Let's take a worse case scenario: what happens to the ATF in a typical automatic transmission if you sit in one spot idling for an hour? Does the fluid not circulate well at idle? Would it circulate better if you increase the engine speed or does it have to be in gear to pump fluid better? How much heat is generated vs driving down the road? My concern is that if the fluid does not circulate well at idle, could the fluid in the torque converter overheat.
ATF and prolonged idling
- Thread starter TallPaul
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It takes about 15-20 seconds to pump a gallon of ATF out of one of the cooler lines and into a jug on my AXOD-E equipped SHO. I do this in Park, so it seems like - at least in my case - there's plenty of fluid going through the tranny to keep 'er cool and lubed.
When I have had temp gauges on ATs, they never ran hot while idling. They needed to be working to get hot, particularly running in the TC operating range.
When idling in gear, the input side of the torque converter will be turning while the output will be stationary. This can generate heat. In my car, though, I've found out there is still a tremendous amount of fluid flow, even at low rpm. I doubt heat would be a problem.
I have heard, though, that certain Dodge Ram trucks have two pumps in the transmission, only one of which is engaged when the trans is in Park. On these trucks, you don't want to idle in park for extended periods. I believe the owner's manual warns against doing so on these trucks.
I have heard, though, that certain Dodge Ram trucks have two pumps in the transmission, only one of which is engaged when the trans is in Park. On these trucks, you don't want to idle in park for extended periods. I believe the owner's manual warns against doing so on these trucks.
Mine are all Fords, but that is a great idea: check the owner's manual. About the last thing anyone thinks to do,
One thing that sparked this thread: I read that (and it is not the same as what I am asking, but may shed light) race cars with auto trannies will rev up to stall in the pits for some kind of testing/prep and then just sit or shut down and that doing that basically cooks the oil in the torque converter whereas if they drove after that it would circulate. Anyway, not going to do that to my vehicles.
Our Isuzu and some Toyotas have transmission temp warning lights. If it comes on the manual says to pull over and idle the car until the light goes off. My assumption is the idling takes the load off the transmission while at the same time continuing to circulate the oil through the cooler (in a part of the radiator usually).
Idling in drive (as in stuck in traffic) is bad news. The converter is making heat due to slip and flow is at a minimum. As the temp goes up, the oil thins and internal leakage increases reducing cooler flow even more. Also if if the ambient is high the engine load + air con will mean higher temps.
Idling in neutral or park is fine - there is almost no heat generated in the trans.
Idling in neutral or park is fine - there is almost no heat generated in the trans.
Dodge trucks WILL blow trannies from sitting at idle IN PARK...the pump will NOT flow the fluid...check the owners manual to see which tranny you have,if you own a Chrysler product.
Patman
Staff member
One day last week it took me almost 90min to get home from work, which is a 25 mile trip. So I was doing a ton of idling while stuck in traffic. I kept an eye on all of my fluid temps via my car's trip computer, and my trans fluid temp never went above 185F. Part of the reason is that I also had my car's computer reprogrammed so that both fans run as long as the car is at low speeds. So my coolant temp never went above 194, which in turn obviously helped keep the trans temp lower too since it's got a tranny cooler. My oil temp barely got above 200 during this time too.
Most transmissions have a completly different circuit that the fluid makes in Park and Nuetral compared to being in gear. Trany's are high pressure systems and fluid flow is always a priority. I do not think you have anything to worry about when ideling in park or nuetral!
Some automatics circulate the oil through more of the transmission in Neutral than Park. Idling in drive should not be a problem as long as the idle speed is low. Yeah There's a lot of churning going on in the converter but with no real horsepower load the fluid temp should remain well within spec and cause no problems.
MolaKule
Staff member
Idling in gear would raise the fluids temperature since you're slipping torque (convertor in stall).
Idling in Neutral or Park, no problem as long the engine coolant doesn't overheat.
AT fluid is always circulating through valve body, TC, and cooler.
Fluid pressure is usually provided by the front pump. Rear pump on some older models is used to determine shift point as fluid pressures will differentiate between front and rear pump.
With electronic controls, an internal pickup sends signal to ECU which determines shift point.
Idling in Neutral or Park, no problem as long the engine coolant doesn't overheat.
AT fluid is always circulating through valve body, TC, and cooler.
Fluid pressure is usually provided by the front pump. Rear pump on some older models is used to determine shift point as fluid pressures will differentiate between front and rear pump.
With electronic controls, an internal pickup sends signal to ECU which determines shift point.
Heat?
I have seen some liken the Torque Convertor to a blast furnance in terms of heat generation.
I have seen some liken the Torque Convertor to a blast furnance in terms of heat generation.
Ed not to be contentious but the combination of converter heat and low flow at drive idle is second only to towing for auto trans damage.
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