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Any tips for my cooling problem

1932 Views 8 Replies 5 Participants Last post by  TheGeek
Hello guys!

Recently I've got my first Gixxer, a 750 K4. When I first got it I flushed the cooling system and refilled it with 100% antifreeze. I've bled the system at the radiator inlet port and it's been functioning well for 3 weeks.

Yesterday was a rather hot day and when I came home from a long ride and put the bike away the temp was showing 106C/222F and I could hear boiling sounds. The bike spit out fluid from the expansion tank overflow. The fan is working correctly and coming on around 104C/220F. Usually the bike cools down quickly when I ride, but yesterday at the end of the ride it was constantly around 104C/220F, even in cool air with +50Km/h.

Now I bought a manual after I did the flush and found out Suzuki wants me to mix 50% antifreeze and 50% distilled water (and not 100% antifreeze). Also I found out you can bleed the system with the bolt on the thermostat's cover.

I wanna diagnose why my bike was boiling and overflowing coolant, but I was hoping you guys have some tips for me. I don't have the equipment to do a pressure test on the radiator-cap or a thermometer to check the thermostat. So I've bought those parts new and they should arrive tomorrow.

Is it okay to proceed like this, or should I do it differently:
1. Drain current (100% antifreeze) coolant
2. Replace thermostat with the new one I ordered
3. Fill system with 50% antifreeze and 50% distilled water
4. Start it up and diagnose if the water pump is working well (I don't know how i can diagnose this, any tips?)
5. Bleed it at the radiator inlet completely
6. Bleed it at the bleed bolt on the thermostat cover
7. Install new radiator cap and expansion tank
8. fill expansion tank
9. clean out the radiator and straighten bent fins

All tips are welcome, thanks!
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If you don't have any symptoms which suggest other problems (like foam or oil in the coolant), then I would just ride it again a few times before panicking.
All cooling systems have a "natural" fluid level, which normally should be between the high and low marker levels on the expansion tank, but it is not uncommon for them to settle "somewhere close". If you keep adding more fluid, it will keep spitting it out when hot, but if you don't add more, it should just stay where it settled last time out.
Just check that it doesn't spit more out next time, and the engine temp doesn't go above what you are seeing now (which are not worrying).
I have a 750K5 and myine holds a level nearer to the minimum line than to a midway point.
Hey Clipper,

Thanks and really good to know! I'll check the coolant level in the radiator tonight. If it's still topped then you might be right (which I really hope!). I'll make sure to let you know after I rode it again, thanks again.
Wow, great tips Dave and The Geek! I really appreciate your help here!

Testing the water pump is easy. Get a clean bucket to drain and reuse your coolant. Pull the hose off the pump and look inside. Crank the engine (don't let it run for more than a few seconds) and watch the impeller.
Awesome, I was gonna take the cover off. But doing it this way saves me from having to find a new o-ring. Great tip.

Since you're boiling at what is essentially the top end of the normal operating range, my recommendation is focus on the cap.
Nice, thanks again. I also think this might have to do with the fact that I used 100% antifreeze. My manual shows the image below. It took me a while to understand but I think what they are trying to explain is that the pressure on the system at a specific temperature differs based on the concentration of anti-freeze. So perhaps my pressure is on the high-side and causes the radcap to open up too soon which in turn leads to pressure-release and a lower boiling point.


The high temps could be because of using 100% antifreeze as water will transfer heat better
Damn, I never knew. I assumed anti-freeze was better at transferring heat. Wel lesson learned, read the fucking manual next time :').

Thanks again, I will let you guys know if it was the culprit!
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So! I took off the fairings and saw that the rad was still filled to the top. I've took out 1L of antifreeze and replaced it with 1L of distilled water. Also I've cleaned the rad-cap. The new one did not arrive so I decided to give it a go and take her for a spin.

The conditions were hotter then yesterday but during the ride the bike was way cooler, somewhere around 90C/194F. In traffic or at idle it get up to about 106C/222F but then dropped down to 100C/212F and the fan shut off. It really seems like the 50/50 mix did a lot better then 100% antifreeze. I did the test-ride with the fairings off so maybe it runs hotter when they are on but I doubt it will make a big difference.

I will still replace the rad-cap since it's in order anyway but I reckon I will cancel the order for the thermostat because I don't think there's anything wrong there.

Thanks again for all tips and advice <3
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