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Overheating. Advice?

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33K views 47 replies 22 participants last post by  rsparky  
#1 ·
Well, i only have a few more days left this year, but I'd like to get this damn overheating issue straightened out. Took the bike to one shop for mapping, but a new map didn't help that issue.

Basically, the overflow bottle boils over after one hard session. A little better with overcast skys, but still overheats. When I come into the pits, it's about 2 bars from the top, and I can see the water boiling over to the overflow bottom. I cut the engine off before I come to a stop, but it doesn't help much.

On the track, I don't think I've seen it go past 3 bars to the end. It clearly is something that happens on the cool down lap (ironic).

Not much to the cooling system, no thermostat, no fan, full kit race motor. Thinking it may be running lean, I did richen up the lower throttle position map on the PC3, which did help a bit. Had a custom map made, but they didn't touch the zero to 2% throttle side. Go figure. No shortage of power, very satisfied in that department. Running Sunoco 100 octane race fuel if that matters.

I got a new radiator cap on the way, and I plan on relocating the overflow bottle to somewhere cooler. Right now, it's behind the radiator. Can't think of much more to do, maybe try to re-wire a fan back on?

Water has been flushed several times, hoses burped with the radiator cap and left screw unpluged. I still think air is getting in there somewhere, cause my Aprilia used to have a similar problem. The 250 had a few bleed screws in the block, I didn't see anything like that on the 675.

Can't believe they haven't flaged me at the track yet, it's pretty obvious what's happening.

Any ideas are appreciated.
 
T
#2 ·
Sounds like you've done all the obvious. If you had air in the systems still, the bike would be hot all the time. Race motors do produce more heat and the 100 octane fuel will certainly make the motor run hotter. Sounds like a bigger rad is needed or fitting an oil cooler will help. That what the race lads here do.
I'd be tempted to fit the fan back on the bike and possibly fit a lower rated temp sender switch so the fan cuts in earlier.
I'm running no fan or header tank, plain water plus a wetting agent (Silkolene) and never have a problem.
 
J
#4 ·
antirich said:
Well, i only have a few more days left this year, but I'd like to get this damn overheating issue straightened out. Took the bike to one shop for mapping, but a new map didn't help that issue.

Basically, the overflow bottle boils over after one hard session. A little better with overcast skys, but still overheats. When I come into the pits, it's about 2 bars from the top, and I can see the water boiling over to the overflow bottom. I cut the engine off before I come to a stop, but it doesn't help much.

On the track, I don't think I've seen it go past 3 bars to the end. It clearly is something that happens on the cool down lap (ironic).

Not much to the cooling system, no thermostat, no fan, full kit race motor. Thinking it may be running lean, I did richen up the lower throttle position map on the PC3, which did help a bit. Had a custom map made, but they didn't touch the zero to 2% throttle side. Go figure. No shortage of power, very satisfied in that department. Running Sunoco 100 octane race fuel if that matters.

I got a new radiator cap on the way, and I plan on relocating the overflow bottle to somewhere cooler. Right now, it's behind the radiator. Can't think of much more to do, maybe try to re-wire a fan back on?

Water has been flushed several times, hoses burped with the radiator cap and left screw unpluged. I still think air is getting in there somewhere, cause my Aprilia used to have a similar problem. The 250 had a few bleed screws in the block, I didn't see anything like that on the 675.

Can't believe they haven't flaged me at the track yet, it's pretty obvious what's happening.

Any ideas are appreciated.
Click to expand...
If it boils in the overflow bottle, I vote for a air bubble in the system. I had that on mine (and I was not even racing).
Air in the radiator means that the cooling system cannot pressurize and therefore will bubble when hot. With no air in the system, the water could go over 100°C without boiling as the pressure goes over 1 bar.

If you already checked for air in the radiator, then I give up.
 
#5 ·
Yea, I believe there's air in there, which is frustrating as Hell. I wish there was some more bleed bolts in the system, maybe i should try cracking open some of the water pump bolts to see if air is trapped.

What's strange is that I'll squeeze that lower hose for a good 10 minutes and bubbles will still come up through the radiator. That doesn't sound right. I even tried rocking the bike back and forth while bleeding it. To get sir in the system, there needs to be a leak, which there isn't. No fluid in the pan, and no white smoke out the exhaust.

I talked to a guy who ran the 08 Triumph AMA FX team. Despite all the trick engine parts, they had no need for an aftermarket radiator or fan set up. I think the WSS team uses a factory radiator as well.

Despite the overheating in the pits, the bike runs great. Just worried that I'm pushing the life of the motor.
 
H
#6 ·
The stock rad should be more than adequate, I'm still running the stocker on mine and it is +20hp over stock. I'd put most of my money on it being air remaining in the system, they are a real pain to bleed. Also could be the cap, and I think I would try re-fitting the thermostat as well.
 
#7 ·
hordboy said:
The stock rad should be more than adequate, I'm still running the stocker on mine and it is +20hp over stock. I'd put most of my money on it being air remaining in the system, they are a real pain to bleed. Also could be the cap, and I think I would try re-fitting the thermostat as well.
Click to expand...
+1

The thermostat is also a flow regulator that keep the water in the radiatior long enough to get cooled.

Never heard of it being an issue in these bikes, but I've fixed a LOT of cooling system problems in cars this way.
 
#9 ·
Sure you've looked at doing this, but what the hell...

Put the bike on stands to level it.

Fill the coolant system, idle the bike until it gets hot in the yard, add coolant while the water is circulating helps me flush out the air before pressurizing the system by putting the cap back on too soon. With the filler cap off, the weight of the water added is generally enough to push the air out though the radiator.
 
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#11 ·
nycstripes said:
Sure you've looked at doing this, but what the hell...

Put the bike on stands to level it.

Fill the coolant system, idle the bike until it gets hot in the yard, add coolant while the water is circulating helps me flush out the air before pressurizing the system by putting the cap back on too soon. With the filler cap off, the weight of the water added is generally enough to push the air out though the radiator.
Click to expand...
I've tried a similar approach with the same logic in mind. Doesn't take long for the bike to start boiling over out of the fill spout. I might want to try it at a low water level with the right side radiator screw off.

I'm going to take a whack at it this weekend, got a track day on Tuesday. I'll start with your method, try to crack a few key bolts, and put the thermostat back in.

Maybe I'll bring my fan with me just in case.

Overall, I think the new 14K redline is stressing the coolant as well.
 
#10 ·
you could have exhaust coming into the flow without smoke. especially since the motor has been apart for all the race bits. ive never had a problem bleeding the system. especially after a couple trips. after it gets hot and cools a cuple of times should even itself out. i dont think it's air.
 
#13 ·
Well, I tried a bunch of the suggested items on this post, and ran the bike in the driveway for 20 minutes or so. I was adding coolant and burping the lower hoses the whole time. After 20 minutes or so, the guage slowly raised in temperature and water boiled over the radiator opening. Shut the bike down, let everything calm down , filled some more coolant, then put the screw and cap back on. Ran the bike for a little while, this time the watching the gauge slowly climb. It got to about 2 bars before max, then water started boiling and filling up the reservoir.

Keep in mind that the bike was just sitting, not moving. No fan either.

Does that sound like the time when the radiator should start boiling? If so, is the cap releasing the pressure too soon?

Or is all of this normal and I'm just being a pain in the ass about it?
 
M
#14 ·
well if the bike is stationary and you have no fan on the radiator then your not really exchanging anyheat from the coolant/water. a fan is supposed to remove heat from the coolant/water by sucking air through the radiator fins when cruising or stopped, if your overheating when stopped or riding slow then it could be that your just not exchanging enough heat from the coolant/water to stop it from overheating. i would try putting your fan back on and go from there.
 
#15 ·
I agree, without the radiator fan the coolant will eventually boil over in any bike just sitting there and running. You might also try to run water wetter or engine ice. With engine ice, the bike should run cooler for you. I caught a post where you said you might be racing, so water wetter should be the way to go since engine ice may not be approved for your race org.
Re-install the fan like suggested and see if the bike stops boiling over.
 
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#18 ·
I'm not running the bike stationary after bringing it off the track without a fan. That would be kind of asking for trouble.

Bike will run around the course at 5 to 3 bars from max. Half way through the cool down lap, it goes up a bar. By the time I enter the pits, it's up to two bars from max and the water starts boiling into the reservoir. Sometimes, it's at one bar before max. I've actually been shutting the engine down when I see my pit, costing the rest of the way. Doesn't help.

Kit engines are not suppose to have a cooling fan, the harness doesn't have the plug for it. The Arrow Stage two pipes don't even allow a fan to fit.

Ive always ran water wetter and distilled water. Never ran anti-freeze on any bike i've owned.

Just got back from another track day at Thunderbolt, 75 degrees and cloudy. I did replace the cap with a new factory cap. Didn't help, except that now it makes a high pitch sound when it boils over. :pout:

Couple of people I spoke to were theorizing that there could be a head or head gasket issue. Pressure from the gasses would keep water from loading up the intake/exhaust port, yet may still introduce air into the cooling system. This was their theory, I don't know how close the ports are on that motor to know if it's possible. Engine is coming apart this winter, I'm sure something like that would stand out.
 
J
#19 · (Edited)
Having this much trouble with overheating sounds very much like a blown or leaking head gasket. Have you tried a compression test? When the motor is hot? I'd look in that direction. How long have you been running since the race kit was installed? You might wanna recheck the head bolt torque.

If the cooling system is air tight (good head gasket), it should eventually bleed itself of all the air. Any trapped air should migrate to the filler neck & out to the overflow when the bike is running. As it cools, it'll pull in coolant from the overflow. A few heat cycles making sure that the overflow bottle is not running dry should bleed the system.

Now, a couple of things to keep in mind. On cooldown, if there is a leak anywhere between the filler neck and the overflow bottle which will allow air back in the system, then it'll pull in air instead of coolant. Check that the filler neck sealing surface doesn't have a nick in it. That'll allow air back in instead of fluid. Check the hose barbs, hose, etc. A few heat cycles like this and the overflow starts to be more filled with fluid and the radiator more filled with air.

Also, the cooldown lap is very stressfull for the cooling system - you've been running the motor full tilt (pushing a lot of air through the radiator) and all of a sudden all that cooling air is drastically reduced as you circulate at a leisurely pace and it overheats just as you pull into the pit. Fit the fan back on the bike, there's still the thermo-switch to turn it on, yes? You can run a lead direct from the battery if needed - be sure to put a fuse inline. If that's not sufficient, you can also fit a manual switch in parallel to the thermo-switch so that you can flip the fan on as soon as you start the cooldown lap. Oh, & like Hord suggested, refit the thermostat too.
 
#21 ·
Thanks for the advice, very thorough. I'll answer each one below:

jhylton79 said:
Having this much trouble with overheating sounds very much like a blown or leaking head gasket. Have you tried a compression test? When the motor is hot? I'd look in that direction. How long have you been running since the race kit was installed? You might wanna recheck the head bolt torque.
Click to expand...
I haven't done a compression test, but that's not a bad idea. I'm assuming a bad gasket will result in lowered compression? What it's it's just in the cooling port and not the cylinder?

The engine was rebuilt last year with one 2 day race on it. Doesn't always mean much, but that's what I know.

jhylton79 said:
If the cooling system is air tight (good head gasket), it should eventually bleed itself of all the air. Any trapped air should migrate to the filler neck & out to the overflow when the bike is running. As it cools, it'll pull in coolant from the overflow. A few heat cycles making sure that the overflow bottle is not running dry should bleed the system.
Click to expand...
I'm not sure if the overflow bottle running dry is a bad idea. There is an overflow hose on the reserve, and wouldn't that suck in air as well? I have seen the bike suck in water from the bottle when it's cooled down, but not always.

jhylton79 said:
Now, a couple of things to keep in mind. On cooldown, if there is a leak anywhere between the filler neck and the overflow bottle which will allow air back in the system, then it'll pull in air instead of coolant. Check that the filler neck sealing surface doesn't have a nick in it. That'll allow air back in instead of fluid. Check the hose barbs, hose, etc. A few heat cycles like this and the overflow starts to be more filled with fluid and the radiator more filled with air.
Click to expand...
This is a good idea. I did replace the cap with a new factory one, which didn't help. However, there is now a very high pitch squeal when the bike overheats, coming form the upper radiator. I wonder if the new cap (with better pressure) is forcing air out of a tiny hole in the radiator. I can see a crack in the neck as being an issue. Might be able to pressure test this.

I did replace the overflow with a new one (Motion Pro) and replaced the overflow hoses. The bike never had the factory overflow bottle on it.

jhylton79 said:
Also, the cooldown lap is very stressfull for the cooling system - you've been running the motor full tilt (pushing a lot of air through the radiator) and all of a sudden all that cooling air is drastically reduced as you circulate at a leisurely pace and it overheats just as you pull into the pit. Fit the fan back on the bike, there's still the thermo-switch to turn it on, yes? You can run a lead direct from the battery if needed - be sure to put a fuse inline. If that's not sufficient, you can also fit a manual switch in parallel to the thermo-switch so that you can flip the fan on as soon as you start the cooldown lap. Oh, & like Hord suggested, refit the thermostat too.
Click to expand...
Yea, I figured this out the hard way. Nothing worse than pushing the bike, and myself, for 8 laps then having to watch the cooling guage for half a lap as a come in. Trying to time when to shut the engine down and roll in is a pain too.

The factory race harness doesn't have the wiring for the fan anymore, but I'm sure it's easy to wire one up directly. Even if it does, the top end 675 race bikes that I've seen all have the fan removed and the stock radiator. Fan may make it better, but it's not curing the underlying problem.

Overall, I'm leaning more towards a head/gasket issue. It's just feels too much like air in the system, which is a common problem with Aprilia 250s (my former bike). This may be my last track day of the year, so next step is an engine tear down anyway.

I really appreciate the overall technical help from everyone. This place is starting to feel like the Aprilia forum :thumbup:
 
#23 ·
I'm also a fan of putting the thermostat back in, its the flow regulator for the system. At certain engine speeds the coolant will not stay in the block or radiator long enough to transfer the heat.
 
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#25 ·
Pull the plugs and make a note of what cylinder they came out of and how they look, carboned, white, burnt electrode, etc... That will atleast tell you if there is a problem in one of the cylinders. I would side with head gasket leak or Crack in the head (magnaflux the head to inspect for a crack). You do not always get smoke with a failed head gasket. Exhaust gas pressure is higher then the water pressure in the cooling system. That can be why the water is just boiling out. Don't bother with a fan yet, Ride the bike normally around the neighborhood etc and see if it starts to over heat.
 
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#28 ·
Yes, this is a thread revival in all its glory! :thumbsup:

OP, did you ever figure out what the issue was?

My bike began exhibiting the same issues this past weekend at the track. The last session of the day I was sitting in the hot pit with the bike idling. While I was about to pull off, one of the corner workers pointed at the bottom of my bike for me to see coolant pouring out.

My observations:
-Ran a full track weekend with no overheating issues
-Temp gauge was displaying normal temperature (maybe 5-6 bars)
-Fan was not on
-Coolant resevior was completely filled and boiling over
-Coolant was pouring out the bottom of the bike

My bike is pretty much stock besides air filter and slip on. I've not once opened the radiator cap or coolant system so this was a complete surprise. I did read a thread on here recently regarding air pockets for people who track/race their 675's but cannot locate that thread.
 
#30 ·
Had similar problems on my 08, after idling in traffic etc the reservoir would boil up like a kettle and coolant would poor out of the overflow. Start the bike up with left side panel removed so you can feel the rubber coolant pipes. Keep squeezing them as the bike warms up and they should go from being able to squash them between your fingers to really firm as the pressure builds. If they don't go really firm after a few minutes then you're losing pressure probably through the rad cap. Replacing my rad cap cured the problem. . . . .I noticed that I'm now getting the same thing on my 2011 675r! Maybe a common fault!

Sent from Motorcycle.com Free App
 
#32 ·
Alright so I'm at a loss on this coolant overflow boiling situation.

I have burped the system, placed the bike on the side stand to refill from the bleed valve, burped the hoses again, moved the bike rearstand and refilled the rad with idle. The bike bike does the same thing with both the old and new rad cap (Stant 11233) where it will warm up to about 3 bars and then the coolant level in the reservoir will rise.

Most likely will be taking the bike to the dealer in the morning as I do not know what else to do.
 
#33 ·
Marcismo55 said:
Alright so I'm at a loss on this coolant overflow boiling situation.

I have burped the system, placed the bike on the side stand to refill from the bleed valve, burped the hoses again, moved the bike rearstand and refilled the rad with idle. The bike bike does the same thing with both the old and new rad cap (Stant 11233) where it will warm up to about 3 bars and then the coolant level in the reservoir will rise.

Most likely will be taking the bike to the dealer in the morning as I do not know what else to do.
Click to expand...
I've had that same issue a few times over the years, but a new radiator cap has always solved it for me. Is it possible the new cap you're using isn't holding enough pressure?
 
#34 ·
Thank you for chiming in.

I guess it is possible, however, this is the cap that was recommended on multiple threads on here. Maybe it's just a bad one?

In on the way to the dealer now to have them check it out. I have a trackday tomorrow and I can't let this linger on unfortunately.

Sent from my HTC One
 
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