running after that to make sure it's purged.

After you stop seeing air bubbles come up through the radiator, put the cap back on, after first making sure the radiator and coolant overflow reservoir are full. Check the coolant periodically, but, unless you left some air in there, you shouldn't have to top it off.

This-is-my-first-time method

This way seems to work well for people who haven't done this sort of thing before and may be worried about the potential for the radiator to burp hot coolant on the bike or their person. It's also meant for those who don't like the idea of filling the radiator and purging air while the bike is running. If this sounds like you, try this:

Make sure your radiator and overflow reservoir are full. Put the radiator cap on. Start the bike and heat it up to operating temperature, preferably by riding it, not idling. The first time you do this after filling, it should reach temp very quickly, since there are many air pockets and it won't cool efficiently. Let the engine cool completely, and you should notice the level in the overflow reservoir has dropped. Refill the reservoir (NOT the radiator - leave the cap ON) and warm the bike up again. Do this until the level of coolant in the reservoir does not change and you're done.

After you shut the bike off, and the engine cools down, the coolant in the engine shrinks and creates a vacuum. Since the combination of the top seal on the filler cap and the coolant in the reservoir prevent air from entering the system, the vacuum draws coolant from the reservoir through a small one-way valve on the lower seal of the filler cap to equalize the pressure - basically purging the air from the system every time it goes through a heat cycle.

If the temperature gauge is higher than normal on your first ride after purging, simply recheck the overflow tank and fill if needed.

That's all there is to it. It maintains itself, so the only time you should remove the reservoir cap is to fill the system with coolant. You don't need to remove the radiator cap. If the level is ever low, you add coolant to the reservoir.

Coolant Flush Checklist

There are three (ok, 4) places to drain coolant.

1. The overflow tank (white, behind the left quarter panel).
2. The actual coolant drain bolt on the water pump, located below and behind the gearshift lever.
3. The bolt below and between the exhausts where they exit from the head. This one is important and often forgotten.
4. The hoses themselves.

It's simplest to do 1 and 2, refill with water and run for a minute or two, then rinse and repeat until only water comes out. Have your radiator cap off during all draining.

Follow above directions for refilling.

My bike overheated. What to do?

The Ninja cooling system rarely gives any trouble. The most common cause of overheating is, in fact, the wrong spark plugs. Take a look at your spark plugs. They had better be either NGK or ND brand spark plugs. If they are Champions, then you probably have more than a cooling system problem to worry about.

OK, then. Start with the simple stuff.

First, check to make sure that the fuse for the fan didn't blow.

Then, disconnect the wire at the connector on the lower left side of the radiator, and put a jumper wire between the two terminals on the wire, and look to see if the fan comes on.

• If the fan comes on, reconnect the wire to the radiator, top off the lost coolant at the radiator cap, then ride the engine around the block a couple times until it gets into the normal zone. Then let the bike idle for a while until it gets up into the 3/4 range. The fan should come on long before it gets to the H line.

• If the fan doesn't come on, then check to see if the connection to the fan motor is properly hooked up. If it is hooked up properly, and the fan doesn't come on, disconnect it, hook up a test light (or equivalent) jumper the radiator temp switch connector, and see if there's power getting to the fan connector.

Now, if the fan works properly, and the temp switch in the radiator is working properly, then it's time to test the thermostat. Pull the gas tank, then open the thermostat housing, an remove the thermostat. Test it in a pot of boiling water to see if it opens.

• If it doesn't open, replace with a new one.

• If it does open, with the thermostat housing open, crank the engine over a little bit, and see if you get coolant movement (this will be messy). If there's coolant, the water pump is fine. If not, then you need a new pump.

Hints & Tips: Cooling System

Bill H writes:

It is noted that riders have concerns about their cooling systems here sometimes. At 81K with no trouble at all with my '88, I am impressed with its design and reliability.

Fundamentally it is a miniature car system, with a small coolant capacity and radiator commensurate with the engine size.

The coolant should be drained (cold only, it is under pressure when hot and squirts hard from that little drain hole even cold!) and refilled every two years. Many owners change coolant every Fall. If neglected the coolant goes "sour" and starts corrosion inside the water jackets of the engine. If changed in a timely manner no corrosion will occur, except from the dissimilar metals effect. The steel tube at the top of the cylinder head sometimes rusts, but mine has not yet failed even so.

People worry about their temp gauge indications, but the Kaw Service Manuals disclose that the running temp they intend (controlled by the thermostat) is about 180-200 degrees F. Less, the thermostat stays closed, more, the automatic fan comes on.

Where I live, 90+ F daytime temps are common in mid-summer, but except when sitting at lights or putting in traffic, the fan never comes on. As has been said here, anything under a 12 o'clock reading of the needle on the dial is okay. That's about when the fan comes on. And even if the fan does come on, with 50/50 antifreeze you are a LONG way from boiling, which, with 15psi in the system, is way up about 235 F or more.

Bottom line: The system is very well designed and highly reliable. One little quirk is that, when changing the coolant, the system always traps some air bubbles. My approach here is to fill the cold system up to the neck under the cap, start up the engine and let it idle just a few minutes to pump the coolant around and purge the air. I don't let it get hot. This usually purges the trapped air, and then I top it up again before replacing the cap. NEVER remove the cap when the system is warm or hot. It is under pressure and will blow scalding coolant out on you.

The reason the automotive industry doesn't put temp numbers on gauges for cars and bikes, but shows 'normal' range and 'red zone', is that in the olden days when they still did, too many drivers fretted about why they had 190 degrees instead of 180, or whatever, and worried Service Managers with it; all of this was needless.

Water-cooling for bikes is a much better approach than the older air-cooling, because the engine running temperature can be controlled by the thermostat. Hence, tuning for maximum performance can be applied by the factory. With air-cooling, cylinder head temp varies constantly and widely, and generally is always much higher than with water-cooling. Typical British singles and twins of yore ran head temps in American summer cruising conditions of 400-450 degrees. With comparable designs, the tendency to detonation ('knocking') increases with temperature rise, and detonation is always a limiting factor in piston engine performance. Another subtler effect is that higher temperatures have long been found to increase wear of moving parts, which accounts for the excellent longevity of water-cooled bikes in recent times.

So, for the old-timers among us, we are grateful for the improvements brought about by water-cooling, and the 250 Ninja is a prime example. It was impossible 40 years ago to get the kind of fast cruising ability and longevity from air-cooled 250s that we enjoy today with the Ninja.