What is the difference, if there is one, between a coolant temperture sender and a coolant temperture sensor?

No differance

They are two separate and distinct sensors.

The CTS coolant temperature sensor send signals to the ECU (computer) telling the engine how hot it is or isn't allowing the computer to send the ignition signals to advance or retard the timing to allow your car to be more efficient. When it goes bad it will and can cause the following conditions:
no start when warm
no start when cold
crappy gas mileage
crappy idleing.

The Coolant Temperature Sender (usually black or brown) lights up the idiot light or the water temp gauge by sending signals to the Coolant temp relay.

Both work on the same principle that resistance to the unit varied with the temp of the water.

So re-capping one sends signals to the computer.
One sends signals to the gauge.

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MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

Thanks for the info. So that would explain alot. The gas mileage has shown a big change and the sudden stop in the gauge not working on the dash. I found both parts but wanted to make sure there was a true difference. Would you pay about 9 bucks a piece for both? Found them at RocksAuto. Anyway was also planning on replacing the EGR valve. The truck is close 90,000 so I thought it would be a good time to change that out also. Any advice on replacing any of these parts?

go ahead and replace both sensor, be careful! don't over tighten, you'll crack the t-stat housing... as for EGR wait until you get sensor problem fixed.. if the engine doesn't idle up at stops or letting off accelerator. don't worry bout it. if it does do this. I can show you a trick to fix, for free..

__________________
MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

thats weird when I looked them up they had the same part number

I went to a website called Rocks Auto. Have had good service from them in the past. They show a temp sender and a temp switch. Ordered one of each. One is a FoMoCo part the other from Wells. They look almost the same. One had some teflon like tape on it that the sender. The other does not have the tape and that is the switch. Side by side outside of the tape and the different shape of the ends they look alike. Based on what I have read here and on line there is a diffrence as to what they do. I went out this morning to replace the sender and my deep socket was not deep enough. So yeah great start to the day. I did replace the EGR valve while I was under there. Lost the gasket and had to go and get another one. I looked all over the engine compartment and I think the truck may have ate the thing. I am still confused with the switch / sender thing. They look the same and as far as I can see sit almost next to each other. I don't have away to send pics but if anyone has a picture showing the location of both that may be of some help to me. Have a good one.

dnt know what engine you have, but this will give u a general idea. of location, should be near thermostat housing

__________________
MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

I have the 3.0 V6 Flex - year 1999. Are the sender and the switch locted close to each other?