FogRunner

There has been allot of talk about aftermarket transmission coolers and low temps. Well recently down here in Houston we have had temps in the low 20's the last two days so I thought it would be a good chance to take some temp measurements from the transmission cooler.

First off I have a B&M transmission cooler 70264 which is 14,000 BTU unit mounted in front of the condenser. I have the transmission lines routed to go from the transmission to the spin on filter which has my temp sender on it, then to the cooler and finally back to the transmission.

The cooler is designed with "bypass feature" as B&M calls it which allows the thicker colder ATF to bypass the cooler by going through two wider channels at the bottom of the cooler.

So now the results.

With the outside temps running in the low 20's I got in the 4runner that had been sitting all night and started driving. My house is just one street off the highway so there no stop and go, just back out of the driveway, go down the street and turn and get on the highway.

Well after 10-15 minutes of driving on the highway the transmission temp was hanging between 105-115 degrees and stayed that way for the rest of my 50 mile trip. On the way back I got into some stop and go traffic and finally with a good hard acceleration on the on-ramp I was able to heat the transmission up to 165F.

As soon as I got on the freeway I got in the left lane and put cruise on 75mph. As soon as I put on the cruise and saw from the tach that the torque converter had locked up, the transmission temp started to fall.

In about 1 minutes after the torque converter locked up the temp fell from the previous 165F down to 105-110F and stayed there from the rest of the 50 mile trip back home.

The above test proves that with the "self regulating" temperature design of B&M and most high quality transmission cooler that a in-line bypass thermostat is unnecessary. It also means that keeping the stock radiator/transmission cooler inline is unnecessary and very risky when you consider the ramifications if it fails and allows engine coolant into the transmission.

As far as the issue of how hot transmission fluid needs to be to function properly, I've spoke with several transmission techs and the going answer is 80-90F. My Chevy Duramax (hey I know but Toyota doesn't have a 1 ton diesel) which has just a large transmission cooler (no connection to radiator) runs around 100-115F also in the low 20's weather by factory design.

Another reason not to use a bypass thermostat or keeping the factory cooler piped in is heat. With just my B&M cooler during the 95-100F summer days this year my transmission never got above 125F on the highway with the torque converter locked up. During stock and go traffic or hard acceleration it would get up to 175F max but very quickly cool back down to the 120-125F range.

Any transmission technician will tell you the colder you can keep a transmission the long the transmission and fluid life will be. With the bypass thermostats your guaranteeing your transmission will never get below the thermostat temp which is normally 165-180F. With the stock transmission cooler still in-line your temps will vary with outdoor temp but in most cases will stay around 165-170F.

So if your considering a aftermarket cooler to protect your transmission from the risk of the stock radiator cooler failure or just want to keep your transmission cooler, forgo the bypass thermostat or keeping the stock cooler in line and just go with a good temp regulating cooler like the B&M or the IPT.


FOG

954rrmike

I have the IPT and have seen temps as low as low as -15C and the truck seems to be working fine. I do not like the look of that external bypass, it seems a little mickey mouse.

mt_goat

Good info FOG.

john4r

I'll just second what fog is saying. Made a 300 mile round trip yesterday. I have an external cooler bypass the radiator. Outside temps ranged from 20-30 during the day.

Tranny runs in the very low 100's on the interstate. Did a paved road climb of about 3 miles that pushed the tranny temp to 140 (pretty steep cycling between second and third on the corners). Then a low speed dirt road, snow actually, climb of 5 miles, lots of switchbacks 15-25 mph and temps climbed to 170 ish. I have an electric cooling fan that did not come on. I do have the ability to over-ride the fan control thermostat if I ever see the tranny getting hot when the radiator isn't. I don't know if that will ever happen.

John

mt_goat

Yeah I took note of my ATF temp yesterday on a short 5 mile trip to the store. On the way back with ambient temps in the 20's my ATF was at 110*F. I run with the radiator ATF cooler bypassed and a Long Tru-cool LPD ATF cooler (4454) All cooling fans were off of course.

Red3.slow

I've been getting some baseline temps with my stock in radiator cooler while I've been waiting for a warm enough day to install my aftermarket. Stock temps have been looking like an average between 124-168 with the air temps being between 14-35

FogRunner

Now think about if its already running 125-168 in cold weather, think whats its going to do in warm and hot weather.

It may not look too warm right now and the reason is in really cold temps the engine is only really using 20-25% of the radiators capacity because a radiator,transmission cooler, and condenser's capacity for BTU dissipation increases greatly as the cooling medium (the air temp outside) drops.

Because of this and the design of the 5VZFE cooling system, the bottom of the radiator where the transmission cooler tank is runs MUCH MUCH colder than the top of the radiator in cold weather. Out if curiosity I stuck a thermocouple in the fins on the top of the radiator which gave a reading of about 180F in 30F weather.

But when I measured the bottom half of the radiator is was 50 degrees colder (130F). Now in the summer time when the air is much hotter, the bottom tank will only be 10-15 degrees cooler than the top half causing the transmission to run no colder than 160-170 degrees.

So basically when the transmission is locked up on the highway the stock cooler is ADDING heat to the transmission.

There is a reason that that vast majority of trucks and commercial vehicles don't use radiator based transmission coolers.

Red3.slow

I don't disagree with you at all, nor am I sticking up for the stock cooler. I was getting base line temps for when I add my cooler.

Also interesting information on the difference in temps within the radiator

FogRunner

I didn't mean to come off sounding as if I was accusing you of taking up for the stock cooler. I knew you weren't and didn't mean to imply you were, I just kinda ramble on in my postings at times and things come out wrong, I blame it all on the lead paint chips I ate as a kid.


FOG

ThePretender

Hey Fog,

Thank you for starting this posting. I appreciate you sharing your data and your good thinking! Thank you for sharing! I tend to read these transmission postings as I am concerned that I am beating my transmission up pretty good with the slow miles and slow climbs in the dirt. Also, I ran a supercharger for about 50k miles before I had TuRD buy it back - I'm sure that also took its toll on the transmission.

I apologize beforehand if this has already been determined and I just missed it. . .

Anyway, I had an "Ah-ha" moment earlier this week. It dawned on me that I am probably measuring the transmission temp right at the transmission since I am using a Scangauge II. I had to check the factory service manual and then crawl under the car. Yes, the sensor for the transmission temp is at the front-right corner of the transmission pan. I was thinking that my temps were a little high since I was running in the 160-190 range while driving around the Lone Pine area right after Christmas. Outside temps were around 35 - 45 and I was doing some climbing. I was expecting it to be in the 150 range like I've seen posted many times.

For the folks that chose to tap into the transmission line on the return side between the cooler and transmission, I'm thinking they will be seeing lower temps since the fluid has already been through the cooler. Since you are measuring on the send side (that fancy filter mount) before the cooler - that may answer why your temps seem a little high to you?

Anyway, that is my theory.

With normal freeway driving, I usually run between 160-190. Like you, I am curious to see what the temps will be during summer when it is in the 90's out here. This will be my first summer since installing the bypass valve and bypassing my radiator.

Steve.

FogRunner

Steve my temps don't seem high to me at all with my oversized B&M cooler with the stock cooler bypassed. With normal freeway driving in Houston's almost 100 degree heat my transmission never gets over 120-130F measured at fluid discharge line on it's way to the cooler.

Allot of people think that the heat itself "kills" the transmission which is does to a point by hardening seals and such, but the real problem is the transmission fluid itself. Transmission fluid manufactures agree that for every 20 degrees above 175F that you run, you cut your transmission fluid's service life in half. When you hit the 230-240F mark transmission fluid is "burned" and it's lubricating properties are destroyed almost instantly.

So the main concern isn't the body or pan fluid temperature. The concern is the highest temp that the transmission fluid sees in the circuit which is measured at the discharge line of the transmission.

By measuring the pan you give yourself a false sense of security because the fluid that is dumped in the pan has just gone through the cooler.

So when you go to make a hard climb hill climb or are really hitting it through the mud your transmission pan sensor maybe only reporting 190-195F. But the discharge temp is sky rocking into the 230-240F range drastically reducing the lubricating properties and service life of your transmission fluid and ultimately your transmission.

I've measured this before and in a loaded unlocked condition (I.E. hill climb) the temp in the pan reported by the OEM sender is on average 30-40 degrees cooler than the discharge temp. So when that OEM sensor is saying 195-200F, the fluid is really seeing temps up to 240F which as stated above destroys transmission fluid almost instantly.

So the best place to monitor is the discharge line of the transmission because we want to see the highest temps the fluid heated up to in the circuit.


On a side note I notice your running a Hayden 1678, I see allot of people with the 1678 or the Tru-cool4454. I tried a 4454 and noticed the temps were rather high. After realizing I could fit a "thicker" cooler in I swapped out the 4454 for a B&M 70264. The Hayden and Tru-cool are 11"x7.5 but only 3/4" thick. The B&M cooler is built like a tank compared to the Tru-cool or Hayden and is same size but 1 1/2" thick. Because its twice as thick it has double the surface area and is able to dissipate allot more heat.



FOG

954rrmike

Does your b&m cooler have a thermal bypass?

FogRunner

Yes it does.

Recently we had a good cold spell and it got down to 25F. The bypass in the cooler made the transmission warm up quick and hold 100-110F with highway driving. Anytime I made it heat up (passing, or flooring it at the toll booth) the temp would drop like a rock right back down to 110F and stay parked there as soon as the transmission locked up.


http://www.bmracing.com/PRODUCTS/Aut...BTU-11x6x1-1-2




FOG

ryani

I just ordered a Tru Cool 4490 which is about 11 inches square. That should be about the same as the B&M's cooling efficiency. I talked to a few transmission specialists and they said to times your Max towing weight by 4 or more to get the size cooler you need if you eliminate the stock cooler.

FogRunner

I thought about going with a large square cooler like the 4490, but I decided to go with the B&M for air flow reasons. By using a thicker cooler with a smaller footprint your block/restrict less airflow to the condenser and radiator.

It's not much of a issue when your on the highway when the "ram air" effect is pushing the air through the cooler/condenser/radiator. But when need the cooler the most when you get into stop and go traffic your trans cooler, condenser and radiator start to suffer because of the engine fan is having to suck the air through the additional restriction caused by addition of a large footprint trans cooler.

This is why I went with a smaller thicker cooler. The thicker cooler does restrict a little bit more air than a thinner one would but it is allot smaller footprint so its impact is much less on overall airflow the condenser and radiator.

The larger/thinner coolers cost less than the smaller/thicker coolers yet allot of car and truck makers choose to use the smaller/thicker because its removed heat better and restricts less air flow to the radiator/condenser.

If you look at allot of fleet and heavy service vehicles you'll notice they use a small but very thick transmission coolers for this very reason. My 95 caprice and 1 ton Duramax are the same way, they both use the small and thick trans cooler.


FOG


(footnote) All this is just my opinions from research and testing. I'm not trying to "bash" or berate anyone's setup or ideas. So if I come off sounding like I'm bashing someones ideas or setup I'm not. These are just my ideas and your milage may very as they say

ryani

Hey no sweat off my back. No offense taken. That's actually a great reasoning behind the short and fat cooler. I prefer mine tall and skinny. Haha sorry that was bad. It's early forgive me

mt_goat

Wow, that is cooling good for you! Do you have a fan on that?

FogRunner

No fan on it, but I should have added that those temps are moving on the freeway at 55mph or greater with the converter locked up. If I get into stop and go traffic in 95-100F weather the discharge temp will get up to 170-175F.

The only time I've ever been able to get my transmission temp to get above 175F is when I was going up pikes peak with a car full of people, and even at that it got to 200F and stayed there the whole way up.


FOG

mt_goat

Ok, I had to look back at my notes. In hot weather my tranny temps run around 160-190 F with a peak of 205 F on a 100 degree F day after a long drive in city traffic. Those temps are measured with an inline sensor before cooler. My radiator cooler is bypassed and I'm using a single Tru-cool 4454 with a fan mounted to it.




I did see temps higher than that once on a long steep climb up to a trail head, I was racing up pretty fast in a low gear (1st or 2nd in 4WD high IIRC).

I am using Mobil 1 ATF.

ThePretender

OK, I just removed the bypass valve. ($30 for a fun experiment - cheap learning experience!)

If I experiencing any trouble shifting, etc. during sub-zero weather or I notice the transmission is running a little hot, I will probably go with a double-wide B&M cooler.

You'll have to pardon my skepticism - I'm a cardholding member of the Flat Earth Society (I still need to see for myself that the earth is actually round).

As for the stock trans temp sensor measuring the temp of the return fluid - I am not sure if that is the case. The sensor is mounted a little above the pan gasket, right in front of the send line. The return line is quite a bit farther back on the transmission.

Either way, this is another great transmission thread!

Thank you to everyone who has contributed so far!

Steve.