Overheating problem on MCX Nytro

[slymax]

So we have 2 of these sleds, almost identical builds. They are both running different tunnels with rear coolers and radiators removed. One of them keeps getting an intermittent overheat. The head gasket has been replaced once and was installed dry. Last weekend it was good for about 75km and then on the second day it started acting up, this weekend it only lasted about 10k before the light started coming on. Seems like it is getting air in the system but can't find a leak and cooling system holds pressure. This motor did have a problem with a hyraulic lock from a problem with a meth kit but the head gasket didn't actually show any sign of leakage the first time it was replaced. The meth kit is removed and now just has LC pistons with stock head gasket. I'm starting to suspect a crack opening at high temp. Anyone ran into this?

 

[thamax]

you might have an air lock somewhere. what is the difference between the 2 sleds cooling systems?

 

[Skydog]

Is the head flat?

 

[slymax]

Head is flat and both sleds have the same cooling setup. It's just weird that the overheating sled seems to keep getting an air lock. The tunnels are a pita to bleed but just seems to be one that keeps giving trouble.

 

[Hornet Handler]

How do you bleed it? Hang it by the bumper?

 

[slymax]

I hoisted it by the front bumper today and purged lot's of air from the system. Hopefully that will take care of it. I also have an new high capacity fill neck coming for a little extra insurance.

 

[Climbmax]

Flop the sled side to side with the filler on the top side the final time.
RS

 

[IRONMAN IRMEN]

The small hose on the pto side rite behind the primary, disconect it and get two of the caps that come on a 1ltr bottle of gear oil. For filling in a small hole, they fit on the top on a regular water bottle. Put them on and connect to the hose with one and the fitting with the other (need a small hose to connect to the fitting) then just squeese the bottles with the filler cap off. It will push the coolent through the system and take all the air out of the motor. Then start the engine let it idle till the thermy opens and just keep adding through the filler cap till you have heat all around the tunnel. Works awsome 5 mins and the job is done. Also keep the caps and a the small hose in your tool kit for when your buddy pushes the limit on boost (24lbs) and spits past the head gasket. Works awsome up the mountain also!!! haha

 

[slymax]

I was wondering about the boost being too high??? I did see a solid 20 on this sled on the trail last trip out but didn't think it would get by the gasket(also have hardened studs) Will lengthen the wastegate rod and hopefully not have problems. We did get a pile of air out(again) Weird that it runs good for quite a while and then acts up, maybe it is going by the gasket under high load. The first time I had grief it was only running 12lbs but stock compression.