Add engine oil!!!

[Truston Gunter]

I have read that with a gas engine, the powerband is between 3-5K RPMS, this makes sense since the truck has no issues holding speed at 75 while in 4th gear, but once it goes to 5th, rpms drop to 2300 but any little incline or gust of wind or even a change in the road ( I assume some asphalt is not as smooth) causes it to downshift and catch back up.  

[Truston Gunter]

Just now, Grumpy Bear said:

 

More cooler to bring the temperature down under 175 F, preferably @ 160 F, during your heaviest/hardest/worse case tow would lengthen it's life by multiples. Not meaning to step on toes with unsolicited advice but I feel for machines.  

 

Just say'n.  

No stepping on toes here, I welcome any and all info and opinions!!! Down here in Corpus, I don't think I've even had my trans temps that low. Even on my wifes SUV which is a full size it flirts with the 180-190 range 

[Pryme]

When not towing, which is the usual for my truck, my trans sits at 151

[Chuck FB]

24 minutes ago, Truston Gunter said:

Since this was my daily driver up until recently, a few times that I have gone between oil changes without towing and in those circumstances I do not have major oil consumption. It maybe consumed a quart after 6K miles which is typical in my experience. Even in my previous trucks with the 5.3L their was some oil consumption. The trip back is mostly flat and going southbound is "downhill". The slight incline for overpasses causes the truck to downshift which is why I lock out 5th and 6th sometimes.

Very interesting and why I had asked, that is vastly different in consumption but also two very different engine load and over all rpm operating scenarios. I also have to wonder as Grumpy Bear mentions engine oil temps, if the oils raised temperature during high load operation is a factor in its high use. That also makes me wonder if different oil formulations and their varying viscosity at temperature ( higher viscosity ) could assist in preventing as much oil from getting past the rings when the engine is highly loaded. 

 

Overpasses, that makes sense and again my driving along not pulling anything and its night time and unaware of the surroundings, one misses those details. That reminds me of a bridge/overpass by Corpus Christi and I thought it was near Mustang Island but it looked like a wall as in steep as one approached it, that was quite the overpass where ever its located.

[Grumpy Bear]

7 hours ago, Truston Gunter said:

No stepping on toes here, I welcome any and all info and opinions!!! Down here in Corpus, I don't think I've even had my trans temps that low. Even on my wifes SUV which is a full size it flirts with the 180-190 range 

 

I used to live in El Paso so I feel your pain. 180 F water stats used to be standard but they have been climbing for a long time. 207 F+ now That also adds 30 F to trans temperatures when it is fluid to fluid counter current exchange. One of the first things I did was get a colder thermostat. But a fluid to air exchanger works as well. 

 

Oil temps in motors working as hard as your get silly as well and the OEM warning system is like the old idiot lights, "Idiot, you just smoked your motor". LOL That may need a regulated cooler as well. Something under 220 F would be rewarded well. 

 

Temperature oxidizes oil, even great oils. Every 10 C /18 F doubles the rate of oxidation. Your factory OLM should consider 212 F as the base line although that itself is a fairytale not well told. I hold mine between 190 and 200 F. 

 

A work around is very short oil change intervals commensurate with the temperature you actually see. Not so lucky for the transmission for other materials reasons. 

 

Example. Regular schedule OCI is 7,500 miles. I don't think they even have a 'severe schedule anymore but the oil does and that number is 3,000-3,750 miles. Every motor is severe in reality. So lets say you measure your oil temperature with a monitoring system and find that spinning 3K at full load for two hours on a 100 F day gives you an oil temperature of say 250F ( i can easily be much higher). That is about a 40 F spread given the 18 F rule (20 make it easy) you half 3K-3.75K then half it again so your oil life running that hot is about 750 - 950 miles.  

 

Not only does it oxidize but the viscosity is tied to temperature. That 30W is a 10W at those temps. 

 

Slowing your roll would also be huge. Combine with a shorter change. Might be able to skip the coolers. 

 

Now having said all that. Most ignore all of this, never measure and dump the truck before it dies. 

[Chuck FB]

40 minutes ago, Grumpy Bear said:

 

I used to live in El Paso so I feel your pain. 180 F water stats used to be standard but they have been climbing for a long time. 207 F+ now That also adds 30 F to trans temperatures when it is fluid to fluid counter current exchange. One of the first things I did was get a colder thermostat. But a fluid to air exchanger works as well. 

 

Oil temps in motors working as hard as your get silly as well and the OEM warning system is like the old idiot lights, "Idiot, you just smoked your motor". LOL That may need a regulated cooler as well. Something under 220 F would be rewarded well. 

 

Temperature oxidizes oil, even great oils. Every 10 C /18 F doubles the rate of oxidation. Your factory OLM should consider 212 F as the base line although that itself is a fairytale not well told. I hold mine between 190 and 200 F. 

 

A work around is very short oil change intervals commensurate with the temperature you actually see. Not so lucky for the transmission for other materials reasons. 

 

Example. Regular schedule OCI is 7,500 miles. I don't think they even have a 'severe schedule anymore but the oil does and that number is 3,000-3,750 miles. Every motor is severe in reality. So lets say you measure your oil temperature with a monitoring system and find that spinning 3K at full load for two hours on a 100 F day gives you an oil temperature of say 250F ( i can easily be much higher). That is about a 40 F spread given the 18 F rule (20 make it easy) you half 3K-3.75K then half it again so your oil life running that hot is about 750 - 950 miles.  

 

Not only does it oxidize but the viscosity is tied to temperature. That 30W is a 10W at those temps. 

 

Slowing your roll would also be huge. Combine with a shorter change. Might be able to skip the coolers. 

 

Now having said all that. Most ignore all of this, never measure and dump the truck before it dies. 

That got me wondering, just what is the OE thermostat rating of the 6.6 gas and I find slightly conflicting numbers but 187 to 190 seems to be the temp rating. Looking on Rock Auto I see an aftermarket company MotoRad makes a few temps, 187 OE, 180, 174, 160. 

 

I haven't a clue nor is it probably easy to find any spec on the mechanical thermostatic fan hub as to what temp they lock up at but I know years back that the theme tended to be that they never kicked in nearly soon enough so the engine was already well above a comfortable operating temperature by the time it kicked in. I played around with the bimetal spring on a hub to lower the kick in temp and covered over the grill for my tests to see where it would lock up engine coolant temp wise, didn't want it kicking in too low either as a locked up fan takes a lot of power and locked up all the time would put a lot of stress on the fan drive. In that particular truck which was a half ton I could drop in a rad with more cores that the 3/4 etc trucks used as the dimensions were the same. What I could not do is put a 3/4 ton fan on it as the drive is more stout to drive that deeper fan that moves more air on the heavy duty trucks of the time vs the marginally built 1/2 ton cooling system. 

[Another JR]

On 6/27/2025 at 5:33 AM, Grumpy Bear said:

 

More cooler to bring the temperature down under 175 F, preferably @ 160 F, during your heaviest/hardest/worse case tow would lengthen it's life by multiples. Not meaning to step on toes with unsolicited advice but I feel for machines.  

 

Just say'n.  

He has a 2020, and based on the transmission temperatures he describes it sounds like he still has the original 196F cooler bypass valve.  First step to lower transmission operating temperatures might be to change to the later 153F valve and change fluid if the fluid has more than 45k on it. 

Edited June 28, 2025 by Another JR
Clarified I’m talking about transmission temperature

[Chuck FB]

8 minutes ago, Another JR said:

He has a 2020, and based on the transmission temperatures he describes it sounds like he still has the original 196F cooler bypass valve.  First step to lower transmission operating temperatures might be to change to the later 153F valve and change fluid if the fluid has more than 45k on it. 

Good point there that I had not thought of, when I was reading his comment on the empty trucks trans temp running around 185-190 I was comparing it to my truck not being pushed and in the 70's outside and assumed it was due to driving fast on a hot Texas day that it ran that hot, not about this high temp bypass for the cooler. Whoever thought that was a good idea for an HD truck to crank up the trans heat that much, good thing someone at GM pulled their head out of their behind and corrected that. Road testing I've seen with the Ford HD trucks with the 7.3 pulling the same load on the same stretch of highway as a 2024 GM gas so both 10 speeds, the Fords temps were even more insane yet, I can't see that making a Ford trans happy either. 

[Grumpy Bear]

48 minutes ago, Another JR said:

He has a 2020, and based on the transmission temperatures he describes it sounds like he still has the original 196F cooler bypass valve.  First step to lower transmission operating temperatures might be to change to the later 153F valve and change fluid if the fluid has more than 45k on it. 

 

22 minutes ago, Chuck FB said:

Good point there that I had not thought of, when I was reading his comment on the empty trucks trans temp running around 185-190 I was comparing it to my truck not being pushed and in the 70's outside and assumed it was due to driving fast on a hot Texas day that it ran that hot, not about this high temp bypass for the cooler. Whoever thought that was a good idea for an HD truck to crank up the trans heat that much, good thing someone at GM pulled their head out of their behind and corrected that. Road testing I've seen with the Ford HD trucks with the 7.3 pulling the same load on the same stretch of highway as a 2024 GM gas so both 10 speeds, the Fords temps were even more insane yet, I can't see that making a Ford trans happy either. 

 

Both on point! I assumed the HD's didn't use a stat but I am happy to be wrong. I often am when commenting on machines I haven't a deep association with.

 

But caution. Changing it can still uncover the fact that there just isn't enough cooler AND that has no effect on engine oil temperature. Just giving additional information.  

[Another JR]

34 minutes ago, Grumpy Bear said:

 

 

Both on point! I assumed the HD's didn't use a stat but I am happy to be wrong. I often am when commenting on machines I haven't a deep association with.

 

But caution. Changing it can still uncover the fact that there just isn't enough cooler AND that has no effect on engine oil temperature. Just giving additional information.  

Yes, under heavy load and climbing in warm conditions the L8T/6L90 transmission oil temp slowly climbs above the bypass valve set point. People here have reported temperatures going as high as 230F in long climbs pulling a large trailer when they begin the climb at around the earlier 196F valve set point. The new lower 153F set point allows you to begin the climb 40F lower, so your peak at the top of the climb is typically lower because climbs are of limited duration. This allows the arguably under-sized supplemental cooler to be adequate for most users. Depending on climb length and grade, and load and drag, a larger cooler may still be needed for some people even with the lower bypass valve set point if they want to keep their fluid temperature at a level that gives long fluid life. 

Edited June 28, 2025 by Another JR

[Chuck FB]

7 minutes ago, Another JR said:

Yes, under heavy load and climbing in warm conditions the L8T/6L90 transmission oil temp slowly climbs above the bypass valve set point. People here have reported temperatures going as high as 230F in long climbs pulling a large trailer when they begin the climb at around the earlier 196F valve set point. The new lower 153F set point allows you to begin the climb 40F lower, so your peak at the top of the climb is typically lower because climbs are of limited duration. This allows the arguably under-sized supplemental cooler to be adequate for most users. Depending on climb length and grade, and load and drag, a larger cooler may still be needed for some people even with the lower bypass valve set point. 

Same would apply to installing a lower temp engine coolant thermostat as long as it didn't cause issues on the other end with running too cold and causing too low an engine oil temp increased sludge buildup and fuel dilution. Starting at the base of a climb with coolant and engine oil and trans temps well in check give that edge over the same fluids at elevated temps as your beat before you start climbing the hill and yes, turning off the air conditioning before a hill in those more extreme hill and temp conditions. 

[Truston Gunter]

This is my trans temp unloaded, also posted a pic of the ambient temp. At least my MPG's are up! lol

[Chuck FB]

33 minutes ago, Truston Gunter said:

This is my trans temp unloaded, also posted a pic of the ambient temp. At least my MPG's are up! lol

That certainly seems to indicate the trucks system forces the transmission to hold a high minimum operating temperature although that type of ambient temperature is not helping at all !. Lately I was paying attention to what my trans temp would settle in at and of course its a different transmission and more than likely the cooling system and how its set for its minimum trans temp. I was in very different conditions than yourself as it was around 60f outside starting out in the morning heading to town and I noted that it took over 35 miles before it reached the point where it stabilized at around 145f and I was driving at around 60 mph. On the return trip hours later it was 75f out and the trans already warmed up from driving around town between stops and so it came up to the 145 a lot sooner and that is where it hovered around and again I was only doing around 60 mph. What it would do driving faster and in a temp like yours and the air con on full blast, good question. 

 

As to your average and best 25 mile fuel consumption, I'm guessing you wore a very light pair of shoes to obtain the 18.5 best ! 

[Truston Gunter]

I'm sure it's the environment, maybe the humidity specifically, but I've never had trans temps that low. Next time I'm driving in my wife's SUV I'll snap a pic for comparison. It too hovers around 180

[Truston Gunter]

I'm pretty sure the "best" was downhill with the wind at my back!!! lol 12-14 is what I usually get on the highway unloaded