Community Forums

sibe · 10-18-2019, 05:19 AM

I recently added a temp gauge to my trans.. 96 minnie 29rq 460. 35K

I had a huge overheat issue with engine temps running 235-240 on climbing hills,, towing a 4500-6200 load..
since I updated cooling and Exhaust, found a bad Cat.. tows better now. maybe hits 220-225 max eng on a 9% grade after 10min of hard WOT pulling on a 85+ degree day

anyway I have not done hot weather tows since , it is been below 80

Last run was 67-75 ambient.. no trailer, engine stayed 183-195, trans stayed 148 to 161 Ran short 80 mile trip last night 59-63 ambient, Engine 180-190, Trans 141 to 157..

Curious if anyone monitors trans temp..or cares???

I have a HD All Alum custom radiator 20% larger cooling area than stock.
ATF flows into Rad Cooler, then to factory cooler outside and into a final Hayden cooler mounted lower on rad supprt..

hoaxci5 · 10-18-2019, 07:34 AM

Where are you reading your trans temp from? My probe is in the test port on the side of the trans and reads quite a bit higher than yours.

GypsyR · 10-18-2019, 09:27 PM

Sounds pretty low. I'd consider 175F the bare minimum temperature I'd want to see in a transmission. I'm happier with 190-195, just like the engine. Bumping 220 or so with either or both at high stress times doesn't bother me.

One reason for those temperatures is transmissions have condensation problems due to heat cycling, just like engines do. If they are overcooled, the fluid never gets hot enough to "boil off" the moisture. Transmission shops see evidence of moisture in valve body separator plates that are sometimes so rust pitted they have to be replaced. Not something you'd expect to see in a part that stays submerged in oil all the time, but.... I've personally seen some GM's where the dipsticks actually rusted away to the point the handle came off. Since seeing some of such firsthand, I've become a fan of thermostatic bypass valves. They don't allow transmission fluid to circulate through the cooler until its temperature warrants it.
The issue of overcooling is a big problem people who bypass the cooler in the radiator and just use an external cooler. Often such people never keep the vehicle long enough to have to deal with the long term damage they've done and so don't see the problem.
Incidentally, some newer Dodge trucks even have little electric heaters inside the transmission to help get the fluid up to proper operating temperature quicker.

And a good question above. Where you take your temperature reading from makes a big difference. I've run with temperature gauges that I knew were off by as 20 degrees. That was OK because they read consistently and I could add the 20 in my head. Lumping in with inaccurate oil pressure gauges I've also had, not that many personal incidences of goofy temperature gauges.

hoaxci5 · 10-21-2019, 06:12 AM

I wanted to wait until this weekend passed to post my numbers to reconfirm, but like I said my probe is in the test port so it's going to be higher than most external probes.

Normal cruising it was 120 degrees over ambient temp. Working hard it was more like 150 degrees over ambient.

This is on a "new" jasper trans installed 2 years ago, they bypassed the stock radiator, and installed a large (but unsure of rating) external cooler, and kept the already installed (previous owner) secondary inline filter.

TeJay · 10-21-2019, 06:39 AM

We have the 5-speed on a 2013 18,000 lb chassis and just came back from a 4,000 mile trip. I'm reading the trans temp through the data stream on a Scan Gauge. The operating temps run from 170 to a max of 180 degrees.

We departed the middle of August and went from AR to ME. Did a couple of days of driving through NH mountains and hills.

sibe · 10-21-2019, 05:27 PM

I was not happy with my operating temps as reading with a data scan when i had issues on a hill pull we had coolant 235 and a few times 245.. never let loose, I held 245 for almost 10 min, it started to detonate,, i backed off and barely made climb, i pulled off motor was 240,,,and trans temp was 230....

I fixed the blocked cat and over killed the cooling now,, I have had big hills now hit 220/225 and had not read trans temp as i am not good with scanner , my son was with me traveling prior watch the stream etc..trying to figure it out..temps that is..
so on those pulls if i hit 180 to 190 trans i feel safe..

I may ditch the 180/185 hi flow thermo and go back to a 190/195..

i was just outside jocking the MH around the yard/field , idling and stuff for about 20 minutes, trans temp was around 167 from backing up sloped driveway 3 or 4 times... dont ask why lol...

GypsyR · 10-21-2019, 06:53 PM

Vehicle manufacturers figured out back in the 1960's that optimum reliable engine power and efficiency was to be found with a thermostat rated at about 195 degrees. The only time I've seen people use a lower rated thermostat was when they were trying to bandaid a cooling issue.
So going back to the factory recommended correct higher rated thermostat would be an excellent move.