‘91 7.3L overheating?
Thread Starter
|
Mountain Pass
Joined: Aug 2025
Posts: 100
Likes: 20
‘91 7.3L overheating?
Past couple days the ‘ol girl has been running a bit warmer everyday. Needle on dash gauge normally is between the ‘O’ and ‘R’ on normal. Last couple days, pulling the camper home, the needle gained a full letter everyday. Today is was pegging on the far side of ‘L’ for most of the day, never exceeded 60mph, on the flat, and downhill needle would fall back to ‘A’, and incline back to ‘L’ , then finally late this afternoon would hang just past ‘L’ for a few miles, doing 40mph, then bam, the needle would fly way past the ‘H’ and the Red dash. Let off on accelerator coast to the shoulder, let idle 5min or so, needle returns to the lower ‘cooler’ side of ‘A’.
Overflow tank never filled up, radiator never steamed over, only 1 time did the ‘engine’ icon illuminate on the dash. All fluids are at normal level. Engine sounds as normal as always. We are traveling out town, on our way home, 225 miles to go.
What would be a good place to start have unknown to me mechanics take a look at/test? Fan belt is tight. TIA
Overflow tank never filled up, radiator never steamed over, only 1 time did the ‘engine’ icon illuminate on the dash. All fluids are at normal level. Engine sounds as normal as always. We are traveling out town, on our way home, 225 miles to go.
What would be a good place to start have unknown to me mechanics take a look at/test? Fan belt is tight. TIA
Last edited by Mr.Lars; Nov 2, 2025 at 09:33 PM.
i ain't rite
Joined: Mar 2005
Posts: 65,591
Likes: 5,617
From: Marlboro Mental Hospital.
my bet is a faulty sending unit for the gauge.
i installed a mechanical temp gauge within a year of buying my 88 for the same reason. gauge saying overheat, but radiator was only 175 degrees by ir thermal gun.
i installed a mechanical temp gauge within a year of buying my 88 for the same reason. gauge saying overheat, but radiator was only 175 degrees by ir thermal gun.
Tuned
Joined: Sep 2024
Posts: 490
Likes: 122
From: Ougadougou
If both your dash gauge and the over temp light were illuminating then you might have a problem sine two sending units failing simultaneously seems unlikely. But if it were just one gauge affected I would lean towards sender failure.
I wonder if the thermostat isn't fully opening? A $33 Equus mechanical temp gauge from NAPA would be a great way to know if you're actually over-heating. Thermostat should begin to open at about 192F and reach fully open at 212F,. If it should turn out to be the thermostat be sure to insist on using a Motorcraft thermostat.
I wonder if the thermostat isn't fully opening? A $33 Equus mechanical temp gauge from NAPA would be a great way to know if you're actually over-heating. Thermostat should begin to open at about 192F and reach fully open at 212F,. If it should turn out to be the thermostat be sure to insist on using a Motorcraft thermostat.
Last edited by WCMtn1990; Nov 3, 2025 at 06:58 AM.
Thread Starter
|
Mountain Pass
Joined: Aug 2025
Posts: 100
Likes: 20
Got into a shop, a couple blocks from the RV park, engine gauge slowly increasing but upper radiator hose stayed cold, heater hoses got hot and heater kicks out heat. Definitely the thermostat, by the time the stat opened, radiator cap released into the overflow tank, first time that has happened. New thermostat and gasket on order.
Tuned
Joined: Sep 2024
Posts: 490
Likes: 122
From: Ougadougou
Got into a shop, a couple blocks from the RV park, engine gauge slowly increasing but upper radiator hose stayed cold, heater hoses got hot and heater kicks out heat. Definitely the thermostat, by the time the stat opened, radiator cap released into the overflow tank, first time that has happened. New thermostat and gasket on order.
Thread Starter
|
Mountain Pass
Joined: Aug 2025
Posts: 100
Likes: 20
Coolant is fresh, earlier this year. I changed it myself. Previous Owner had converted to the ‘Red Stuff’. I thought about going back OEM green, but figured why spend all that time and effort multiple times flushing to get all residual coolant.
Logistics Pro
Joined: Jun 2017
Posts: 3,986
Likes: 515
From: Edmond, OK
Hopefully that thermostat gets you on the road.
I'm not sure what "red stuff" coolant is. Is it compatible with the OE green coolant?
I'm not sure what "red stuff" coolant is. Is it compatible with the OE green coolant?
Trending Topics
i ain't rite
Joined: Mar 2005
Posts: 65,591
Likes: 5,617
From: Marlboro Mental Hospital.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 6 Best Deals Available on New Fords & Lincolns Right Now
Brett Foote
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Verdad Gallardo
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Logistics Pro
Joined: Jun 2017
Posts: 3,986
Likes: 515
From: Edmond, OK
The Peak extended life coolant I get from Sam's Club is yellow. It says right on the bottle that it's compatible with all coolants.
https://www.samsclub.com/ip/13602603777
I'd just worry about compatibility. Especially with the 7.3l tendency for cavitation with the wrong coolant.
https://www.samsclub.com/ip/13602603777
I'd just worry about compatibility. Especially with the 7.3l tendency for cavitation with the wrong coolant.
Trailering
Joined: Nov 2005
Posts: 24
Likes: 3
From: Ca, USA
If both your dash gauge and the over temp light were illuminating then you might have a problem sine two sending units failing simultaneously seems unlikely. But if it were just one gauge affected I would lean towards sender failure.
I wonder if the thermostat isn't fully opening? A $33 Equus mechanical temp gauge from NAPA would be a great way to know if you're actually over-heating. Thermostat should begin to open at about 192F and reach fully open at 212F,. If it should turn out to be the thermostat be sure to insist on using a Motorcraft thermostat.
I wonder if the thermostat isn't fully opening? A $33 Equus mechanical temp gauge from NAPA would be a great way to know if you're actually over-heating. Thermostat should begin to open at about 192F and reach fully open at 212F,. If it should turn out to be the thermostat be sure to insist on using a Motorcraft thermostat.
Thread Starter
|
Mountain Pass
Joined: Aug 2025
Posts: 100
Likes: 20
would have preferred a Motorcraft original but, as we are in Van Horn Texas, and all there is here is a NAPA, with the nearest Ford dealership is well over 100 miles, my options were slim. Next stop is my Son’s house for a couple days, then the final leg home. ‘Fredrick’ will be due for a lube, oil, & filter when home, will acquire an OEM stat at that time.
Tuned
Joined: Sep 2024
Posts: 490
Likes: 122
From: Ougadougou
would have preferred a Motorcraft original but, as we are in Van Horn Texas, and all there is here is a NAPA, with the nearest Ford dealership is well over 100 miles, my options were slim. Next stop is my Son’s house for a couple days, then the final leg home. ‘Fredrick’ will be due for a lube, oil, & filter when home, will acquire an OEM stat at that time.
