Why do head gaskets have much smaller coolant passages that the head and block?

[rjrobin2002]

Why do head gaskets have much smaller coolant passages that the head and block? Is it to keep water pressure up?

I thought they had sent me the wrong one, but found the original and it was same way.

 

[rjrobin2002]

The only two that match the shape are the rear 2 coolant passages.

 

[Broncobowsher]

Since the heads fit either side there are large ports at both ends. But flow is from the rear of the head to the front.

The water out of the heads has a matching port in the rear that is blocked or barely used.

 

[rjrobin2002]

Ok, that makes sense. So all the other holes are drains.

 

[Broncobowsher]

No. Spot cooling. Not drains

 

[Glass Pony]

Verify that the front of the gasket goes to the front. Like broncobowsher said about cooling some of those holes are stepped up/down in size for a reason.

 

[rjrobin2002]

I did, the gasket says front for the front.

 

[Steve83]

Why do head gaskets have much smaller coolant passages that the head and block?

So that most of the coolant will flow through the whole block, then through the whole head. If they were all the same (large) size, then the coolant (like anything else) would take the path of least resistance, and flow mostly from the water pump, up the front coolant journals, through the big head gasket holes, and back out to the radiator - withOUT cooling the majority of the block & heads.

The way it's done, a little coolant takes the short path (so that it doesn't get too hot), but most goes all the way to the back of the block before moving into the heads.

Is it to keep water pressure up?

No, the coolant is pressurized to make its boiling point higher - so it doesn't boil off the hottest metal, which is in the heads. So the pressure coming out of the pump going into the block doesn't need to be as high as in the heads. If the gaskets restricted it so much that the pressure dropped going into the heads, the coolant would be more-likely to boil where the engine is hottest. The total area of all those holes in the gaskets is enough to allow all the water pump's flow to pass through easily to the heads. The pressure drop occurs at the thermostat, which is a flow restriction.