How long of a drive? Mine takes a full 20-25m to go from cold (az cold, not actual cold) to 180. Are you sure you hot the 698 and not 678? Maybe your bypass is stuck open? The stated temp is 180 on the hayden so if yours never hits that, Im not sure what you’ve got going on.
Have you guys considered that too cold is bad too? 160 sounds great, but I have to think Toyota put a thermostat and warmer in for a reason. Cold fluid is higher friction and viscosity. I would think there is a very specific reason Toyota went through all the trouble of bypassing their own cooler at a decent engineering complexity cost.
20 years as a Naval Propulsion Engineer including Nuclear Power. We didn't even unlock the main engine throttles until the lubricating oil in the reduction gears hit 120°. So yes I have considered that too cold is bad too. Last week it was twenty below zero here, yes Fahrenheit, and today it is supposed to hit 40° above. I am taking off work this afternoon to take advantage of the heat wave and shoot 5 stand down in Wi. with some retired friends.
When it is below zero I use the remote start to warm the vehicle up first including the ATF. It will only run for 10 minutes before it shuts off but will run another 10 minutes after another restart but will not do it again, 20 minutes is the max runtime. And is usually enough. Many cities have laws against idling even in the cold unless it is below a certain temperature and even then have time limits. Which is why Toyota has the timer on the runtimes for remote start. It was SOP to idle a vehicle in the cold before tree huggers started writing laws, just saying.
But the real reason for the transmission warmer is CAFE (
Corporate average fuel economy) which is US government vehicle mileage standards that are meant to punish car manufactures that don't increase fuel economy. They have been around since the 70's and every year get more punishing and cost the auto makers more money. They pay millions of dollars a year in fines and the projected fines are going up. Right now it works out to $15 for each .1 mpg below the government standard set by politicians, not engineers. Multiply that by the difference in total mpg missed then multiply that by every vehicle they make. It is a lot of money, millions of dollars in fines every year. And one of the reasons new vehicles are going up in price so much.
The ASE has shown that heating ATF can increase mpg by up to 1%. That is a lot of money that they don't have to pay in fines. And that is why there is a transmission heater in the GX.
Once it warms up for the start of 6 weeks of piss poor sledding here I will pin the Tstat open on the heater. Trick is to time the unpin before the cold comes back. And why I went with a 698 instead of a 678. Remote start warm up with idling increases sump temps and is the only time pan temp will be higher than converter temp. 10 minute idle at 15° above zero.
It will still take it ~15 minutes driving to get up to 160° and I am happy with 160°-175° and wish it lived there all year personally.
