need help losing coolant

[mxdad7475]

We have two cr85r's.I did a top end about 5 weeks ago.Everything was running fine.About 3 weeks ago coolant started leaking out while my son was riding could'nt tell where it was coming from.After cleaning the bike to see where it is coming from i found it.It comes out of the over flow tube.I have change the cap and put on another head gasket,with no luck.Today i started the top end on the other bike and thought i will switch the radiators to see what happens.After it warms up it blows out of the overflow hose.As long as you don't rev it up it is fine.Also checked the water pump forgot to mention that.Coolant isn't going anywhere else just out of the over flow Any ideas would be helpful Thank

 

[kuchera89]

my friends kx125 does the same thing after he changed the top end. we never fixed it cause its a p.o.s.. have you checked the impeller in the pump?
im no pro but id fill up the pump and hoses then put on the radiater, maybe the pump isn't pumping cause it dosent have anything to start suction with. im an idiot so if it doesnt work, i warned you.

 

[mxdad7475]

Coolant is circulatingis.I took the cap off while it was warming up to see if anything strange was going on.Also took the water pump cover off to make sure it was spinning.There is no coolant in the oil.Thanks for any info

 

[Tdel]

If you are topping it off every time while cold it will loose coolant. As the coolant gets hot it expands and creates pressure. Once the pressure exceeds the spring on the cap it heads for the overflow tube. If you can see the fluid in the radiator after the ride once the bike cools down it should be ok. Did you resleeve the cyclender? If so you are reducing the cooling effects of the water jackets and adding more heat to the system thus your bike will run warmer than before. Try adding some redline water wetter it really does work.

 

[mobrown]

He's right on...

Tdel is correct. 2 strokes (unlike 4-strokes) don't have capture tanks to hold the overflow once the fluid expands thus it just goes out thru the overflow tube. You should lose a little fluid if it is compltely full.

Tdel also makes a good point... if your cylinder is sleeved then the thermodynamic characteristics of your cylinder has changed.

The only other thing to check is for any kind of obstruction in the fluid circuit. Are there any dings in the radiator that would restrict flow? If you have it apart again check the passages in the head and cylnider to make sure nothing fell in during assemby/installation. Never tried Redline Water Wetter but Tdel seems to know what he's talking about :nod:

Good luck... keep us informed.

 

[mxdad7475]

The cylinder is new.put it on in oct.04.We had to replace the cylinder after the piston ring snag the exhust port.We replaced everything in motor,seals,bearings,crank,rod,cylinder,piston etc.Everything has been fine.Went ahead and done another topend 5 or 6 weeks ago.Everything has been fine until a couple of weeks ago.I stop him on the track and noticed the coolant.From all i have seen running it in the shop and in the yard it will blow all coolant out,haven't pushed it that far yet.Do not want to blow it up.I am going to take it back apart and check everything again.Thanks again for all info.........

 

[maddmack]

I ride a 87 cr 500 and last year had the same problem and to make a very long story short alls it was the rad was restricted and I pulled the rads off and flushed them with a garden hose and it worked like a dream.

 

[Tdel]

Based on the newest information, I would first go with a new cap, if the spring or seal is bad the system will blow the coolant out because the cap holds the pressure in. You can also take the cap to most garages and have it checked. If the cap is good and it does not fix the problem, make sure that the radiator is free of obstructions and clean (internally and externally). In your description, it appears that the coolant loss is only from the overflow, therefore I am assuming there are no other leaks in the system. If this is the case, my next guess would be the head gasket; if combustion gasses are getting into the cooling system they will exceed the sealing capabilities of the rad cap and empty your system. Since you stated that it is a newer cylinder and you used new gaskets, I would guess that the head is warped. Make sure the head and cylinder are both square they may require milling. So in closing, you should have every thing fixed by this weekend!

Tdel

 

[mxdad7475]

Well i took it back apart to check everything.This is what i found.Rad and cap where good.There was a little black mark on the head between head and gasket.Milled head and cyclinder, found it had a low spot on the head.Replaced everything and broke it back in.Ran a few laps in yard pretty hard to see what happens no coolant leaking.Seems that was the problem but not to jinx it we will run it at the track tomorrow.Crossing fingers.thank for all info.Lesson learned will check that from now on

 

[oldguy]

Sounds like you had either a slight head warp or a bad head Gasket/o-ring. Either would allow blowby from the compression which in turn would go into the cooling system. Once enough gets in there it would act like a pressure system and force coolant out of the overflow hose.
An easy way to confirm this is to run the bike with the rad cap off and watch the coolant as it circulates. If the blowby is the cause the coolant would appear very bubbly

 

[mxdad7475]

Well the problem seems to be fixed now.He rode the bike yesterdaywith no problems.So i guess it was a problem with the headand was getting blow by.I would like to thank everyone for there info.Thats what i like about this sport you can have a problem and there is always someone willing to help out.Even the guy you are going to race against will help out .Thanks again