Ok so when I drive my Ranger, the temp gauge kinda moves around a lot. Sometimes it goes a little over the "N" in "NORMAL" on the gauge, then comes down below the "N". Then it stays there for a while while I'm drivint etc, and then sometimes it moves a little towards the mid range of the gauge. But never over middle. It is very random, no sense at all.
But then when I turn the engine off for about 5 - 10 minutes, and then restart it, the gauge is a little over half way. But then when I start driving, it quickly goes down to around the "N" again. What's going on? I replaced the coolant, thermostat, and radiator cap and still it's doing this. HELP. Maybe the temp sending unit by the thermostat?

Thanks.

 

Hows the heater working?

You most likely have a partially blocked heater core

On a few years the Ranger heater core is the water pump by-pass, no valves on the heater hoses, coolant always flows thru the heater core as part of the cooling system operation.
If heater core gets older and doesn't have good flow temp will go up and down randomly.
Same thing will happen if by-pass valve is faulty on newer models

Good news is the new core is $15-$20, and takes about 20min to swap out the first time, if you ever do it again, 10minutes, lol.

Remove the two hose clamps on the heater hoses and remove the hoses from the core
Inside the cab, passenger side, there are 4 screws(5/16ths I think), pointed up, holding the bottom of the heater box, remove these 4 screws and the cover/bottom

Put a towel down under the heater box
Reach in and pull heater core back, away from firewall and lower it down and out
It will have coolant in it so try to keep it tipped back, but that's what the towel is for.

There is weather stripping around the face of the core, it is most likely is rotten, so you can't transfer it, you can put on new weather strip, up to you

You can also just get a coupler, and remove the two heater hoses from the core and connect them together, use the hose clamps that are already there

 

Hm I see. It heats but takes a while maybe. I'll change it then probably if its not hard. Thanks.

Any more ideas please? Thanks.

 

Wheres the coolant bleeder screw in this engine?

 

Lower passenger side of radiator usually but not all have them.
Lower radiator hose is removed if you want to drain the system to replace all the coolant

Unless you want to drain the whole system just remove one heater hose and let some coolant drain out.
Heater hoses are high on the cooling system so you won't lose much coolant installing the new core.
If you have a hose that "kinda" fits heater core port then put it on and blow into the hose, this will push out most the coolant left in the core, so when you remove it, it is less likely to drip coolant in the cab

After core is installed, try to fill it with water or coolant before installing the hoses, then install just one hose on the core and refill radiator until coolant is coming out of open core port and its hose, then put hose on.
This will get most of the air out of the system.
(when refilling the whole cooling system you should also do the above, remove either heater hose from core and refill the system, this allows an exit for the air in the engine while refilling)

Leave rad cap off and start engine.
Top up rad with engine running if needed then put cap on and let engine warm up

 

Well the radiator had cracked so had it replaced today. Running cooler, but still moving, from below the "N" to right to the "N". Weird. And when I turn the engine off for a few and restart it, the gauge still goes to a little under half. Hm.

 

Maybe there is some confusion about the Temp Gauge.

The positions of the N O R M A L letters are different on different years, so don't use them

There is 1/4, 1/2, 3/4

Just below 1/2 to just above 1/2 is where warmed up engine should be.

1/2 is 210degF on Ford Temp Gauge

Warmed up engine should be 185-195degF

Going up a hill it should go up to 210-220degF that's normal

In the summer running at 1/2 can be normal depending on outside temp

1/4 after 10 minutes is bad, means something is wrong with thermostat

If gauge creeps up to 3/4 then it is starting to overheat, time to pull over, there is air in the system, lost coolant or clogged system.

An engine needs to run with coolant at 200degF, best MPG and cleanest oil only happens when coolant in engine is at or above 190degF, the faster an engine can get up to that temp, the longer it will last.
Running under 190degF causes carbon build up and oil can't burn off the water and blow-by contamination
That's from the guys at S.A.E., Society of Automotive Engineers, not my opinion

 

It did this with the old thermostat, and then I replaced the thermostat on Sunday with a 195 degree one and it's still doing it. Might be a bad sensor I'm thinking.
Like I said, had the radiator replaced today, they flushed the whole engine professionally with the power flusher they have....
Hm.

 

Temp SENDER is cheap to replace

Temp Sensor is used by the computer only, has 2 wires, SENDER has 1 wire in a 1993

If you turn off a warm engine then wait a moment then turn key back on the Temp Gauge should be higher, the engine metal is heat soaked and coolant is not circulating so you will see the heat being pulled away from the metal as higher temp until coolant starts to circulate again, or engine metal cools down

 

So in this pic, which is which? The sender goes to the gauge right? And what does the sensor do? Thanks.

 

Temp sensor is for computer
Temp sender is for dash gauge

All engines need to be "Choked" at Cold start or they will stall out
A choke plate on a carb reduced air flow and increased vacuum at the Jets to suck in more fuel, cold engine needs Rich mix, it also increased idle RPMs via idle screw cam, and increased vacuum also increased spark timing, via vacuum advance on distributor.
Choke plate was operated by a spring that pulled plate closed when cold, then as spring was heated up, via exhaust gas or electric heater, it pushed choke plate open bit by bit until spring was heated up fully.


Fuel injection can't use a Choke Plate, no Jets to suck extra fuel from
The ECT(engine coolant temp) sensor is there to set the Choke on a cold fuel injected engine
It also can't use an idle screw because computer would have no control of idle, to set it higher when cold.
So there is an IAC(idle air control) valve so computer can set idle

When you turn on the key the computer starts up and looks at ECT voltage(temp)
After starting, if coolant is cold, it will set a Rich mix and set high idle, Choke Mode

Because this is a very important part of a cold engine starting and running it has is own sensor, no sharing with dash gauge wiring because that would just add another layer of problems if dash wire or gauge had a problem.

In the early 2000's some Fords just had the ECT sensor, for the computer, no sender for dash board gauge, what Ford did was to add software to the computer and a wire to the Temp Gauge, so the computer controlled the Temp Gauge from then on.

 

Cool thanks for all the good info.
So in that pic I posted, which one is which?

Thanks sir.

 

2 wires is a sensor
1 wire is a Sender

 

All above thread makes sense. But I have a slightly different issue with overheating:

my 2002 B3000 runs at 1/2 heat gauge 'most' of the time but then randomly will go to 3/4 or more (pointing at the H) for no discernible reason. Last time it happened, I was running about 60 mph for 20 minutes or so and when I slowed down, and shut off the AC, it cooled back to 1/2. Seems to me maybe the radiator is not doing what it is supposed to?

Engine top end was recently rebuilt, new heads and valve job, but I don't see where that would cause this. I'm getting ready for a 'cross country' trip to New Mexico across West Texas and expect ambient temps to be close to 100; I don't need my truck over heating then.

 

Try by-passing heater hose valve.
So out of intake then directly back to water pump, no valve, and no flow to heater core.

If either of these hoses are partially blocked temp will go up and down randomly, yours doesn't sound random, but this is a free test

Does your AC condenser(in front of rad) have an electric fan on it?

So do some don't, if it does see if it is working

 

Did you check to see if the electric fan comes on with the A/C?

Have you inspected the fan clutch?

You can also try to back flush the fins of the radiator and condensor to clear them of bugs, dirt and debris.

All of this is assuming the rest of your cooling system is up to par, meaning it holds pressure, no leaks, a good pressure cap, a properly functioning thermostat and has the proper mixture coolant- distilled water in it with no air trapped in the cooling system from previous repairs.

 

Hmmmm, some of the suggestions I've done, others I will look into. But I don't think I have an 'AC cooler fan'. Also, unless I'm mistaken, won't a bad fan clutch stick 'on' rather than free wheel if it goes bad? Seems I read that on one of the forums (DPO included a new clutch with truck but I didn't think it needed it....could I be wrong?)

When I first got the truck, it would run WAY hot if pushed fairly hard but we discovered that the cat was plugged up and the truck could not 'exhale!' Cleared that problem and it seemed to be OK.

The rest of the cooling system does seem to be fine.

Thanks for the suggestions, will work on them as time permits.

 

No on the clutch fan, it is actually more common for it to fail to engage fully, which is why people say to rollup a newspaper and see if you can use it to stop fan while warmed up engine is running, if you can then clutch has failed.

But in any case fan does nothing above about 35MPH, vehicles speed is pushing more air thru than fan can suck thru, so fan is redundant as speed increases.
At 60 MPH even AC fan might be un-needed, which is why you don't have one.

Thermostat not opening fully can cause high speed heat up, failing radiator cap can as well(longshot)

 

I do not know what engine you have, if you have a 2.3 Duratec DOHC you should have a AC cooling fan.

Both if equipped should operate properly to prevent overheating and longevity of your engine.

I try to keep things simple, meaning I like to make sure the basics work rather than blow off a important part that may go untested ( even if it may or may not be causing your symptom )

If you combine a engine that has air trapped in it with a engine that does not have a properly working fan clutch and or electric cooling fan ( if equipped )

You will experience overheating and a unreliable temperature gauge, if this is the case you do not know exactly when the engine is overheating.

Because you claimed the temperature went down from 3/4 to 1/2 once you shut down the air conditioning.

This makes me think that not enough air is going across the condenser or radiator fins.

This may be clogged fins or inoperative fan or fans or some obstruction of air flow in front of the condenser..

Even missing rubber gaskets that attach to the condenser that help keep the air flow going through the fins of the radiator can contribute to the problem.

As far as I can tell by researching available parts from rock auto, only the 2.3
shows a electric radiator cooling fan.

If you were provided with a new fan clutch by the previous owner, I would install it.