Temperature gauge stuck on cold , and fan is always on. Replaced the thermostat and temp sender, tachometer doesn’t work as well( but I don’t care about that) the fan is not locked up when off. Is there a fuse/relay im not keen about?
2002 Ranger 4.0 v6 manual
thanks

 

Welcome to the forum

Fan clutch is mechanical, not electric
It locks up when the center of the radiator gets hot enough

Start cold engine and open the hood
Feel upper radiator hose and the 2 heater hoses at the firewall, all cold of course
Let engine idle for 3-4min
Feel the hoses again
Heater hoses should be warming up
Upper rad hose should still be cold, if upper rad hose is warming up like heater hoses then thermostat is stuck open, new or not, for sure

Vehicle radiators are there for EXTRA heat, often not even used in the winter months, that's what the thermostat is there for, it blocks coolant flow thru the radiator, engine coolant at 185-195degF means best MPG and cleanest oil, so until coolant gets above that there is no circulation thru the radiator, and even if there is a little circulation, the center of radiator never gets hot enough to lock the fan clutch

Just 2 fuses for instrument cluster in 2002 Ranger, fuse 11 and fuse 26 in cab fuse box

There are two temp units on a 2002 4.0l Ranger
ECT sensor, 2 wires, green/red and grey/red, ONLY used by computer, its a 5volt sensor
Coolant SENDER, also 2 wires, red/white and black/white, only for dash board temp gauge, 12volt sender

Unplug the SENDER connector and GROUND the red/white wire to battery negative
Turn on the key, engine off
Temp gauge should go up to HOT, all the way up
Of not then red/white wire is bad or the gauge is, in either case you would pull out the cluster to test the red/white wire or replace the cluster

If gauge does go to HOT then red/white wire and gauge are OK
But now test the black/white wire
Jumper the red/white and black/white wires together, key on, should see HOT again, if not the black/white wire is not grounded, needs to be grounded

2002 cluster can be replaced with a 1996 thru 2003 Ranger cluster, plug and play, same wiring, black or white face are the same electrically, manual or auto
Always replace the 6 Backlight bulbs anytime a Cluster is out, they are cheap and a pain to replace, lol

 

I think my question belongs in here...

2002 XLT 4.0L 4x4 AT (5R55E) 258,000 miles

TLDR: I overheated the truck. The thermostat housing, thermostat, and sensors were all replaced. Now the gauge doesn't appear to come on at all. Could the overheating have damaged it? Or... any ideas why after an overheat and replacing those parts what might have been overlooked or damaged that could cause the gauge not to work?

Full story if anyone is interested:
After exiting the freeway onto a city street I felt like I noticed steam around the outside of the truck, but it was running great, the gauges all looked good, and nothing smelled off. There was a lot of traffic so I figured it must have been coming from a different car (as in, I passed through someone else's plume) or a manhole or something. My destination was less than two blocks off the exit. ... A couple hours later I went to drive home. I got back onto the freeway but before reaching even the first exit, temp gauge shot up, truck lost power, check engine light came on. ... I pulled off the next ramp and called for a tow, they gave me a 2-hour eta. ... It was about 2am, cold (couldn't start the truck to run the heater), and nothing around (the last time I'd been off that ramp there was a 24hr gas station/convenience store but now there was just a vacant lot). ... I checked my GPS and was only 1.5 miles from where I'd come from. So, I made the mistake of letting the truck cool for about 30 minutes then driving back to where I'd been. ... This time I stayed on surface streets (so under 30mph). ... It ran fine until about the last two or three blocks (maybe less, I was close enough to my destination that I could see the building and where I wanted to park in front of it) then the temp gauge maxed out again. The check engine light didn't come on though until after I'd pulled into the parking spot and come to a complete stop (so a matter of seconds before I turned shut the truck off).
The shop I towed it to told me broken thermostat housing and I approved the repair. He went on to say "Usually when you overheat you blow a head gasket." - "You guys will check for that after replacing the housing, right?" - "Yeah."
They call me with the follow-up "We got the housing replaced but the gaskets are gone. Sometimes when that happens the heads crack and will have to be replaced too." - "So, the head gaskets did blow?" - "Yeah, that engine is so old, over 250,000 miles, they're not going to survive that." - "Oh, well the gaskets aren't that old, we just had you guys put new head gaskets on it a couple years ago." (He wasn't familiar with that history because, although this was a place we'd been going for decades, the owner, who I'd always dealt with, had passed away between that overhaul job and this break-down.) He couldn't find the invoice but based on what I'd told him was done, replaced timing chains, manifold gaskets, head gaskets, new injectors, main seal, cam kit, etc. he said "That sounds like almost a whole rebuild. For probably about a grand more you could have gotten a new engine." - "I know, I wanted to but they were a few months out and I needed a vehicle." (This was in 2022 at the "end of Covid" when all the supply chains were still catching up.) - "Oh, well this is going to be much more extensive. Probably a new motor." - "If the heads are cracked you mean?" - "No, they're definitely cracked. The machinist said they cracked. It only runs for a few minutes and then the temperature is way up." - "Can't you just replace those?" (In my head I'm thinking "You just said sometimes the heads crack, now you're saying they're definitely cracked.") - "We could, but then you're putting new heads on a block with 250,000 miles on it. And you could have cracked that too. Plus, there's probably ring damage."
The estimate for the new engine they gave me is $9,700.
I paid for the housing replacement and asked them to leave it parked outside over the weekend so I could clear my stuff out while it waits for me to make a decision.
When I went down there to get my stuff out, for kicks I popped the hood. As I'm poking around, I open the radiator. It looks dry. Hmmm... Then I notice on the invoice they'd left in the truck for me that they listed replacing the thermostat housing, and the sensors, but not the thermostat. Maybe they did, maybe they didn't (if they did, they didn't charge me for the part) but it's only a $25 part that takes five minutes to replace. So I go to the parts store to grab a couple jugs of 50/50 and a thermostat. I throw in the new thermostat, and top off the radiator (it took almost a whole jug of fluid). ... I start the truck and let it run a few minutes. It seemed fine. No water in the exhaust, no white smoke, the oil looks good, the heater blows hot, no steam in the engine compartment, no knocking. ... I figured, they've already told me it needs a new motor so since it has to be replaced anyway I'm gonna roll the dice and take it for a spin. I cruise around the building a few laps then decide to attempt getting it home.
Home is about six miles / 10 minutes away, with a significantly steep uphill for part of it. ... No problems. ... I get home and open the hood, there's no steam, and I can rest my hand on the radiator cap comfortably. (As I'm typing this I can't remember if I took the cap off to see if the coolant level had changed.)
BUT the temperature gauge never moved at all. It just sits in the resting position. In fact, I noticed that even when just powering the truck on without starting it, all the gauges move when the key is clicked on except the temperature gauge. (Even the oil pressure gauge rises ever so slightly from the resting position to the "I'm awake and ready to show you what the oil pressure is once you start the engine" position.) ... I checked the fuses, they're fine. And the shop, according to the invoice, replaced the sensors. ... Could the over-heating where the gauge maxed out twice, followed by the shop overheating it during their test, (they said the temperature shot up, not that the gauge shot up) have done something to the gauge?

 

Temp gauge is not hard to test

2002 4.0l will have a temp Sender and a temp Sensor on the top of thermostat housing
Sender is 12volts and only used by dash board gauge
Sensor is 5volt and only used by the computer
So not interchangeable

Sender will have 2 wires, red/white and black/white
Black/white is a ground wire, test for that, 0 ohms to ground
Red/white runs to the Temp Gauge, if you Ground this red/white wire and turn on the key the Temp Gauge should go all the way up to HOT, if so then wire and gauge are OK

Since the black/white wire "should be" a good ground, if you jumper(short) the red/white and black/white wires together and turn on the key then Temp Gauge should also go up to HOT