Hi guys, I have been working on my NC31.

Few months back I replaced head gasket because milky oil was found & losing coolant & overheated. Did the oil & coolant change when I closed everything and it runs fine - no bubbling from radiator nor losing coolant. Changed oil again after one month and it still looks a bit milky. I thought it would be clean after few oil changes.

Everything's fine until recently I start to lose water again - one time I found coolant low in reservoir then top it up to "max" line. I'd ride for 30 mins and there was more coolant in reservoir and makes sense to me. However I let it cold for overnight the level is between max and min which means 50-100cc lost. This happens every ride I need to keep filling reservoir.

Opened rads cap when it's still warm (one hour after ride) and its not full (missing about 50-100ml i think). so I put the cap back and let it overnight - the rads is full again and reservoir is less water so it's sucking coolant.

unlikely HG failure to me - not again!
would it be the water pump leaks internally into oil?
or maybe just externally leak from the hoses that I've not found yet.

thanks for your help in advance.

found a pic online which is very similar to my oil colour


saw there is mechanical seal available for water pump but the manual didn't say anything about it.
Is the pump rebuildable? might give a try to replace the seal.



any clues?

The radiator cap must have a good seal if in doubt at all replace with a new one.
Check the reservoir when the bike is cold ( mine is usually halfway between the max and min mark) after a ride check again it should have risen as the radiator heats up so the water expands and is pushed back into the reservoir.
As it cools the water is drawn back into the radiator but this only works if the radiator cap is efficient and in good working order.

got the cap changed 6 months ago so suspect it works well.
I tighten all the hose clips today and see what's going on.
do i need to change the engine oil or i can still use it for a while?

cheers!

yvescheung wrote:got the cap changed 6 months ago so suspect it works well.
I tighten all the hose clips today and see what's going on.
do i need to change the engine oil or i can still use it for a while?

cheers!

If you suspect the oil has been contaminated change it + filter , if you don't you could suffer expensive damage.
Changing it will give you peace of mind instead of worrying about it.

i ordered a new water pump and gonna change it, will see if it's seal failure
will do oil & coolant change anyway as well
hope it is only the seal not cracked block or head gasket

i changed the entire water pump last weekend as didn't know if i can replace the seals only.
so far the water level is stable now though i have to see one or two more weeks
but strange that old pump seals look fine to me i dont see it leaking
hope this is the end of story

yvescheung wrote:i changed the entire water pump last weekend as didn't know if i can replace the seals only.
so far the water level is stable now though i have to see one or two more weeks
but strange that old pump seals look fine to me i dont see it leaking
hope this is the end of story

Remember when the water heats up it comes under pressure which is when if there is weakness in the system it leaks.
give it a good run and get it up to temperature if its going to leak it will then.
Fingers crossed.