Radiator Bottle Leak Even after Buying New

[pwuser149351654643]

Aoa friends
So i have an alto vxr
Its radiator coolant level used to decrease and that used to transfer in reservoir bottle.
Asked the mechanic, changed 2 caps.
But @Xulfiqar bhai taught me coolant going in reservoir tank is normal.
So my bottle was not airtight, changed the bottle. With a genuine one. Still it not air tight, n when the car is hot, Coolant expands, Coolant leaks from the bottle cap sides.
So i want to ask what can be done to make sure its airtight?
Can i use another Japanese cars bottle( which don't leak) with a little alterations in my bottle holder?
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[Xulfiqar]

Are you filling it to the very top?

Its only filled to max or H or F line, not more than that. The hot expanded coolant/water is stored here and will be sucked back to radiator once engine cools down.

Make sure the hose from the radiator to the tank is good and even the hose going to the bottom of the tank is good and airtight. It works like a straw in a bottle,

[pwuser149351654643]

Its only filled to the maximum line. I don't top it up full. I totally understood your concept in your previous replies. I will now buy 2 steel clamps and clamp the hose pipes. Lets see.

[pwuser149351654643]

Plus

Alto Radiator Bottle has a single pipe going in. The overflow valve opening works only one way. Air doesn't go in. Coolant can just come out.

It leaks from the sides, marked as red.

[Xulfiqar]

I think you are mistaken that this bottle is airtight, its not

The cap isnt airtight either. Its just an open reservoir for expanded coolant, you will see the level rise on a hot/warm engine, and thats normal too as long as its sucked back into the radiator on cooldown.

[pwuser149351654643]

Chalen thank you.
You have solved my big tension.
Now after opening cap after complete cooldown of engine, the coolant has completely returned back to radiator.
May Allah bless you.