ZX6R Overheating


After the first couple of sessions at the track, when I got back to the pits coolant pissed out and then I noticed that the temp gauge was flashing HI. At first I thought it might just be an air pocket from not bleeding the system properly when I swapped out the coolant for Water Wetter so I ran it without the radiator cap on for a while (once it had cooled down obviously) and kept topping it up. Sadly it still kept overheating after only a few laps and I noticed that the fan wasn’t coming on.

I couldn’t do any more at the track so at home the next day I had a closer look. I found that someone had installed a second fan on the radiator with a manual switch but it wasn’t connected to power. It shouldn’t need any fans while it’s moving and Lonny, the guy I went to the track with had a 2004 ZX6R that had the fan deleted and his ran hot but didn’t overheat. So I removed the second fan and cleaned the connections on the stock fan wires and that was all it took for it to start working. I disconnected the radiator hoses and flushed it with the hose pipe, checked that there were no major blockages in the air fins and buttoned it all back up. I warmed it up to see that the fan came on and then when I ran it up and down the street the temp started coming down so I’m hoping that it’s sorted.

Update – 2nd track day

Second time at Grand Bend and this time we were on the Long track layout. Sadly the bike was still overheating and leaked coolant back in the pits but this time I could get 5 or 6 laps in before it started flashing HI. We took the thermostat out and put it in boiling water and it seemed as though it might be sticking a little so we put it back together without the thermostat – hardly any difference.

This time when I got back from the track I totally removed the radiator, filled it with CLR and left it for a while before flushing with the hose. It definitely seemed to flow better after that so I decided to put it back together, put the thermostat back in and test it. The thermostat must have fell out slightly and lodged against the housing somehow because the corner broke off the thermostat housing during re-assembly. I also think the housing must have been weak because I didn’t reef on it at all. Found a housing on eBay and now waiting for it to arrive (sometime in November), probably be too cold for any sort of testing though.

Crankcase Bolt

While tinkering with the cooling I noticed oil dripping from this bolt.


It turns out that this is one of the main crankcase bolts that clamps the crankshaft bearings on either side of the con rods. I started tearing into the engine to install a heli-coil in the upper engine case and got down to the throttle body. Then I had to pop to TSR to get a bolt that had rounded on one of the clip-ons and Denny suggested trying a longer bolt in the crankcase to get me through the end of the season and found one for me. There’s only one more track day this season so I decided to give it a shot. I installed the bolt in the hole until it bottomed out and it was a touch too long so I found a suitable washer to use as a spacer and bolted it back up. Haven’t seen any more oil leaking on the few test runs.

Update 2 – Thermostat housing

The thermostat housing came in complete with a thermostat so I decided to take a break from the CBR600RR rebuilding and switch to the ZX6R. I gave the thermostat a bit of a clean and then very carefully installed it and the housing. It all seemed to go pretty smoothly so I put the tank back on, filled up with water wetter and wheeled it out into the yard for a test … couldn’t get the thing to fire at all! The battery drained quickly so I pushed it back in and took the tank off to look for any broken wiring or separated connectors or something – couldn’t find anything. Reinstalled the tank and tried again now that the battery had been charged a bit … still nothing, not even a splutter! Back in and remove the tank, ugh.

This time I decided not to rebuild until I had found a potential cause. I was chatting with my buddy in the UK and he pointed out that if it was running before, it can only be something simple that I have touched that is causing the problem. After giving it some thought I remembered that I had removed the seat bracket to repair the stripped bolt holes with some aluminum brazing. After inspecting the bracket I found that there was a sensor on the bracket that had UP molded into it but it was pointing down!?

The connector on it points up towards the seat and I think I had not seen the UP label and installed it with the connector pointing away from the seat. I flipped it over and tried it … fired right up!!
Sweet!! So I topped up the water wetter and then the reservoir tank, put the seat unit back on and put it away.

Update 3 – Wet race

Finally got chance to try it again in my first wet race. I bought some old rain tires off some guy at Grand Bend but they felt horrible. I still managed to go out and even though it was wet I did quite a few laps with no sign of any overheating.

Next Post

CBR600RR Frame Sandblast and Paint

Once the CBR600RR was stripped down to the engine separated from the frame, I decided to look into getting it sand-blasted. A lot of people online suggest using walnut shells as a media instead of sand to reduce risk of damage to the aluminum frame. I figured that in these […]

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