Hello, I just purchased a 2005 3.0 ranger. I noticed the radiator cap was leaking after driving it home, coolant reservoir was empty. After it cooled off I opened the radiator and it was maybe 2 inches low, but the truck was not over heating.

the next day I put a radiator fill funnel on it, filled the radiator and funnel, then started the truck and turned on the heater. I watched the funnel the whole time the truck was warming up and no air bubbles came out of it except when I filled it originally before starting it, so now I’m very confused. Isn’t air supposed to come out since the radiator had air in it? Or could it if just not been low enough for air to go into the engine?

After topping it off and the new cap I added about an inch of 50/50 into to reservoir and I don’t think the level has moved at all hot or cold. Still dosent over heat.

any advice is appreciated, just concerned as why no air came out, I was totally expecting air

 

You probably caught it time, I'm going to guess the coolant level never got low enough to get air into the cooling system, If heater is putting out hot air you should be OK.

 

Welcome to the forum

You have an Overflow cooling system vs a Degas cooling system

Overflow system uses suction to work
Cold engine full radiator
Rad cap rated at 14psi
As the engine warms up the coolant EXPANDS in volume like any liquid will and this creates the pressure in the cooling system
IF......the pressure in cooling system exceeds 14psi then the large valve in rad cap is pushed open and hot coolant will flow thru the overflow hose and into the BOTTOM of the overflow tank
Bottom of the tank is important, because if there was any air in the engine cooling system it would end up at the top of radiator and it would be pushed out FIRST and over to the overflow tank where it would just bubble to the top and be gone, overflow tank is vented

Overflow tank is only used when coolant expands enough to exceed rad cap rating, so may not be used at all in normal driving when outside temps are not that hot
But lets say it is used, and hot coolant was sent over to the overflow tank
After you shut off the engine the coolant in the engine starts to cool down and SHRINK in volume, eventually it will reach 0psi pressure, and then -1psi because coolant is missing, its in the overflow tank
There is a small valve in the center of rad cap, and it will be pulled/sucked open by the -1psi pressure which will pull coolant from the BOTTOM of overflow tank back into the radiator

So the system is self purging of air and self refilling of coolant if everything is working as it should

If you open rad cap on cold engine it should be FILLED TO THE TOP, no air at all
If it not then there are a few things to check

Obviously if the overflow tank was dry then it sucked in AIR, lol, so fill overflow tank to COLD line and top up rad

Overflow hose can crack/leak, its way easier to suck in air than coolant so thats what happens, as engine cools down air gets sucked in instead of coolant

Leak in engine side of cooling system, again air is way easier to move that coolant so the leak allows coolant to go out, but also allows air to be sucked back in as engine cools

Blocked overflow tank, because coolant is sucked back in from the bottom of the tank, any debris in the tank can clog it up, so make sure tank is clean