Auto box okay at 60mph but getting hot at 70mph

[Dave]

The fluid runs through the cooler all the time the engine is running. Thats where the temp sensor is located, and thats why the trans temp drops quickly once locking up.

 

[Lorin]

The fluid runs through the cooler all the time the engine is running. Thats where the temp sensor is located, and thats why the trans temp drops quickly once locking up.

Dave, this question of flow through the cooler when the TC is locked just isn't well understood I think. If there is flow, then an auxiliary cooler will undoubtedly solve my problem but if there isn't, I need to figure why I'm getting the temps I'm getting. I'd always thought there was no flow, just from what I'd read. Then a few people suggested there is flow all the time. There's even been mention of a flow diagram for the A442F though I can find no other mention of such a thing. But then there's Jon's test he described earlier which seems pretty conclusive in showing there being no ATF flow through the cooler when the TC is locked.

 

[Sarmajornz]

If there was no flow through the cooler when locked up the trans would slowly but surely get cooked especially if the temperature was high after a climb up to a plateau and you then cruised across the top in lockup. The trans would have no effective way to shed heat without flow in lockup.

Mine always cools down very quickly after a hill climb on the open road once I start cruising again.

 

[Jon Wildsmith]

When the TC is locked the trans is no more likely to cook than a manual gearbox. Temp rise with the TC locked is most likely heat soak from a hotter engine.

 

[Sarmajornz]

I think you missed my point there.

Someone has suggested that there is no flow through the transmission cooler when the torque converter is in lockup.

If the transmission gets up to 125C while working hard and with the torque converter unlocked and fluid flowing through the cooler and then when the torque converter goes into lockup, if the flow stops through the cooler the heat in the trans will stay there and cook the transmission.
There must be flow through the cooler when the torque converter is locked up to allow built up heat to be disapated through the cooler especially if the heat is coming from the hotter engine.

My transmission normally runs around the 70 C mark in summer and a little bit cooler in winter.

 

[Jon Wildsmith]

I didn't miss your point. In your example above, when the TC locks, the TC has stopped putting heat into the ATF so the box will start to cool down regardless of flow through the cooler or not unless something else is keeping it warm. The ATF only needs cooling when the TC is unlocked.

If you do get stuck for an explanation Lorin you could try speaking to Rodney at Wholesale, you do have one of their valve bodies etc after all and I always found him very helpful when I was fault finding on mine.

 

[Lorin]

I didn't miss your point. In your example above, when the TC locks, the TC has stopped putting heat into the ATF so the box will start to cool down regardless of flow through the cooler or not unless something else is keeping it warm. The ATF only needs cooling when the TC is unlocked.

If you do get stuck for an explanation Lorin you could try speaking to Rodney at Wholesale, you do have one of their valve bodies etc after all and I always found him very helpful when I was fault finding on mine.

Cheers Jon, I did email Wholesale a while back but still waiting for a reply. Until I saw a picture yesterday of the TC attached to the engine, I had no idea of its size or where it was located in relation to the engine. I also now understand as you say, that if the TC is locked, there's no way for the transmission to generate significant heat. It just reinforces the need for me to get some accurate temps of the engine, coolant and the transfer box when the transmission is at the high temp. This Saturday morning I will get some temp data and see if it starts to make more sense.

 

[Rich Sims]

As Jon says when locked up it shouldn't make much more head than a manual which just rely on air flowing around the box to keep cool, do you have transmission guards restricting flow around your box?

These boxes do have oil pumps which supplies oil to the clutch packs and and to the electric controlled lock up of the torque converter and I assumed that this pump also pumped oil around the cooler but maybe not?

 

[Jon Wildsmith]

The oil pump supplies quite a few circuits including the cooler but like the clutch packs there are valves to control the flow. My understanding is that the cooler circuit is turned off when the TC is locked. Maybe I misunderstood or mis remembered this but it makes sense to me for a few reasons which would then be speculation on my part so I haven't mentioned those

 

[Rich Sims]

you would have though it would be temperature controlled to stop it from running too cold!

 

[Jon Wildsmith]

you would have though it would be temperature controlled to stop it from running too cold!

That's one of the reasons I think no flow through the cooler when locked makes sense. Another reason is I suspect the cooler flow and lockup function are the same circuit to be able to fit all the functionality required up that little shaft the TC sits on but I am guessing / speculating on that one.

 

[Lorin]

Yesterday I confirmed that the radiator is free of any blockages and then drove at 70mph until I saw the gearbox temp at 100C. I then stopped and pointed an IR thermometer at everything I could. The transmission pan was by far the highest temp anywhere at 95C. Nowhere on the engine, radiator or transfer was above 80C.

I also got this reply from Wholesale Autos:

"We have experienced a similar issue on late 5 solenoid A442f transmissions ( no cable ).

In these units we have changed valve bodies and all internals and been unable to resolve the issue until changing the entire case.

Still unable to determine why this was the issue as everything seems ok and suspect some sort of pressure leaking into the cooling circuit but unable to find where.

I have not experienced it on a transmission like yours but it is very similar.

It is likely it will be unresolvable without complete replacement unfortunately.

Regards"

Not the best news! If I keep my speed below 60mph there's no issue - not ideal but potentially the only solution.

 

[Jon Wildsmith]

to me the Wholesale reply is ambiguous as to whether the temperature itself is a problem or simply that you shouldn't usually see the raised temperature on the gauge and the cause of that is thought to be a leak into the cooler circuit which keeps the temp sensor in contact with fresh hot ATF. Perhaps they could clarify that for you?

I'd see if you can check temperatures on other trucks with the IR thermometer to see if 95c is all that unusual allowing for differences in load on the drivetrain (maybe go faster in a less well built truck?). It doesn't seem an excessive temperature to me.

 

[SeaJay]

have you tried increasing the line pressure? the lock up clutch may be slipping with the extra load going from 60 to 70mph and just need a tad more grip. Just a theory, but 5 min job and free

 

[Ctwo]

I had a similar issue with my H61 at high speeds ( well relatively high speeds!), the ATF was getting hot due to the route of the pipes to and from the oil cooler. They both passed really close to the exhaust down pipe from the turbo. Lagged the ATF pipes and fitting an exhaust shield seemed to do the trick!

 

[Lorin]

I had a similar issue with my H61 at high speeds ( well relatively high speeds!), the ATF was getting hot due to the route of the pipes to and from the oil cooler. They both passed really close to the exhaust down pipe from the turbo. Lagged the ATF pipes and fitting an exhaust shield seemed to do the trick!

I hadn't even considered having a look at the route the pipes take. Definitely worth a shot, cheers.

 

[Lorin]

Bit of an update on this. Yesterday I drove for 3.5 hours continuously at 65mph. The transmission temp never went above 80C. Today I drove for 2 hours at 65 and again the temp sat at 80C. I then upped the speed to 70mph for the last 1.5 hours. Over the course of about an hour the transmission temp rose very slowly from 80C right up to 120C before I ran out of road to keep going. I do not know if it would have just kept rising. I then pulled over and using an IR thermometer I checked some temps. Unfortunately the battery died quite quickly meaning I couldn't recheck my readings but those I did get suggested the temp was actually highest right by the temp sender in the ATF line. I got the following readings: temp sender elbow in the ATF line 111C; ATF return line 66C; transfer case 72C; transmission drain plug 88C; pan 84C; engine coolant 76C. Obviously things would have started to cool down the moment I stopped. I'm also worried the IR thermometer might not have got particularly accurate readings given the battery was clearly very low.

I clearly need to get some more reliable temperate readings and wonder if there is any other tool I could use to check the temps other than an IR thermometer? I haven't been able to check any other 80s to see what's normal but I can't believe other transmissions are getting this hot.

have you tried increasing the line pressure? the lock up clutch may be slipping with the extra load going from 60 to 70mph and just need a tad more grip. Just a theory, but 5 min job and free

I will look into this.

 

[kingtom]

Another good tool is the stick on temp tape. Probably got a proper name. You get them for motorcross bikes. Stick them on and they record the highest temp.

 

[kingtom]

231758397507 ebay number. Had a quick look no doubt you can find them cheaper somewhere though my wifi is pretty crap out here. I belive you can get 2 types. Ones that record the highest temp and ones that change with the temperature so can be reused. Hope that makes sence

 

[Shayne]

Check the viscous fan for rub marks , i had this problem though i had to go a little bit faster than 70 to distort the fan cowl allowing it to rub .