300 MXC overheating

mboyd · 09-04-2010, 09:54 AM

I recently purchased an 00 300 MXC. Within 10 minutes of even fast riding the coolant is boiling. It had waterless coolant, and I could hear it in a rolling boil. It is all stock and the radiators have no damage anywhere. It has a JD jetting kit and starts/runs perfectly so I doubt jetting is the culpret I flushed the radiators and no debris or trash came out. I put water back in it and same problem. The coolant seems to be circulating well when you look into the radiator neck. The radiator cap has been replaced with no improvement, and the thermostat is new and opened up nicely when we put it in hot water. Still, within 10 minutes the pipe, water pump and radiators cant even be touched, even the clutch cover is burning hot.

The only clue I have is that the previous owner said it all started when he did a routine coolant and Y radiator hose replacement. He said everything was fine before, and he made no other changes other than changing the hose, and adding the new coolant. Somthing about changing to the waterless coolant and 2 radiator hoses caused it. He said he checked the water pump and the fins looked good and it turned strongly when he kicked the bike over. This makes no sense, but I know him personally and believe him. The motor turns over smoothly, clutch is like butter and the bike rolls nicely, no nothing seems to be dragging. It starts easy, and runs perfectly until the idle rises, then I know it is overheating.
Please help me with this, its my first KTM

bajadog · 09-04-2010, 07:19 PM

If the bike ran cool before the hose change, then I'd look at the
which hoses were changed.

Also, if they changed to those cheap shiny silicone hoses, I
have read that they can collapse under a vacuum.

Eastcoast John · 09-10-2010, 11:58 AM

Hi,
I've got experience with "waterless coolant" and I have a couple questions.

Assuming that it was an actual waterless coolant (either Ty Davis' coolant or Evans), you shouldn't hear any boiling. The bubbles created are really small, there's never a "rolling boil". If you hear it boiling, there's either water in the coolant (5% water content or more and it acts like a water based antifreeze) or an air pocket. If you saved the coolant that came out, you could have it tested for water content.

If any radiator hose collapses due to a vacuum, there's something wrong with the rad cap or the venting. The caps have 2 springs. We're all familiar with the big strong one that defines the system pressure. Less well known is the small return valve spring. The disc on the underside of the cap is held closed by a light spring which you can feel by pulling on the disc with a fingernail. A collapsed hose can be due to the vent line being blocked, possibly by melting the plastic connection to an expansion tank.

It sounds like you have some other issue making it overheat. My guess is that the hoses and coolant were changed to fix a problem.

The easiest option is that there is an air bubble in the system. It would cause overheating regardless of what type of coolant you have. The KTM manual for the 950 ADV S (Technical bulletin TB 0533 10/15/04) says to raise the front wheel 2 feet to prevent air pockets. Two feet with the 950 is actually pretty hazardous, so for them to suggest it, you know it's important.

mboyd · 09-12-2010, 02:21 PM

With both the waterless, and water coolant, within a few minutes I could hear the coolant boiling. It sounded like popcorn popping inside the radiators.It seems to boil within about ten minutes, oddly enough it does not seem to make a difference if you go fast or slow. The bike kicks over really easy and rolls smoothly. Nothing feels like it is dragging in the motor or the chassis. I did make sure to bleed the radiator on the waterless and the water coolant. It did not help.
Somthing big time is wrong, I have never seen a bike get this hot so fast. Within a few minutes, back when I had the waterless stuff in, it didnt blow out but I could hear it popping and boiling inside the radiators. Water does blow out so I know the cap is working. All 3 rad caps we had did the same thing.
I looked at the water pump and it looked great. No pitting, no trash, impeller looked great. Took out the spark plug and worked the kick starter, impeller spins fast. All of the hoses were free of any obstructions. I kicked it over a few times with the spark plug out, the motor spun freely and the piston gradually slowed to a stop. It did not abruptly stop or slow down like somthing inside was binding up. I tried to grab the impeller with my hand to keep it from turning but couldn't, turns very strongly. I wrapped the rad hose that sits on the pipe with the heat wrap and another hose to shield it from the heat. I have not been able to run the bike to test it. I wish there were a good way to check the water flow with the bike running.

Eastcoast John · 09-13-2010, 08:33 AM

If there is an air pocket, it will be located in the engine/hose/pump area (rather than the radiator). Look for a place where a high point would allow air to be trapped such as in the head, pump cover, or if a hose travels up and then down.

Sometimes there is a bleed bolt installed. It would be a 10 or 8 mm bolt, probably with a copper or aluminum washer on the head or at the top of the pump. These bleed points are often added to a model after the problem is identified by the manufacturer so a later model might have one but the earlier doesn't. The next improvement over the bleed bolt is a vent line that runs up to the radiator.

Installers of waterless coolant in cars face difficulties with air pockets due to the complex nature of auto cooling systems. In some cases, they peel off the rubber seal on the rad cap to temporarily make the system zero pressure. After the customer drives the car for a week, they'll put the seal back and everything is bled out. *If this is done with a water based anti-freeze, it will boil over.*

With waterless coolant, my dirtbike is set up to run at zero pressure. This was due to a trail fix for a pierced radiator and I've just not changed the cap back out of ambivalence.

If you don't have an air pocket, I'm at a bit of a loss as to what the trouble is. (I know it would be impossible to hook up the hoses backwards so that the coolant flows in the wrong direction?)

Eastcoast John · 09-14-2010, 06:00 PM

It's occurred to me that a hose could collapse under "normal" conditions as bajadog has said. If there is a restriction like a closed thermostat and the pump is madly pumping away, the hose on the pump intake could flatten if it isn't strong enough to hold its shape.

mboyd · 09-15-2010, 11:24 AM

I was able to go out and battle this beast some more today. I pulled and checked all the radiator hoses, no obstructions. I wrapped the hoses with the radiant heat wrap, removed the T-stat, refilled it with coolant and fired it up without the cap. I could see the water circulating pretty well, an occasional cluster of bubbles went by. I filled the water just over the fins. When I blipped the throttle the water level instantly fluctuated higher, so it seems to be flowing very well.
Rode the bike down the street in second about five times. Didnt boil, but the idle started accellerating and everything was blistering hot, just like usual. I noticed a bit of smoke in the exhaust, and when I checked the water level in the radiator, it seemed a bit lower. Maybe it is a bad head gasket?
I am about out of ideas

, other than replacing all the top end gaskets and maybe the rings while I am in there.

Eastcoast John · 09-15-2010, 03:40 PM

Have we talked jetting? A symptom of lean jetting is a high or racing idle. When your bike runs out of gas, the idle goes up at the end. Lean (too much air) burns hot. The plug will look white and dry.

mboyd · 09-15-2010, 06:28 PM

I think the jetting is OK. It has a JD kit in it with a 170 main, and the red needle on the middle clip per his recommendation. The plug looked great, a light chocolate brown. It idles perfectly until it is about to boil over. Thats how I know I need to shut down the engine. I think the lean condition causing the idle to climb is due to the intense heat in the motor. The radiators, water pump and case cannot even be touched with gloves on even after 4-5 second gear runs on the street. I suspect a leaky gasket is letting superheated gas into the water.

Eastcoast John · 09-15-2010, 08:38 PM

Or an air leak in the intake after the carb? In the old days the crank seal would leak air into the mixture.

Exhaust gasses leaking into the cooling system would over pressurize the system and coolant would come spurting out of the vent.

I'm having a hard time visualizing it getting so hot without you saying that water is boiling out the vent. If water isn't boiling, you're not overheating.

Your gas cap vent is blocked or has its one way valve in backwards. You ride it and the fuel level drops causing a vacuum in the tank which starves the carb. Your idle goes up as it leans out and you think it's overheating because that's what the previous owner said. Just a thought.