The Ranger is running a little too hot for my comfort level at idle. It will hover around the "L" in NORMAL on the gauge.
(Even after an hour, in repeated tests, it doesn't go to the red.)
While driving - even at 5mph around the neighborhood - the gauge will sit right in the middle between R & M.
I've let it idle in the driveway for over an hour several times (ambient temps between 100 & 105) and the gauge rises to the upper part of the scale.
I have yet to repeat this test at 115 ambient but I don't think the results will be much different.
I believe it should remain mid-scale - no matter what. My friend says as long as it's within the white marks, it's OK.
I would be a lot more comfortable if it sat mid-scale.
Throughout all this, highway driving has been normal, including a round-trip to Prescott with a couple good elevation climbs and it runs great with very stable temps.

Over the past few months, I have replaced nearly everything replaceable in the cooling system.
Pump, hoses, fan clutch, belt, T-stat, radiator, heater core, and fan. (And, yes, I've checked the oil for goo.)
Only after all this did I notice the high temp at idle.
And, yes, I've done a cooling system pressure check and hydrocarbon test.

So, I replaced the fan clutch. Then I installed the old fan clutch, then put the newest clutch back in.
I've even changed the fan to a 10-blade (as opposed to the 9-blade).
I've repeated the idle tests with 3 different clutches and the 10-blade fan, all with similar results.
The 10-blade fan seems to have made a slight difference but still, the engine at idle is warmer than I would like.

So, is the high temp at idle considered normal?
Someone also suggested the water pump design had changed as a result of service bulletin - but I've not been able to confirm this.
Is this normal? Abnormal? What's left?

Thanks.

 

Higher temp at idle has always been an issue with gasoline engine, which is why computer ignores O2 sensors and runs engine Richer at idle

You are using a fan shroud correct?
That's required for best cooling at idle

Manual or automatic trans?

Dual or single core radiator?
Manuals often had single core, switch to dual core and use dual core shroud with it

If automatic you always add a 2nd trans cooler, it could be trans is running warmer which can add a few degrees to radiator, its also bad for transmission to run above 200degF

If you have AC are the condenser fins clean, the condenser is in front of radiator so if its fins are dirty there is less air flow thru radiator

In general when temp goes up at low speeds or idle its a Fan issue, not enough air is being pulled through the whole radiator
Lack of a shroud or dirty fins can cause that, also bad fan clutch

Its possible for water pump impeller blades to be dissolved by old coolant, so less circulation at lower RPMs

The N O R M A L letters don't help as Ford changed that almost yearly, lol
Use 1/4, 1/2 or 3/4 for needle
Just below 1/2 is expected after full warm up
Just above 1/2 is fine when engine is under load
But should stay under 1/2 at idle even in warm weather

Does turning heat to HOT and fan on high lower the idle temp?

 

It's a manual trans.
Yes, I have a fan shroud. When I purchased the truck, it didn't have one but I installed one a couple months ago when I replaced the belt, pump, and clutch.
The new radiator (as well as the old) is a dual core. The AC condenser is clean and relatively damage free.
I've made every effort to keep the truck in stock configuration (Though Ive not used Motorcraft parts.)

And this is where one of my questions originates: perhaps there is a difference in a Motorcraft water pump?

Likewise, there seems to be a "Heavy Duty" clutch which I believe I have. As mentioned, I've run this at idle with 3 different fan clutches.
(One is a slightly larger diameter, while two were a smaller diameter. The two configurations appear to be the common choices when looking at the options online.
While there could be some sort of performance difference, I noticed no significant difference from one clutch to another over the course of tests with three different clutches.)
Likewise, I have trouble hearing much audible difference in airflow from when the fan might be engaged and when it's not. (Others have told me I should hear a noticeable difference.)

Turning on the heat does affect the cooling a little. The gauge will drop for a bit and then eventually return to 3/4 scale and for the most part, hold there.

In the course of testing, I did set a 20" box fan in front of the grill. That added air flow would drop the gauge to near mid scale.
So, it doesn't take much additional flow to keep the gauge at mid scale. It just cant seem to do it on its own at idle.

Oh, I also repeated the test with a 180 t-stat vs. a 195. and as someone suggested in an earlier thread: the high temp didn't change.
Only the lower temp when the cooling system started to work.

So it seems my cooling system is performing at 90+ percent capability. But I really would like to have that 100% feeling.
Not sure what else to do...

 

After engine has fully cooled off, like overnight, open the hood and spin the fan, should be cold locked, hard to spin
Start engine you should HEAR the fan noise, then it will go away after 10 seconds or so
After 30 seconds shut off engine and spin the fan again, should be unlocked, easy to spin
After the next more than 15 minute drive when you come home, engine off, pop the hood and spin the fan should be LOCKED again just like when cold and even more so

Fan clutch works from radiator heat
On the front of it is a bi-metal spring that expands as it is heated by radiator temp, this closes valve inside the clutch prevent the oil inside from passing easily and that causes the fan blade to spin closer and closer to water pump pulley speeds, i.e. locked to provide more air flow based on radiator temp
When cold the oil is thick so simulates "locked", after 10 seconds of spinning the oil warms up so unlocks the clutch

After engine/radiator is fully warmed up you can pull back the shroud and run your hand over radiator fins, should be warmer near upper rad hose and then get cooler as you get to lower rad hose, should be nice and even heat NO cooler spots, those are blocked passages, feel near the center, that what fan clutch uses to detect radiator heat


And just as a long shot can you get a thermometer, like one of those IR types, to get confirmation on actual temp, just wondering if you are chasing a ghost

You don't mention the YEAR of the Ranger but if its a 1995 or up you can use an OBD2 reader to see ECT sensor's TEMP, its a separate unit from the sender used by the dash gauge

It will sound stupid but.................when engine is running you can feel air blowing back away from the fan, right?
I know but have to ask, I have had fan blades reversed OR fan belt reversed on pulley so water pump is spinning backwards
Exactly the same symptoms as described

 

Of everything mentioned, the one that would best fit my circumstance would be the reverse fan scenario.
It strikes me something I would do - inadvertently of course - but it seems to fit with the way things go for me.
I'll have to check it after while as the truck is currently in the afternoon sun and it's about 112 out there right now :(
I'm fairly confident with the belt routing as I still have the diagram under the hood and have checked it closely - but I'll check it again.

As for the clutches, all three have performed similarly. None of them seem to ever rotate "freely."
The best I can do is give the fan a flick with my fingers. When cold, I get about one or two blades of rotation. (30 -45 deg?)
I never see any significant difference after the 30-second "warm up." Nor do I see much difference after everything is at operating temps.
If I had only one clutch, I would suspect it to be bad based on the testing I've done. But I have three clutches.
One is a couple weeks old that I purchased by itself. One is only a couple months old and it came with the water pump kit.
(Both of those came from AutoZone and carry a warranty - if they prove to be defective.)
The third clutch is a different casting with a larger diameter. It was on the truck when I bought it and brand and age are unknown.
But all three perform similarly; so I'm hard-pressed to return the newer clutches without a little more definitive story.

I've been waiting for an excuse to buy an IR thermometer and this might be it.
I'm fairly confident in the radiator as it is only a week or so old.
But, like you said, maybe I am chasing a ghost.
Since I'm only looking at relative temps as shown on the gauge; I'd really like to verify actuals.

Oh, it's a '94 so I don't have OBD access that I know of.

 

No, a 1994 is OBD1 so not easy to access specific data

Yes, I would be hard pressed to think 3 fan clutches are bad
BUT................there should be a big difference in fan spin after cold start and shut down, cold, and after driving for 15+ minutes and gauge is at 3/4 so that's confusing
Unless you are chasing a ghost

Fan belt routing matches pullies, i.e. ribbed to ribbed, smooth to smotth

These serpentine belts have a ribbed side and a smooth side, and the pulley will either be ribbed or smooth, so if any belt is routed correctly then these surfaces will match up
i.e. 4.0l has a smooth water pump pulley so smooth side of belt will be on it, 3.0l has a ribbed water pump pulley so ribbed side of pulley will be on it
Just for future reference and easy to remember

I also have a 1994 4.0l and it runs at just below 1/2 even at idle, will climb up above 1/2 a little on a long up hill grade with my load of tools in the bed, but returns to below 1/2 within a minute once I am on the flat ground again

Running dual core radiator, but no AC

Check radiator level after engine is cold, pull off cap should be filled to the very top NO AIR at all
You are using a self purging system, so any air inside will be forced out to overflow tank on warm up and then coolant will be sucked back in on cool down