Calling all thoose with the B&M cooler
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octanejunkie
Elite Member
The trick with trans fluid is to run it around the same temp as the engine, which is why it goes through the radiator for cooling. According to most trans manufacturers, the place to measure trans fluid temp is in the pan, before the fluid goes to the pump.
In my experience with hot rods, aux trans coolers are usually installed inline after radiator cooling. By the time the pre-set probe in the B&M cooler reads 180° (supposedly set for 175° according to B&M), which is below engine operating temperature, the fluid in the pan is probably much hotter. So the measurement after the radiator is almost useless; in my experience.
In other cars I've added the probe from an adjustable thermostatic relay (like https://amzn.com/B000C39C72) and wired the ground of the B&M or other fan-cooled, fin-type cooler and power he fan off a non-switched fused battery connection or another relay. When used with a trans temp gauge reading the temp of the fluid in the pan, you can adjust the fan on on/off temp on the aux cooler to help out as soon as needed.
I also run a trans temp gauge in most customs, but factory vehicles rarely have trans temp gauges for drivers, but many do sense it via the ECM. in the absence of a gauge, an infrared no-touch digital temp gun pointed at the pan after driving will also work, but requires pulling over to read, but then again so does adjusting the relay's set point.
In my experience, the only time additional trans cooling should be needed on a factory style vehicle is when pulling heavy loads for extended periods of time. It is possible to over-cool a transmission,
Obviously if 4-wheeling, I would consider a deeper pan with more fluid volume (more fluid means cooler fluid) in addition to an aux cooler.
Disclaimer: I do not have direct experience with the 4runner and transmissions/usage, but I do have vast custom and hot rod experience which is where this information and advice from experience come from. Hope I'm not making mistakes posting this.
In my experience with hot rods, aux trans coolers are usually installed inline after radiator cooling. By the time the pre-set probe in the B&M cooler reads 180° (supposedly set for 175° according to B&M), which is below engine operating temperature, the fluid in the pan is probably much hotter. So the measurement after the radiator is almost useless; in my experience.
In other cars I've added the probe from an adjustable thermostatic relay (like https://amzn.com/B000C39C72) and wired the ground of the B&M or other fan-cooled, fin-type cooler and power he fan off a non-switched fused battery connection or another relay. When used with a trans temp gauge reading the temp of the fluid in the pan, you can adjust the fan on on/off temp on the aux cooler to help out as soon as needed.
I also run a trans temp gauge in most customs, but factory vehicles rarely have trans temp gauges for drivers, but many do sense it via the ECM. in the absence of a gauge, an infrared no-touch digital temp gun pointed at the pan after driving will also work, but requires pulling over to read, but then again so does adjusting the relay's set point.
In my experience, the only time additional trans cooling should be needed on a factory style vehicle is when pulling heavy loads for extended periods of time. It is possible to over-cool a transmission,
Obviously if 4-wheeling, I would consider a deeper pan with more fluid volume (more fluid means cooler fluid) in addition to an aux cooler.
Disclaimer: I do not have direct experience with the 4runner and transmissions/usage, but I do have vast custom and hot rod experience which is where this information and advice from experience come from. Hope I'm not making mistakes posting this.
Last edited:
mtbtim
Elite Member
Since I've started monitoring my trans temps, I realized you can definitely spike your temps when climbing long grades or mountain roads. You don't even have to be carrying a ton of weight to do it either, but carrying a bunch of gear or people definitely makes it worse.
I recommend that anyone who drives up in the mountains, goes 4wheeling, or tows, add an external cooler in series with the stock cooler. The external cooler will drop your temps around 20 degrees but it will ultimately depend on the cooler size you install. The other thing that everyone should know is turning off the overdrive when climbing grades or mountain roads and driving around 60 mph or less will lower your temps by another 20+ degrees by locking up the torque converter.
And yes, I agree that you can overcool your trans. This is something I think people who have bypassed their stock cooler in the radiator, and either live in colder climates or visit cold climates maybe didn't give enough consideration before they made their decision. The stock cooler in the radiator helps raise the trans temp quicker because the cooler is bathed in the engine coolant.
phattyduck
Elite Member
This is a point I see a lot... but it is at the BOTTOM of the radiator, where the coolant is at its coldest. Also, the radiator doesn't even get (much) coolant flow until the thermostat opens, which is after the coolant gauge reads normal operating temps (or even a Scangauge reads operating temps). Also, the temps at the bottom of the radiator will vary widely with outside temps because flow through the thermostat will vary widely - low flow when cold outside, leading to possibly more widely varying temps at the bottom of the radiator...
It would be interesting to see actual numbers on this (radiator outlet water temps).
-Charlie
octanejunkie
Elite Member
+1 [MENTION=139000]phattyduck[/MENTION]
I agree the toyota tank placement seeming not-ideal, but the factory seems to find it acceptable and it works for most all passenger applications.
FWIW, I have taken all my customs to cross-flow rads, and the trans cooler is always on the cold side, so it makes sense that the cooler on a down-flow rad is on the cooler bottom - also cleaner and safer for plumbing hot oil.
I would love to see if anyone has done a BMW style rad swap on a 4runner by installing a 1-1/2" single row cross-flow radiator with electric cooling fans. It is an awesome cooling setup.
mtbtim
Elite Member
If you monitor your coolant and trans temps, you know that the engine coolant rises very quickly while the trans temp can take a while to reach normal operating temperature, which according to the FSM is around 158-176. How much the trans cooler in the radiator helps rise the trans temp, who knows. But, logic tells you it has to have some effect if you know the principles of heat transfer. The hot engine coolant is going to transfer heat to the trans cooler and thus the trans fluid via conduction.
If you visited the websites of companies that sell trans coolers, they never advise to take the stock cooler out of the equation and one of the reasons is because you lose the benefit of heating the trans fluid to an optimum operating temperature quicker especially when operating in cold climates.
phattyduck
Elite Member
Engine coolant temp - at the engine - does rise quite quickly. Then the thermostat can finally start opening and heat the radiator. The engine temp will be at/near operating levels before the radiator gets any warm/hot coolant.
For the engine oil cooler on the block, this means it is a temperature stabilizer (coolant is always flowing through it, at engine temp). For the trans fluid in the bottom of the radiator, not so much.
I would imagine the main reason whey aftermarket cooler manufacturers don't recommend getting rid of the stock cooler is that they don't want to suggest that people take cooling power away before adding back their cooler. Stock trans coolers have wilding varying capabilities (possibly better than the aftermarket cooler), and they don't want to risk the chance of their customer being worse off after putting on their product...
It is just too bad that the whole "pink milkshake" thing exists... if that wasn't a worry, we wouldn't have this debate.
-Charlie
For the engine oil cooler on the block, this means it is a temperature stabilizer (coolant is always flowing through it, at engine temp). For the trans fluid in the bottom of the radiator, not so much.
I would imagine the main reason whey aftermarket cooler manufacturers don't recommend getting rid of the stock cooler is that they don't want to suggest that people take cooling power away before adding back their cooler. Stock trans coolers have wilding varying capabilities (possibly better than the aftermarket cooler), and they don't want to risk the chance of their customer being worse off after putting on their product...
It is just too bad that the whole "pink milkshake" thing exists... if that wasn't a worry, we wouldn't have this debate.
-Charlie
