Today i changed coolant fluid according to Haynes maintenence schedule.
I drained the fluid opening the drain plug and sprayed all of my garage floor with fluid since i didn´t realise ther would be som much pressure.
To my surprice after completely draining all of the fluid, there was still fluid in the coolant tank.
There was not a word in the haynes manual regarding this.
I thought a lot about how to drain the tank and I found the solution which I would like to share with you all.

First i disconnected the hose from the upper filler (where you fill the coolant) and then I moved the hose outside the fairing.
Then I extended the hose to lead down to a bucket.
Then I used air pressure to get the fluid out of the tank.
Look at the pictures to understand what I mean.

I still have one question.
What is the tank used for?
I understand that if the coolant is boiling it has to go somewhere, but the fluid in the tank is not recycled.
When it is full, the fluid goes on the street.
So what is the upper and lower level for on the tank?



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I thought it would be same as a car, flush the system with pressured water

 

I had my Haynes manual open to the radiator section about three feet from the drain plug. Sprayed all over it.

The overflow tank prevents air from getting in the radiator, lets you check level without taking off the radiator cap, and lets fluid out as the water expands and lets it back in when cool.

 

The recommended flushing method is in the Hayne's manual that I have..... You have to look in the radiator flushing section, not the coolant change section.

It recommends that you drain all the fluid out, then fill it back up with water and run the engine for about 10 minutes (until it's warmed up and actually circulating the radiator fluid because it's warm enough to open the valve). Then, drain again, fill up again and repeat. Then after that drain down, you fill up with your 50-50 mix, run it and top up if necessary (please don't open your radiator cap while the engine is HOT!!!!).

I was going to do this myself, but when I looked in the cap I saw that the radiator fluid looked all nice and clear and still bright green versus the more yellow appearance when it has aged a bit.... I may still do it depending if I see the temp getting high this summer....

 

Flush it, Flush it good.

 

OK
I will repeat.
When draining the fluid with the bolt on the bottom left side, the fluid in the tank is not drained.
I you want to flush, fine.
It still doesnt solve the problem.
You will still only flush everything except the tank where the same crappy old coolant mix still is floating around.

Whats the purpouse of the tank, anyone?

Edit
Didn´t see slowpoke´s answer.
So you mean that when the fluid is hot it runs down the pipe to the tank and when it´s cold it takes the same way back?

 

Leave the cap in place when you open the drain near the water pump. It keeps the overflow bottle in the loop and will draw the fluid from the tank, same as how it works in regular service.

Also, inspect the cap gasket before to reinstall. After some time they take a set or deteriorate in the vicinity of the raised lip in the filler neck. If the cap's not sealing properly it can allow overheating due to not maintaining higher than atmosphere pressure. Often people don't realize how important the cap is to preventing boil over. In the higher yet normal operating range, the engines can exceed water's boiling point and the only thing that prevents boil over is the increased pressure.

Replacement caps from Honda are expensive but are also available at the autoparts store if you match it up. I don't recall a specific model number but do recall it's the same as MANY Mitsubishi models in the '90's and maybe later. A whole bunch of them use the same cap for a lot of years. The pressure rating is 13PSI, same as the original. Take yours along to match up.

 

The purpose of the tank is to allow for expansion and contraction in the cooling system without allowing air to enter the system. The presence of air dramatically increases corrosion, especially right at the level where the wetted parts meet the air. Partially filled water vessels that can corrode do so at a MUCH more rapid rate than vessels that are TOTALLY filled. Water works or industrial piping guys are aware of this. Example: City water systems hold up fine with iron pipe and lines that are totally filled and are trouble if allowed to operate partially filled.

The cap is a combination two way check valve, one way includes the pressure relief function. The center assembly can lift complete allowing the coolant to be drawn from the tank, and then seats in the opposite direction requiring the exhausting water to flow through the pressure relief valve. It's the siphon function side of the valve that's often not understood or missed in its entirety. Look one over closely and you'll see it.

 

Excellent
Many thanks!