Antifreeze problem

Did a search and came up dry, so I figured I would start a new tompic. Just picked up a '10 yz250f. Engine was rebuilt 17 hours ago with 81 hours on the clock. They guy we bought it from, said that it had an antifreeze leak. When we looked at it, it has a leak at the bottom of the right rad. Right on the tube. I am getting it tigged to fix it, but, today when I drained the antifreeze it was a brownish color. Really strange as when we looked at it, I drew a little up on a tissue an it was nice and red.


I am thinking that he put the wrong type of anti-freze in prior to us coming to look so it wasn't mixed. We ran it for about 30 minutes or so and mixed it up really well..... The stuff that was leaking on the floor since we got it did look kind of reddish though. So for now I have it in a clear glass bottle, waiting to see if it will seperate out or not. We did immediately drop the oil and it is nice and clean so no coolant in the oil.


So long story short, here is what I am thinking..... Either some oil got into the antifreeze some how (the weep hole is not leaking anything at all) or it is a mix of incompatible coolants. My thinking is if it is oil it will seperate by sitting a day and antifreeze will not.


Plan is to fix the rad, flush the cooling system with water a few times, and then fill her up and let the boy take it for a rip. Then check the drain again. If all is good, then I let the boy race it this weekend. If still problems then my guess is the inner water pump seal is somehow letting oil in and it is not coming out the weep hole....


Anyone have this happen before, or have any other suggestions..... Sorry so long.




Sounds like your on the right track.  My guess would be someone used the wrong coolant or topped it off with the wrong coolant.  If you want, go ahead and let it sit for a day or two and drain.  If you do have oil and coolant mixed, oil is less dense and will float on top.  Should be able to see by just looking in the radiator since the right-side rad will be higher if you have the bike sitting on a regular side stand.  Another tell-tale sign is the milky looking fluid, but that might be kind of difficult to tell if its a small amount of oil in a lot of coolant.

Thanks!! Checked this morning on the way out of the house, and it is seperating, will see when I get home tonight, but it is probably oil in it. Plan is to flush it with water once I get the rad repaired and then fill it with new coolant and run it to see what is happening.


One thing that I am thinking about is that maybe I do have a warped head. It is possible for it to warp in the right spot to let some oil into the coolant is it not? I have never heard of it, but thinking there is a possibility. Only way I will guess that will be if oil continues to get into the antifreeze. I should mention though that I did let it idle with the cap off and there was no bubbling nor pressure building in the tank, so that may be a dead end.....


I guess will have to take it one step at a time.


Any other ideas or has anyone else experienced this?



Edited by greezemonkey

If you had a head gasket leak you would see oil residue in the antifreeze.  While the bike is running remove the radiator cap rev the motor if the antifreeze foams then you have a combustion chamber leak in to the cooling system

So by foaming, will it not bubble as well? Will give it a try. So seems like we are definately on the right track here with this one....

the first time I bent one of my radiators I took to my radiator guy ( I have had him rebuild 3 car radiators)

he told me that the radiator tanks were very thin and he couldn't weld it

he told me to clean the area good and use epoxy

and it worked

I have bent the same radiator again( gnarly single track ) I straightened it again

and epoxied it again and it worked again

pep boys has a good selection of epoxys

I used ' bi-metal epoxy '



So just to finish up as I always hate when the OP never comes back and clears up the issue:


Got the tank tigged. Worked great, no leaks.

The antifreeze I drained from the bike did seperate, but not as expected. It was not oil, instead a greyish brownish sludge that settled into the bottom of the glass bottle I poured it in. Not sure what it is, maybe something from incompatible antifreeze, or contamination, or who knows at this point.

Flushed the cooling system with hot water several times. Ran it a bit wiht just water in it the last time to get as much as possible cleaned out.

Filled it with the right antifreeze and let the boy take it for a good run and stretch it out for 20 minutes or so.

Brought it back and checked: No bubbles, no frothing, everything looked good. Drained it again to see and antifreeze looked good.

Filled it again with fresh.


At this point I think we are going to just let him run it this weekend as it is the last race of the season and just keep an eye on it. will take his old bike as well just in case, but I am feeling pretty good that it was just some contamination or something like that. With the fact that they only hold less than a litre, it wouldn't take much to mess it up.


Thanks for all the help.

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