E40D T.C. Lockup

[backwoodsboy]

How many of you guys are running a torque converter lockup switch? Any noticable decrease in transmission temperatures?
My truck isn't a tow-pig, but I've noticed trans temps getting up in the 200-220 range while climbing up to my favorite hunting spot. Nothing crazy, just a steep, swtich-back, forestry access road. Basically low speeds, moderate RPM, and 4x4 engaged. My understanding of factory PCM is that the T.C. is unlocked at speeds less than 25mph. So basically all I'm doing on these hour long climbs is compressing my fluid and heating it up. Someone correct me if I'm wrong.
Ran a search, but most of the applications I found were guys towing heavy.

[elrojo63]

well i think part of your problem is the low speeds. You dont have an added tranny cooler right? An electric fan one might be a good idea to keep temps down. I always thought a lockup switch was more for deceleration purposes

[jlarsen]

i tend to just throw it in 4 low if the temp starts climbing. It drops it right down. I do it a lot when I tow up windy dirt roads where speed doesn't matter, but that's a 4R100 and a bigger trans cooler.

[backwoodsboy]

Yeup, I've got an oversized tranny cooler. P.O. installed it when he cooked the second stock E40D and installed a built one. I've given an aux electric one some thought, but if I could fix my issues simply by locking the T.C. that would save me some money.
Jlarsen, how does 4-Lo decrease transmission temps? If anything, it seems that engaging low range would do the opposite. More RPM for the same number of wheel rotations --> more heat. Or maybe I'm missing something.

[jlarsen]

what I'm thinking is higher rpm circulates fluid faster and faster fan speed. It helps. I tow my boat on some ugly dirt roads with steep grades. I know of a lot of transmissions that don't make it up and down. I've tried it in 4 wheel high and didn't make it far before i hit 230. Threw it in 4 low and it dropped to 190 fairly quick and stayed under 200 the rest of the way. Roughly a 10 percent average grade for 7 miles and a 6 percent grade for 10 miles.

[backwoodsboy]

Didn't doubt you for a second my friend. I'm just the kind of guy who likes to know 'why' something happens, not just that it does. Seemed a little counter-intuitive to me.

[jesilvas]

Faster RPMs with an unlocked TC will just heat up faster.
When you do a TC lock, you don't have all that added slippage, therefore eliminating that heat factory. Only thing is, you have to drive it like a manual. Keep RPMs up in your power band. For me with it locked, any RPMs below 1000 and it starts rattling and sounding bad. Just play with it. It's really quick to learn.

[backwoodsboy]

So i was correct with my initial thought, that engaging low range would increase transmission temperatures?
I'm no transmission expert, but it seems to make sense given the TC is a hydrodynamic fluid coupling. More rotations of the flywheel --> more fluid compression --> increased heat.
Given a TC takes the place of a mechanical clutch, keeping rpm's in the powerband makes sense. No complete stops with TC locked, yada yada. I don't plan on using this extensively around town. Mainly on long distance, steep, 4x4 climbing. It would also be nice to use it as an engine brake on the way back down.
Out of curiosity, what kind of switch did you use? single-pole single-throw? A link would be great.
Also heard that locking the TC in first gear can cause some issues, as not enough fluid is circulated to properly cool the tranny?

[jlarsen]

I don't know. It sure seems to work. I just leave it in 4 low manually shift 1st and 2nd most of the time. Maybe it could be that with the higher rpms the fans drawing the air thru the cooler faster. But this is towing. I've never thought about a lock up switch but it might be something to look into

[jesilvas]

There is a write up for a TC lock up mod here.
It's not more fluid compression that makes heat but the clutches slipping against eachother creating more heat and friction.
You don't wanna use the TC lockup when you're slow. You won't have enough RPMs for it to be effective. Just play with it and you'll see what you can and can't do though. I love mine.