Meziere Electric Water Pump-Bypass Hose Modification

Both the 100 and the 300 Series Meziere Electric Water Pumps use the same Meziere WP127 Backing plate which attaches to the timing cover on the front of the AMC V-8 engine in place of the stock water pump.

When using this backing plate there is no nipple connection for the stock bypass hose that normally runs straight up to the thermostat housing/water neck. There are several options when addressing this issue.


Let's first take a look at how a stock AMC-V-8 Engine circulates coolant.
Stock- The bypass hose allows the stock water pump to move coolant with less resistance before the thermostat opens since the coolant can flow through the block/head/water neck and back into the pump. Recirculating coolant helps to warm up the engine more quickly, without running the coolant through the radiator, until the thermostat opens. On a stock engine if the bypass was closed at both the water pump and water neck, the pump would encounter more resistance because it would be pushing coolant against a closed thermostat and would build pressure and put more drag on the belt drive system and could cause cavitation.


There are several options available when running a Meziere.

Option 1- Some folks prefer to block off the bypass hose hole on the thermostat housing/water neck and run a thermostat that comes with holes drilled in it, drill the holes themselves, run a washer style spacer in place of the thermostat or leave the thermostat out altogether. This allows at least some coolant to flow even if the thermostat is not open yet.

Option 2- Jim Lamberson came up with a clever solution by making an adapter that allows the bypass on the thermostat housing/water neck to connect to the upper radiator hose using aluminum tubes welded at an angle. Nice work Jim.

Here is how coolant flows when using a system like Jim's.

On a setup like Jim's, with the upper radiator hose modified for a smaller hose fedding from the bypass on the water neck, a limited volume of coolant could still flow freely through the running electric pump, block, head, water neck, upper radiator hose, through the radiator and back into the pump. Once the thermostat opens a higher volume of coolant will flow.

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When using a Meziere electric water pump, coolant flow can be controlled manually with a switch. So it can be left off until the coolant reaches the temperature at which the thermostat opens and then turned on to flow coolant through the entire system. With a little practice you can launch off the starting line at the same temperature each time which will help to make your ET's more consistent.

It should also be noted that when using a Meziere Electric Water Pump System there is no provision for the heater core. If a heater core is important to you, the connection on the back of the intake manifold is still availabe on the one end. And instead of connecting the other end to the factory style water pump a connection can be made to the radiator hose system.