Downshifting Etiquette

[jmansfield]

When downshifting/engine braking down a grade what rpm and/or speed are you looking at before downshifting to 2nd and 3rd? Is there a speed/rpm you avoid to put less load on the drivetrain?


For me (98 automatic, 279k miles), I try to keep my downshifted rpm under 3000rpm. So I won’t downshift to 2nd above about 47mph. O/D off I won’t engage above about 65. This is mainly for downhill grades, though sometimes I do it coming to a stop off the freeway too.

 

[phattyduck]

Unless it is a long, sustained hill (or offroading), I generally don't downshift in the auto. I will sometimes turn of OD (so, I guess kinda downshifting) if there is traffic on the freeway and I don't expect to be going over 55mph for a while to get better engine braking or for long downhills at speed.

Otherwise, there isn't much of a reason to use the 2 or 1 shifter positions unless you are starting from a stop and want to limit your top speed while coasting or keep the trans from shifting to control the truck better with the gas pedal. Brakes are much easier to change than transmissions...

I even apply that general rule in my manual trans vehicles. I will often downshift to 4th (or, whatever gear is ~1:1) for slowing down from speed, but won't shift to any gears lower than that until stopped or speeding up again. So, just coast down to ~1500 rpm in whatever gear, then push in the clutch and use the brakes down from there. In that case, brakes are cheaper/easier to replace than synchros and clutches. Racetracks are the only place where I use engine braking aggressively.

-Charlie

 

[gamefreakgc]

Lower RPM's while going downhill would be less strain on the drivetrain since there's less resistance. Are you talking about coming down the pass on I-80 per chance? I see you are in California. At highway speeds I normally just keep it in O/D or "4th" gear but then again I don't engine brake in an automatic.

Now when I had one with a 5 speed, I would downshift to 4th at highway speeds and downshift to 3rd if I was going less that 50 MPH. But that's a 5 speed so you've got an extra gear to work with. The auto gears are so large it's a dramatic increase in RPM's from one to the next.

 

[jmansfield]

Lower RPM's while going downhill would be less strain on the drivetrain since there's less resistance. Are you talking about coming down the pass on I-80 per chance? I see you are in California. At highway speeds I normally just keep it in O/D or "4th" gear but then again I don't engine brake in an automatic.

Now when I had one with a 5 speed, I would downshift to 4th at highway speeds and downshift to 3rd if I was going less that 50 MPH. But that's a 5 speed so you've got an extra gear to work with. The auto gears are so large it's a dramatic increase in RPM's from one to the next.

I haven’t gone down the I-80 but yea, same idea — long mountain grades. Coming down the 120 from Tioga Pass was a recent event

 

[jmansfield]

Nobody here engine brakes on an automatic?

I get that an automatic trans is a lot more complicated but i don’t see an issue with it. Manual says nothing about not doing it, and not having a direct coupling between engine and trans seems further advantageous

 

[thennen]

Nobody here engine brakes on an automatic?

I get that an automatic trans is a lot more complicated but i don’t see an issue with it. Manual says nothing about not doing it, and not having a direct coupling between engine and trans seems further advantageous

Looks to me like this whole discussion has been about automatic transmissions. As for myself, where I am in Ohio, I almost never find myself in a situation where engine braking (downshifting) is beneficial. I might do so on a long downhill grade so as to stay off the brakes, but not much of that here.

 

[phattyduck]

Nobody here engine brakes on an automatic?

Unless there is a situation where you risk overheating the brakes, there is no reason to downshift the automatic trans manually. The reason you have to press the button on the top of the shifter is that there is a 'risk' to the operation and Toyota wants to make sure you don't accidentally do it.

If you have a good reason, go ahead and do it. Slowing down for your average stop is not a good reason - there is a nice wide pedal right there for you to use to slow the truck down...

-Charlie

 

[JMat]

Nobody here engine brakes on an automatic?

I do all the time... I spend a lot of time in the the mountains and Tioga Pass is one I do on a pretty regular basis, even with the 199mm TBU I downshift. If your behind a slow camper in a long line of cars going down Tioga Pass Rd and only use your brakes you're likely to over heat your brakes pretty quickly.

My general rule of thumb is to have the RPM's under 2800(never over 3000), when I downshift, and at 2500(or below) even better. I lived in the mountains and commuted to work for 15 years, got my rig when it had 30k on it and it now has 350k and it's none the worse for wear.

On a side note I almost never rev the engine over 3500 and that's really more like 3000. The only time my rigs 3.4l gets over 3500 is, ironically) when I'm trying to pass someone on a mountain road.

 

[MSRP.]

Rarely have to panic stop with the 4R being taller than most vehicles, but if I can see ahead that everyone is coming to an abrupt halt, yes, I'll throw off O/D just to buy a few extra feet of stopping distance.

 

[gamefreakgc]

Nobody here engine brakes on an automatic?

I get that an automatic trans is a lot more complicated but i don’t see an issue with it. Manual says nothing about not doing it, and not having a direct coupling between engine and trans seems further advantageous

I think the reason why many don't is the torque converter. Yes, there's no direct coupling like a manual has but the torque converter under some circumstances can generate a lot of heat. Heat is not your friend in an auto. I don't know enough about transmission operation to say if downshifting with no engine load will create extra heat for the torque converter or not.

 

[jmansfield]

I think the reason why many don't is the torque converter. Yes, there's no direct coupling like a manual has but the torque converter under some circumstances can generate a lot of heat. Heat is not your friend in an auto. I don't know enough about transmission operation to say if downshifting with no engine load will create extra heat for the torque converter or not.

I have watched on my obd ii reader that downshifting dropped coolant temps and trans temps (I have stock radiator where trans fluid is cooled inside of the coolant). The effect was substantial, the lowest coolant temps I’ve seen are during downshifting.

I’m sure you can run into other instances where you may not see that. However it makes sense that downshifting will increase rpm, increasing fan flow on radiator, yielding better cooling

 

[Charlievee]

Down shifting etiquette? Like when some one is riding your rear and you go 5th to 3rd no brake lights to piss them off? Nope, never done it. Lol.

 

[jmansfield]

I do all the time... I spend a lot of time in the the mountains and Tioga Pass is one I do on a pretty regular basis, even with the 199mm TBU I downshift. If your behind a slow camper in a long line of cars going down Tioga Pass Rd and only use your brakes you're likely to over heat your brakes pretty quickly.

My general rule of thumb is to have the RPM's under 2800(never over 3000), when I downshift, and at 2500(or below) even better. I lived in the mountains and commuted to work for 15 years, got my rig when it had 30k on it and it now has 350k and it's none the worse for wear.

On a side note I almost never rev the engine over 3500 and that's really more like 3000. The only time my rigs 3.4l gets over 3500 is, ironically) when I'm trying to pass someone on a mountain road.

Yeah, on a day to day basis I try to have my downshifted rpm under 2500 as well. In more dire situations like coming down a mountain pass with a lot of weight I will try and stay under 3,000.

Driving the car in general I accelerate gradually, don’t ever like my rpms above 3000 except for the occasional clearing out of the cobwebs

 

[Bad Luck]

I just use my brakes if coasting doesn't work for me. Brakes are meant for stopping. Engine/transmission meant for going. I don't want to confuse the gremlins in my 4Runner any more than they already are.

 

[toyotaspeed90]

No reason to do it. A bit baffled how some claim lower temps. Higher rpms might turn the engine (and waterpump) at a faster rate but it's also generating more heat.

Further the speed of your fan should be determined by the fan clutch not engine rpm.

Lastly flow through the radiator is greatest while moving - the fan is for very low speeds or idle/stopped. Increased fan speed is actually a resistance for air naturally flowing through the radiator.

Downshifting for engine braking isnt all that effective on an automatic as the resistance is far lower (nature of a torque converter) than a manual with a clutch.

Our T4R is a manual so I shift as needed for power. Our LX470 is obviously an auto. Only times I've felt the need to control shift is in deeper snow / steep hills or heavy towing on steep hills. That's more about power band/delivery than braking.

 

[jmansfield]

No reason to do it. A bit baffled how some claim lower temps. Higher rpms might turn the engine (and waterpump) at a faster rate but it's also generating more heat.

Further the speed of your fan should be determined by the fan clutch not engine rpm.

Lastly flow through the radiator is greatest while moving - the fan is for very low speeds or idle/stopped. Increased fan speed is actually a resistance for air naturally flowing through the radiator.

Downshifting for engine braking isnt all that effective on an automatic as the resistance is far lower (nature of a torque converter) than a manual with a clutch.

Our T4R is a manual so I shift as needed for power. Our LX470 is obviously an auto. Only times I've felt the need to control shift is in deeper snow / steep hills or heavy towing on steep hills. That's more about power band/delivery than braking.

Maybe you don’t go down many mountain grades. There’s absolutely a reason...

Regarding temps, I encourage you to try it yourself sometime, same grade once downshifted once not, you’ll get cooler temps. Not sure what speed fan clutch engages/disengages but whether it’s fan speed or water pump flowrate

 

[toyotaspeed90]

Maybe you don’t go down many mountain grades. There’s absolutely a reason...

Regarding temps, I encourage you to try it yourself sometime, same grade once downshifted once not, you’ll get cooler temps. Not sure what speed fan clutch engages/disengages but whether it’s fan speed or water pump flowrate

You've clearly never played with highly modified vehicles with cooling issues.

Higher rpm always = more heat unless your cooling system cannot properly cool the engine when stopped/idle.

Overheating at speed because of lack of airflow from the fan isnt a thing. It just isn't. Overheating at idle while stopped (when a fan matters - as in, the fan is doing all of the work to pull or push air) due to lack of CFM is a thing.
Likely, higher rpm (so long as your cooling system is up to snuff) does not translate to higher cooling capacity.

Fan clutches are mechanical based on temp and/or engine speed (disengages at higher speeds and engages at higher temps).

The ONLY caveat i can come up with would be that your cooling system is struggling, the tstat isnt ever closing, and the root problem is masked by the higher coolant volume moving through the radiator at speed. However, that means theres another problem.

 

[jmansfield]

You've clearly never played with highly modified vehicles with cooling issues.

Higher rpm always = more heat unless your cooling system cannot properly cool the engine when stopped/idle.

Overheating at speed because of lack of airflow from the fan isnt a thing. It just isn't. Overheating at idle while stopped (when a fan matters - as in, the fan is doing all of the work to pull or push air) due to lack of CFM is a thing.
Likely, higher rpm (so long as your cooling system is up to snuff) does not translate to higher cooling capacity.

Fan clutches are mechanical based on temp and/or engine speed (disengages at higher speeds and engages at higher temps).

The ONLY caveat i can come up with would be that your cooling system is struggling, the tstat isnt ever closing, and the root problem is masked by the higher coolant volume moving through the radiator at speed. However, that means theres another problem.

Lot of bad information here...

For starters... No, I’ve replaced my radiator and thermostat, I know how the cooling system works and no, the fact that I’m seeing cooler temperatures is not a sign of a greater problem. My car runs a cool 186-188 during normal operation (thermostat is 82C). It makes perfect sense, you’re just being stubborn.

The fan clutch engagement lessens with increased rpm (more on that to follow) and yes, you will generate more frictional heat at a higher rpm. However, when going downhill in gear, especially a higher gear, your ECU will cut fuel from the injectors if the throttle is not engaged and the rpm is above a certain speed. That’s why it’s more fuel efficient to go downhill in gear than in neutral. In neutral the injectors must continue to burn fuel to keep the engine from stalling. So yes you get more frictional heat but you get less combustion heat. So no, higher rpm does not always mean more heat generated, only more frictional heat. Also, your cooling capacity overall does increase at higher rpm. Ultimately your cooling capacity is what dictates whether or not your car will overheat (talking extremes here). You don’t blow head gaskets because you’re running a car at 2500 rpm lol. The engine is always generating heat, the cooling system is what saves it. Obviously this is the extreme end, but you get the idea. Increasing rpm on the water pump will also help cooling as you’re passing more mass flow through the block and the radiator (even after the thermostat closes there’s slight bypass via jitter valve). Finally, the fan clutch is not an on/off switch. At higher rpms your fan still spins faster, the slip just increases. You seem to imply that above a certain speed my fan will not go any faster. Simply not true.

Anyway, whether or not the engine is getting cooler is a totally moot point, maintaining control of your vehicle and avoiding warping your rotors is the real reason you do it. Going down a grade, especially on a one lane road with a full load or in icy conditions, you absolutely can not ride your brakes. The people on here claiming there’s no reason to do it clearly have not experienced these conditions. If there were no reason to do it or if it were bad for the trans, do you really think the engineers would let me select a lower gear? Don’t you think the FSM would say something about it? C’mon lol. There’s absolutely no harm in downshifting with an automatic, try it sometime.

 

[Bad Luck]

Lot of bad information here...

For starters... No, I’ve replaced my radiator and thermostat, I know how the cooling system works and no, the fact that I’m seeing cooler temperatures is not a sign of a greater problem. My car runs a cool 186-188 during normal operation (thermostat is 82C). It makes perfect sense, you’re just being stubborn.

The fan clutch engagement lessens with increased rpm (more on that to follow) and yes, you will generate more frictional heat at a higher rpm. However, when going downhill in gear, especially a higher gear, your ECU will cut fuel from the injectors if the throttle is not engaged and the rpm is above a certain speed. That’s why it’s more fuel efficient to go downhill in gear than in neutral. In neutral the injectors must continue to burn fuel to keep the engine from stalling. So yes you get more frictional heat but you get less combustion heat. So no, higher rpm does not always mean more heat generated, only more frictional heat. Also, your cooling capacity overall does increase at higher rpm. Ultimately your cooling capacity is what dictates whether or not your car will overheat (talking extremes here). You don’t blow head gaskets because you’re running a car at 2500 rpm lol. The engine is always generating heat, the cooling system is what saves it. Obviously this is the extreme end, but you get the idea. Increasing rpm on the water pump will also help cooling as you’re passing more mass flow through the block and the radiator (even after the thermostat closes there’s slight bypass via jitter valve). Finally, the fan clutch is not an on/off switch. At higher rpms your fan still spins faster, the slip just increases. You seem to imply that above a certain speed my fan will not go any faster. Simply not true.

Anyway, whether or not the engine is getting cooler is a totally moot point, maintaining control of your vehicle and avoiding warping your rotors is the real reason you do it. Going down a grade, especially on a one lane road with a full load or in icy conditions, you absolutely can not ride your brakes. The people on here claiming there’s no reason to do it clearly have not experienced these conditions. If there were no reason to do it or if it were bad for the trans, do you really think the engineers would let me select a lower gear? Don’t you think the FSM would say something about it? C’mon lol. There’s absolutely no harm in downshifting with an automatic, try it sometime.

So you agree that engine braking will create more heat then? "However, when going downhill in gear, especially a higher gear, your ECU will cut fuel from the injectors if the throttle is not engaged and the rpm is above a certain speed. That’s why it’s more fuel efficient to go downhill in gear than in neutral. In neutral the injectors must continue to burn fuel to keep the engine from stalling. So yes you get more frictional heat but you get less combustion heat. So no, higher rpm does not always mean more heat generated, only more frictional heat."

Higher flow rate does not always equate to better cooling. If this were the case then a cooling system without a thermostat would stay cooler because there is no restriction. Half of the job of the thermostat is to regulate the flow of coolant to allow the coolant enough time to absorb the heat from the motor. Coolant/water mixture doesn't absorb heat as quickly as pure water does. "Increasing rpm on the water pump will also help cooling as you’re passing more mass flow through the block and the radiator (even after the thermostat closes there’s slight bypass via jitter valve)."

You will reach an rpm range where the fan clutch will slip at a higher rate than the engine rpm increases effectively limiting the fan clutch speed. "Finally, the fan clutch is not an on/off switch. At higher rpms your fan still spins faster, the slip just increases. You seem to imply that above a certain speed my fan will not go any faster. Simply not true."

It's safer in low traction conditions to use your brakes. The reason behind this is your brakes have ABS/Stability controls and your engine does not. If your engine braking exceeds your traction then there is no automated controls to help regain traction by increasing wheel speed. "Going down a grade, especially on a one lane road with a full load or in icy conditions, you absolutely can not ride your brakes. The people on here claiming there’s no reason to do it clearly have not experienced these conditions."

 

[jmansfield]

Higher flow rate does not always equate to better cooling. If this were the case then a cooling system without a thermostat would stay cooler because there is no restriction. Half of the job of the thermostat is to regulate the flow of coolant to allow the coolant enough time to absorb the heat from the motor. Coolant/water mixture doesn't absorb heat as quickly as pure water does.

You will reach an rpm range where the fan clutch will slip at a higher rate than the engine rpm increases effectively limiting the fan clutch speed.

It's safer in low traction conditions to use your brakes. The reason behind this is your brakes have ABS/Stability controls and your engine does not. If your engine braking exceeds your traction then there is no automated controls to help regain traction by increasing wheel speed.

If all else is equal, more flow always makes better cooling. Always. It’s given by the equation Q=mcdT. m is mass flowrate, Q is heat. (Again, all else equal here). The thermostat will regulate flow rate rate of the coolant along with the water pump. You always have a very slight bypass of the thermostat with that jitter valve, then once it cracks you get a lot less dP across the valve (more flow if the pump is running). So the rpm on that water pump matters to coolant flow rate (along with thermostat).

Do you have some fan clutch data? Everything I’ve read says even fully disengaged you get 20/30% of shaft speed, which tells me fan rpm is never truly capped.

You won’t have any brakes to stop you in the first place if you ride them down an entire grade! That’s the entire point lol. And my point still stands, it’s even safer to be in lower gears in low traction scenarios. Why do you think your transfer case further gears you down upon engaging 4Lo lol.