What does normal look like... (Jeep JL 3.6 temperatures)

[ChrisW]

As we enter the summer season, @Sam Selim and I have been watching the gauges on our Jeep JL 3.6L 4x4's - which quickly raises a question...what does normal look like?

 

Our hobby means we push cars harder and in unusual conditions, often in ways for which they were not directly designed. A quick glance will tell you if everything is OK (i.e. all the needles are below red-lines), but over time many of us develop a gut feeling for what looks normal and when things are outside of what we would expect to see.

 

I decided on today's drive with @Mark B to snatch a few data points and look at things with a bit more detail:

 

 

 

Couple of major points to relate my gut feelings to what you see:

• The oil pressure on the Pentastar engine varies with RPM, with typically around 30 PSI below circa 3000 RPM, rising to 70 PSI when revving higher - the key point is just to ensure you don't have too low oil pressure (<<30 PSI).
• Oil temperature is a leading indicator: if you push hard, it moves up quickly, and vice-versa. This is to be expected, as engine oil has the dual job of lubricating the engine as well as drawing heat.
• Coolant temperature is a lagging indicator: The coolant temperature rises when pushing the engine, but at a slower rate - it also cools down less quickly too. Also on the Jeep JL, the fan will kick into max power at 110 degC and pull the temperature down again. If you see the temperature going beyond 110 degC and can't hear the fan (or the temperature keeps rising), it's time to do something (like come to a stop!).
• Transmission Temperature: It's a slow mover with plenty of margin to the limit value. However my suspicion is that once this gets hot, it will take some time to cool down again.

 

What does normal look like on your car, and what are the big red flags for you?

[Zubail]

Let me pull data from my car scanner from last week when I was on Jebel Shams and Akhdar

[Zubail]

On my Expedition Timberline, the cooling is simpler than your JL. There is no separate air-cooled transmission cooler from the factory. The gearbox uses a heat exchanger that runs engine coolant against the transmission fluid. This means the ATF basically cannot get colder than the coolant. When the engine gets hot, the gearbox has nowhere to dump its heat. I log data with CarScanner and an OBDLink adapter: ATF temp, coolant, intake air, RPM and boost.

I drove up Jebel Akhdar to the Saiq plateau and back. The trip had three very different parts:

Going up (about 38 min, around 38°C at the bottom): For the whole climb I kept the gearbox locked in 3rd gear manually. I did not let it shift higher. This held the revs around 2500-3000 and stopped the gearbox from jumping between 3-4-5 all the time on the corners. Less shifting under load means less heat, and the car felt more stable. With this, ATF went from 92°C up to 110°C, and coolant reached 108°C. You can see the heat exchanger limit here — ATF and coolant climbed together and stayed only about 2 degrees apart. Intake air went from 39 to 61°C. No knock, everything normal.

On the plateau (about 26 min, around 2000m): This was the easy part. ATF stayed between 77 and 99°C. The air up there is cool, so intake dropped to 36-54°C. The car was relaxed.

Going down (first 8 min): ATF went back up to 106°C, even with engine braking. The interesting part: knock retard jumped to almost 7°. This was on a closed throttle while braking with the engine, going downhill. High revs, hot engine, thin air at altitude. The computer pulled timing to protect itself. I only use Super 98, so it is not the fuel. Just something I did not expect to see going downhill.

What I think is normal, and what worries me:

• ATF below 105°C is fine. 105-110 I watch it. Above 115 I would stop and let it cool.
• Coolant near 100°C in summer is normal for this car. The radiator is working hard but it is okay.
• After a hard climb, the ATF temp can keep rising for a few minutes after you stop. So I let it idle 5 minutes before turning off.

One question for you all: my "Fan Speed Desired" reading stayed at 0% the whole time, even at 110°C. I am not sure if CarScanner is reading the wrong value for the Ford fan, or if something is wrong. If anyone knows the correct fan PID for the 3.5 EcoBoost, please tell me.

The biggest help was holding a gear manually on the long climb. Much less shifting and the car feels more stable.

PS. Car was loaded (Me, wife and 2 kids, and full trunk of different staff)

Edited June 6 by Zubail

[Frederic]

On 6/6/2026 at 4:19 PM, ChrisW said:

As we enter the summer season, @Sam Selim and I have been watching the gauges on our Jeep JL 3.6L 4x4's - which quickly raises a question...what does normal look like?

 

Our hobby means we push cars harder and in unusual conditions, often in ways for which they were not directly designed. A quick glance will tell you if everything is OK (i.e. all the needles are below red-lines), but over time many of us develop a gut feeling for what looks normal and when things are outside of what we would expect to see.

 

I decided on today's drive with @Mark B to snatch a few data points and look at things with a bit more detail:

 

 

 

Couple of major points to relate my gut feelings to what you see:

• The oil pressure on the Pentastar engine varies with RPM, with typically around 30 PSI below circa 3000 RPM, rising to 70 PSI when revving higher - the key point is just to ensure you don't have too low oil pressure (<<30 PSI).
• Oil temperature is a leading indicator: if you push hard, it moves up quickly, and vice-versa. This is to be expected, as engine oil has the dual job of lubricating the engine as well as drawing heat.
• Coolant temperature is a lagging indicator: The coolant temperature rises when pushing the engine, but at a slower rate - it also cools down less quickly too. Also on the Jeep JL, the fan will kick into max power at 110 degC and pull the temperature down again. If you see the temperature going beyond 110 degC and can't hear the fan (or the temperature keeps rising), it's time to do something (like come to a stop!).
• Transmission Temperature: It's a slow mover with plenty of margin to the limit value. However my suspicion is that once this gets hot, it will take some time to cool down again.

 

What does normal look like on your car, and what are the big red flags for you?

This is fantastic information to have and since i am also behind the Jeep wheel, will monitor this closely as well. 

1. 2008 Pajero.

Engine temperatures were always under control as long as there was proper airflow from driving. During idling on hot summer days, you could see the engine temperature creeping up a bit and the AC becoming more stuffy. The only well known issue we faced was high transmission temps when doing a self-recovery. That's why most people install the Aux fan on the tranny cooler.

2. 2008 Xterra and 2012 Pathfinder.

Is equipped with a very confusing gauge on the dash. On the GCC models the needle would be all the way at the bottom, even at 95C. On the US Spec it would be more towards the middle like this:

 

Luckily there was a special function mode that allowed you to monitor the digital readings while off-roading. Normal temp range was 90-96C. Idling was also a bit of an issue, and it would slowly creep up further. Giving some throttle while idling would bring it down back to 90-92C quickly. Lots of people install the Nissan 350Z thermostat that opens a bit earlier. This helps.

On older 4x4's it was often quite obvious that the fan clutch was on the way out, so it would never really go to full speed because the silicon fluid from inside the fan clutch was lost or not on the right level anymore. Can be refilled but for 450dhs it's better to just replace with a new fan clutch. 

3. 1999 Pajero and 1999 Trooper

Hardly ever faced any issues, with temperatures in the low to mid 90's even while pushing. Most likely due to the smaller engines (generates less heat), more space in the engine bay, and manual transmissions.

Of course this was only achieved with new radiator, fan clutch, and properly maintained cooling system.

On the Trooper i've installed an aux fan that helps to pull in some more air while idling in the desert. 

4. Nissan Patrol Safari 2021

Due to the big engine and cramped engine bay, things generally run a bit hot. I've never had issues as the car was almost like new, but i remember seeing 102-104C during a technical drive with Davie in the middle of summer around noon time. Many offroaders that want to push the Patrol will go for bigger fans (Mercedes fan for example) to keep things under control, as well as upgrading the transmission coolers. If thinking about tuning then this definitely becomes a necessity.

 

[Frederic]

Putting ChatGPT to work:

You can almost split these into two generations:

• Traditional off-road engines (1990s–early 2010s): generally operate around 85–92°C. This includes the Patrol TB48, Toyota 1GR-FE family, Xterra VQ40, and older Pajeros.
• Modern gasoline engines (mid-2010s onward): often target 100–105°C during normal driving. Examples are the Pentastar V6 in the Wrangler and Ford's EcoBoost engines, reflecting modern strategies for improved fuel economy and lower emissions.

This is one reason people moving from a Patrol, FJ Cruiser, or Xterra into a modern Wrangler often think the Jeep is "running hot"—when in reality, it's operating exactly where it was engineered to.

[Zubail]

Interesting,  f150 raptor is the only with aux air to oil transmission colling, and what about ranger raptor?

[Frederic]

Same list for Transmission Temps:

There are essentially three generations of thermal management among these vehicles:

• Older Japanese 4x4s (1990s–early 2010s): Coolant 82–95°C, ATF 70–95°C.
• Modern naturally aspirated designs (Toyota 5.7 V8, Prado 250 transmission): Coolant 88–96°C, ATF 80–98°C.
• Modern American turbocharged platforms (Ford EcoBoost) and the Pentastar: Coolant 95–108°C, ATF 85–100°C.

The interesting exception is the Jeep Pentastar: although it's naturally aspirated, its coolant temperature strategy is much closer to Ford's turbocharged EcoBoost engines than to the older Japanese V6s.

 

 

 

Why not just make every engine run cooler?

Cooler isn't always better.

Running too cool can cause:

• higher fuel consumption
• increased engine wear (especially during warm-up)
• poorer oil lubrication due to higher viscosity
• higher emissions
• carbon deposits

Running somewhat hotter provides:

• better thermal efficiency (more energy from the fuel becomes useful work)
• lower friction because the oil reaches its intended viscosity
• cleaner combustion
• faster catalyst light-off

The downside is that higher temperatures reduce the margin before overheating becomes a concern, so the cooling system must be designed accordingly.

[Zubail]

1 hour ago, Frederic said:

ATF 85–100°C.

On 6/6/2026 at 7:54 PM, Zubail said:

There is no separate air-cooled transmission cooler from the factory.

Ecoboost (if not Raptor with external cooling for ATF) temperatures for ATF are very close to Coolant temperature, as it's one cooling system. 

 

 

[_Herman_]

on the FJ I have never seen the coolant over 93, oil I have seen at 95 max.  What worries me is the ATF, on a spirited FB+ that often goes to 105, occasionally higher say 110 and in extreme cases 113-114.  No aux cooler fitted, but it is in the planning. 

The trouble with ATF oil is that high temps cause trouble in the long term, and you don’t see them as you don’t change ATF often nor do you have a dipstick to check the color. 

Below a bit of an indication on what temp does to the oil, forget about ‘lifetime oil’ for this hobby!