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Discussion Starter · #1 · (Edited)
I’m assuming these triangular holes in the block are coolant passages. Is that correct?

If so, how does it work? Because despite the fact that the head gasket has those triangular holes also, there are no corresponding holes in the actual head. So it seems the coolant would just hit a wall and circulation wouldn’t be great.

Can someone explain, please?
 

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No. There are just for making the castings.
 

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You see heads slightly corroded there all the time. Doesn’t hurt a thing so don’t let that scare you if you see it at those places.
 

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The general cooling system is arranged like this. The water pump discharges into the top of the block on the intake/exhaust side. The main flow goes through ports into the head located below each of the four exhaust ports. A much smaller flow goes up between the pushrods on each cylinder. This flow is restricted by orifices built into the head gasket. The coolant then goes to the thermostat housing at the end of the head. From the housing, the coolant either goes to the radiator (if the thermostat is open) or the bypass line to the water pump inlet when the thermostat is closed. The thermostat has a bypass valve to prevent bypass flow when it is open.

The only other flow is to the heater. The heater supply is from the back of the head and returns to the bypass area within the thermostat housing.

The only difference with Defender and Disco setup is the Disco setup uses a smaller bypass line and this appears to cause a reduction in heater flow.
 

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"A much smaller flow goes up between the pushrods on each cylinder. This flow is restricted by orifices built into the head gasket "
So there any way to better this flow with very slight modifications to the head gasket?
 

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"A much smaller flow goes up between the pushrods on each cylinder. This flow is restricted by orifices built into the head gasket "
So there any way to better this flow with very slight modifications to the head gasket?
You could. You would not want to go too crazy as it could reduce flow to the exhaust ports. I've thought that it may be useful to open up the orifice on cylinder 4. This gives some more flow to the back corner of the head. It also seems that head gasket failures are most commonly cylinder 4 to the push rods, so perhaps more flow there would help prevent this.
 

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you can increase flow by drilling a new hole in the block on the intake/exhaust side if you are using the later model 300 head or a 2.8 head.

No real need they generally run cool unless you are making 2-3x stock power.

i did this on my engine when rebuilding
 
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