Serious Overheating PROBLEM! HELP!

[Fast350ex]

My hybrid yz426 has a serious overheating problem. It uses a 250r radiator, and I have an ESR in-line temp guage. Everytime I ride it overheats to about 250 degrees F, after about 3 hard laps it boils over, but I have an overflow bottle and it squirts out the breather hole. I have tried engine ice, and liquid performance coolants with no effect. I have also tried adding too2cool additive to several differents types of weights and brands of oils which didn't work worth a $hit. My only option left is to try an oversized radiator, but i would hate to spend the dough and still have the problem.

Please, any help would be greatly appreciated.

[Rulz]

Switch to evans, just make sure you drain all your coolant first.
http://www.evanscooling.com/main27.htm

[racerx573]

Make sure you water pump impeller is working properly. A larger radiator would help too if you have the money, or pick up a used dirt bike radiator and run some Y hose to connect a dual rad set up.

[Fast350ex]

The water impeller is working properly. It doesn't leak coolant, it just boils over. Can I get the Evans coolant locally, or do I have to order it?

[Rulz]

If you have some type of performance or speed shop, they usually have it. The drag racers use this stuff alot. I used it in both my CRF hybrids with no issues whatsoever

[Fast350ex]

Could it be a headgasket?

[TampaBoy813]

I had 2 hybrid...yz & cr's and both over heated with good water pumps and oversized radiators...

[ss440ex]

I had one hybrid...a YZ426
Looked after and maintained three others,
YZ450
YZ444 13:1
YZ426
All with the stock water pumps and using a OEM 250r radiator.
In 100deg plus Texas heat.

Never seen an over heating issue!:)

[ktmquad]

Most guys run the 250r rad. I used the 450r rad. It holds about 30% more fluid than the 250r rad. It is a cheaper way to get an oversize rad w/o the extreme cost. All I did to mount it was to lower the bottom mounts. You can usually find a used 450r rad for under $100. I bought my rad new for $65. I bought it before the quad was even out. Pretty weird that they had parts out for the quad before they had the quad. I also use Water Wetter from Redline Performance w/ distilled water. Hope this helps!!

[CrackerboyLV]

Mine (426 bored to 444) overheats every race. It's fine for MX but will overheat after about 30 min of hard riding (distilled water with water wetter, Oversize PWR Radiator). Our races are usually about an hour long so I end up having to replace the head gasket after every race.

I see that Boysen makes an oversize water pump, has anyone tried this? How about an oil cooler from a 05 450r? Battery powered fan? I'm open to suggestions...

[KPatterson]

racerx573, can you tell me more about adding a bike radiator? have you ever done it before? Thanks-Kyle

[907Rider]

Check your Thermostat, if it doesn’t open properly or at all you will over heat like crazy. Also try using less water and more coolant.

[Drewltr450]

you blew your head gasket check it im 99% sure.

[hontrx265r]

I'm with everyone who said head gasket, I'll almost 99.9% on that, I had the same problem. It heats up really fast because the combustion chamber is blowing hot air into the coolant and adding pressure to your system (hense the quick blow by past the tank) To the other guy who blows his head gasket every race I would guess you either need to quit using cometic head gaskets, buy an oem yamaha one and shave it for your 444 or your head/ cylinder is warped and they need to be put on a lapping table and smoothed out. Good luck guys

[Fast350ex]

I have an o-ringed cylinder with a copper head gasket. I guess I'll have to try evans coolant.