[30 Closed Cab PU]

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Originally Posted by Jim/TX/GA

Partially blocking the radiator with something (cardboard, thin pressboard, etc.) is the way to go. Block about 1/2 of it. If it seems to run too hot, trim it down to only block the bottom 1/3rd. Don't over think it. It will be fine.

When you block the radiator, it allows coolant to circulate well through the block while the engine warms up, to help keep the temperatures in the block more uniform. It will take longer for everything to get fully warmed up, but eventually it will get there.

A closed thermostat in the upper hose really stops coolant from moving in the engine block. Those small vent holes that they have added to the thermostat do not let much coolant flow through the block while it is warming up, so the water is stagnant while heating up. This puts a lot of thermal stress on the block, head, and head gasket.

Then the thermostat opens and a rush of cold water comes into the hot block from the radiator. More thermal stress. The warm water hits the thermostat and it partially closes again. You get these cycles of hot and cold water in the block until the coolant temperature is stable in the block and the radiator (similar to the partially covered radiator).

If you really want to use a thermostat, you need to add a bypass hose between the upper outlet hose, on the engine side of the thermostat, and the water inlet on the side of the engine. I used a 5/8" heater hose. This lets coolant circulate through the block while it warms up with the thermostat closed.

Once the thermostat starts to open, some of the hot water goes into the radiator, but most of it goes back in the inlet side of the engine. The engine warm up is fairly fast and very smooth -- no big temperature swings up and down. Much less thermal stress.

I have a temperature gauge installed in the water outlet and I can watch the coolant temperature go up nice and smoothly.

Hi Jim,
Any chance you can post a picture of your motor showing the above? Am considering converting my A to thermostat next year once my cooling issues are resolved.


Thanks