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Discussion Starter #1
Heres whats going on.
Motor starts right up and idles good. After a few minutes of driving it slow (5 mph or so) in the driveway the coolant over flows into overflow reservoir and comes out the res cap. While driving it, it run great at very low throttle, but acts as if its missing or running out of gas until I let off throttle then it runs good again.
-Gas tank is full and gas is new.
-Cooling fan working and temp sensor controlling it as it should.
-No wet on the plug nor coming out of exhaust.
-I dont see great flow (but a tad) in radiator while idling and rad cap off.
-I changed the thermostat and no change of symptoms.
-I did see about 1/8" of what looked like oil in the air box but I didnt see any in the intake pipe when I took filter off nor was filter oily on the bottom.

Im looking for what to check next, and then after that, if its not the fix.
-I suspect a pump issue, the impeller stripped out on its shats maybe.
-Gasket blown, but Id think it would show on the plug and out of tail pipe.
-Oil in box is pointing at a carb issue, but Im in a grey area when it comes to carbs and internal engine stuff...
Any help would be appreciated.
 

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Have the radiator cap checked,about any auto parts store can do this
 

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Heres whats going on.
Motor starts right up and idles good. After a few minutes of driving it slow (5 mph or so) in the driveway the coolant over flows into overflow reservoir and comes out the res cap. While driving it, it run great at very low throttle, but acts as if its missing or running out of gas until I let off throttle then it runs good again.
-Gas tank is full and gas is new.
-Cooling fan working and temp sensor controlling it as it should.
-No wet on the plug nor coming out of exhaust.
-I dont see great flow (but a tad) in radiator while idling and rad cap off.
-I changed the thermostat and no change of symptoms.
-I did see about 1/8" of what looked like oil in the air box but I didnt see any in the intake pipe when I took filter off nor was filter oily on the bottom.

Im looking for what to check next, and then after that, if its not the fix.
-I suspect a pump issue, the impeller stripped out on its shats maybe.
-Gasket blown, but Id think it would show on the plug and out of tail pipe.
-Oil in box is pointing at a carb issue, but Im in a grey area when it comes to carbs and internal engine stuff...
Any help would be appreciated.
Depending on what machine, oil in airbox isn't that unusual, especially on the earlier XP Sportsman models.

Before you start taking things apart have the cap checked as already suggested, and clean the mud out of the radiator until you can see light through every slit. Pump impeller could be stripped...but you thought of that.

Stew
 

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Discussion Starter #5
Im sorry. Its a 1999 Sportsman 500. (Pre HO model.)
The radiator is spotless inside and coolant is very clean and full. The fins are mud/debris free outside too. Im not seeing any leakage from rad cap at all. Only overflow from the coolant reservoir cap when it over flows. Its fill level is at the max level line before starting.
Im not feeling its a radiator or cooling fan issue at all.
Its inside the motor section of the coolant loop. My feelings anyways.

I originally felt the running rough could of been a coolant leak inside motor, ie a blow head gasket or the like. But with no signs on the plug or wet/coolant coming out of the exhaust Im not thinking thats it. Even if it were, I wouldnt be getting over heating and coolant reservoir over flowing after 5 minutes.
I still need to check the oil for coolant.

Ive read that running rough can be a result of overheating, but it happens prior to getting to hot or having the temp light come on. It occures only when I increase the throttle. Not idle or even slow speeds.
Im steering towards having 2 issues really, thinking I still have something in the coolant loop not right and a carb issue.
It was suggested the cooling pump impeller wearing out around the impeller shaft over time. So need to open it up to check.
The bike running rough really feels like its being stavered or flooded during increased throttle use. Maybe this issue resulting from the original over heating when I didnt notice the temp light on the first time I experienced this. It got very hot that day.
The quest for knowledge continues... LOL
 

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Discussion Starter #6
Pressure in the cooling system probably means head gasket blown.
Its possible its a smaller leak that does not show on the plug or exhaust so I havent ruled it out completely.
But im not thinking that would cause the overheating Im seeing in such a short time.
The bike runs great at idle and starts great.
I even can rev the motor when parked and not hear bog down, sputtering or lack of motor preformance.
 

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Discussion Starter #7
bump...
 

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Did you check the exhaust gasket or manifold. My son's 700 was overheating because of a leaking exhaust gasket between the manifold and exhaust pipe. Could also be the same thing if manifold is leaking. I did not see where you had the radiator cap checked. I could be the cap is opening up to soon and dumping to much coolant.
 

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Im sorry. Its a 1999 Sportsman 500. (Pre HO model.)
I originally felt the running rough could of been a coolant leak inside motor, ie a blow head gasket or the like. But with no signs on the plug or wet/coolant coming out of the exhaust Im not thinking thats it. Even if it were, I wouldnt be getting over heating and coolant reservoir over flowing after 5 minutes.
I still need to check the oil for coolant.
I have seen headgaskets go one some old euro cars go, the only indication was excess pressure in the cooling system. Some of the compression was leaking but the gasket hadn't yet deteriorated to the point where the cylinder would take in some coolant. If you let it sit and idle, do you see any air bubbles coming out of the coolant? It doesn't take much sometimes.
 

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Discussion Starter #10
Did you check the exhaust gasket or manifold. My son's 700 was overheating because of a leaking exhaust gasket between the manifold and exhaust pipe. Could also be the same thing if manifold is leaking. I did not see where you had the radiator cap checked. I could be the cap is opening up to soon and dumping to much coolant.
No I havent had the cap checked yet. Not seeing any leaking what-so-ever at the cap so its seated good, not sure if it has more function then that. I assume by the questions to have it checked it does. LOL
Is the cap design to have the spring heat sensitive to allow coolant into radiator when hot from overflow resevoir? If so, then when its cool and it opens I can possiblyget back pressure to over fill the overflow?
I would agree with that up to the point the reservoir was full. I would think the pressure would then still flow threw the motor to keep it from over heating and causing rough operation.
But I could be way off on this too. LOL
Thanks for the input. Its another thing to check out.
 

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Discussion Starter #11
Im sorry. Its a 1999 Sportsman 500. (Pre HO model.)
I originally felt the running rough could of been a coolant leak inside motor, ie a blow head gasket or the like. But with no signs on the plug or wet/coolant coming out of the exhaust Im not thinking thats it. Even if it were, I wouldnt be getting over heating and coolant reservoir over flowing after 5 minutes.
I still need to check the oil for coolant.
I have seen headgaskets go one some old euro cars go, the only indication was excess pressure in the cooling system. Some of the compression was leaking but the gasket hadn't yet deteriorated to the point where the cylinder would take in some coolant. If you let it sit and idle, do you see any air bubbles coming out of the coolant? It doesn't take much sometimes.
I dont see any bubbles at all. Though I havent ruled out a gasket issue either. Thanks for the input.
 

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Discussion Starter #12
Well I still am exploring this issue.
One more piece to the puzzle was that I decided to check my oil for coolant. I did not start the bike. I just pulled the dip stick cap off oil reservior to see what was on the dip stick. It looked clean, or as clean as used oil can look.
I then took the drain plug off for a sec a got about 2oz of oil in a small cup.
I didnt see anything until I dumped the oil out of cup and saw what looked like very very small droplets of water. I also saw what looked like extremely small alum dust particals if the sun light hit it just right...

I admit its been a long LONG while since the oil has been changed. Maybe 4 years, but 3 of those the atv was in storage sitting...
I didnt feel I had a big coolant leak in the oil but not sure what those droplets could of been.
Condesation maybe? Coolant?
Yes its well past time it gets changed. LOL
Im gonna wait until my atv mech friend can look at it though.
 

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The radiator cap has a pressure rating lets say 10lbs . This pressure in the cooling system raises the boiling point of the coolant . The spring on the cap gets week and changes the pressure of the cooling system and it will over heat and spit coolant into over flow
 
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