Dust or oil in water coolant reservoir

Hi All,

new member here from Italy . I'm 24 and I own a cb500 (2003 model).

I've noticed the the coolant reservoir is completely black on the inside (no pic attached because it's difficult to portrait it effectively).
Hence, to probe it, I've stucked a gloved finger inside the reservoir. Pulling it out it was covered in a medium grey stick mud. Could be oil, could be dirt, could be an awful mix of both.
Coolant levels and oil level are regular within 12 months inspection window. Engine runs cool (ok, we're in winter now, but even during summer the temp gauge lies in the middle tick of the H/C scale).

Here's what I plan to do:

unmount the water coolant reservoir and clean it completely
unload completely the coolant circuit, wash it with water + isopropil alcohol, and fill it again

maybe it's just dirt? After all, the circuit has nevern been dried out in 21 years.

I cannot believe that the head gasked failed! The engine runs smooth and gives me the best chills every time ;-)

Any tips/suggestions or experiences you want to share with me?

Thanks a lot!

Luca

I suggest cleaning the entire circuit, putting in new fluid and waiting.

If it were recent oil it would float

Luca, don't miss to drain and wash the expansion tank
also, open and check the thermostat housing, how are things inside.

hey man, by coolant reservoir you mean the expansion tank ?
if yes, don't worry. i had the same issue, nothing bad. 
drain everything, disassembly it, wash it and reinstall

Hi Luca and welcome to the forum. We're happy to see you

I'm kind of assuming that the coolant in your bike has been changed at least a few times. Because coolant - and thermostats + filler-neck lids - are consumables.

• Coolant because it deteriorates in 2 years. There goes your internal corrosion protection...
  
• Fillerneck-lids because the rubber seal eventually cracks and/or the overpressure valve mechanism gets old.
  
• Thermostats because they wear out and get stuck or fail to open all up.
  

When working on the cooling circuit, I've been told this:
Emptying the coolant circuit and letting it sit empty allows the air now in the system to cause corrosion.
Flushing with water is said to trigger a corrosion process.

So, maybe flush with coolant?