hard downshift
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hard downshift
I pull a 12,000 lb fifth wheel with the F350, v10, 4.30 rear end. I cruise without overdrive at 3000 RPM (~65MPH). On a 6% or higher grade the truck begins slowing down to about 50MPH and slams into a lower gear reving to about 3800 to 4000 RPMs. Is this damaging the engine or transmission? At what RPM does engine welfare become an issue?
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hard downshift
travelinf350
You wrote
At what RPM does engine welfare become an issue?
The V10 loves rpm, and in your shoes, I would not worry about turning it up to 4800 every now and then. Unless you have defeated it, the computer will not let you exceed about 95mph and will not let the engine RPM exceed 4950-5100.
Additionally this is a well designed counterballanced engine that has some rare quirks, but mostly loves to work hard. (with a non-factory temp guage I have never seen the coolant temp climb more than 15F over normal)
You should be worried about the tranny! The 4R100 is notorious for bad behavior under certain conditions and is terribly expensive to replace or repair.
We have had many discussions here and on the SuperDuty forum about OD towing and other Tranny related chats.
Bottom line is that the PCM controls the engine AND transmission via an adaptive learning process. When you tow a load, the PCM will lock, and unlock the Torque converter on slight grades, and if the speed and rpm drop then it will command a downshift.
Not all torque converters have the same RPM drop or gain (Mercon fluid temperatures radically change the viscosity).
If the fluid temp exceeds 230F then it starts to oxidise and looses al LOT of it's lubricity, and also the dampening effect of viscosity. The result being harsher shifts and possible internal wear and damage.
When the TQ is locked, there is no fluid shear happening, and the fluid temp is kept fairly stable by it's own volume and the Factory cooler.
As the TQ starts the unlock dance, the load causes a great amount of torque shear, and the fluid Rapidly gains temerature that the Factory cooler can't shed fast enough.
If you are not using a GOOD trans temp guage, get one!
If you suspect that the fluid is scorched, change it!
If you do these heavy load trips over steep grades often, get an auxillery cooler(preferably with a fan).
At all times keep the Mercon temp under 230F.
Read up on re-training your PCM. Several owners use their trucks mostly for light work and commuting, and think that re-training the computer before a long weekend camping trip helps with hills, and overall fuel milage.
My two attempts at re-training did not yield any MPG increases. I do think that the tendency to rapidly downshift was changed (would hold a gear longer up mild hills).
You wrote
At what RPM does engine welfare become an issue?
The V10 loves rpm, and in your shoes, I would not worry about turning it up to 4800 every now and then. Unless you have defeated it, the computer will not let you exceed about 95mph and will not let the engine RPM exceed 4950-5100.
Additionally this is a well designed counterballanced engine that has some rare quirks, but mostly loves to work hard. (with a non-factory temp guage I have never seen the coolant temp climb more than 15F over normal)
You should be worried about the tranny! The 4R100 is notorious for bad behavior under certain conditions and is terribly expensive to replace or repair.
We have had many discussions here and on the SuperDuty forum about OD towing and other Tranny related chats.
Bottom line is that the PCM controls the engine AND transmission via an adaptive learning process. When you tow a load, the PCM will lock, and unlock the Torque converter on slight grades, and if the speed and rpm drop then it will command a downshift.
Not all torque converters have the same RPM drop or gain (Mercon fluid temperatures radically change the viscosity).
If the fluid temp exceeds 230F then it starts to oxidise and looses al LOT of it's lubricity, and also the dampening effect of viscosity. The result being harsher shifts and possible internal wear and damage.
When the TQ is locked, there is no fluid shear happening, and the fluid temp is kept fairly stable by it's own volume and the Factory cooler.
As the TQ starts the unlock dance, the load causes a great amount of torque shear, and the fluid Rapidly gains temerature that the Factory cooler can't shed fast enough.
If you are not using a GOOD trans temp guage, get one!
If you suspect that the fluid is scorched, change it!
If you do these heavy load trips over steep grades often, get an auxillery cooler(preferably with a fan).
At all times keep the Mercon temp under 230F.
Read up on re-training your PCM. Several owners use their trucks mostly for light work and commuting, and think that re-training the computer before a long weekend camping trip helps with hills, and overall fuel milage.
My two attempts at re-training did not yield any MPG increases. I do think that the tendency to rapidly downshift was changed (would hold a gear longer up mild hills).
Last edited by Fredvon4; May 27, 2003 at 09:23 AM.
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hard downshift
Thanks Fredon4. Very informative. It would be useful if Ford included similar information in its user's manual.
You have given me some peace of mind so I no longer worry about the pistons and other engine parts wrinkling up the hood as they come loose at some high RPM's.
Now the only concern I have is the transmission burning up beneath my seat. (Just kidding).
Thanks again.
You have given me some peace of mind so I no longer worry about the pistons and other engine parts wrinkling up the hood as they come loose at some high RPM's.
Now the only concern I have is the transmission burning up beneath my seat. (Just kidding).
Thanks again.
