I have a 1973 F100 with a 360. How much should I fill the radiator with coolant? All the way to the top or should I leave a little room?

also, is this a low pressure system where I can idle it without the cap?

 

Welcome to the forum mrsalty, I'm no expert but yes I believe these are all low pressure systems. My 79 400 idles quite nicely with the cap off, the level will rise and fall as the system burps itself. If you're doing the coolant it's not a bad time to do a flush.

 

Thank you.

So how full should my radiator be in general? How full should I make it?

 

Do you have a over flow bottle?

Fill it till you can touch it with your finger tip, so like 3" from the top. Then park it on a slope or a set of car ramps, (nose high) and let it idle with the cap off till the thermostat opens and it starts to cycle and burp out the air.

I would also turn the temp controller to heat, to let it exercise itself.

 

Guess I've been keeping my radiators to full then, I usually fill them to the top of the tank

 

Since these rigs weren't equipped with a coolant recover/overflow system, I recommend filling it 1/2-inch over the coolant tubes. The coolant will expand a bit so leave a lil room.

With an FE you'll need to buy up to three gallons of coolant (12 quarts).

Btw, to completely drain the system on an FE, pull the pipe plug on each side of the engine... below cylinders 3 and 7. You'll be amazed how much coolant is left in the block. If after removing the plugs nothing comes out, poke the hole with the small screwdriver and stand clear for the torrent of scale, rust, and yuck to come flying out... Ewww.

Ensuring a 50/50 mix.....
- Dump in one gallon of straight coolant. (four quarts)
- Refill the now empty jug with water - usually recommended is distilled water and dump that in... that makes eight quarts int the system.
- Now take the still full jug and refill the empty jug half-way... you now have two one-gallon jugs of 50/50 mix.
- Fill the system... don't forget to open the temp valve/lever to "hot" so the heater valve is open.
- If you need more, mix up another 50/50 mix using the unopened jug of coolant.
... don't forget to label the jugs if they have been premixed.

 

If you fill it too full initially, some coolant will burp out the overflow when hot. It will find its own level. As long as the radiator tubes are covered when checked cold and it is not dropping/leaking, all is good.