My brother has a 98 300EX. It is blowing oil out of the breather tube that connects to the back of the head. It only does it when its hot and if the oil is to the full line. What could be the problem and what has to be done to fix it? Thanks.

 

I don't know much about 4 strokes but it sounds like there is too much pressure in the crankcase?
ERIC

 

Check and see if the oil filter has been put in backwards. I did this and had some oil problems.

 

02 baja,

Make sure when you check the oil you don't screw the dipstick in. Always check hondas without screwing in the stick.

 

So if the crankcase is overfull, oil be blown out this hose? Anybody else experience this?

 

I had the same problem.

I had this problem for about a year and a half, and finally had to have the topend rebuilt. It turned out that the piston and rings were just worn. I have a 98, and a 96 300ex and they both ran great. Lots of power, but the 98 would just blow oil out the crankcase breather tube when I would have it wide open in just about any gear. It only did it when it was wide open. It also had a lot of smoke blowing out that tube when it was warmed up as well and smelled like it was burning oil.

Turns out the reason it only did it while wide open was because the rings could hold the oil back with normal to moderate rpm's, but when the throttle was wide open, and the rpm's were really high, the rings could not hold the pressure back and the oil would blow by the rings.

Now that the topend is rebuilt, there is no more oil or smoke coming out of the tube.

I asked about this on all the forums, and called local mechanics about it and got all the usual answers. Too much oil, bad rings, bad piston, it is supposed to do that.......

But now I know it was the piston and rings. You may not need to totally rebuild the topend. I just had to because mine was really worn bad because a lot of dirt got in there on the last ride I went on before I took it to the shop. You could just replace the piston, rings, and hone the cylinder wall if everything else is in good shape.

HTH.