Gonna start this story somewhere in the middle. Got the truck back together and it seems she runs towards warm. Got no way of measuring, so I don't know what the truck is doing. I was conditioned that anything on the gauge between N-R was ok, but you'd have to watch it close to make sure it wasn't going passed the R. I can't remember what the gauge used to read when I got the truck, but I think it didn't. Because they terminal was snapped off in the harness connector. So no background information. Couldn't find the new sender I got, so I ordered another one with a bunch of parts from rockauto I think. It was a WVE(NGK related) 1T1116. It's got a black insulator, not sure if that's important. Another thing to note, I'm not confident with my emissions stuff or vacuum hose routing being correct or functional, nor do I know how well the carb is dialed in. Truck seems to run and sound good, but being near deaf, doesn't mean much. So, the truck idled between 750-1000 RPM for the duration of this story. Vacuum advance uses both ported and manifold vacuum so there is always advance at idle. Just more flavor text. Now, with the truck idling, and up to temp. Gauge reads in the M-A range. My gauge face had gotten hot at some point in it's life and the plastic sagged. Having a couple of spare clusters I swapped in another one when I fixed the alignment of the Odometer wheels and greased the Speedometer cable to fix a bouncing needle. Now with the truck idling, it's in the A-L range. I took my daughter out in the truck and drove outside of town on the highway(55mph) for about 13 miles. The gauge slowly climbed to the top, didn't peg out, but nearly so. Don't think she was running hot. Or rather, she wasn't overheating, no idea how hot she was running. Got a 195* thermostat, but had a 160* when I got it, and don't know why. Turning the heat on didn't cause the needle to drop at all or change it's behavior. Heat coming out the vents was good and strong, but didn't seem out of the ordinary as far as temperature goes. I did get faint whiffs of hot coolant but the engine bay is covered in it from a leaky radiator, radiator swap, and me spilling it. Last night I swapped in the first temp sender I bought, since I found it. It came in a masterpro ignition box with M18127 2-8331 Temp. Sender/se printed on it. Had a red insulator(Motorcraft one has green insulator) Truck still idling the same, took awhile to come up to temp. I was checking the gauge and feeling the upper radiator hose. Felt to me like the 195* thermostat opened with the gauge dead center of the R-M. Idle that way for awhile. I drove her 20 miles and it never moved. But right before I got into town I laid on her some and got her up to sixty or so. Gauge went up to the L and stayed there. Left her idling when I got in and fiddle with the carb some and dropped the idle RPM down since I knew she was good and warmed up. Basically reset the carb. Needle never moved from L and nothing felt too hot. Actually the upper radiator hose didn't seem hot enough, although it did have some heat to her. The heater core hoses were much hotter. Radiator felt cool, fan was pulling cool air through it. When I shut the truck off, radiator temp went up pretty quick. Which seems normal to me. I marked the coolant level in the overflow. After the engine cooled off I went out to check, needle went back down to C like it should, radiator is still full, and it didn't pull any out of the overflow. I'm kind of stumped on this one.

 

All the trucks I have had, the 195-200 temperature was at the "o" in "normal". But you will never know what the problem is unless you get a aftermarket gauge.

P.S. Even the 84 Bronco II I just bought, the thermostat temp is at the "o". What is weird about that one, the gauge is mounted vertically, with the word "normal" going from the top down. The needle rests at the bottom. So on this little truck, 3/4 of the gauge is not even used, since the thermostat temp is way up near the top of the travel of the needle. I have never put a real gauge on this vehicle, but I am confident in what I am seeing, because I transferred my electric fan setup from the other ranger to this Bronco, and I did not reset the temp controller. So I can see when it comes on, I had it set around 210 and I can line that up with the Bronco gauge and the way the engine is acting.

You heard it before, I will say it again, the factory gauges on these trucks are lousy.

 

What motor you have? You running a shroud? Clutch fan?
Could buy a cheap IR temp gun at HF to do some checking.

FYI I have a 300 six has a new stat think 195* new radiator with shroud and non-working AC condenser in front of radiator.
My gauge just about makes it to the first line before NORMAL. I get what I think is pretty good heat and the radiator & heater hoses get hot where you can hardly keep a hand on them.
The other thing that points to mine maybe running too cold is the milkshake under the oil fill cap and when checking oil the dip stick tube has the shake also.
I cant remember if I changed out the temp sender or the oil sender or both I did something to get the gauge working.
Think oil so maybe I need to do the temp now? Where did I put that new temp sender now?

What I have been meaning to do is take my IR temp gun and measure at the stat to see what it says but when I get home from work the last thing I want to do is any work at all.
Oh I also blocked off part of the radiator the other day to see if that would do anything, if anything the gauge went down!
My coolant level has not moved since the truck was put on the road back in November.

So till you can measure the temp it is all a guess just like me.
Dave ----

 

My 351m has a 192 stat that’s correct for the engine (think i bought a Stant model). My truck temp gauge will generally sit around the A at temperature. PO tied a mechanical gauge into the elbow and it reads right around 190 at temp. I’ve shot the elbow and it’s not higher than 190, so I’m satisfied all is working. The temp sender is a new Motorcraft unit. Coolant system was chemical flushed and replaced with distilled and green concentrate.

At 160-170, the gauge will show more in the R range. I’ve got limited data above 190, but I don’t think the gauge output is linear across the full range - seems to climb faster above 190.

Based on my experience, I’d confirm with an IR gun and let it rip.

 

+1 on that.

Get a sturdy paper bag. Cut a pair of eye holes. Wear bag over your head (not while driving) and go into Harbor Freight. Purchase said infrared thermometer. Go home. Measure actual temperature at thermostat housing.

If the gauge roughly matches the actual temperature, then investigate the cooling system.

If the gauge disagrees with the actual temperature, then investigate the indication system.

If you don’t want to spring for an infrared thermometer, another option is to rig up an electromechanical arm at your computer. Grant me full access to remotely operate this arm. Set up a webcam and create a YouTube channel for broadcasting. If you post, “I replaced the (insert name of expensive component) and nothing changed,” I shall activate the arm and slap you a few times.

The resulting video should be very entertaining, but I still think you’d be better off to first determine if you’ve got an indication issue or an actual temperature problem.

Your call.

 

I think I'm going to put in some pillar pods with a temp, oil psi gauge, and a volt meter probably. But that's a later thing. It seems like the gauge is actually working, up until it goes to the right. Then it doesn't come back down. So, what are the chances the engine is actually staying that hot whether I'm driving it or letting it idle? I agree this is all speculation with out a way to measure, and I don't have one, nor will I be getting one soon. I forgot to add I tested the senders. The masterpro before it went in, and the WVE when it came out. They both approached zero ohms when I held a lighter to them. And they both were still climbing, but had almost stopped at 860 ohms held against an ice cube. So they responded the same, the only thing I could think of was they have different heat ranges, since I couldn't measure at specific temps. Or, they are exactly the same. Even though they act differently installed. Need to add that to the list of things to check when time and money allow. Need to put a Motorcraft on the pile and come up with a good method to test them consistently.

It's a 4.9l with a non clutch fan.

I'm thinking there is either a difference in the output from the different senders, or the gauge has some unusual behavior at the top of the range. Or there is another factor at play I haven't considered. Like a faulty regulator on the cluster and higher voltage output when the engine is up to temp.

Anyone know anything about two terminal temperature sensors? I have a couple of them on hand from a different job. Wonder if I could put one of those in and read its output with a DVOM and measure that way.

 

The two prong sensors are usually for the computer system. Who knows if the ohms are the same or not. You can fiddle with them and get the gauge to read anything you want, but that is not really the point is it? If you are worried about your engine, I would go to the local store and buy a cheap mechanical temp gauge, the last time I looked they were about $15-$20. Hook it up and just wire tie it or something and let it hang under the dash. Just to keep an eye on the engine. Don't use any tee's or anything on these senders,, the probe needs to be in the flow of coolant going by.

You can decide later if you want to do something more permanent.

 

I had an issue with an aftermarket sender giving me unusually high temp readings.

My temp gauge was working just fine. I pulled my engine and rebuilt it, and when I sold the 2bbl carb and intake I forgot the factory temp sender in it. So I go to the auto parts store and order a new sender (can't remember what brand it was, but it wasn't the cheapest one available). Temperature started reading too hot all the time. Not pegged hard to the right, but high up on the range all the time, either on the "L" or a little past it. However, checking everything with an IR gun temps looked perfect at 195 at the thermostat housing. I dropped by the Ford dealer and ordered a new sender, installed it, and boom...temperature started reading correctly again, right in the middle, or between the R and the M. Just my 2 pennies worth. I'd try a factory Ford sender if an aftermarket one isn't reading properly.

 

For sure want to try them side by side and see what the difference is. Maybe the insulator color is just manufacturer's preference and has nothing to do with device function. But it'll a long time coming before I can get anymore parts or tools.

 

If the regulator was flaky then the fuel & oil gauges would read funky too.
As a test to see if it is the sender or gauge and you don't have the $20 for the IR gun get jumper wires and run the temp wire over to the oil psi sender and the oil psi wire to the temp sender.
If the oil gauge now reads high the temp sender is bad.
If the oil gauge reads normal the temp gauge is bad.

If the temp gauge reads normal the temp sender is bad.
If the temp gauge reads high the temp gauge is bad

The thing to remember doing this test is the oil gauge is now the temp gauge and the temp is now the oil gauge.
Dave ----
Dave ----

 

They read a little different..

 

I appreciate that. I may play around with it some, see if it matches up. I know when the thermostat opens, and I know the temp and I have tested that, so I'll probably use that as a benchmark. I think I've even got a harness connector for it, I'll probably solder some leads on it so I can connect my meter easily and see if I can map out my coolant curve. What I'm curious about is the resistance values, are they linear? If I can map a couple of points can I calculate any given temperature given the resistance?

 

I think the "ECT sensor" was only for vehicles with computer-controlled engines. This sensor fed coolant temp data to the computer only, not the gauges.

A separate coolant temp sensor fed info to the gauges. All three gauges (coolant temp, oil pressure, fuel quantity) are the same internally, with different labels on the face. The sensors all operate 10 ohms = high, 73 ohms = low. Details here, see the second page:

Fuel Tank Selector & Gauges - Gary's Garagemahal (the Bullnose bible)

 

I'm looking for a secondary way to measure coolant temp with what I have on hand, being short of cash in this time of crisis lol. Plus the whole MacGuyver thing is pretty cool, chicks dig it.

 

No idea if the values are linear. You could rig up a spare temp sensor and thermometer in a pot of water on the stove. Make a chart of the temperature and resistance as you heat up the water.

I've done this with the temp sensor from another vehicle, and it worked great. One tip, heat the water very slowly. If the water temp is rising quickly, it's hard to get a stable reading. It works best to raise the temp in steps.