My 94 Ranger 3.0L 5speed 2wd temp gauge is staying on the cold side but the heater is working good and I used a laser pointing thermometer at the thermostat housing and got 180* after running for a while and I also noticed that the fuel economy had gone down along with the power. I was getting 340 miles to a tank but now I'm getting 280 per tank.

 

Where do you live? All cars get worse mileage in the winter, between that crap winter gas and the fact it takes longer to heat up that old iron block you mileage will suffer. So after taking that into consideration, the first thing I would replace is the thermostat, cheap and easy and effective. It might look ok but it could be opening too soon and not alowing the engine to heat up as fast. I don't make it a habit of working on Fords for a living (God bless you Ford techs!) but the stuff I work on every year when it gets cold shows up with check engine lights and a P0128 because of a stat opening too soon. (thank you Opel for paying my bills)

 

You may have more than one problem.

The in dash temp gauge has its own one wire temp sensor on the engine. If you disconnect the sensors electrical connector & ground it, the temp gauge should read full scale & that will indicate that the wiring & temp gauge are ok & the gauge temp sensor may belong on your suspect list.

On the mpg drop, we need more clues, like do you have a CEL lit & if so what trouble code Numbers does the computer have stored, or if the mpg drop happened suddenly after some event, or slowly over time. As Phinxter has said, we normally get lower mpg in winter & the colder the weather & shorter the trip, the lower the mpg will be, but if you have a CEL lit, you likely have other problems, so run this puppy by your favorite autoparts store for a no cost computer trouble code scan & post All code Numbers, as they can offer up good trouble shooting clues.

If you don't have a CEL lit, look to a dirty MAF sensor, worn out O2 sensors, sticking open, or wrong temp range thermostat (you should be using a 195 deg thermostat) & running 5W-20, or the origionally specified 5W-30 motor oil in your 3.0L Vulcan, a dirty air filter, clogged fuel filter, are some things that come to mind that could mess with fuel trim/mpg.

More clues would help us make a better guess.

 

Yeah those things too, might as well throw tire pressure in there as well, it drops in cold weather, not that it affects mileage by a huge amount but a smidge.

I haven't drove my Ranger alot and I have had it about 8 months but my Plymouth gets 28mpg all day in the summer and 24-25 in winter. I end up getting about 60 miles less per tank in the winter. Maybe theres really nothing going on here unlees of course you've had your truck many years and you know better.

 

I took the wire and grounded it like you said Pawpaw and the gauge made a full sweep so I went and got one off another engine and the gauge started to go up as the engine started to warm up so I thought that was it but then the gauge stopped and went back a little and stayed there. I put cardboard in front of the radiator and let it idle for a couple of hours and the gauge said it was cool. I notice that the lower radiator hose stayed cool after hours of idling so i thought the thermostat was staying closed so I tried to take it out so I could run it without one to see if it would warm up but the screws were hard to turn and I don't want to break them. I'm soaking them with PB Blaster overnight and try again tomorrow. At one point I checked the temp with a laser thermometer and I was getting 220* at the thermostat housing but the gauge said it was running cool with the replacement sender
.

 

Sounds like the thermostat is sticking open & causing over cooling, if the lower radiator hose never warmes up.

 

I tried to remove the thermostat but wasn't able to remove the screws. They are really rusted in there. I took the radiator hose off the housing and stuck a screwdriver and dislodged the poppet to the side so that I was sure the coolant could get by and drove for 100 miles. The temp got checked several times with the laser thermometer. At the housing around 197* the lower hose by the radiator 160* with the radiator covered with cardboard, outside temp in the high 40s. The dash gauge always said it was not up to temp. It went up to the first line when I was on the highway doing 65 but then it went back down just below that line where it stayed most of the day. Tomorrow I'll try to get those screws out again.

 

I think your temp gauge is ok, but here is a thread where we talk about how to sorta check/calibrate the temp gauge meter movement with resistors in place of the gauge temp sensor & test the temp gauge senders resistance values. https://www.ford-trucks.com/forums/5...rong-temp.html

Soak the fastners in a good rust penetrant overnight & see how it goes.

 

Today I got a temp sending unit, Standard TS58, red box and a 10 Ohm, 10 watt resistor, Thermostat and gasket. I checked the gauge with the resistor and it went up to around 7/8 in the normal range and stayed there. Then I replaced the sending unit and turned the key, the gauge went to the bottom of the normal range. I started it and went for a 20 mile ride and the gauge went to about half way and stayed there. I then pulled over and uncovered 1/4 of the radiator and the gauge went down about an 1/8. Next time I go out I'll take out more cardboard. Next I'll get to work on the fuel economy and power.
Oh, I think I'll leave the old thermostat in there and deal with it in the spring in case I break a bolt.

 

Sounds like the temp gauge is reading normal.

Fords thermostats are designed to fail in the open position, so we don't overheat the engine & warp something.

 

I found my fuel/power problem. It was the fuel filter. The stuff that came out of there was nasty.Last place I looked because I replaced it only a few months prior to my having problems.

 

OK, good find, fix & feedback. Sounds like you've been buying some dirty gas. There are branded stations like Sunoco, EXXON, ect, that have filters on their pumps, that'll help. Fill up at high use stations, so you likely get fresh fuel.

 

something else to consider when buying gas. We finally got it here where I live.
Top Tier Gasoline