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Running hot at slow speed.


July 7, 2005
Reaction score
City, State
Talladega, Alabama
Year, Model & Trim Level
1992 XLT 4D 4wd
I have a '92 XLT with about 3K on a complete motor job, including new water pump, T-stat and hoses. Radiator is about two years old with no sign of deposits inside the filler neck area. With the 95* + temp we've been having here, with A/C on at idle or in traffic the truck will run hot (3/4 or more of the temp guage). Once it gets this way, I have to drive about 10 min. at highway speed before the temp will come back to the "normal" position of about 1/3 of the way on the guage. A/C system was flushed, new "o" rings, accumulator/drier, PAG oil, etc. I have replaced the fan clutch and added a bottle of "water wetter" and the radiator is full.:rolleyes: I have cleaned the condenser with A/C coil cleaner. Also, when she's hot it feels like I have to use a lot more throttle to get the same acceleration, and the A/C blows bearly cool until the temp comes back down. Any ideas on the engine cooling and A/C would be appreciated.

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With the hot weather the past few weeks of course its gonna run hot! The ac makes the car run hotter! especially if your at a stand still in city traffic! If you can you dont need to use the ac then dont!

did you use the correct fan clutch? automatic transmission and A/C equipped vehicles use an extra beefy one.

yeah any vehicle in standing traffic with the ac on will be hot.

don't count out rad cap failure.

I second the motion, on the fan clutch theory. And, the radiator cap....can be pressure tested.

Aloha, Mark

Mine does the same thing. I've replaced EVERYTHING cooling & AC related with new Motorcraft parts. No change. I'm glad it's not my main car. I could not live with it in south Fl. No way.

And yes the car will run hotter in hotter weather, but the cooling system should be able to handle the extra heat. Any other car I've been in does not act like the explorer in hot weather. That's just a BS answer.

whats wrong with 3/4 temp on the factory gage?
the factory gage may be your problem
It may be running right at 215-225 degrees when its 95 out and your running the AC at slow stop and go speeds,...pretty much normal.

How old is your thermostat?

the factory gage sucks, have you considered getting a real temp gage with numbers on it?

Also you may want to check your radiator, on the 91 they sometimes have a single row radiator and a 10 blade want the 2 row radiator and a 11 blade fan.

do you have a full fan shroud or the little half shroud thingy?
IMO there is a reason why Ford continued to make improvements to the 4.0L cooling system, 90-92 is okay, 93-94 is better

Man, this is discouraging. I have the same problem ('93) and I've done almost everything you've done to remedy it. My idle-overheating only got worse after I changed the fan clutch (Motorcraft heavy duty from Rock Auto) and put a new 11-blade fan in. Bad clutch, maybe.

I wondered about the water pump after some mechanic wrote that he'd seen blades worn down so much they didn't pump efficiently, but you've even changed your pump out.


Maybe an electric fan is the way to go.

My '93, with the factory "towing package" and "super engine cooling" has a 9-blade fan, 1-inch thick single core (or really tight double core) radiator, stock fan clutch, and the ONLY thing that affects the cooling system performance is the thermostat. From one Motorcraft 'stat to the next, they all act differently. The original 'stat from the factory kept the needle in the middle of the gauge all the time, now with the newer 'stats, it's a little over the middle with the A/C on, and a little to the left in cooler weather with it off.

Mine did the same thing tonight as I drove it home.. I am going to change the coolant and thermy though.. and radiator cap as well.
It is only 70 degrees here during the day.

same deal here

Okay my truck before never went over the r of normal on the temp gage tell the last 2 or 3 years. Before even in 109 air temps it stayed cooler then it is now
I have replaced the radiator with a two row one same as stock by the way. The truck has the tow package and heavy duty cooling with extra oil cooler factory stock. So I replaced as I said the radiator, water pump, hoses, thermostat, fan clutch, serp belt. flushed the motor ad heater core and now when it is about 80 it is running at the m and a of normal and the ac starts blowing hotter air this is in city or when stopped at fast food window stop sings or lights any thing longer then 2 or 3 mins.. When doing flat land hwy speed of 60 top 70 same air temps it runs at the n some times touching the o of normal

Have you tried this?

One easy thing to check is the front of the A/C condensor. If the tranny cooler rubber lines are leaking, the ATF will mix with road grime and block the air flow through the condensor and thus radiator. If this happens, remove the grille and tranny cooler to clean the condensor fins, and replace the rubber lines and clamps.

Hope this helps.


I've just recently rebuild a motor and installed it in our '92 X. It has new sensors, new fan clutch, new radiator, new radiator cap, new thermostat (180) in addition to the rebuilt motor..

At idle, no a/c on, at 100F outside temp the gauge is at about the O.
Driving around (not quite stop/go, but stop go enough) the temp can rise up to the A in normal.

I have an infared temp sensor and as far as I can tell the between the M and the A is about 190F (infared temp of the upper radiator hose)..

My question is.. What should the temp be reading at the upper hose (when it goes into the radiator)?
With a 180 thermostat should it be 180F at the upper hose with the light load (idle, no a/c) or should it be cooler
Also, with the 180F thermostat, what should the temp be with the a/c on? Whats normal? 200? 210? When do I worry?


Have you tried this?

One easy thing to check is the front of the A/C condensor. If the tranny cooler rubber lines are leaking, the ATF will mix with road grime and block the air flow through the condensor and thus radiator. If this happens, remove the grille and tranny cooler to clean the condensor fins, and replace the rubber lines and clamps.

Hope this helps.


Checked, cleaned and fixed all of this before I posted from reading here as I was hoping it would be my lucky day but not to be still doing it.
I also noticed when I stop kind of fast the temp also jumps up tell I get rolling again and then back down after about a half mile or so
thinking thermostat but never had one act like that before but the only thing not changed out yet besides the fan blades as I know there from a non ac x but have worked great for some years now even towing so this has me gray matter up in a fit as I am a control freak and want to fix it now before it gets to out of hand and cost me a lot more later .I want to hit 300,000 or more with this same motor and not having to work on any motor parts like heads or such if I can get that lucky

well I did get mine fixed last thing changed out was the fan blade. put in a 11 blade fan and boy dose it pull air. I also changed out the thermastat and that ended my running hot. now the truck runs at the or of normal and only hit the front of the m when realy hot out side and I have been running long .I waited to post my fix tell I got back home after a 1,500 mile trip with lots of freeway and stop and go so I am happy and loving my nice cold air as a side bonus to the fix. I did test the old thermastat and it was working just not opening fully and was a bit slow in opening to my thinking . When tested side by side with the new one it was easy to see why it would get hot when in stop and go hope this helps some one down the line