What is the function of coolant reserve tank in DT300 ?

[Ericson]

Hi !

2011 Kymco Downtown 300i with 29000 km.

Today, I decieded to replace antifreeze. Coolant level in reserve tank was at full mark before I begun.

I removed the radiator cap, removed airbleed screw and unscrew 8mm bolt near water pump To my surprise only about 300 ml of fluid came out. There was no fluid in airbleed hole before drainage.

I flushed the system with destilled water and refilled until  water was coming from air bleed hole. For this refill I used radiator fill cap.  This time I got about 700 ml of fluid from water pump drainage. During this operation coolant level in reserve tank didn't move.

During this all this work I was thinking why reserve coolant tank stays at the same level when the system is clearly missing fluid. I'm also surprised that when reading forum you guys recommend to suck out fluid from reserve tank and fill it with new coolant. This some what diffrent that car antifreeze replacement procedure where draning fluid from radiator causes fluid level to drop in reserve tank.

Kymco manual says that you should refill coolant via reserve tank but from my ponit of view it's some how not connected to rest of the system - what am I missing here ?

I made about 100 km since purchase of this bike from second hand including 80 km highway ride @ 70 mph. Coolant temp was in the middle all the time.

[Iahawk]

a few interesting things, here...one, that you only initially drained 300ml of coolant out on the change, could be the prior owner didn't fill up the coolant all the way, or you have a leak? Filling coolant is not a fast 'dump it in and go' process..if you do that you can trap a lot of air in the system, possibly what your previous owner did?

The other odd thing is the Kymco manual stating to refill the coolant system through the overflow tank. While that is possible in theory, when finished you'd end up with an overflow tank way overfilled. That's not a good thing.

The usual way is to drain the coolant then refill through the filler neck and then fill the overflow tank. The overflow tank's purpose is to provide additional coolant to the system should it be needed (system is underpressurized) and to accept overflow coolant from the system if it's over pressurized. That's why overflow tanks have markings on them for minimum and maximum coolant level. Back in the bad old days the extra coolant would just vent onto the ground...

[Ericson]

The overflow tank's purpose is to provide additional coolant to the system should it be needed (system is underpressurized)

Well - this makes me wonder why overflow / reserve coolant level stays the same when there is no fluid in radiator - during second drain I drained 700 mls of fluid - still reserve tank level stayed the same - near full - which makes me wonder how it is connected to a cooling system.

From my current experience reserve tank in DT300 doesn't refill fluid when clearly there is no fluid in radiator. It makes no sense to check coolant level via reserve tank then when its level doesn't respond to radiator being almost empty... but to be fair Kymco manual says to check fluid level on normal operating temperature so maybe thermostat has to do to something here ? All this work I described was on cold engine.

I guess I will have to take fairing off to see what's going on...

[NorWeWa]

Part of the manual problem seems to be language problem.  Topping up the coolant is through the overfill tank. The procedure for refilling the coolant system is described under the section for removing the radiator. Two hoses come off the overflow tank. The top hose off the tank is a short hose that routes down a ways and is an air vent. There is a hose off the very bottom that connects back to the radiator, and connects to the top of the filler just below the cap.  I found with my recent coolant change the same problem of only getting a partial drain off the water pump plug bolt.  I could not get the system to take a full refill till I took out the under seat tray and opened the air bleed bolt on the thermostat and filled via the radiator till coolant came out the thermostat air bleed hole.  Kymco seems to have made some changes with a couple hoses for different model years for the Downtown. The overflow tank works once the system is full, but if air is in a hose somewhere coolant will not move back and forth from the overflow tank. 

Art