There a little air bubbles in my over flow. The heat is usually a hit or miss. Usually blows cold air. Burped numerous times. New thermostat. Not overheating. But the hoses get hard as a rock. No milky oil cap or white smoke. Should I flush the system or is it the gasket?

 

Welcome to the forum

We assume Ford Ranger but what year and what engine?


Glove test is quick and free, and will tell you instantly if you have a head gasket leak or cracked head.
Cold engine
Remove radiator cap
Remove overflow hose from rad cap opening and plug that opening with vacuum cap or gum or putty or ??
Place latex glove over rad cap opening, seal with rubber band, or you can use a balloon instead, or even a condom will work.
Unplug Coil or coil pack, you want a No Start for the test

Once glove is in place crank engine and watch the glove
If you have a cylinder leak glove will bounce up and down each time that cylinder is on compression stroke.

If there is no leak then glove will just lay there, no bouncing

If glove does bounce and you want more info, remove 1 spark plug at a time and crank engine.
When glove stops bouncing then last spark plug removed was from leaking cylinder, put it back in to confirm.

 

The glove didn't move. Could it be a blocked radiator? If I unscrew the drain plug nothing comes out. Ive replaced the cap already also. I had a lil heat this afternoon.

 

What year Ranger?
What engine?

Common for sediment to clog the drain plug on any radiator, depending on the year you unscrew the drain plug then pull on it, it will slide out a bit then stop, pinch the two prongs you now see together and pull it the rest of the way out.
Now put a running garden hose against the hole to push sediment up and then remove hose and sediment should start draining out with the coolant.
You can also use a bendable wire to poke in and move sediment out of the way to get it to start draining

Flush radiator out

As coolant heats up it expands in volume, that is what creates the pressure in the cooling system, at 15psi or so Rad caps Larger Valve should be pushed up and hot coolant will start to flow to overflow tank.
Radiator hoses will have 15psi pressure in them at this time so should be hard.
If hoses get hard before coolant gets hot then you do have a cylinder leak, might have to redo that glove test.

After you shut off a warmed up engine the coolant starts to cool down and Shrinks in volume, so pressure starts to drop, and it will drop to below 0psi, at -1psi the Smaller Valve in the radiator cap will open and Suck coolant from overflow tank back into the radiator.
So radiator should be FULL to the top when cold, check that

If hoses feel too hard then get a new radiator cap

If you have a small leak in the cooling system then that will leak a little coolant of course, but what also happens is AIR is sucked into the system as it cools down, the air is easier to suck in than the coolant in the overflow tank.
So even if you purge the system, the next time it heats up and cools down air will come back in.

 

I've replaced the cap already. I hoses don't garden up till way after the temp gauge is half way. There's water in my upper hose after I shut it off. And the small hose from cap to overflow. The radiator is full after I shut it off and I open it. Sometimes if I rev it up it'll get warmer. But as I drive it'll get luke warm. But runs fine and doesn't over heat. When I squeeze the upper hose the air sound comes from the thermostat a rear and overflow.

 

2000 4.0 6cyl. 2 wheel drive automatic.

 

I would put tape on the overflow tank to mark the level COLD, or use the line if visible.
Then keep track of it for a few days to make sure it is staying the same when COLD.

HOT mark can't be used for level tests because it is dependent on coolant temp, but COLD is COLD, lol.

2000 Ranger will use a Bypass valve for heater hose connections, 4 hose connector with vacuum valve controlling flow to heater core.

Since you said heat can be "iffy" I would back flush and forward flush the heater core
After engine warms up a bit turn Heat control to HOT
Feel the two heater core hoses, the warmer one is the IN and the other one is OUT, mark them
After engine cools down, remove the two hoses from the By-pass
Point the IN hose down at the ground
Turn on garden hose and hold it against the OUT hose, this is Back-Flushing, reversing the flow thru the core to push out any larger debris that may be clogging passages.
Once flow is good, reverse the flow, flush the core.

What I do on my vehicles is to reverse the heater hoses every 2 years when I change the coolant, this reverses the flow and hopefully makes core last longer, I also back-flush at that time as well.
Heater cores themselves have no IN or OUT, only the water pump and hoses have IN and OUT

Heater system is a high spot so you won't lose much coolant doing this.

Does engine temp slowly climb when stopped?
That could be a sign that the fan clutch is failing
Before starting cold engine, pop the hood and spin the fan blade, shouldn't spin, should be hard to turn.
Start engine and let it run for 30sec-1 minute, shut it off
Now try to spin fan blades again, should be easy to spin, clutch is unlocked

After driving it for the day, or after engine temp(and rad) is warmed up, shut off engine and try to spin the fan blades, should be same as when cold, hard to turn.

The fan clutch has a bi-metal spring on the front that is heated up by radiator heat, this spring engages the lock that makes fan spin closer to engine RPMs when max air flow thru rad is needed

When stopped or driving slowly there is little airflow thru radiator, that's the only time fan is really needed, your comment about temp gauge dropping when driving made me think of fan clutch issue

 

Wrong thread i just posted in.