Jump to content
Sign in to follow this  

Radiator Help

Recommended Posts

Ok, so i have just done a full top and bottom rebuild on my 1990 kx 250, all seemed to be going well, then i started it up the other day and realized when cold my radiator overflow was pouring out coolant when on the throttle, im unsure as to why as:

Does it when cold, head gasket is new and i have pulled it off , doesnt seem to be leaking on ispection, the cylinder was freshly boared and honed and from inspection seems to have no cracks, my thought being that the cooling system may be presurising from a leak in the cylinder, there is slight rusing insdide the cylinder, the radiators arnt blocked but i did notice they smelt a little of exhaust, the only thing i can see is there is a slight lip between where the two cases are bolted back together where the base gasket for the cylinder mates to both surfaces could this be the cause? i dunno im pretty stuck guys lol

Share this post


Link to post
Share on other sites

You may have had an air pocket in the cooling passages. I had a trials bike that had air in and I ended up blowing a coolant hose. It builds up pressure and the cooling fluid doesn't circulate. I always tip my bikes side to side to try and get the air out when filling. I also leave the cap off so I can see the fluid circulating and add some when all of the air has made it out.

Maybe after 21 years the cap can't hold any pressure?

Share this post


Link to post
Share on other sites

Yeah i guess air in the system could be the cause, I reccon the cap is working alright , and that wouldnt be a problem when its cold would it? ohh and i tryied blowing through the system the cap seems to be sealing, the slight bit of rust in the bore worries me greatly too that would indicate water yeah?

Share this post


Link to post
Share on other sites
Yeah i guess air in the system could be the cause, I reccon the cap is working alright , and that wouldnt be a problem when its cold would it? ohh and i tryied blowing through the system the cap seems to be sealing, the slight bit of rust in the bore worries me greatly too that would indicate water yeah?
either headgasket not sealing or cracked some where in the top end. It could be in the porting some where and not in the cylinder. I am assuming it is sleeved if is it showing rust. I would not run it until you figure it out or you will trash it and be out alot to redo it all again.

Share this post


Link to post
Share on other sites

Yeah i think your right, yep it has been re- sleeved , i think it's on its last bore now , i have another cylinder there i might get that on it and see what it does. Frustrating after spending all that cash getting the bore honed !

Share this post


Link to post
Share on other sites

Thanks for all your help guys, I stuffed around pulling the cylinder off thouroughly checking everything, dissasembled and reassembled my powervalves in the end it was as simple as resurfacing the head with emery paper on a thick peice of glass, changed the head gasket(even tho it had a new one on it) and put a coating of copper sealant on it, problem seems to be fixed! I was nearly out of hope lol! Oh and im pretty sure that the head repair shop stuffed up the timing of the powervalves to, not 100% sure but they seem to be in a different position after following the workshop manual, and it revs out heaps better!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×