How Hot is toooo Hot???

[Full-Timers]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tom N:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Full-Timers:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tom N:
BTW, Workhorse does not recommend extended idling with the 8.1.
-Tom </div></BLOCKQUOTE>
Why? </div></BLOCKQUOTE>

Quoting the Workhorse Gas Manual, "Idling for extended periods and/or low-speed operation." is one factor that creates a severe operating condition and we have enough of those in a motorhome application. </div></BLOCKQUOTE>Thanks Tom but can anyone define “extended period of time”? I usually leave my motorhome running until I make sure it is positioned where I want it, levelers are down and slides are out. I feel this also gives time for the transmission and engine to cool down after a day of driving.

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Full-Timers:
Thanks Tom but can anyone define “extended period of time”? I usually leave my motorhome running until I make sure it is positioned where I want it, levelers are down and slides are out. I feel this also gives time for the transmission and engine to cool down after a day of driving. </div></BLOCKQUOTE>Full-Timers, I do the much of the same routine that you do and I'm sure that it doesn't take hours under maximum load in gear, on a hot road surface to setup the rig.

Allowing the rig to idle in neutral as it's cooling down while your jacks are being extended and rooms set out I don't believe will contribute to an overheat or idle abuse.

There is also a very aggravating condition that your motorhome can not sustain well and that is extended operation in reverse. The cool pack receives hardly any cooling. When I back into my driveway I can typically watch the temp go up on my SGII. Once I stop and place the tranny in Park, I will run in idle until the temp comes down to a comfortable temperature for the engine.

If you consult your owners manual it does address extended idle.

[edgray]

I would just like to add that Allison recommends you pull over to a safe location and run the engine at a "high idle" with the tranny in neutral or park to cool down an overheated transmission. They said this method is better than just turning off the engine because it circulates the overheated fluid thru the cooler and can prevent damage. Overheated fluid should be replaced as soon as possible thereafter. ED

[CJBROWN]

ATF temp over 275 is cooking it and it breaks down and the life is shortened dramatically. I forget where I saw the chart, but for every 10 degrees over about 250 there's a reduction in fluid longevity. When it does breakdown it looses it's lubricating properties and your trans eats itself. I laugh at some of these guys pulling big loads with their half-ton pickups, saying, "oh, it tows it just fine." And their tranny goes out down the road and they blame it on the manufacturer, "dang Fords" or "cheap Chevys".

BTW, this is why we like synthetic ATF, it is more thermally stable and does not breakdown as readily as a standard ATF. In fact, it's about three times more durable.

It's use will generally reduce operating temps as well. But most of us are running castrol transynd in these allisons anyway, so you're covered. If you're not, or you're not sure, have the fluid changed out. I chose to go with amsoil torque-drive in my two allisons, but it's not on their 'approved' list.

[edgray]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I forget where I saw the chart, but for every 10 degrees over about 250 there's a reduction in fluid longevity. </div></BLOCKQUOTE>
CJB: the chart in the chassis guide (pg 68) shows the fluid lifespan in miles:

175* = 100,000 miles
195* = 50,000
212* = 25,000
235* = 12,000
255* = 6,000
at each 20* increase, the life is cut in half again.

at 295* it shows only 1,500 miles, and over 400* shows 30 MINUTES!

This is for "petroleum base " ATF. It also says: "Chart assumes that oil temp remains constant for the miles indicated. Temps that appear for short periods, such as climbing hills, etc., would need to be averaged against normal operating temps to determine actual life expectancy"

I believe in using Transynd or other approved synthetic fluids for the reasons you stated. I've already changed out my first Transynd install, just to insure I'm doing all I can to prevent a failure. ED

[CJBROWN]

Hey, there you go. Thanks Ed.
It's even worse than I remembered!

I guess that's why we were talking about trans temp gauges in another thread. They'll generally run about 150 in normal driving, but not unusual at all to spike to 220-240 pulling a grade with a load. Not using a synthetic ATF in any rig that's under load is just plain dumb, IMHO.

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by CJBROWN:. </div></BLOCKQUOTE>CJBROWN, Heat was one of the motivating factors for me to upgrade to full synthetic transmission fluid (as much as possible).