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So my expansion tank started leaking, which helped tear open the return oil cooler line, I wanted to ask whether or not I have to bleed out the lines after i replace it, and where should i clamp the lines down so that i won't drain out the whole system. Or alternatively, would it be better to just drain out all the coolant and then recycle it back in after.
 

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I'd probably just replace the coolant (and did when I had to replace the lines once). I don't believe it will really last a lifetime. Either way you will need to bleed the system where the hose goes into the heater core. You pull that line half way off until you see a little hole in the fitting. Run the engine until the coolant squirts out of the hole then push the line back on.
 

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Correct, a common misconception is that the spinning coolant pump helps bleed air out of the cooling system, but it actually pulls air in. You'll see that when idling, with the purge hole in the heater hose streaming out coolant, that if you rev the engine, the flow will stop until the RPMs return to idle. That's because of the low pressure caused by the pump.
 

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Meh, I never had an issue doing it that way on my B5 AEB (I just let it idle though too). I will not insist my method is the smartest way to do it after reading TomVW's thread though.
 
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