So i have a 1997 CBR f3 that i cant get to stop leaking. I just finished rebuilding it and started it up to run. Found a clamp or two i missed tightening in my eagerness to get it started up. I let it warm up to and a few hoses leaked because i didnt get them tight enough. Went for a few short rides and it worked great. I went for a longer (45min) highway ride and found some fluid coming out by the cap as i cruised but it was staying cool. Got off the ramp and got stuck on some traffic where the temp gauge began to rise. It hit the red and the fan still didnt come on. Had to pull over a few times to let it cool down before i got back on the highway where it stayed cool but still spewed some coolant out at the cap. I figured it was a bad cap so i got a new one and slapped it on, got a $3 switch for the fan because i didn't want to fork out $50 for the thermo switch. I let it idle till it warmed almost to the red and flipped the fan on and it cooled down to the middle of the gauge. Went out of another long ride hoping everything was fixed. After i got her warmed up without any leaks i took her for a little speed sprint and it started spewing coolant at the cap pretty bad. After riding a few more times i discovered it only leaked when it was warm and i was accelerating hard. I poked around a little more and found that the reserve tank wasn't getting any flow/vent. Tried to blow some air through the vent tube with the compressor and didn't get anything through so i figured it wasn't venting when it got pressure up. Got a new hose ran it into the reserve tank and now the reserve tank leaks when i accelerate hard. My only idea is that the pressure cap isn't quite sealing to the 16lbs it should or the extra acceleration is just pushing too much coolant through the system to hold....I got a new filler neck that i'm gonna try to hopefully get a better seal because there is some build up in the old neck that may be compromising the seal. I'm just checking to see if anyone has had a similar problem or if you guys have any other ideas for a fix if this doesn't work.

 

It sounds like there could be an air bubble or a blockage somewhere. The cooling system should be able to handle whatever amount of flow the water pump can generate. Also, I'm pretty sure the overflow tank only gets coolant flowing to it when the pressure gets too high. Hence the name overflow.
Maybe try bleeding your cooling system or flushing your radiator and cooling system separately. If the problem persists, maybe the thermostat is faulty and not allowing enough coolant to flow through.
I'm sure someone else on here can offer you some help as well as these are just some general ideas.

 

Thanks for the reply man. It very well could have some air bubbles in it because it's gotten so low on coolant several times. I'm just wondering if that would be the cause of the overflowing.

As for the overflow tank. I noticed that because i had filled the radiator up with green coolant and the overflow with water. When i saw that the overflow was still clear I figured it wasn't venting (which it wasn't).

Someone mentioned a leaking head gasket as a possible root of the problem. I'm really hoping it isnt because just finished getting everything back together...

I'm gonna try this new filler neck this weekend and run it a bunch to work any air out. I may throw in a new thermostat while I have it all apart as well. Anyone know if you can get the correct thermostat at auto parts stores?

 

I just had a thought. The bike had been sitting for quite a while before i got my hands on it and it hadn't stored properly. Could it be possible that my radiator is gummed up on the inside so that when run the bike harder it cant handle the extra flow of coolant so it just overflows? If so, is there some process/chemicals i can use to clean it out and allow it to flow better? Just for the heck of it here is a pic.

 

I've used powder dishwasher detergent to flush radiators before. Maybe that'll help

 

Hey so update here. I changed the filler neck which was good because it doesn't leak around the top of the rad cap anymore. Now my problem is that my coolant fills up the overflow tank after running it hard for a few seconds then it all just stays there while the engine gets hot. If i dont stop the engine will overheat because all the coolant is in the overflow tank........

 

Are you turning the fan on manually?
Try turning it on earlier if you are.
You might have too much coolant also.

 

My bike is doing the exact same thing. I will keep watching to see if there are any updates

 

Yep, i turn the fan on manually. Right now i pretty much leave it on all the time. Turn it off on the highway sometimes and turn it back on before i get off the ramp.

So I noticed when I let the bike cool that the coolant from the overflow wasn't sucking back into the rad. I slapped the old rad cap back on and ran it for a few mins to warm up. Shut it off and the coolant sucked right back in. Seems to have solved 70% of the overheating. I'm not sure why the new cap wasnt working....same pressure, same shape...

However!! It still manages to spray coolant out the filler neck when i'm cruising at 70 and twist the throttle to pass (90). If I let off it stops and runs fine. Only happens when it is warm and only at highway speeds.

I have 4 possible solutions.
1) be content going 70mph (probably what i should do but that would be no fun)

2) Remove the tstat and let the coolant flow more freely

3) Find some special coolant that runs at a lower temp

4) Try another rad cap.

I think i'll try solution 4 and then 2. If that doesn't work i'll give 3 a try.

 

Nice!
Are you sure there isn't a small pinhole in the hose near the cap?