Threshold to use tow haul mode?

[BluePB]

What would be a reason not to change the mode to Tow/Haul early on in the decision making process?

Fuel economy would be the reason not to. I have towed my 6000 lb travel trailer with my 3.5L Powerboost in normal mode with 10th gear manually locked out and seen about a 10 percent reduction in fuel burn compared to towing in tow/haul mode under similar conditions. Normal mode performance is entirely adequate and there is a modest increase in the amount of transmission shifts as it has to come down to 7 or 8 on hills whereas tow/haul will pretty much stay in 8 at highway speed. BUT I also experienced an overtemp warning one time towing in hot weather on the highway and then coasting down an offramp in regen braking / engine off. The engine does not seem to like the abrubt transition from high power to off., which is probably one of the reasons the tow/haul mode keeps the gas engine running at all times and uses engine braking instead of regen braking even though it is defeating most of the advantage of the hybrid drive train. So now I keep it in tow/haul mode, enjoy the awesome power and performance, and don't worry about the gas. Compared to my previous truck (Chevy 5.3L 6-speed), the 3.5L PB gets better fuel economy running empty but surprisingly worse fuel economy towing. The 3.5L PB power and performance are far better, which apparently does not come free.

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[Samson16]

Fuel economy would be the reason not to. I have towed my 6000 lb travel trailer with my 3.5L Powerboost in normal mode with 10th gear manually locked out and seen about a 10 percent reduction in fuel burn compared to towing in tow/haul mode under similar conditions. Normal mode performance is entirely adequate and there is a modest increase in the amount of transmission shifts as it has to come down to 7 or 8 on hills whereas tow/haul will pretty much stay in 8 at highway speed. BUT I also experienced an overtemp warning one time towing in hot weather on the highway and then coasting down an offramp in regen braking / engine off. The engine does not seem to like the abrubt transition from high power to off., which is probably one of the reasons the tow/haul mode keeps the gas engine running at all times and uses engine braking instead of regen braking even though it is defeating most of the advantage of the hybrid drive train. So now I keep it in tow/haul mode, enjoy the awesome power and performance, and don't worry about the gas. Compared to my previous truck (Chevy 5.3L 6-speed), the 3.5L PB gets better fuel economy running empty but surprisingly worse fuel economy towing. The 3.5L PB power and performance are far better, which apparently does not come free.

Excellent post. Thanks for taking the time.

 

[HammaMan]

Fuel economy would be the reason not to. I have towed my 6000 lb travel trailer with my 3.5L Powerboost in normal mode with 10th gear manually locked out and seen about a 10 percent reduction in fuel burn compared to towing in tow/haul mode under similar conditions. Normal mode performance is entirely adequate and there is a modest increase in the amount of transmission shifts as it has to come down to 7 or 8 on hills whereas tow/haul will pretty much stay in 8 at highway speed. BUT I also experienced an overtemp warning one time towing in hot weather on the highway and then coasting down an offramp in regen braking / engine off. The engine does not seem to like the abrubt transition from high power to off., which is probably one of the reasons the tow/haul mode keeps the gas engine running at all times and uses engine braking instead of regen braking even though it is defeating most of the advantage of the hybrid drive train. So now I keep it in tow/haul mode, enjoy the awesome power and performance, and don't worry about the gas. Compared to my previous truck (Chevy 5.3L 6-speed), the 3.5L PB gets better fuel economy running empty but surprisingly worse fuel economy towing. The 3.5L PB power and performance are far better, which apparently does not come free.

We've come to the conclusion that tow/haul in the PB is to keep the cooling system on. Quite surprised there's not an aux water pump -- in coasting that'd keep the temps even lower not dealing with the ICE.

 

[EricR]

You should see his build thread.
He's a meticulous madman.

Meticulous is the type you want for anyone even remotely related to the word "Pilot".

 

[Samson16]

We've come to the conclusion that tow/haul in the PB is to keep the cooling system on. Quite surprised there's not an aux water pump -- in coasting that'd keep the temps even lower not dealing with the ICE.

You've convinced me. 10% fuel saving is not enough incentive to run hotter than necessary. I run 93 in it so I'm already babying her lol.

I think the aux water pump will come with the PHEV powertrain. Unfortunately the ICE for that will be the 2.3l turbo 4, so the original PB will still be the one to have for big boy towing.

Pure conjecture but fun!

 

[Snooker_ML]

This is a great thread for us PB towers. Not having a paper manual I really haven't read anything on how to use Tow/Haul. I have a big ass travel trailer that it tows like a champ. I live a mile high and my first trip towing along relatively flat I-25 I was shocked to get only 7 mpg using Tow/Haul. I switched to Tow/Haul and it got better (not definitive). Being an engineer I'm now embarrassed to say we finished a 4000 mile trip from Colorado to the NW coast with lots of LONG hills and I did the entire thing in Normal. I'm more of a motorcycle guy and don't know about automatic transmissions and turbos!

I didn't stare at my gauges constantly but the engine and trans temps stayed right in the middle when I did look. I don't know if I overheated anything but Electric Only mode rarely ever came on and I thought "gee it has plenty of power, I don't want it to use higher rpms so just use the Normal shift points" but there is obviously more to it than that.

I also used the highest octane available everywhere (91 here, 93 other states) and driving about 66 mph I got 9.0 mpg for the entire trip.

Now that I understand about the turbo cooling I will use Tow/Haul on my Midwest trip in a month from now and see what my mpg is. Thanks for the info and I hope I didn't damage anything.

What's the best PID to attempt to monitor Turbo temps, simply for knowledge?

 

[Snooker_ML]

I also have questions about downhill high speed Interstate braking with a heavy trailer (7500#). 2023 Powerboost.

On my long trip in Normal mode on long 65 mph downhills, my old school brain was trying to avoid the brake pedal entirely, since the RPM's were at 0, I had no way of knowing when engine braking was occurring, when regen was occurring, or when brake pads were in use.
My typical mode was to not touch the brake pedal, then use manual mode to downshift and I could hear what sounded like engine braking but not really sure. Sometimes the RPMs would show up (ICE ON) so I could verify the gearing (maybe 4k dunno).

My first question is not about reasons I should have been using Tow/Haul, but rather:
1. When you press the brakes (on a long downhill), Is there a way to tell if it is still in Regen or if it is using brake pads?

2. If the ICE is off (RPMs show 0) (on a long downhill) with or without the brake pedal pushed, Does the engine crankshaft turn for engine braking or is it ever decoupled? If you do push the brakes does it switch between regen and brake pads; does it every decouple the engine braking; does it switch back and forth? @Big Dog Daddy asked this once but never heard an answer

My other issue with Tow/Haul is similar to what I've seen others report - it downshifts for passing but then really has trouble upshifting when you let off the gas a lot. Has this been addressed or is it working properly? It's very annoying and sometimes you are stuck in a low gear and cannot speed up the way you need to, so it is unsafe.

 

[Big Dog Daddy]

2. If the ICE is off (RPMs show 0) (on a long downhill) with or without the brake pedal pushed, Does the engine crankshaft turn for engine braking or is it ever decoupled? If you do push the brakes does it switch between regen and brake pads; does it every decouple the engine braking; does it switch back and forth? @Big Dog Daddy asked this once but never heard an answer

This seems to be a mystery of the Powerboost. We need someone to get creative and mount a gopro under their hood and take a ride. ?

 

[Snakebitten]

I would be stunned to find out that the crankshaft was spinning while the tachometer stated 0

Wouldn't you hear the exhaust? It would be an air pump, at least.

But I don't have any mountain to go test a downhill run with a tiny house in Tow.

 

[Big Dog Daddy]

I would be stunned to find out that the crankshaft was spinning while the tachometer stated 0

Wouldn't you hear the exhaust? It would be an air pump, at least.

But I don't have any mountain to go test a downhill run with a tiny house in Tow.

Thinking about it, your right, the crank shaft can't be turning or there would be no need for the belt driven starter.

 

[Oxford_Powerboost]

I also have questions about downhill high speed Interstate braking with a heavy trailer (7500#). 2023 Powerboost.

On my long trip in Normal mode on long 65 mph downhills, my old school brain was trying to avoid the brake pedal entirely, since the RPM's were at 0, I had no way of knowing when engine braking was occurring, when regen was occurring, or when brake pads were in use.
My typical mode was to not touch the brake pedal, then use manual mode to downshift and I could hear what sounded like engine braking but not really sure. Sometimes the RPMs would show up (ICE ON) so I could verify the gearing (maybe 4k dunno).

My first question is not about reasons I should have been using Tow/Haul, but rather:
1. When you press the brakes (on a long downhill), Is there a way to tell if it is still in Regen or if it is using brake pads?

2. If the ICE is off (RPMs show 0) (on a long downhill) with or without the brake pedal pushed, Does the engine crankshaft turn for engine braking or is it ever decoupled? If you do push the brakes does it switch between regen and brake pads; does it every decouple the engine braking; does it switch back and forth? @Big Dog Daddy asked this once but never heard an answer

My other issue with Tow/Haul is similar to what I've seen others report - it downshifts for passing but then really has trouble upshifting when you let off the gas a lot. Has this been addressed or is it working properly? It's very annoying and sometimes you are stuck in a low gear and cannot speed up the way you need to, so it is unsafe.

1) - good news - yes you can tell! If you go into the EV coach screen, it shows a green or white bar while braking. As long as you are in the green zone, you are regen only. If you go outside the green zone either by braking too hard or by running out of regen ability (battery fully charged, this happens fast while towing down a hill), you will see the word “charge” turn white and the bar outside the green zone.

Another more rudimentary way to tell is if you see the engine pop back on while braking, you have fully charged the hybrid battery are the engine has come back on to help the brakes out.

2) As mentioned above, 0rpm is 0rpm. The engine is decoupled from the transmission/wheels. It provides no braking force when off. This is another reason tow haul mode leaves it running. BTW - you STILL get regen benefit in tow haul mode. It will still use regen along with engine braking to stop the truck before resorting to disc brakes.

 

[Snooker_ML]

Thanks for that great info. That also explains why braking on a long hill, I see the engine RPMs turn back on in Normal mode. I knew there was a clutch to disconnect the motor/generator from the ICE, I just didn't know how/when it is deployed.

I also never understood how to use the green zone around your current mph so be thanks!

I was on Tow/Haul with trailer today 95 degree weather and engine temp was 209 and trans was 224.

It's Tow/Haul mode for my next long towing trip in 3 weeks. Then maybe I'll be asking how to get the tranny to upshift when I let off the gas pedal after accelerating - is this a problem for others and/or is there a fix? I haven't used it enough to experience it.

I think the workaround is to either switch to Normal mode for a moment OR to use Manual and up shift

 

[Oxford_Powerboost]

Thanks for that great info. That also explains why braking on a long hill, I see the engine RPMs turn back on in Normal mode. I knew there was a clutch to disconnect the motor/generator from the ICE, I just didn't know how/when it is deployed.

I also never understood how to use the green zone around your current mph so be thanks!

I was on Tow/Haul with trailer today 95 degree weather and engine temp was 209 and trans was 224.

It's Tow/Haul mode for my next long towing trip in 3 weeks. Then maybe I'll be asking how to get the tranny to upshift when I let off the gas pedal after accelerating - is this a problem for others and/or is there a fix? I haven't used it enough to experience it.

I think the workaround is to either switch to Normal mode for a moment OR to use Manual and up shift

To clarify - the green zone im referring to is not the one on the speedometer - I’m not 100% sure on how useful that one is…it is under the “EV Coach” screen in the instrument cluster. You can add this to “MyView.”

tow/haul is intended to keep RPM higher and not upshift as early. Even if you flip to normal mode temporarily, it will likely downshift when you go back to tow/haul. Higher RPM keeps coolant flowing faster and turbo boost down - both decreasing heat in the engine and improving fuel economy. Additionally, maintaining a lower gear reduces the frequency of shifts to reduce transmission heat. I would let it do its thing.
While we expect to see steady state cruising between 1000 and 2000 rpm when empty, 2000-3000 is more the norm when towing decent weight.

 

[Calson]

With my F-150 the GCWR is 16,100 lbs and the curb weight is 4,705 lbs so tow haul mode may be advisable for a trailer load of more than 7300 lbs. As I can easily monitor the ATF temperature there is no need to engage it unless it is warranted.

When trucks started to ship with ATF temp gauges many drivers started to freak out. They were used to watching the coolant temperature and thought that ATF should be in the same temp range which is incorrect.

On a long steep grade with a load my truck's ATF temp will rise but once I start downhill the temp will rapidly fall even on 100+ degree days.

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