Hey guys,

My CBR recently started overheating all the time. I figured the coolant in the system was really old. Anyhow, I drained the coolant and replaced with distilled/de-ionized water. Bleeded the system, refilled the coolant back to proper levels. I let the bike idle to operating temperature. When the bike temp gauge reached just above half way, the fan kicked on. However, the coolant already started to boil over. Fluid was coming out of one of the hoses. What could be the cause of this problem?

I am trying to sell this bike. On friday, I had it sold but when I had delivered it to the new owner, the bike overheated. Needless to say that deal died. I had it towed home and am now trying to troubleshoot. I already have my new bike in the garage and need this one gone! I am an honest person so I want this fixed before I sell it. What should I replace?

Radiator cap?

 

Which hose was it coming out of?

Have the cap pressure tested, or just replace it, if you have doubts that it is holding the pressure that it's supposed to.

 

Coolant expansion.

 

Check the cap....

 

Thanks demon. I'll go buy a new one tomorrow.

Could it possibly be a faulty thermostat? I mean, the coolant started to boil as soon as the fan came on. That fan came on too late! Could it be reading a lower temp than it actually is?

 

Anything is possible...
The system is supposed to build some pressure. If the cap is no good, it won't hold it.

You can pick one up from any auto parts store for half the price of the dealer. Just bring the old one with you to match up pressures and style.

 

Do you know which cars (year and model) are compatible with the F4? I've been reading some accords and civics.... but which year?

Thanks for that suggestion. The cap should be 1.1 bar i think.

 

I don't know remember off the top of my head.

There are only 2 cap sizes, and 2 pressure ratings (a few rare exceptions). The smaller size has 2 styles. It shouldn't be too difficult for even the dumbest parts guy to get the right one out of 6 caps to choose from. They may even have them on a self service shelf. Bring the old one with you, to ensure it's right before you leave the store.

 

Ok. So I replaced the rad cap. Rode the bike today and it didn't overheat. I let it idle for a bit and the fan came on without the bike overheating. How long should a bike be able to idle without overheating?

I'm not even sure what "Normal" operating temperature is nowadays. I rode the bike for two months without issue so I didn't really ever pay attention. Now, my eyes are so glued on the temp gauge I even got a speeding ticket today! I didn't even realize how fast I was going.

 

It should be able to idle with the fan on until it runs out of gas or battery voltage. Now, I say "should" because it should, but I wouldn't let it....