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Bought a cheap 2004 Ford Fiesta from a relative which has a cracked expansion tank that drips when the engibe gets hot.

I suspect it's been like that for quite awhile and so he would have kept topping it up with neat water/without anti freeze.

Would this mean that the antifreeze level in tge coolant system would now have been weakened/diluted, or would it not be affected as the coolant never gos lower than the pipe and doesnt circulate in the system?

So basically when i change the tank or repair it with epoxy, can i just top up the tank with 50/50 anti freeze, or will i have to change the coolant in the whole system?

Have to buy a hydrometer etc?

  • Get the mixture strength tested at your local garage or just drain it and fill it starting from scratch. – Solar Mike Oct 14 '19 at 16:51
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If you're right about him topping off the radiator with just water than you'll have a diluted solution. You should bite the bullet and invest in new antifreeze.

Also, try to replace the tank. Stop by a junk yard or search the internet. Trying to fix it won't be worth the effort. Good luck

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    I tried a couple ways to repair one , and it is not "worth the effort". – blacksmith37 Oct 15 '19 at 2:42
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The coolant in the engine expands and contracts with its temperature. When it expands, the liquid goes into the expansion tank and mixes with what's already there. When it contracts, some goes back into the engine, and that is more dilute. It then circulates around the engine, mixing it there too.

Even if the volume change is less than the volume of the connecting pipe, there is still movement of liquid in and out of both ends of the pipe, and it will mix.

So yes, it gets mixed, and you should drain and refill the coolant system. But I would wait to see if a repair has worked.

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