Cooling transmission when idling
07-18-2018, 06:45 AM
#1
Cooling transmission when idling
It's my understanding that when towing, to cool your transmission, you can pull over, shift to neutral and let it idle. When I tow, my transmission is always at 170. That's not overheating. Engine 190 ish, oil 200 ish. Yet when I pull off the interstate and idle at a rest stop for instance, my numbers go up. Engine to about 205, oil 210 ish, trans to 175. Then once back in interstate they go down. Although it takes a while. So idling seems counter intuitive to me. Thoughts?
07-18-2018, 07:51 AM
#2
nathan3306
Hmm, sounds like you may have some air restriction going on. I was always taught, when transmission temps rise to an undesired temp, you should never shut it down. Always, park it and let it idle until the temps come down. With your temps rising as it sits, maybe the coolers are blocked or dirty, and it is not allowing the motor's fan to do its job by cooling them or the fan is no longer pulling in sufficient air. You may want to run some water through the radiators and cooler to clean them off. I wouldn't use a pressure washer but a normal garden hose on a light spray will not hurt the cooling fins.
07-18-2018, 10:50 AM
#3
Just turn the truck off. There's no reason to not shut it down if it's hot. It will begin to cool down immediately and won't get any hotter. The second you pull over and shut the engine off, there's nothing generating heat anymore, and the only thing that can happen is a cooling of all the components.
Vehicles also cool down the most when moving, not idling. The air flow created by the vehicle moving is much more than the fan could ever do when stationary.
Vehicles also cool down the most when moving, not idling. The air flow created by the vehicle moving is much more than the fan could ever do when stationary.
07-18-2018, 12:02 PM
#4
Senior Member
Seems about right based on my testing. It was about 28C outside yesterday and after doing some 'spirited driving' I got my temps up a bit. Cruising around town I was about 5 degrees higher than once I got on the highway and got some good airflow going. Even driving hard on rural roads (80-120 kph) the temps stayed lower than driving slow. As soon as I would slow down they would creep up for a bit, then if I calmed my driving down the would come back down.
07-18-2018, 12:07 PM
#5
Grumpy Old Man
Turning off the overheated engine or tranny can cause coking of the oil, and coked oil can ruin the engine or tranny in a heartbeat. But your example is not about an overheated tranny, just a normal vehicle stopping at a rest stop. Yes, the temps should rise because the slow idle RPM is not enough to pull enough air through the coolers to offset the heat coming off the hot engine block and tranny. But until the tranny temp gets up over about 210°, then it's normal so don't worry about it
With an overheated tranny you don't let the engine idle at a slow idle RPM. You need enough engine RPM that your engine fan is pulling lots of air through the tranny heat exchanger and the radiator. At least 1,200 RPM, and 1,300 to 1,350 RPM is even better bit irritating to listen to. So if your tranny is overheating (more than 225° F, or if the idiot gauge jumps from the green into the yellow zone), then pull over and stop, put the tranny in neutral or park, and elevate the idle RPM to at least 1,200. If your tow vehicle does not have a hand throttle, then you must sit there and twiddle your thumbs while you maintain the elevated engine RPM with your foot, until the tranny temp falls below about 220°. If you don't have a digital tranny temp gauge in your F-150, then wait until the idiot gauge on the dash jumps out of the yellow zone back into the green zone. Yes, it can take a while, and twiddling your thumbs is boring. Been there, done that.
The idiot gauge for tranny temp in Fords is weird. Green means go, but yellow means stop and cool off. Red means your tranny is probably already toast. 225° is the redline, but a Ford tranny engineer will advise you that if you can see the top of the pass up ahead, then continue over the pass. Then stay downshifted to keep the engine RPM elevated as you go down the grade, and your tranny temp will quickly correct itself.
With an overheated tranny you don't let the engine idle at a slow idle RPM. You need enough engine RPM that your engine fan is pulling lots of air through the tranny heat exchanger and the radiator. At least 1,200 RPM, and 1,300 to 1,350 RPM is even better bit irritating to listen to. So if your tranny is overheating (more than 225° F, or if the idiot gauge jumps from the green into the yellow zone), then pull over and stop, put the tranny in neutral or park, and elevate the idle RPM to at least 1,200. If your tow vehicle does not have a hand throttle, then you must sit there and twiddle your thumbs while you maintain the elevated engine RPM with your foot, until the tranny temp falls below about 220°. If you don't have a digital tranny temp gauge in your F-150, then wait until the idiot gauge on the dash jumps out of the yellow zone back into the green zone. Yes, it can take a while, and twiddling your thumbs is boring. Been there, done that.
The idiot gauge for tranny temp in Fords is weird. Green means go, but yellow means stop and cool off. Red means your tranny is probably already toast. 225° is the redline, but a Ford tranny engineer will advise you that if you can see the top of the pass up ahead, then continue over the pass. Then stay downshifted to keep the engine RPM elevated as you go down the grade, and your tranny temp will quickly correct itself.
07-18-2018, 12:36 PM
#6
Turning off the overheated engine or tranny can cause coking of the oil, and coked oil can ruin the engine or tranny in a heartbeat. But your example is not about an overheated tranny, just a normal vehicle stopping at a rest stop. Yes, the temps should rise because the slow idle RPM is not enough to pull enough air through the coolers to offset the heat coming off the hot engine block and tranny. But until the tranny temp gets up over about 210°, then it's normal so don't worry about it
With an overheated tranny you don't let the engine idle at a slow idle RPM. You need enough engine RPM that your engine fan is pulling lots of air through the tranny heat exchanger and the radiator. At least 1,200 RPM, and 1,300 to 1,350 RPM is even better bit irritating to listen to. So if your tranny is overheating (more than 225° F, or if the idiot gauge jumps from the green into the yellow zone), then pull over and stop, put the tranny in neutral or park, and elevate the idle RPM to at least 1,200. If your tow vehicle does not have a hand throttle, then you must sit there and twiddle your thumbs while you maintain the elevated engine RPM with your foot, until the tranny temp falls below about 220°. If you don't have a digital tranny temp gauge in your F-150, then wait until the idiot gauge on the dash jumps out of the yellow zone back into the green zone. Yes, it can take a while, and twiddling your thumbs is boring. Been there, done that.
The idiot gauge for tranny temp in Fords is weird. Green means go, but yellow means stop and cool off. Red means your tranny is probably already toast. 225° is the redline, but a Ford tranny engineer will advise you that if you can see the top of the pass up ahead, then continue over the pass. Then stay downshifted to keep the engine RPM elevated as you go down the grade, and your tranny temp will quickly correct itself.
With an overheated tranny you don't let the engine idle at a slow idle RPM. You need enough engine RPM that your engine fan is pulling lots of air through the tranny heat exchanger and the radiator. At least 1,200 RPM, and 1,300 to 1,350 RPM is even better bit irritating to listen to. So if your tranny is overheating (more than 225° F, or if the idiot gauge jumps from the green into the yellow zone), then pull over and stop, put the tranny in neutral or park, and elevate the idle RPM to at least 1,200. If your tow vehicle does not have a hand throttle, then you must sit there and twiddle your thumbs while you maintain the elevated engine RPM with your foot, until the tranny temp falls below about 220°. If you don't have a digital tranny temp gauge in your F-150, then wait until the idiot gauge on the dash jumps out of the yellow zone back into the green zone. Yes, it can take a while, and twiddling your thumbs is boring. Been there, done that.
The idiot gauge for tranny temp in Fords is weird. Green means go, but yellow means stop and cool off. Red means your tranny is probably already toast. 225° is the redline, but a Ford tranny engineer will advise you that if you can see the top of the pass up ahead, then continue over the pass. Then stay downshifted to keep the engine RPM elevated as you go down the grade, and your tranny temp will quickly correct itself.
Last edited by BlackBoost; 07-18-2018 at 01:04 PM.
07-18-2018, 07:57 PM
#7
Senior Member
It would seem at idle you're way below optimal operating temperature and still pushing all fluids through the cooling system. You should be accomplishing cool down. The quality of your fluids could be suspect.
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07-23-2018, 10:17 AM
#8
Senior Member
Just turn the truck off. There's no reason to not shut it down if it's hot. It will begin to cool down immediately and won't get any hotter. The second you pull over and shut the engine off, there's nothing generating heat anymore, and the only thing that can happen is a cooling of all the components.....
07-23-2018, 11:04 AM
#9
Well, that's physically impossible. As soon as the engine turns off, it stops generating heat and begins to cool down immediately. The heat may SPREAD to other components, but it won't increase. You need something generating heat in order to increase temperature. This is why modern engines continue to pump coolant after your turn off the engine. The blocks and heads are usually made of different metals that cool down a different speeds. Keeping the coolant flowing during cooldown makes sure they cool down at the same rate by circulating the hot coolant around until it's cooled down enough to not matter.
07-23-2018, 01:56 PM
#10
Senior Member
Well, that's physically impossible. As soon as the engine turns off, it stops generating heat and begins to cool down immediately. The heat may SPREAD to other components, but it won't increase. You need something generating heat in order to increase temperature. This is why modern engines continue to pump coolant after your turn off the engine. The blocks and heads are usually made of different metals that cool down a different speeds. Keeping the coolant flowing during cooldown makes sure they cool down at the same rate by circulating the hot coolant around until it's cooled down enough to not matter.
This is correct, in the modern engines coolant will continue to flow and help keep the heat 'balanced' (ie. not allowing one component of the system to rise in temperature). But overall once the engine is off no heat is being made.