Transmission heater and/or thermostat

I currently have the TruCool LPD4589 installed as a replacement for the factory Toyota transmission cooler. Over the summer, this proved to be exactly the amount of cooling I needed to maintain good temps (max 170F) with an unlocked converter up steep grades in the heat, and I definitely don't want to give up any cooling capacity.

Now that winter is rolling in, I find the transmission unable to obtain the minimum operating temperature (120F) during my morning commute in 40-50F ambient. My commute isn't that long, 30 minutes, but its apparently not long enough to get the transmission up to temp. By the time I get to work, sometimes it hits 120F, but mostly sits at 110F.

The obvious choice is to install a thermostat before the cooler and after the radiator, to warm the fluid up to a proper operating temperature during a short commute (clearly the engine radiator currently isn't doing much, and will do even less in the dead of winter).

My only problem with a fluid thermostat is the potential for the device to fail in a closed position, which would cook the transmission if the failure occurred in the summer. I'm sure there's plenty of very reliable thermostats out there for transmissions, but I'd like to entertain some less intrusive options for now. Although I don't mind hearing about anyone that has a transmission thermostat.

My two other ideas were an inline fluid heater (similar to a fuel heater) or one of those silicon heating pads.

The idea there is to have an electric heater hooked up to an ignition hot source, and with a built in thermostat. When I start the truck, the heater turns on, heats up to the thermostat cut-off and turns off.
I couldn't find much in the way of inline electric heaters that aren't for large industrial equipment or heat to 200F. But I did see some options for the silicon heating pads with built-in thermostats. But there are not so many 12 volt versions with a thermostat, unfortunately.

I'm not having great luck finding any good aftermarket thermostats, or 12 volt heating pads.
What are others doing to prevent over-cooling their transmissions?

 

Keep it simple, an old trick is to block off a part of, or all of, the cooler with a plate. Duck tape a piece of cardboard to block off part of the cooler, if that works make a permeant plate from aluminum, summer roles around, remove plate.

 

Thats definitely a solution. Although I would prefer to implement a set it and forget it method (hence why I was avoiding 120v heating pads).

 

You have to mess with it twice a year, if that to much for you the only real option is a thermostat. Wouldn't use heating pads, they are a bit of a fire hazard.

 

https://derale.com/product-footer/fluid-coolers/tempcontrol/fluid-control-thermostats/13011-detail

is your option.

Or replace the trucool with a hayden bypass cooler with a built in thermostat bypass channel

https://www.haydenauto.com/en/produ...oil-coolers/patented-internal-by-pass-coolers


I will say, our 5 speed transmissions are TOUGH see below my PSA post - that 4runner is still chugging along without issue today

 

I did see a lot of those thermostats, but almost all are 180F. It sounds dangerous just opening the thermostat 5 degrees above what the fluids maximum temperature should be.

Also, I read up a little on the Hayden coolers, they use the same "internal pressure by-pass design" as trucool (although trucool calls it LPD, low pressure drop).

 

Those tstats are FULL open by 180, start to open at 160, and are constantly 10% flow through the cooler. 175*F trans fluid temp is no where near max temp, 210 consistent start worrying.

The hayden cooler has an actual thermal opening, trucool simply has different sized openings and works on lower viscosity at higher temps to flow more through greater areas of the cooler, toyota WS fluid is pretty thin even cold so its good to have a thermally actuated thermostat vs relying on viscosity.

 

I'm hesitant about transmission fluid over 175F. I hear the fluids are rated to 230F, but its hard to swallow.
I've also heard the normal operating temperature range for these transmissions is 120F to 175F, never actually seen that in a manual though.

 

I've never seen a transmission run that cool on any vehicle, most run right around the same as the engine coolant temperature (180-200F) during normal operation. As stated above if your under 210F your just fine, even exeeding 220-230 won't instantly fry your trans although you start getting much above that and fluid life starts dropping dramatically.

Modern electronic transmissions make alot of shift and torque converter lockup desicions based off fluid temperature and engine temperature, some (not sure about Toyota) won't go into lockup if the fluid is below a certain temperature in order to aid in bringing the fluid up to temperature faster.

 

I actually think blocking air to the aux cooler is the simplest solution.

Thermostat is a good idea but I always hate adding more items to a crucial pressure line. Less is more.

This also feels like a case of overthinking.

 

Convert to an RC-62 and use standard gear oil.

 

I’m in the same boat, installed a large cooler in series with the factory cooler and temps are hovering around 100-115. Thinking about just removing the aftermarket cooler and leaving the factory one

 

As much as the factory one is sized correctly for daily driving, I drive forest services roads almost every week and need the extra cooling. Pulling steep grades slowly in 2nd gear (and low range) generates a lot of heat.
Before I had to pull over every half mile or so because the temp flying past 210F.

 

Were you looking at pan temp or torque converter output? The later will fluctuate way more and is not an accurate representation of the trans temp.

 

That was the pan temp. My pioneer head unit only supports the pan temp reading. (Plus it doesn't fluctuate very fast).

So I expect that when my pan was hitting 210F on the stock cooler, the converter was cooking some fluid.

 

I run the atf thru the OEM cooler , magnefine filter , derale 180 thermostat , stacked plate additional cooler and then back to transmission. Works great