96TrailSurfer
New member
I have previously posted about ATF temperature spiking in my A340F transmission when I let go of the gas. I think I narrowed it down to a specific issue - the torque converter (TC).
In short, when I am driving at highway speeds (over 80-85km/h) or uphill for any extended period of time, ATF temp is generally fine: 150-200F, measured by a sensor in a t-fitting installed on the flex portion of the outlet pipe.
Once I release the gas to slow down or coast downhill, ATF temp quickly spikes by 50F or more, and if I don't rev back up quickly enough, the ATF light comes on (I believe that happens at around 275F). It happened to me twice this weekend: (1) I was climbing to a mountain pass and, once I reached the top, I had to slow on on the down slope because of slower traffic - temp spiked and ATF temp light came within a 30 seconds; and (2) driving at about 100 km/h on flat highway, had to suddenly brake because of traffic, again, had to pull over to cool it down. Otherwise, I managed temps by keeping it in O/D and lower gear to always have a load on the tranny.
I had the tranny looked at by a shop last week and they didn't find any issues. Flow rate checked out fine, as did the ATF fluid and the filter (this was before my recent drive through the mountains).
Here is what I think. As long as the transmission is under load, the Torque Converter (TC) is engaged. The TC uses ATF as a fluid coupling between the impeller and the turbine. As soon as I let go of the gas, the TC disengages, and the ATF from the TC is released into the housing. ATF inside the TC is generally the hottest ATF in the transmission - hence why the outlet pipe and the stock temp sensor are located right by the TC outlet. What seems to be happening is that the ATF inside the TC is way hotter than it should be, and that's what I see am seeing.
This is reinforced by the fact that, lately, I've felt like the truck has become quite sluggish, as if the transmission is not transferring enough power. Of course, if the TC is not transferring power (kinetic force) from then engine to the transmission, power is lost as heat.
So, has anyone had similar issues with their transmission or the TC? Any ideas? useful links? Can the TC be replaced by itself without replacing the entire transmission?
I did overheat my transmission a year ago when I had blocked flow, could it have damaged the TC?
Things that have checked out OK:
- temp sensor - temp reported correctly
- cooling loop - stock rad in series with an external cooler, plus a fan on the cooler. I also just serviced the fan clutch on the rad (please, no "get rid of the stock rad" comments, unless you think this is somehow causing the issue)
- ATF flow - the shop said flow was fine, to spec.
In short, when I am driving at highway speeds (over 80-85km/h) or uphill for any extended period of time, ATF temp is generally fine: 150-200F, measured by a sensor in a t-fitting installed on the flex portion of the outlet pipe.
Once I release the gas to slow down or coast downhill, ATF temp quickly spikes by 50F or more, and if I don't rev back up quickly enough, the ATF light comes on (I believe that happens at around 275F). It happened to me twice this weekend: (1) I was climbing to a mountain pass and, once I reached the top, I had to slow on on the down slope because of slower traffic - temp spiked and ATF temp light came within a 30 seconds; and (2) driving at about 100 km/h on flat highway, had to suddenly brake because of traffic, again, had to pull over to cool it down. Otherwise, I managed temps by keeping it in O/D and lower gear to always have a load on the tranny.
I had the tranny looked at by a shop last week and they didn't find any issues. Flow rate checked out fine, as did the ATF fluid and the filter (this was before my recent drive through the mountains).
Here is what I think. As long as the transmission is under load, the Torque Converter (TC) is engaged. The TC uses ATF as a fluid coupling between the impeller and the turbine. As soon as I let go of the gas, the TC disengages, and the ATF from the TC is released into the housing. ATF inside the TC is generally the hottest ATF in the transmission - hence why the outlet pipe and the stock temp sensor are located right by the TC outlet. What seems to be happening is that the ATF inside the TC is way hotter than it should be, and that's what I see am seeing.
This is reinforced by the fact that, lately, I've felt like the truck has become quite sluggish, as if the transmission is not transferring enough power. Of course, if the TC is not transferring power (kinetic force) from then engine to the transmission, power is lost as heat.
So, has anyone had similar issues with their transmission or the TC? Any ideas? useful links? Can the TC be replaced by itself without replacing the entire transmission?
I did overheat my transmission a year ago when I had blocked flow, could it have damaged the TC?
Things that have checked out OK:
- temp sensor - temp reported correctly
- cooling loop - stock rad in series with an external cooler, plus a fan on the cooler. I also just serviced the fan clutch on the rad (please, no "get rid of the stock rad" comments, unless you think this is somehow causing the issue)
- ATF flow - the shop said flow was fine, to spec.
