I'm completely stumped and so is my local garage. I have a 1999 Ford Ranger XLT 3.0L Flex fuel with only 77k. We can't seem to get the radiator to stop overflowing the reservoir tank. The coolant will go into the overflow tank and not be siphoned back into the radiator. This usually only happens when it is really cold out, below 20 degrees. This also causes a no heat in the cabin of the truck until, what I can only assume is enough pressure or heat from the engine to open up the t-stat and let whatever coolant is left in the radiator circulate into the heater core and then i get heat, really hot heat. I had the thermostat replaced and the radiator because it was rusty inside from sitting for a couple of years with only a few hundred miles being put on it a month (this was my dads truck, and after he passed away it didn't get driven but a few times a week by a neighbor to keep it running)

Once the truck cools down, I can siphone the coolant out of the reservoir about 2/3 of a gallon and open up the radiator cap, and dump it back into the radiator to fill it back up.

The shop has flushed the coolant system 4 times to get the coolant to not look like lake water. They thought that the pressure in the radiator was a little high and that could be caused by a head issue, they have run every diagnostic test to see if the head gasket or head is bad, and it passed everyone. When the weather warms up, it runs fine for a week, but eventually it will overflow again. I'm pretty desperate now. With only 77K on the engine, I would love to keep it running as my dad gently drove it and it is in really great shape.

 

May be a stupid question but did you replace the radiator cap? Also I would check the tube that goes from the cap/neck to the reservoir. It may have a kink or some type of restriction. The pressure coming out of the radiator when hot will overcome this but the suction back in when cooling may not be able to.

 

I've replace the radiator cap 3 times thinking I might have had a faulty one. I think that when the radiator was replaced, that they overflow hose was replaced as well. I'm heading over to the shop now to ask them.

 

The heater hoses have a by pass valve, remove it and check that the valve is not loose, its vacuum operated, just push on the arm and make sure it works and valve is not broken away from the arm(loose)
This valve is ONLY USED in MAX AC setting, its not a heat control, it shuts off flow thru the heater core completely when extra Cooling in the cab is required
But the water pump needs this coolant flow, so coolant must either flow thru the heater core or when valve is closed if flows directly back to water pump



Only other reason heater would go cold, AFTER being hot, is that AIR is getting into the system
Heater core is a high spot on the firewall so any air in the cooling system will end up there and can block coolant flow, so heat goes cold
REVing the engine(water pump) can sometimes clear this "air dam" and heat will return

The only way air can get in is from a cylinder leak, which means a bad head gasket or cracked head
It pumps air in when a cylinder fires, this extra air and pressure will cause coolant to flow out of the rad and into the overflow tank filling it up and even overflow it
And because its "extra pressure" in the system when engine is off and cools down no coolant would be sucked back in to the radiator from the overflow tank

Do Glove test, free and simple test

 

CAN be a piece of something has become a check valve in the overflow hose.
Carefully remove hose (to keep whatever it is inside) and check.
Air expands a lot more than fluids when hot. Steam's about 300 times more volume than water.
HOPE YOU FIND THE PROBLEM. Others want to know.

 

Check the line that runs from the coolant over flow reservoir to the rad, look for very tiny pinholes, cracks, chafing on sharp areas.
Never assume a new thermostat is good, always check with your old one in the kitchen with a pot of water on the stove to make sure it opens.
Start with cold water and watch while the comes to a near boil.

Other things that can happen with the 3 litre is when it sits, lots of rust and silt build up in the bottom of the block which causes poor heat distribution and there is not really any drain plug to flush the block.
Water also flows through the lower intake manifold, it's an area that is also prone to blockage.

Regardless, if it's not sucking the coolant back into the rad, then there is a hole somewhere _ faulty rad cap, bad seal on the rad cap etc. _ or as mentioned above.

 

Issue resolved. Even though the glove test proved negative, the shop tried the dye test and this time it came back positive for a blown head gasket, and boy, was it blown! It was blown in 3 spots. 2 of the pistons looks brand new because of the amount of coolant that was flash steaming them clean. Shop replaced the gasket, and the water pump for good measure because that was starting to rust out as well. The truck is running like a champ now!

Thanks to all of you for suggestions, etc.

 

Good work

Thanks for posting the update

Never had a glove test fail to show a cylinder leak, but have had false positives on the chemical tests, but good that its fixed

 

GLAD TO HEAR IT'S FIXED!!! (i have the 3.0)
Hint: Next time someone has loss of coolant and can't find where it goes SMELL your exhaust for the aroma of antifreeze.

 

You have a cracked head. I had the same exact problem !!