Engine Temp Issue

[SFB]

I have recently noticed during driving that my temp gauge would start drop, then would return to its normal position. I'm a gauge watcher, an old habit from less reliable older cars. I thought I had a faulty gauge. Plugged in my OBD Fusion into the port and used my iPhone for a temp gauge. It's not the gauge itself, the coolant temp does drop, well at least according to the reading which is from the same source! I have had my truck since new and I have never noticed this before. Before I take it in and spend the 100 bucks for either a repair or to just be told they can't find anything, has anyone here had the same issue? or is this normal and I just never noticed before? I am wondering if I have a faulty thermostat. Opinions please and thanks for the knowledge.

UPDATE
Issue resolved, what I suspected thermostat is stuck open, under warranty for which I am thankful because its only 100 copay, had they found nothing it would have cost me 220 for diagnostics. Need a rental which is also covered. Therm won't be in till tomorrow. Im anticipating having to pay for antifreeze though, assuming they'll not reuse old since I am at 66K. cannot find anything that says fluids are covered.
Thanks for all the input guys.

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[Grumpaw]

What is the temp range your referring too ? How big is the temp swing ? And, how does the type of driving/speed/load affect the temp swings ?
I have seen the temps swing as much as 20 degrees depending on outside temps while towing, traversing a grade, stop n go traffic, ect.
To add, the normal operating coolant temp is between 195 and 220 degrees. Placing a load, like towing, heavy bed load, climbing a grade, stuck in traffic on a hot day, all can have the coolant temp climb to 230-235 degrees....still nothing to worry about.
Personally, I have hit right at 235 while towing our travel trailer up a 5-7% grade for 4-5 miles. Upon hitting the crest, temps came down quickly, which is normal and good for the Ranger.
Also, while maybe not showing on whatever gauges info you have, the trans fluid temps will be close to what the coolant temps are. Trans temp are not even considered at normal operating temps until it reaches 210-215 degrees.
Need a bit more info other than your original query.

 

[SFB]

What is the temp range your referring too ? How big is the temp swing ? And, how does the type of driving/speed/load affect the temp swings ?
I have seen the temps swing as much as 20 degrees depending on outside temps while towing, traversing a grade, stop n go traffic, ect.
To add, the normal operating coolant temp is between 195 and 220 degrees. Placing a load, like towing, heavy bed load, climbing a grade, stuck in traffic on a hot day, all can have the coolant temp climb to 230-235 degrees....still nothing to worry about.
Personally, I have hit right at 235 while towing our travel trailer up a 5-7% grade for 4-5 miles. Upon hitting the crest, temps came down quickly, which is normal and good for the Ranger.
Also, while maybe not showing on whatever gauges info you have, the trans fluid temps will be close to what the coolant temps are. Trans temp are not even considered at normal operating temps until it reaches 210-215 degrees.
Need a bit more info other than your original query.

I’m referring to coolant temp! I have no other temp gauges on the dash! I am now using a gauge on a program on my phone through a plug in on the OBD2 port. According to my phone gauge it’s not even getting to operating temp! Driving on the freeway this morning it took miles to even get close to the trucks gauge of its normal position . So I think my thermostat might be stuck open. Believe I’m going to have to take it in. It never got to 180. I have an extended warranty. Truck is at 66k miles.

 

[Msfitoy]

What is the temp range your referring too ? How big is the temp swing ? And, how does the type of driving/speed/load affect the temp swings ?
I have seen the temps swing as much as 20 degrees depending on outside temps while towing, traversing a grade, stop n go traffic, ect.
To add, the normal operating coolant temp is between 195 and 220 degrees. Placing a load, like towing, heavy bed load, climbing a grade, stuck in traffic on a hot day, all can have the coolant temp climb to 230-235 degrees....still nothing to worry about.
Personally, I have hit right at 235 while towing our travel trailer up a 5-7% grade for 4-5 miles. Upon hitting the crest, temps came down quickly, which is normal and good for the Ranger.
Also, while maybe not showing on whatever gauges info you have, the trans fluid temps will be close to what the coolant temps are. Trans temp are not even considered at normal operating temps until it reaches 210-215 degrees.
Need a bit more info other than your original query.

I'm a gauge watcher too and even though my OBD gauge read 225 sometimes during very hot days, the dash needle never moves beyond middle...

 

[Grumpaw]

My Scan Gauge lll has coolant and trans fluid temps programed on the first page of gauges. I can tell you the coolant temp goes up fast, usually within 10 miles or so, depending on outside temps, to around the 195 or so area. Trans temp takes a lot longer to rise.
If your coolant temps are at 180 after a prolonged drive then yeah you might want to have it checked out.

 

[SFB]

My Scan Gauge lll has coolant and trans fluid temps programed on the first page of gauges. I can tell you the coolant temp goes up fast, usually within 10 miles or so, depending on outside temps, to around the 195 or so area. Trans temp takes a lot longer to rise.
If your coolant temps are at 180 after a prolonged drive then yeah you might want to have it checked out.

My 10 mile freeway drive home temp never got beyond 183, I believe it should be 200ish correct?

 

[Msfitoy]

My 10 mile freeway drive home temp never got beyond 183, I believe it should be 200ish correct?

Correct...you being in CA, that's very low for highway...

 

[SFB]

My Scan Gauge lll has coolant and trans fluid temps programed on the first page of gauges. I can tell you the coolant temp goes up fast, usually within 10 miles or so, depending on outside temps, to around the 195 or so area. Trans temp takes a lot longer to rise.
If your coolant temps are at 180 after a prolonged drive then yeah you might want to have it checked out.

Mine does not have trans temp, time for a different setup
thank you

 

[RangerBill]

Mine does not have trans temp, time for a different setup
thank you

Have you checked for any DTC codes? I believe that the OBD-II system does checks to see if the thermostat is performing as expected.

 

[RangerBill]

Thermostat operation from the shop manual:
Engine Cooling - System Operation and Component Description

System Operation

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. Coolant is sent from the coolant pump through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core and turbocharger with coolant. The coolant pump, operated by engine rotation through the accessory drive belt, circulates the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant flows through the radiator circuit to transfer engine-generated heat to the outside air.


The engine uses a cold side thermostat. This means the thermostat is located at the lower radiator hose connection to the engine, where coolant enters the engine after being cooled by the radiator. During initial warm-up, the cooler coolant from the radiator quickly closes the thermostat after the warm coolant in the engine opens the thermostat slightly. The thermostat opens and closes several times before the coolant coming from the radiator is warm enough to allow the thermostat to remain open. The engine must run much longer than a vehicle with a hot side thermostat before the thermostat remains fully opened.


The degas bottle holds surplus coolant and removes air from the cooling system. It also allows for coolant expansion and system pressurization, replenishes coolant to the cooling system and serves as the location for service fill.


The thermostat monitor is a function of the PCM and is designed to verify correct thermostat operation. The monitor executes once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, DTC P0125 or P0128 sets, and the MIL illuminates.


Thermostat Opening Temperatures

Starts to open	92°C (197.6°F)
Fully open	106°C (222.8°F)

 

[SFB]

Have you checked for any DTC codes? I believe that the OBD-II system does checks to see if the thermostat is performing as expected.

No DTC codes

 

[SFB]

Thermostat operation from the shop manual:
Engine Cooling - System Operation and Component Description

System Operation

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. Coolant is sent from the coolant pump through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core and turbocharger with coolant. The coolant pump, operated by engine rotation through the accessory drive belt, circulates the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant flows through the radiator circuit to transfer engine-generated heat to the outside air.


The engine uses a cold side thermostat. This means the thermostat is located at the lower radiator hose connection to the engine, where coolant enters the engine after being cooled by the radiator. During initial warm-up, the cooler coolant from the radiator quickly closes the thermostat after the warm coolant in the engine opens the thermostat slightly. The thermostat opens and closes several times before the coolant coming from the radiator is warm enough to allow the thermostat to remain open. The engine must run much longer than a vehicle with a hot side thermostat before the thermostat remains fully opened.


The degas bottle holds surplus coolant and removes air from the cooling system. It also allows for coolant expansion and system pressurization, replenishes coolant to the cooling system and serves as the location for service fill.


The thermostat monitor is a function of the PCM and is designed to verify correct thermostat operation. The monitor executes once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, DTC P0125 or P0128 sets, and the MIL illuminates.


Thermostat Opening Temperatures

Starts to open	92°C (197.6°F)
Fully open	106°C (222.8°F)

No lights and no DTC recorded. Of course I am getting up in age I use to work building and pulling radiators of the old copper and brass design and am a little familiar with the cooling system. I do suspect there are differences these days though but I think a thermostat is still a thermostat. Although you did say the PCM monitors the thermostat, how does it do this?

 

[RangerBill]

No lights and no DTC recorded. Of course I am getting up in age I use to work building and pulling radiators of the old copper and brass design and am a little familiar with the cooling system. I do suspect there are differences these days though but I think a thermostat is still a thermostat. Although you did say the PCM monitors the thermostat, how does it do this?

My assumption is it monitors temperature rise over time taking into account ambient air temperature.

 

[SFB]

My assumption is it monitors temperature rise over time taking into account ambient air temperature.

Thank you

 

[SFB]

I'm a gauge watcher too and even though my OBD gauge read 225 sometimes during very hot days, the dash needle never moves beyond middle...

Mine sits just an RCH under half, ive watched that gauge on mountain roads at over 8K in elevation or going through Needles AZ at an outside temp of 112 and it will barely move, the only move I have ever noticed is the Arizona one where it moved just a another colored hair closer to the half way mark. This truck has an awesome cooling system, this is my only engine issue I have had and I am glad it's not an issue the other way. I really enjoy the ability to put out a question and get helpful responses, a great community.

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