Hey everyone,

Our quad is really starting to get annoying! My boyfriend has rebuilt the top end twice now. It still pukes antifreeze out of the overflow after twenty minutes or so of riding. The fan is on all the time as it is on a toggle switch. Each time we have put new gaskets on. What could be the problem? It's a brand new cylinder, head, piston and gasket set...

 

Sounds like it is overheating. First thing I would check is that the radiator is clean/unobstructed. Once mud builds up and clogs the fins they overheat easily.

 

If he didn't bleed the 10mm bolt on the top rear of the head(close to the temperature sensor) trapped air can cause it to overheat. Just open the bleed bolt enough until you see only coolant no air bubbles. If you let this go on very long damage can happen to the head,new cylinder and piston!! Common thing for most people to over look when installing a new top end on the 350 and 400 engine. If you've had to replace head gaskets after this has happened because they have blown, it's possible the head or cylinder may have already warped. You may need to have this checked out. Plus once you have it back together don't forget to purge the air from the coolant by way of the bleed bolt.. OPT

 

When we put it back together we did bleed it from the top (I helped). So if the radiator is over pressurizing then it would be from? I say this because of the puking antifreeze from the overflow cap. Is there an easy way to clean out and flush the radiator and hoses? To know that if there is an obstruction you are getting it?

 

The outside radiator looks clean, but how do we know if when we flush it out if it's dirty inside? Is there anything besides water we should use?

 

Have you pressurized the cooling system or just replaced the 13 psi radiator cap? If the radiator is clean front and rear,the head has been bled, but still spewing out into the overflow bottle,could be just a faulty radiator cap. Most auto stores have em for about 6 bucks.You can flush the system by simply having a garden hose in the radiator with the radiator drain open,engine running until just water come out,but best after flushing drain all the water out,fill with coolant and bleed the head again. OPT

 

My over heated due to a air lock in the system once, and I had to burp the system. You know if its a air lock if the top rad hose is hot and stiff after warm up but the bottom rad hose is still cool and soft.

Both hoses should be hot and stiff at the same time after warm up.

I burp it by slowly adding coolant in to the rad hole while the motor was idling and shaking the ATV by the handle bar. It did a big burp out the rad cap hole and started flowing normal once more.

 

my scrambler did that too; turned out to be the fan was on it's last legs and was not turning fast enough. I had separated the motor to find it all corroded inside. I replaced the fan and it has worked gr8t since.