About six months ago my temp gauge would only go a little way into the temp range. I replaced the thermostat. No change. Not over heating. Last week noticed I was about a half gallon low on coolant and it was coffee colored. Flushed the radiator. After idling for twenty minutes the water in radiator was cold, out of the block hot. Lower hose cold, upper hot. Pump isn't leaking, oil is at normal level and not white or foamy. Waiting for the metal clip to come in so I can change the sensor for temp gauge. Doesn't make sense. Fan comes on so the sensor going to computer should be working correctly. Not over heating so shouldn't be head gasket. Any advice would be appreciated.

 

You have a stock electric cooling fan on a 2002 Ranger 4.0l SOHC?


I thought only the 2.3l Rangers got those, the I4 engine?

Engine heats up coolant and thermostat opens, the hot coolant flows out the upper hose to the rad, then down thru rad and flows back into engine, 15-20deg cooler, in the Lower rad hose.

So hot upper hose and cold lower hose would mean blockage in rad, 20deg cooler lower hose would be normal.

Or water pump could be on it's last legs, blackish coolant could mean electrolysis has eaten away the impeller blades on water pump, so circulation is very slow, thru the engine and thru the rad.

Older coolant will cause electrolysis, metal parts are eaten away, water pump blades are especially vulnerable.

 

the electric fan uses a separate sensor

the temp gauge uses it own sensor screwed into a coolant passage in the block

the older green prestone type of coolant was laden with calcium and clogged up coolant sensor ports badly

locate this sensor and replace it , do not try to clean it / you will damage it even more

 

looking at the diagram at the Ford dealership, the temp gauge sensor is located on the thermostat housing on the left side of the two.

 

that was one of my thoughts. But why isn't the engine over heating and throwing up a code?

 

the temp gauge sensor is 1 wire sensor on the older rangers

the sensor needed a metal body for grounding , the sensor operates on the negative power side not the positive .
the coolant pressure pushes on a valve inside the sender , thus the gauge reads what temperature the coolant is at.

 

your engine could be an anamoly , though

2002 shows 2 different senders for the temp gauge

 

i picked up my 2001 sport trac two weeks ago, and have the same temp gauge, hot upper cold lower hose issue. i flushed my coffee colored coolant last week and picked up a gauge censor. i suspect the water pump but wont be surprised if it were a clogged radiator.

 

you would be surprised what sludge resides at the bottom of a radiator

i would personally go out and buy a brand new radiator rather than trying to flush out an old 1

 

not trying to shoot down anybody's theory about the cause, I just don't want to start replacing the radiator, pump and everything else until I'm sure. these are pics of the sensor and thermo housing. the wire looks pretty short, but I'm going to try and unplug it, plug in the new sensor and put it in a cup of hot water. gauge moves, right sensor. I just don't get it. If coolant isn't circulating why isn't it over heating and throwing a code?

 

sensor and housing

 

if the gauge does not move , then i would start tracing a possible short in the connector

sometimes flushing out a weathered radiator and re-installing it only to have it leak down the road is not worth it
i made that mistake once in my past , lesson learned , if the radiator cooling fins are breaking off , replace the radiator

 

i have not given the radiator a proper inspection yet, $120 shipped does not sound too bad for a new radi. but the time needed to swap in the new one does. i just took a look in the reservoir and my fresh coolant is all muddy again. ill be visiting a friends shop today as i need an inspection and will try re-flushing the system again with a hose and the thermostat out, concentrating on the radi. hope it cleans it out without uncovering any leaks. either way ill post up my finds/results afterwards.

 

the gauge barely moves into the low range. hell it might be something as simple as the new thermostat is bad.

 

Found this on a related topic suggestion, not sure if my 2001 is the same way but i was thinking about the heater core, since it doesnt blow hot, just warm i am leaning towards a clogged radi & core.

I also have a slight engine stumble/missfire at idle, not sure if its related.

 

Could be the heater core is getting plugged up, that would effect engine temp but only when heat was on.
The later model Rangers often used a 4 hose by-pass valve, 2 hoses to heater core and 2 to engine.
These can break and heater won't heat up hot just warm.

Google: back flush heater core

Lots of how-tos on that, all vehicles use the same heat for vehicles, hot engine coolant circulation thru a small radiator in the passenger compartment