Hello I am a new owner of a 1965 Datsun 320 pickup truck. The truck runs and drives well, but after running for maybe 15 minutes coolant comes out of the coolant release hose. I understand that this is the purpose of the hose, but it is a lot of coolant and I imagine that the radiator would be empty after a 20 minute drive. I replaced the old radiator cap with a new aftermarket one and am still getting an overflow, and will be replacing the thermostat tonight after work. As a new owner, and as a new user of this forum, I would like to hear any thoughts about this.

Also, have any 320 owners out there installed an overflow tank so that the overflow hose doesn't just empty out on the ground?

Thanks very much for any direction you can give!

I have never experienced your problem. Have you flushed the radiator and engine block? I suspect your problem will go away with the new thermostat.

Forgot to ask, what does your temp gauge indicate? Hot? Normal?

The temperature gauge indicates normal. I hesitate to put too much trust in the gauge because the other gauges (gas level, mileage) are non functional.

I have decided that it would be good to install an overflow tank regardless. That said, do you have any ideas?
Thank you!

Great, thanks for the advice about the new thermostat Gemmer. I emptied out the coolant, removed the old thermostat, and dropped a new one in last night. There was no gasket around the thermostat or on the housing itself. I am guessing there ought to be one, yes?

There is no gasket for the thermostat itself. There should be a gasket between the engine block and thermostat housing. There are complete parts lists and service manuals for 320’s on this site. Suggest you take look.
You can get an external thermometer and dip it in the water with the radiator cap off. This will verify the temp and whether your temp gauge is working. It will also show at what temp the thermostat opens to allow water to flow through the radiator and engine block. If the engine is operating properly, then there really isn’t any need for an overflow tank.

Right on! Thanks.

The situation you are describing is normal if you have filled the radiator full to the top.
Pre mid 60's old school cooling allowed the coolant to "find its own level" As the coolant heats up it needs room to expand.
if the radiator is already full it will pass out the overflow hose. A level at about the top of the radiator core usually
allows enough room for expansion. As Gemmer stated this should work good. BUT we are dealing with 50+ year old
clogged radiators and sludgy engines and in practice the cooling does not work well as it should. If you drive at higher
speeds and in hot weather you will find the "level" gets lower in the radiator to allow more expansion room. This level may
provide sufficient cooling but it is concerning when you look in the radiator and do not see any coolant!
I added an overflow tank from a roadster of the same era and it works great. I can keep the radiator filled to the top.
There is room on the passenger side near the radiator to place it and it looks like it belongs there.
I may have an extra if you want to add one.
Ted.

Sent you a PM.
Ted

X2 the last post. You can easily add a separate overflow tank but it needs a vent hole high up in it and the level of antifreeze in the tank must be kept above the end of your overflow hose so that any displaced coolant into tank then sucks back into rad as it cools. It's an in and out thing then and normal.

Heated coolant increases in volume, simple physics.