The good old thermostat...
Mine pooped itself a few days ago. Locked shut. Figured it was a good idea to replace it.
This isn't a thread on the for's and against's of running a thermostat, but rather a few tips for those who've never changed one on a Gen II before.
A first time DIY replacement can be daunting for some who've never even raised their tank before and I've seen the many questions out there.
I like to remove both left and right fairings. The left to remove pipe at the lowest point in the cooling system in order to drain the coolant first, and later on to squeeze your hand in there!
The right fairing is removed to access the radiator, cap, return hose and overflow bottle.
I don't remove the tank entirely; I remove the seat and the two front tank mount hold down bolts. Raise the tank and chock in place (hold it up).
I then go ahead and replace the busted thermostat.
There's only two bolts to remove.
The thermostat is located on the side of the engine closest to the rider below the intake manifold.
Nothing else needs to be removed. Leave the airbox and manifold and everything else alone.
To get to these bolts, you access the left side bolt of the thermostat through the left side of the bike.
Put your hand under the frame between the wires and under the ABS system and use a 8mm open end spanner or a ratchet spanner is even better!
You can see my forearm reaching under in the bottom right corner. There's enough space unless you're the incredible hulk.
Whilst you're in there, navigate the 8mm spanner to the left side bolt and crack the seal.
You can easily undo it with fingers. Just don't drop it. I could fit my left hand underneath the bolt in case it fell down.
Once that's off, move to the right side of the bike and reach over the top of the frame and under the tank with a 1/4" ratchet, an 8mm socket with 2" extension like this one.
Navigate through the jungle of wires and lines with a handy phone light and you'll see the right side bolt head. Crack the seal and undo it, but not fully! This bolt if dropped will be almost impossible to find/retrieve!!!!
Once the bolt is loosened, remove the ratchet and just turn the extension shaft with your fingers.
So you don't drop the bolt out of the socket and down the engine cavities as you pull the bolt out, first squish some blu tac into the socket to tack onto the bolt head to hold it there like this......you'll never lose the bolt when you pull it out!!
Bolts are out, the easy bit is remove the cover, push it down and aside.
Pull out the old thermostat with long nose pliers and replace the new one with bleed hole facing up.
No gaskets needed. The thermostat has a built in rubber seal.
Ensure it's seated correctly and replace the cover.
Reinstall the left side bolt first because it is easier and helps align the other hole.
For left side, finger tighten and move to the right side.
For the right side, grab the blu tac 8mm socket. Squish the bolt head into the socket so it aint going anywhere! Then easily guide the socket extension home into the bolt hole past everything that is in the way. Easy!
Tighten each side and done.
Now to test the whole system...
Once drained, I purge the system and flush the radiator with a hose of good pressure through the top cap and see if the water flows out the bottom of the radiator as quick as it goes in. If water flows freely, that's a good sign for now. Ok let it drain away. ....the radiator seems to work ok!
Now for the engine...Hook the bottom hose back up, remove the top hose at the right side of the radiator and fill the radiator with water, start the engine and run up to operating temp whilst continually filling the radiator as quick as the water flows out of the top hose coming from the engine.
Water will come out of the top hose when the engine heats up enough and you'll see water flowing out of the hose because the new thermostat has opened! Ok the thermostat works!
Why did I remove the top hose? This will flush out any crap in the water jacket and out of the bike in a total loss system because we want to flush it all out and not let gunk go back into the radiator.
Shut off the engine, let it cool down and drain all of the water. We don't want water left in it.
Replace all hoses and clamp tight.
Open the 8mm bleed bolt at the top of the thermostat.
At the radiator, fill with your icey blue coolant or whatever flavor you prefer.
Fill the overflow bottle too. FILL.
Leave the radiator cap off for now.
Start the bike and let it heat up. Keep an eye on the radiator fluid level.
When it coolant level drops, keep topping it back up.
When the thermostat opens at operating temp, air will move about the system and the radiator coolant level will drop quickly. Top it up.
Air will continuously bleed out of the thermostat bleed bolt.
Replace the radiator cap securely and leave it on. Let pressure build.
As the coolant gets hotter, it expands and helps puge the air. Tilt the bike left and right a few times to remove trapped air.
Shut off the bike and you'll hear the bleed bolt hissing air out in the silence.
When it stops hissing, lock the 8mm bleed bolt off tight.
As the bike cools down, that full bottle of overflow coolant will get sucked back in.
Once the bike is cool, the coolant level in the overflow may be below minimum. Top it up.
If the bike is cool enough, remove the radiator cap and inspect the coolant level. Top it up if need be.
The bike has now been burped and bled. There may still be a little bit of air in the system here or there, but this is fairly thorough.
Check all connections and test run the bike again. If all good, then replace fairings and go for a short test ride.
Hopefully no more overheating or overlow peeing expensive and slippery coolant on the ground when you shut off the engine!
The overflow leaks down to the bottom center of the fairing, right in line with your rear tyre.... very slippery. A thermostat is much cheaper to replace than paying for an expensive lowside because of a slippery rear tyre...
Why do I run a thermostat? ...only to maintain a steady temp regardless of season.
Mine pooped itself a few days ago. Locked shut. Figured it was a good idea to replace it.
This isn't a thread on the for's and against's of running a thermostat, but rather a few tips for those who've never changed one on a Gen II before.
A first time DIY replacement can be daunting for some who've never even raised their tank before and I've seen the many questions out there.
I like to remove both left and right fairings. The left to remove pipe at the lowest point in the cooling system in order to drain the coolant first, and later on to squeeze your hand in there!
The right fairing is removed to access the radiator, cap, return hose and overflow bottle.
I don't remove the tank entirely; I remove the seat and the two front tank mount hold down bolts. Raise the tank and chock in place (hold it up).
I then go ahead and replace the busted thermostat.
There's only two bolts to remove.
The thermostat is located on the side of the engine closest to the rider below the intake manifold.
Nothing else needs to be removed. Leave the airbox and manifold and everything else alone.
To get to these bolts, you access the left side bolt of the thermostat through the left side of the bike.
Put your hand under the frame between the wires and under the ABS system and use a 8mm open end spanner or a ratchet spanner is even better!
You can see my forearm reaching under in the bottom right corner. There's enough space unless you're the incredible hulk.
Whilst you're in there, navigate the 8mm spanner to the left side bolt and crack the seal.
You can easily undo it with fingers. Just don't drop it. I could fit my left hand underneath the bolt in case it fell down.
Once that's off, move to the right side of the bike and reach over the top of the frame and under the tank with a 1/4" ratchet, an 8mm socket with 2" extension like this one.
Navigate through the jungle of wires and lines with a handy phone light and you'll see the right side bolt head. Crack the seal and undo it, but not fully! This bolt if dropped will be almost impossible to find/retrieve!!!!
Once the bolt is loosened, remove the ratchet and just turn the extension shaft with your fingers.
So you don't drop the bolt out of the socket and down the engine cavities as you pull the bolt out, first squish some blu tac into the socket to tack onto the bolt head to hold it there like this......you'll never lose the bolt when you pull it out!!
Bolts are out, the easy bit is remove the cover, push it down and aside.
Pull out the old thermostat with long nose pliers and replace the new one with bleed hole facing up.
No gaskets needed. The thermostat has a built in rubber seal.
Ensure it's seated correctly and replace the cover.
Reinstall the left side bolt first because it is easier and helps align the other hole.
For left side, finger tighten and move to the right side.
For the right side, grab the blu tac 8mm socket. Squish the bolt head into the socket so it aint going anywhere! Then easily guide the socket extension home into the bolt hole past everything that is in the way. Easy!
Tighten each side and done.
Now to test the whole system...
Once drained, I purge the system and flush the radiator with a hose of good pressure through the top cap and see if the water flows out the bottom of the radiator as quick as it goes in. If water flows freely, that's a good sign for now. Ok let it drain away. ....the radiator seems to work ok!
Now for the engine...Hook the bottom hose back up, remove the top hose at the right side of the radiator and fill the radiator with water, start the engine and run up to operating temp whilst continually filling the radiator as quick as the water flows out of the top hose coming from the engine.
Water will come out of the top hose when the engine heats up enough and you'll see water flowing out of the hose because the new thermostat has opened! Ok the thermostat works!
Why did I remove the top hose? This will flush out any crap in the water jacket and out of the bike in a total loss system because we want to flush it all out and not let gunk go back into the radiator.
Shut off the engine, let it cool down and drain all of the water. We don't want water left in it.
Replace all hoses and clamp tight.
Open the 8mm bleed bolt at the top of the thermostat.
At the radiator, fill with your icey blue coolant or whatever flavor you prefer.
Fill the overflow bottle too. FILL.
Leave the radiator cap off for now.
Start the bike and let it heat up. Keep an eye on the radiator fluid level.
When it coolant level drops, keep topping it back up.
When the thermostat opens at operating temp, air will move about the system and the radiator coolant level will drop quickly. Top it up.
Air will continuously bleed out of the thermostat bleed bolt.
Replace the radiator cap securely and leave it on. Let pressure build.
As the coolant gets hotter, it expands and helps puge the air. Tilt the bike left and right a few times to remove trapped air.
Shut off the bike and you'll hear the bleed bolt hissing air out in the silence.
When it stops hissing, lock the 8mm bleed bolt off tight.
As the bike cools down, that full bottle of overflow coolant will get sucked back in.
Once the bike is cool, the coolant level in the overflow may be below minimum. Top it up.
If the bike is cool enough, remove the radiator cap and inspect the coolant level. Top it up if need be.
The bike has now been burped and bled. There may still be a little bit of air in the system here or there, but this is fairly thorough.
Check all connections and test run the bike again. If all good, then replace fairings and go for a short test ride.
Hopefully no more overheating or overlow peeing expensive and slippery coolant on the ground when you shut off the engine!
The overflow leaks down to the bottom center of the fairing, right in line with your rear tyre.... very slippery. A thermostat is much cheaper to replace than paying for an expensive lowside because of a slippery rear tyre...
Why do I run a thermostat? ...only to maintain a steady temp regardless of season.
Last edited:
