Greetings y’all. I’m stumped w this truck.
My coolant is bubbling and puking out the reservoir.
-Replaced reservoir thinking it had a leak or bad cap.
-Replaced thermostat 2 months ago.
-Replaced radiator w thermostat (had small leak)
-Not overheating at all, but gets a little warm after it pukes out enough coolant at highway speed.
-Good compression on all cylinders. Less than 3 lb variation, cold and warm.
-No coolant in oil. No oil in coolant.
-No appreciableloss of power.
-Owned truck for 6 years and it’s never overheated on my watch.

I’m stumped y’all.
Bubbling stops appx 1 min after shutdown, and it’s nowhere close to hot.
Anyone else had this happen?

2001 2.3 154k 5spd

 

Ranger 2.3l Duratec engine uses a Degas cooling system, doesn't have an overflow tank like other Rangers
The white reservoir is a Degas Bottle or tank, just FYI, it has the 15psi radiator cap, well Degas Cap in this case

This type of system was used in the "good ol' days", lol, when radiators were not filled to the top, there would be a line stamped on the outside of Rad as the FULL line, which leaves an air gap in the top of radiator to allow for coolant expansion, again just FYI
Degas bottle has a Full line cold, and the air gap remaining inside for coolant expansion

If Degas bottle is bubbling air and pushing air and/or coolant out passed the 15psi cap then you do most likely have a cylinder leak into cooling system, i.e. head gasket or cracked head issue
And should have some white tail pipe smoke

What happens with a cylinder leak
Each cylinder has 160+psi when cranking engine over, and 1,000+psi when firing
IF a cylinder is leaking into cooling system it pumps in "air"(exhaust) because Cap is only rated for 15psi
That's the "bubbles" you see, not from boiling, just "air" injected from a leaking cylinder, it will eventually become boiled coolant because when the "air" in the head displaces enough coolant for the head to get too hot in that location, any coolant that gets in will flash to vapor, even more bubbles and can be violent discharges from Degas bottles overflow hose
An engine is a compressor, so if its leaking then the compressed air will over power the cooling system

Try Glove test
Disable spark
Remove degas cap
Put a latex glove over opening and seal it in place with rubber band or ziptie
(can use a balloon or even a condom instead of glove)
Block overflow hose port
Cooling System is now sealed

Crank engine over(no start), watch glove, should just lay there
If it start to bounce/inflate you have a leaking cylinder
At this point you could remove 1 spark plug at a time and crank engine again, when glove stops bouncing last spark plug removed was from leaking cylinder

If glove doesn't move, reconnect spark
Start engine
See if it inflates, if so you have a leaking cylinder

There really is no other explanation for air bubbles in degas bottle, after a refill and start up there can be some bubbles from air trapped in heads and heater hoses, but it would have no Pressure to expel air or coolant, and bubbles would stop after warm up when all the air had been moved to the high point, i.e. Degas bottle
A water pump is not really a "pump", per say, it just circulates coolant, doesn't cause pressure changes

 

Hey Ron.
ok. So did a few things. Have an old test kit to test for exhaust gas in the coolant bubbles. Changes from blue to yellow if it detects exhaust gas. Test was negative. Stayed blue for 8 full minutes. So then I grabbed the lower radiator hose. Cold as the dead. Upper hose is hot as can be, and the lower is cold cold.
so I changed the thermostat w a Motorcraft thermostat. After a run test - same result. Still bubbling and lower hose is still cold.
Radiator was changed 8 months ago because of a tiny leak, but never got hot.
So the lower hose is still cold while the upper is very hot.
The small line in the coolant reservoir is flowing, so i THINK the water pump is circulating.
Other than a physical blockage in the radiator or hose - what could be causing the lower hose to not have flow ??

 

Which thermostat did you replace yours with? One from 2001-2003, or one from 2004+
The thermostat that should be equipped on your truck should have an electrical connection.

FWIW it takes FOREVER for the 2.3 to get warm enough to cycle coolant. It doesn't really make enough heat to quickly come to temp, or get hot enough to require a lot of coolant flow through the radiator when at idle.

Also, are you sure the water pump is functioning correctly? It's worth it to check to make sure the impellers are still there, though your coolant would likely be brown if it was together long enough for those to rust away

 

Look at your water pump pulley, it should match the belt side, i.e. belt has a smooth and ribbed side, pulley will have either smooth or ribbed pulley, they must match or water pump is spinning the wrong way
While its not likely route a belt backwards its also free to look at it, lol

Yes, as Turismolover22 either thermostat is not opening or water pump is not working, if lower rad hose is not heating up after 8 to 10min of driving or idling
Check heater, it should start getting warm within 3 or 4 min if there is circulation from water pump

 

Coolant is a beautiful clear green. Fairly new since radiator was changed 8 months ago.
Changed thermostat w another Motorcraft- still cold lower hose. Boiled thermostat and it opened. Bypass hose on thermostat housing is warm/hot and flowing.
So thermostat isn’t opening.
Would an electrical fault in the wiring harness cause the thermostat not to open ?
Thermostat is set at 208dF. 2001 spec I believe.

 

2001 thru 2003 2.3l did have electric thermostats, powered by fuse 41 in engine bay, but there would be several codes if that fuse blew, it also powers Heated O2 sensors
PCM is also the Ground for the heated thermostat, so it would set a specific core if there was no 12v passing thru the heater's coil, seen on that ground wire with Key on

But could be a wiring issue if either the ground or 12v wire can't carry enough amps to heat up the thermostat
The PCM "monitor" is based on resistance through the heaters coil, so if a corroded or partially broken wire has enough resistance the thermostat doesn't open and PCM still sees the 12v flowing

People do switch to 2004 to 2011 2.3l non-heated thermostats, and add a Resistor between the two wires to "trick" PCM into thinking heated thermostat is still connected, but that is done to save money, lol, not because heated thermostat isn't working

If you have the old thermostat, gut it, remove center valve section, so there is flow, leave the outer ring to mimic wide open t-stat as close as possible
See if that solves the overheating, may actually run too cool, but at least you will know that's the issue

 

Ok. Well I have 12v on the wire, but don’t think I can measure Amps. Had a few frays, so I replaced a section and verified 12 v again to the plug. Cleaned the connection, and still No Joy. Same issue. It’s definitely not opening.
1. what amps should be going to the harness?
2. will it try to warm the thermostat when cold ?
3. what ohm resistor do people put in if they bypass the old one?

 

Yes, when key is on the thermostat heater should be on
Lower rad hose thermostats need to open 15 to 20deg colder than upper hose thermostats
So if Ford is wants upper engine to be at 190degF then lower hose thermostat should be 170degF

Instead of making 170degF thermostats they added a heater to pre-heat it so it would open at a lower temp

In 2004 and up they had the lower temp thermostats, so didn't need the heater anymore, I think they used 180degF which is OK


Thread here has info on resistor to use: Duratec cooling mods -- Need to clear CEL - Ford Ranger Forum

Some people just ziptie heated thermostat up out of the way after putting in the 2004-2011 model, and you can do that and install the resistor later so you can drive it for now