I have a 2000 magnum 500 that keeps overheating. It spews coolant out of the reservior cap. The radiator is not clogged, the water pump is working, the fan is working, the thermal switch that triggers the fan is working and the thermostat is not sticking so what in the #$% is wrong with this thing?!?! Any ideas are welcomed. Thanks

 

Does it do it right away after starting it (like within 2 min) ?
Is the radiator clean (outside) ? blow it out with air, then wash it with a garden hose.
How do you know the waterpump and thermostat are working; if I might ask?

 

DID YOU TAKE THE TIME TO REALLY CLEAN ALL THE DUST AND DIRT COATING THAT COVERS THE RADIATOR?

Assuming that all the cooling components are good as you stated, I would do a compression check first.
Check your plug for any abnormal color. If that checks out I would then check timing.

Does it run the same as before it overheats as it did before the problem?
Did you make sure you purged all the air out of the system when you refilled it?

Try these first and then post back, there are a lot of knowledgeable people here.

 

Had a real freaky one like yours, the lower hose had gotten snagged by a branch, pulling it through it's eyelet & kinking the hose, the hose wouldn't relax back to it's original position, the result was no coolant flow. This probably didn't happen to yours, as it seems that u checked all of that. Make sure the rad cap seals also, the filler necks are **** to warping. Every pound on a rad cap raises the boiling point by 10 degrees.[img]i/expressions/face-icon-small-wink.gif[/img]

 

Well, let me tell you exactly what is happening. When it started overheating I took the thermostat out and hose off and cranked it up. There was no water coming out of the motor. So, I thought the water pump wasnt working so I took the top hose off the water pump and cranked it up. It threw water everywhere. So, I thought there might be something stopped up in the engine. I ran water thru it both ways with the water hose and water ran freely. Put it all back together and it still blows water out of the reservior.

 

from a cold start, how long does it take before it pukes out?

 

Probably around 5-10 minutes.

 

could be a bad cap also. Be sure to check the filler neck and seal on the cap for any gunk.

 

Does anyone know if the pump fins are plastic??????? On my YZ the fins are plastic mated to a steel shaft. The fins spun on the shaft and the engine overheated. {triedntrue} It may be worth your time to pull the cover off and visually check the waterpump just to make sure.

 

Thrash, I had thought about the impeller and what it is made of but I figured it was ok since it was moving water.? Do you know what the expected life of the water pump might be? My speedo went out on mine so I don't know exactly how many miles/hours is on it but it still has the original tires with 1/4 tread so I would guess it about 1800 or so.

Zbart1, I cleaned the radiator best I could. You can see through it and the fins aren't bent. I haven't check compression(I assume you are thinking about a blown head gasket) but I runs fine and there is no water in the oil and no steam out the tailpipe.

AtvnRocks, How do you know if the rad cap is sealing or not?