Coolant Temp Sensor Issues - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 11-18-2014
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Icon4 Coolant Temp Sensor Issues

Hi,

I'm hoping someone else has had this issue:

My '00 Ranger, 3 lt flexfuel, has 172K miles on it. The water pump finally gave up and I had to replace it. After getting the entire front of the engine "decluttered" the old pump came off without a hitch. The new one went right back on. After reassembling the thing it turned out the the nipple on the elbow, that also is the mounting postion of the temperature sensor, was also leaking. Again the whole thing comes apart. I was lucky in that the local Ford dealer had the elbow in stock (for only $26) but not the sensor, which broke upon removal. I went to NAPA and got the sensor and a new lower hose, which has the bypass the goes up to the elbow. I got it all back together, again, and all is well except the gauge on the dash reads colder as the engine warms. Any suggestions?
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Old 11-19-2014
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If what you are referring to has 1 wire connected it is a sender, not sensor.

Fuel injected engines have 2 coolant temp readers.

The ECT(engine coolant temp) sensor has 2 wires and is connected only to the computer, the computer uses this sensor to run engine rich with a high idle when cold, as sensor warms up idle slowly drops and fuel mix gets leaner.

Coolant temp sender has 1 wire, it is only connected to the dash board temp gauge.

These look similar but are not the same, so are not interchangeable.

Because these are both Engine Coolant Temp(ECT) readers it can be confusing for the DIYer AND the auto parts guy who is looking it up, lol.
Easiest thing is to look at what they bring to counter, if it has 1 wire connection it is the Sender for gauge, if 2 wire connections then it is the Sensor for the computer.

I don't have a 3.0l so don't know which one is on the elbow

Last edited by RonD; 11-19-2014 at 12:20 AM.
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Old 11-19-2014
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Here's a picture from a 3.0 to help. The lower left has the single wire, and is the coolant sender for the cluster gauge. The one to the right has the two wires, and is the coolant sensor for the PCM:
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Coolant Temp Sensor Issues-coolant-sensor.jpg  
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Old 11-19-2014
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Ok, thanks for that, but your reply doesn't really help me figure out WHY it worked before I replaced the water pump and doesn't work with a new sensor now.
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Old 11-19-2014
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"Because these are both Engine Coolant Temp(ECT) readers it can be confusing for the DIYer AND the auto parts guy who is looking it up, lol."

You have the wrong sender
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Old 11-19-2014
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Another possibility if you did install the correct sender: did you use teflon tape on the threads? If so, you only want this tape on the upper part of the threads, as the sender itself needs to make a good ground. It is the function of the sender to provide a variable ground for the cluster gauge to work.

Do this: remove the wire that connects to this sender you replaced. Turn the key to "on", don't start the engine. Ground this wire. Did the gauge needle move? If so, the wiring and gauge are good, and the sender is bad, or its threads are not making a good contact to metal.

Thanks to RonD for providing this test to me awhile back. He's the Ranger man. I swear if he ever runs for any political office, I will move there, and vote for him.

Last edited by bucko; 11-19-2014 at 03:25 PM.
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  #7  
Old 11-20-2014
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Thanks, now that I can use. Soon it warms up a bit, I'll try that.
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Old 02-14-2015
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Hmm? Question.. My ranger temp rises as I accelerate . Then I let off throttle, it slowly falls back in middle , normal range.. Do I replace Pump? Fan clutch? Or thermost. Fluid is great, no visual leaks, all that said, I crank truck open rad cap, rev engine I do notice fluid circulating , I'm stumped on this one.. Please help. Thanks
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Old 02-14-2015
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I take it the oil pressure gauge doesn't also go up with RPMs?

Reason I ask that both are electrical and would do that if Alternator was going out.
i.e. battery voltage at idle(12.5v) then 14v above idle.

Normal failure of fan clutch is when engine temp rises at idle then goes back down when driving, so opposite of what you see.

An Engine, of course, generates much more heat under load, so accelerating would cause rise in head temp, the flow of the coolant thru the heads needs to increase at this time which is why an RPM matched water pump is used, it increases flow with RPM increase since it runs at crankshaft RPMs.
So your issue reads like a circulation issue, or more a lack of circulation issue.

So your guess about the water pump would be a good one, its impeller blades can get eaten away by electrolysis reducing the flow volume so at idle there is enough circulation but not enough under load even with higher spin RPMs.

But a 1/2 open thermostat or clogged radiator will act the same, it allows flow but not full flow.
You can test for this by leaving rad cap off and warming up the engine until thermostat opens.
Leave cap off and have someone rev the engine to about 2,000rpms and hold it there, if coolant starts to come out the rad cap opening then I would suspect rad is getting clogged up, water pump will pull in coolant from lower hose at the same rate it is pushing it out of the upper hose so no coolant should come out the rad cap opening.
You can also feel the rad after it is warmed up, shut off engine, loosen fan shroud and move it back, run you hand over the rad fins, there shouldn't be any colder spots, you should feel nice even heat all over, a colder area means a clogged spot.

Put cap back on and rev engine again, squeeze the upper and lower radiator hoses, if lower hose is getting much softer than upper hose then rad could be the issue, coolant is being pulled out by the water pump faster than it can be replaced, this could also point to thermostat not being open all the way, it limits flow to upper rad hose.

If both hoses feel the same then I would suspect water pump, its flow is equally poor on both hoses.


There is also the by-pass system used when engine is not using the rad, during warm up.
I assume the heater works fine, that is part of the by-pass system.
Generally if by-pass system has a clogged valve/hose you would see more random heat up/cool down cycles, but it could match RPM.
But if heater is working normally, hot heat, I would take this off the table.

Last edited by RonD; 02-14-2015 at 11:33 AM.
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  #10  
Old 02-15-2015
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Hey, Mr dean.... Thank you for reply.. A lot of good info, I plan to jump on this as soon as weather here gets a little warmer... Thanks again Sir...
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  #11  
Old 11-28-2016
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Coolant temp gauge not working lukewarm heater

I just had a problem with my tempature gauge not working correctly and my heater was only lukewarm on my 2000 ford ranger 4.0l. The problem was my thermostat not working being open all the time, letting radiator coolant to enter the engine always. The engine never warmed to 195 degrees because of this. Also, I replaced the coolant temp sender (one wire for dash gauge) and the coolant temp sensor (2 wire for PCM). They almost look identical except thehere are 3 tabs on the units and the one in the middle for the sender tab is offset a little so the sensor connector won't fit. That's how you can tell sender from sensor. Sensor tab is straight in the middle. Even though the sender is only 1 wire, the actual sender will still have 2 flat pins in it.
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