Last week's puzzler! The answer is a long one. So here you go.

The one from my neighbor who listens to our show, about bleeding cooling systems. Actually, he's the only one of my neighbors who still talks to me. The rest of them don't! 

Anyway, he wanted to know, why do most newer cars need their cooling systems bled while older cars do not.

It has to do with with placement of parts. Modern car manufacturers tend to try to make the cars sleeker and in doing, they tried to make the hood more aerodynamic. So in that effort to do this, they have to lower the engine and the radiator. At that point, the ground gets in the way, because the engine scrapes the ground! Kidding...

Because they have lowered things so much, the place where you put the coolant into the radiator is actually lower than the heater. It creates a probem because the bubbles of air that are going to get trapped in the system go to the highest point. Air rises, which means bubbles go up.

And that's what happens in your car if your heater core is above the rest of the engine and the rest of the cooling system and therefore it must be bled or purged of air. And if it's not purged in some cases, the coolant won't circulate correctly, causing the thing to overheat. And in other cases, the heater won't work.

So that's the answer. Bubbles go up!