2002 Ranger XLT extended cab, 4.0L SOHC, 5-speed manual, 4X4, 86,000 miles.
Took truck to local one-man radiator shop for simple coolant system flush & fill. Normal maintenance; nothing wrong with the truck. Trying to support local small business.
Took the Dummy 3 days, and now my temperature guage does not register at all - nada.
He replaced t-stat, and it's working fine.
For some unknown reason he took it upon himself to replace the temp sending unit in a perfectly functional system. New sending unit resulted in no reading at temp guage, so I instructed him to replace original sending unit. Still no guage reading, even with original sending unit re-installed, which worked just fine before he removed it.
He tells me guage will peg to max if sending unit wire is grounded, indicating guage is not defective.

Before anything else, I'd like to do some meter testing on my own. Can someone guide me to exact location of temp guage sending unit on 4.0L SOHC? (C'mon, save an old man some time locating it, huh?)
Is the wire from sending unit to temp guage made of calibrated length/explicit resistance material?

Any other suggestions gratefully accepted.
My expectations are that my findings will indicate a needed trip to local Ford service dept or other "reputable" service center for replacement of sending unit with genuine Ford replacement part. Unless the wire is of set resistance, and has been compromised, seems sending unit is most likely suspect. Any other ideas? Rock? Ken? Anyone?
Thanks.

Note: I had to edit this before posting to eliminate my emotional (and vulgar) adjectives and adverbs.

 

If grounding the wire pegs the gauge, the problem is in the sending unit. If the coolant is not high enough to contact{immerse} the sending unit probe, it will not report the temperature. The wire is not calibrated. The resistance of the sending unit will be a 'ballpark' number, and likely no two units are exactly the same resistance at a specific temperature, beyond luck, anyway. You can check your original unit with a VOM and some hot and cold water. The resistance will vary. I would look more closely at the connector where the sending unit wire attaches. With time, the wire can break internally, or the contacts not make good contact with the sending unit. If the wire has frayed or broken strands, you may get a gauge peg if you hold it exactly the right way, and no response when it is put back into its original position on the sending unit.
tom

 

Thanks, Tomw !!!
What you say all makes perfect sense to me ("ballpark" number, etc.)
I appeciate the userful information and the suggestions!
We'll be giving it a shot...
Thanks again.
Thumper out...

 

When the coolant was changed he may have gotten a huge air pocket trapped that never got burped out. Park it on an incline,remove cap, set heater on high and run it till fully warmed up and see if any air burps out and top off with coolant if level drops. Are you getting any heat out of the heater since the coolant was replaced? Here's a link to show sensor location . Click engine coolant temp sensor diagram at bottom of page for 4.0 , then choose thermo housing 4.0 in next page to open diagram picture. It's part 12A648 according to diagram.

http://www.fordparts.com/Commerce/Ca...=Ranger#Search

 

That thermostat housing is plastic so, be careful with it - It's a 2-piece unit that's bonded together - where it's bonded, the seam tends to split which causes coolant to dump out all over the place. I just had mine replaced for this reason and the local Ford dealer keeps them in stock... When we got the new one, we had to drill out the boss for the second sensor...

 

Thanks to all for your excellent responses, link to diagram, etc.
Thumper out.

 

Okay, final post on this thread to let y'all know the outcome:
Turns out the pins in the wiring connector attached to the temp gauge sending unit were pulled out, necessitating replacement of that pigtail of the wiring harness.
Also, Dummy who did the original cooling system flush & fill, and for no justifiable reason replaced the sending unit and caused this whole dilema, replaced the perfectly good original sending unit with one which was incorrect and had wrong placement for connecting pins, thus destroying the connector on wiring harness. After my demanding that he re-install the original sending unit (which worked perfectly well); he said he did so. He did NOT! (So now besides being a cheat, he's a liar) The one now removed (with the incorrect connectors) was in fact NOT the factory original, but the replacement which he needlessly installed and initiated this whole problem.
Anyway, after replacement of the wiring pigtail/connector, and replacing the sending unit with correct part, all is well and temp gauge functions correctly, and exactly as prior to this whole fiasco. Whew! What an ordeal for such a small thing....
While legal action to recover expenses incurred due to Dummy's ineptness is tempting, I believe he's not worth my effort, but shall instead communicate far and wide the potential for negative results when taking a vehicle to him for any type service.
(Considering purchase of an advertisement in the small local county newpaper warning of same)
Thanks to each and every one of you who assisted in resolving this issue.
Thumper Out!
(Geez, I got thru that whole post without calling him one single curse word...) :-)

 

Thumper: Sorry to hear about your problems, but also glad you got them resolved. On a side note, be VERY careful about posting negative things about this guy in public papers. This can come back and bite you in you know where. Don't ask me how I know.

 

Truth is a good defense against claims of libel from what I've heard. Facts, and facts alone that cannot be refuted are perfect defense, though it may be a PITA.
tom

 

File a complaint with your local Better Business Bureau. It lets you voice your complaint and warn potential customers without having to deal with any libel issues.