Pinned Trans Thermostat observations

I installed a trans cooler right before my S/C was installed a couple years ago.

so, just after this summer I did a drain and fill.

I decided to leave the thermostat pinned open.
because, among other things, I'm running north of 9psi on my Harrop S/C.

now I've got a few months running it in cool-ish Houston weather.

my observations: (pan temps only) I use Scangauge 3

It runs just like it did before.
It has topped out at 172 degrees.
more so - it appears to hold a ~100 degree delta from ambient to pan temp.
today was ambient 36degrees - after 30 hwy miles it topped out at 143 degrees.
when it's 70-ish degrees outside, it maxes ~165-170.
when it was 80 degrees it still maxed at 165-170.

I am wanting to see what 105 degree Houston weather will do.
I suspect it will top out at ~175.

I'm guessing since the puck is still attached, the engine is warming the trans to a certain temp & the external cooler is keeping it to respectable numbers.

now - before all you Transmission experts jump in and say "it's running too cool" - I am kindly asking you to provide proof. technical proof...that what I am doing is detrimental.

...because EVERYTHING I read, you want your transmission to run as cool as possible (within reason)

and EVERY time I see a dead Tundra transmission video, it died because of heat.
EVERY TIME

and...(clutching pearls) I use Valvoline Maxlife.

I'm all ears on the ups and downs of a pinned thermostat.

 

I would agree that running with it pinned will not hurt anything. Possible you will lose .25 MPG with cooler fluid…lol

 

I thought about doing this as well. Here for the long haul to see your results.

 

What did it usually run at without it pinned?

 

195 no matter what.

 

Does it seem like it takes longer for the trans to warm up from cold?

 

Seems to me it would reach operating temperature faster if allowed to cycle and it would still maintain around 200 degrees which is fine. So for a faster warmup, mine is unpinned and allowed to cycle.

 

not really.

it appears the motor, via the puck, is warming the trans.

it will jump to 120-ish, then slowly creep up - depending on ambient temps.

mind you - USUALLY - I am only city driving for 10 minutes & the remainder is all hwy with TC locked in 6th. to/from work.
so that initial warm up may be coming from unlocked TC.

but once I hit the hwy, the trans creeps to ~100 degrees over ambient. I guess because there is no heat being generated by unlocked TC.

 

I monitor pan and converter temp on mine and the converter temp definitely drives the pan temp, especially in stop and go traffic or offroading. It gets warm real quick, then the pan temp creeps up.

 

so, is your pan temp generally 195?

 

I thought about doing this last summer after doing drain & fills, might have to try this out while towing the TT this summer.

I don't know if I buy the "running too cool" thing either, or trucks shift just fine in negative temps before they're warmed up.

 

It seems to top out around there during normal driving or flat highway, like you described. I would say 180-200 is its normal operating range

 

There is a point where heat is beneficial to roast away condensation that occurs. Also really cold fluid is more viscous so it doesn't flow with the same velocity and pressures which means reduced lubrication.

 

Pinned mine right from the get go. As cool as possible is a win

 

genuine questions (not being smarmy in the least):

1. do you think the difference between 175 & 195 is detrimental?

2. water evaporation occurs at all temperature above freezing. The evaporation rate is probably irrelevant between 175 & 195 degrees. agree?

 

No, I think as long as you are above 140, your GTG.
Yes, pretty much agree.

 

If slow crawling, meaning reduced airflow, pinned could cause it to run hotter depending on many other factors, yes or no?

 

Agree with ya there.
I'm not saying they should always run really cold, just that they can without damage

 

I run an extra cooler sequentially with heat exhanger for 11 years in my other non-Toyota Aisin-equipped vehicle. The ATF temp is around 100 F third of the year.

 

Wouldn't the t-stat be fully open in that scenario anyway?? or am I thinking straight, haven't had coffee yet

 

rookie numbers, man! I carry a deep freeze in the bed 24/7 and rerouted my trans lines into it. I'm only happy if my transmission lines , warmed up, are encrusted in a thin layer of ice

 

https://advancedtransmission.com/wh...perature range for,, and, ultimately, failure.


The optimal temperature range for transmission fluid is 175 to 220 degrees. Above that, for every 20 degrees, bad things happen, starting with the formation of varnish at 240 degrees, followed by seals hardening, plates slipping, seals and clutches burning out, carbon being formed, and, ultimately, failure.

 

This is an old Volvo wagon. It puts itself on fire if used continuously for over 2 hours below Arctic Circle. I stop at every major gas station and dump a bucket of ice into the engine compartment when traveling on interstate in summer.

 

Not caffeinated here yet either, but my quick answer is it would obviously depend on the fluid temp which would depend on many other factors like speed, how much blockage is caused by insect buildup on the coil, temperature, etc. I think there could be certain conditions that would actually allow for some cooling to take place if it was left to cycle and obviously, if necessary it remains open. I think it comes down to there are a few pros and cons both ways and the best compromise was to include a thermostat to split it down the middle, so that's what became the design with the option to pin in certain situations where the balance is tilted to one side.

 

Does anyone know the temp when the thermostat starts to open and close or when it's fully open?

 

Don't have anything for the below 175 figure? Just curious what it says if anything. Yes, too lazy to follow the link and afraid it will lead to ten other research topics that will consume another 2 hours. Ha!

 

It's somewhere in the other transmission cooler threads, iirc about 190.

 

Mine has been pinned since I made a similar post asking if it would cause harm sometime last year. I have noticed no ill effects, just cooler temps. My brothers 18’ 2500HD trans fluid temp rarely goes over 160-170 even when hauling his TT over the hot summer months in hilly terrain. If the designers of an HD application transmission find that temp to be sufficient on the high end, then I think I’m just fine having mine operate in that range most of the time by having it pinned open. If I could get a 155-160 degree thermostat for the trans cooler then I would go that route and leave it unpinned but that isn’t an option to my knowledge.

I don’t buy the moisture/condensation issue personally. The transmission is not like an engine that creates moisture as a byproduct of combustion. If there is any moisture it will be very miniscule, and the temps that the transmission fluid reaches even with the Tstat pinned open are more than sufficient to dry it out IMO.

 

It doesn't, lol.

From what I've seen online about colder temps.

1. Leads to harder shifts
2. Can cause leaks due to less viscosity of fluid being forced around
3. Can inhibit OverDrive engaging.

Most articles state 175 (+/- 20 degrees) is perfect.

Living in Texas this seems like a good setup. If he was in Michigan running 140 all the time? Probably not.