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 ?

Like the man says, those holes are sized like that for a reason. Some older engines that don't cool right, those gaskets have eroded over the years and are allowing too much flow where it shouldn't be going.

Originally Posted by southerner

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

Thanks for the good info. It's a 1982 Jeep CJ7 with this V8 swapped in. I think the problem was due to combination of timingadvance, .030 over, and unreasonably crazy cam.

I run a full aluminum radiator, and dual electric fans.

After I re-do the engine this winter (new cam, etc), I hopefully will have eliminated the cause. There is (after this swap) no good reason why it should still run hot at all. Putting in a Edelbrock higher flow good quality water pump, higher flow tstat, and should have everything in good tune after this.

Thanks again.