Thread: Head gasket limits coolant flow? Check out the pictures

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Those big holes in the block are that big to get the casting sand out after the casting process. Those small holes in the gasket are all you need. It slows the water down so that it actually has time to pick up the heat from the cast iron surfaces of the block and heads and evenly distribute water flow. What is sometimes done on race blocks is that 3/4 inch threaded pipe plugs are added to the 3 big water passages that go down the side of each bank then they are decked flat with the head surface and then drilled out front 3/16" middle 1/4" rear 5/16". As you notice the holes get larger as they go to the rear of the block and get furthur away from the water pump. This helps even out the flow and prevents local hot spots in the block and heads. Say if you opened up the gaskets to the size of the block holes 3/4" the water flow will take the path of least resistance so the front of the block and heads will be cooler but the rear of the engine will boil.

I would check for other reasons thermostat, air flow, fan speed, type of fan.
What type of vehicle is it in ?