My 1996 aerostar is getting hot when it idles. I changed the thermostat and the clutch fan and put in antifreeze. If I go fast it does not get hot only when I am idling, also now there is a root beer colored foam present when I look in the radiator. Would a radiator flush solve the problem?

 

If you have root beer colored liquid in the cooling system, it's got some serious rust problems. I would get the Prestone flush kit that installs onto the heater hose to try to reverse-flush the cooling system. The intent here is to get rid of solid rust that might be plugging cooling tubes. Then I would try to clean it with one of the many cooling system cleaners available from your local auto parts store. This is to clean off rust that might have formed on the parts inside.

Another likely problem is the water pump impeller has rusted away, so it doesn't do much at idle, and pumps enough at higher engine speeds to cool the engine more. If the reverse-flush cleaning doesn't help, I would check the pump. This of course would require removing it.

 

Also pressure test the cooling system. Most auto parts stores loan out for free a radiator pressure tester with deposit- Autozone

What engine? 4.0L they develop cracks in the heads, leak combustion gases into the coolant, makes a corrosive rusty mess.

If no compression leaks in pressure test, then clean.

use Use Prestone AS101 Super Radiator Cleaner

Best to remove the radiator and flush out both directions using a radiator brush on the cap opening side to knock off the chemical deposits that build up on the ends of the tubes inside.

Also use a hose to blow out the block thru the thermostat opening. don't forget to blow out the heater core/s hoses and the cores themselves, use low pressure here, less than 30 psi.

Think new thermostat and water pump after all is clean

 

Offering some other ideas if the previous ones don't pan out. Are you sure that the root beer isn't from oil?

I had some issues with my '97 running hot (but not overheating) due to internal cooling tube blockage in the radiator. It turns out the previous owner had put in some kind of leak stopper. It might have stopped the leak, but it also plugged up the radiator. Also check for leaves, etc. blocking the airflow to the radiator.

Regarding the radiator flush, I had one done by a mechanic using the typical chemicals and machine to try to get rid of all the leak stopper. He warned me ahead of time that the water pump might fail (leak) afterwards. Sure enough, it did. It wasn't even that old.

 

May just need a new radiator....There may be other problems as someone may have put too much stop leak in there and clogged things up.