Willys F134 Coolant By Pass Hose

[dgoodenow]

Guys: I recently purchased a Willys F134 engine that came from a 1964 CJ5. This one I'm told was running well but I notice it does not have the head to water pump bypass hose. Instead there are plugs in each of the holes. Does this engine need the bypass, or is it ok to run it the way it is? Thanks.

[bmorgil]

Its not a bypass like you are thinking dg. It is just a water supply for the heater. If a heater was not required, it came with the ports plugged.

[dgoodenow]

Great. Thanks.

[dgoodenow]

Thinking more about this, it seems that the short hose between the water pump and the head would allow water circulation through the head and the heater and back to the water pump, before the thermostat opens?

[bmorgil]

You are correct dg, good catch! The F134 has a bypass. You need it to help keep air out of the system and to allow a small amount of water to flow around the intake valves when the thermostat is closed. I was thinking the L134. There should be a plug or a valve in the rear of the head for a heater hose and a plug in the pump. Those were used for the heater on both the L and F.

[dgoodenow]

Now I'm really confused. If the heater outlet in the head is caped off, there can be no circulation from the water pump through the head until the thermostat opens, so why would the bypass hose be needed? I got the plug out of the water pump, but the plug in the head will not come out. It must have been in there for many years and I am afraid to do damage to the head if I try anything more aggressive. If this engine has run for years without the bypass, and I have no intention to add a heater, I'm thinking this configuration is fine, but I would the thought of the group? Thanks for all your help.

[bmorgil]

The F134 added the coolant passages around the intake valve seats when they moved the valves into the head. The L head does not have valves in it or water passages, and consequently there isn't a by-pass. The by-pass hose is there to provide water to the intake valve seats when the thermostat is closed. This prevents the seats from burning up early. Air in the head can also create hot spots that can form cracks. On the F Head the by-pass hose should be installed if there is no heater or the heater valve is closed. Will it work without it? Sort of, as long as the heater is installed and the valve is open. Is it correct not to use it on the F Head? No. Is it better with the hose? On the F Head and all engines with a by-pass it is required.

Here is a note from a Willys bulletin on the subject:

On models CJ-3B and CJ5 there is an external water bypass tube in the cooling system. This tube runs from water pump to cylinder head and provides a means for a small amount of the coolant to bypass the thermostat for rapid initial warm up. It also eliminates the formation of hot spots and steam pockets in the cylinder head.

[dgoodenow]

I got it. The flow from the bypass hose is from the water pump through the head and down into the block back to the water pump. Thanks.