Auto transmission cooler theory

[mbavers]

A question for the board. I am having my M1008 TH400 rebuilt. I'm thinking of adding a cooler. I am tempted to add the cooler BEFORE the radiator (trans fluid to cooler, to radiator, back to trans). Here is why:

The optimum trans operating temperature range is about 200 degrees F. Everything I've read suggests that you don't want the trans fluid too cold. Obviously, the trans is meant to operate at this temp, because the fluid runs through the coolant radiator which is about 200 F. If the manufacturer wanted it cooler, they would not run it through the radiator.

If you cool it AFTER the radiator there is a chance of it reentering the trans much cooler than 200F. If you cool it BEFORE the radiator there is a better chance of having it exit the radiator at about 200F. So, in this case, the radiator is a moderating mechanism, keeping the fluid within a safe range.

That is my thinking. I am soliciting input.

 

[MarcusOReallyus]

I agree with your thinking. Most will not. Most will say that you are crazy, and I'm out of my mind. Most will say to put it AFTER the radiator.

Why? Because that's the way we've always done it, and of course, that's all you need to know, right? Also, because every aftermarket trans cooler manufacturer in the world tells you to put it AFTER the radiator. That proves it! Right?

But why do they say that? Because they are selling the benefits of COOLING your transmission, and putting it after will get it cooler. That doesn't mean it's the best thing for your vehicle, it means it's the best thing to make sure their trans cooler has a reputation for getting your trans cool.

If you put it BEFORE the radiator, you dump the excess trans heat out into the air, instead of into your cooling system. If it's still too hot, it will dump some more into your cooling system. If it's gotten too cold, it will take heat OUT of your cooling system.


The newer transmissions have thermostats in them for this very reason. The worst is too much heat, but every mechanical device has an optimum operating temperature, and colder is NOT always better.

Last summer I replaced the trans on my family van with one from the dealer. Re-manned, but warranted by Ford for three years, but only IF you replace the existing cooler, and add one BEFORE the radiator (and add an external filter). That's right, for a 96 van, Ford wants that extra cooler before the radiator. That means I have three - one before the rad, the rad cooler, and one after.

I'm going to add one to my Jeep, and it's going BEFORE the radiator.

 

[davo727]

Since you are in Alaska and im in Houston we may benefit from setting up our transmission coolers differently. Down here too much trans cooling is not likely.

 

[cucvrus]

Oh I am so confused. I never even thought of any of these theory's. I was told/taught the idea operating condition of the engine and transmission was to have all the fluids the same temperature. And if they were different the cooler one would help cool the hotter one. But yes it works the other way. But keep in mind. The cooling system was designed to keep properly maintained and operating vehicles in the correct operating temperature range. If something is failing and running low on fluids (that is not included in the design). No amount of cooling is going to help cool a failing transmission / low coolant radiator / low engine oil condition. Something as simple as 1 belt can put the best cooling system into the RED in a few seconds. So if your transmission is getting hot and making your transmission over heat then the problem needs to be found and addressed. Same goes for the engine. Everything running as designed and no failures and IMHO you should be good as gold. My experience has been I have towed and plowed with CUCV's. When everything was operating as designed. I had no cooling issues. When something began to fail and I experienced higher temperatures. i fixed the failure or correct the issue that was causing the higher temperature. But before or the radiator with the auxiliary cooler. I never thought it out so I just don't do it. Have a great day. I am still confused over this. If it ain't broke don't fix it. I live by that and it makes my life easier.

 

[Katavic918]

It doesn't make any difference in. You are still heating and cooling for the exact same duration.

 

[wheelspinner]

It doesn't make any difference in. You are still heating and cooling for the exact same duration.

Sure it does; If the T/Cooler is first, and the ambient temp is very low the external cooler may very well drop the fluid temp much below the 200* mark that is generally agreed to be optimum. The fluid then travels to the radiator, and the Delta between the coolant and the t/fluid causes the fluid temp to rise. The fluid is then returned to the tranny at optimum temp properly conditioned and not just cooled; If the T/cooler is second, the T/fluid will go through the radiator and be conditioned by the coolant, then travels to the T/cooler and becomes cooled ( as the cooler is supposed to) which can result in much lower return temp than optimum. SO now its cooled to the maximum level, and not conditioned.

 

[MarcusOReallyus]

Since you are in Alaska and im in Houston we may benefit from setting up our transmission coolers differently. Down here too much trans cooling is not likely.

This is an excellent point!

Oh I am so confused.

Nothing new about that!

I was told/taught the idea operating condition of the engine and transmission was to have all the fluids the same temperature. And if they were different the cooler one would help cool the hotter one. But yes it works the other way. But keep in mind. The cooling system was designed to keep properly maintained and operating vehicles in the correct operating temperature range.

And we all know there is no possibility that the industry could learn better practices over the years, and make improvements! And we all know there is no possibility that the industry could cut costs by designing things to be merely adequate, instead of being optimal. So there's never any way for the aftermarket industry to do something better than what the manufacturers did! There is no possibility that a hobbyist could ever improve on the factory design!

No! That could never happen!

It doesn't make any difference in. You are still heating and cooling for the exact same duration.

Nope. It's not just about time. There are two huge differences.

1. Heat gradients. The larger the difference in temperature between two points the faster the heat will transfer. I'll make up some numbers out of thin air to illustrate. If the fluid coming out of the trans is at 300 degrees, it will lose heat faster than if it were 200 degrees. Putting the same cooler before the radiator will be more efficient because that fluid will be hotter (when at operating temperature) than the fluid after the radiator. Same cooler, more cooling. Basic thermodynamics.
2. Where the heat goes. With the cooler before the radiator, a lot of heat does NOT get put into your cooling system. It's dumped into the air before it ever hits the radiator. When it's after the radiator, your engine cooling system takes the brunt of the heat.

But as cucvrus says, the system works well when maintained, for most conditions. But Alaska isn't "most conditions"!

 

[cucvrus]

WOW Now I am really out of it. My hat is back on my head and out of the ring of theory. All I know is I am good with my stock setup. It worked all these years for what I use it for and that is all I can ask. There is always someone that tries to build a better mouse trap. And it the end you get the same results. Run it hard maintain it harder and when it breaks fix it correctly. Do NOT redesign it and short change the repairs. I am not an engineer and don't attempt to be one. When better trucks can be built. IMHO General Motors/Ford will be building them. And that's about all I am going to say about that. Now I am more confused. In today's world that does happen a lot. When I tell employees/co-workers what to do to fix things they check the internet to see if I am right. What did we older guys do before all these opinions clashed. We done what worked for us and gave us the results we were looking for. Cause without the internet I would have just done it and never met 99% of you guys or heard your opinions. Peace have a great day.

 

[Lonnie]

My take is that unless you are snow plowing, or towing heavy loads, you likely don't need an auxiliary cooler.

Generally, I always buy a large enough cooler to totally eliminate the factory radiator cooler & install a trans temp gauge if I am using something for severe duty, but... I don't live in alaska, where you may have low temps that I never encounter in PA.
The trans will probably be happy with anything near 150 degrees & I prefer to keep it under 200. 175-200 is considered normal pan/fluid temps

In your case a small auxiliary cooler before the radiator may make more sense to prevent overcooling in cold weather & would help to reduce temps in summer months.
Also in this case, it is easy to block airflow in cold months to the aux cooler & have it function similar to OE. In any event, install a temperature gauge if you think you are really working the transmission hard enough to worry about it.

 

[Skinny]

I vote for the cheapest way out to be putting one before the radiator to shed as much heat as possible and let the radiator cooler ensure the trans fluid is at operating temp.

If you have money to burn, buy a completely independent fan cooled unit with a thermostat and have a temp gauge for the driver to monitor.

I think anything in between is guessing...2 cents.

 

[Drock]

My take is that unless you are snow plowing, or towing heavy loads, you likely don't need an auxiliary cooler.

Generally, I always buy a large enough cooler to totally eliminate the factory radiator cooler & install a trans temp gauge if I am using something for severe duty, but... I don't live in alaska, where you may have low temps that I never encounter in PA.
The trans will probably be happy with anything near 150 degrees & I prefer to keep it under 200. 175-200 is considered normal pan/fluid temps

In your case a small auxiliary cooler before the radiator may make more sense to prevent overcooling in cold weather & would help to reduce temps in summer months.
Also in this case, it is easy to block airflow in cold months to the aux cooler & have it function similar to OE. In any event, install a temperature gauge if you think you are really working the transmission hard enough to worry about it.

Agree with Lonnie, a Trans temp gauge will answer all these questions.

 

[hatzie]

Sure it does; If the T/Cooler is first, and the ambient temp is very low the external cooler may very well drop the fluid temp much below the 200* mark that is generally agreed to be optimum. The fluid then travels to the radiator, and the Delta between the coolant and the t/fluid causes the fluid temp to rise. The fluid is then returned to the tranny at optimum temp properly conditioned and not just cooled; If the T/cooler is second, the T/fluid will go through the radiator and be conditioned by the coolant, then travels to the T/cooler and becomes cooled ( as the cooler is supposed to) which can result in much lower return temp than optimum. SO now its cooled to the maximum level, and not conditioned.

200* operating temp is too hot. According to TCI you want 150-175*.

 

[Katavic918]

Sure it does; If the T/Cooler is first, and the ambient temp is very low the external cooler may very well drop the fluid temp much below the 200* mark that is generally agreed to be optimum. The fluid then travels to the radiator, and the Delta between the coolant and the t/fluid causes the fluid temp to rise. The fluid is then returned to the tranny at optimum temp properly conditioned and not just cooled; If the T/cooler is second, the T/fluid will go through the radiator and be conditioned by the coolant, then travels to the T/cooler and becomes cooled ( as the cooler is supposed to) which can result in much lower return temp than optimum. SO now its cooled to the maximum level, and not conditioned.

Ok. I suppose you're right.

 

[Bob H]

Seems to me a factory installed auxiliary trans cooler is before the radiator.
Every aftermarket cooler I have bought came with instructions that say to place it before the radiator.

If you have a 210° thermostat, the coolant mixture entering the radiator will be near 210°, the temperature at the exit of the radiator would be considerably cooler than that, ( in the 150 to 175° range. The typical radiator trans cooler is in the exit side of the radiator.

I have the same aftermarket trans cooler configuration in my 500HP summer car, as well as my snow plow truck. Now my mud truck currently has just an aftermarket trans cooler.
This was due to laziness, as the engine's in the back and the radiator is up in the front. That trans is about done & will be replaced before next season & at that time it will be done properly as described above.
Automatic transmissions have 2 enemies, hot & cold.

 

[mbavers]

I thank you all for the great input.

 

[rustystud]

The way the factory installs them is really the best way. Why ? Because you will loose most of your transmission heat to the radiator cooler. It is the best conductor of heat after all, copper tubes next to water. The air flow through the aux cooler will not generally bring down the temperature enough. Remember the returned oil goes to the transmission sump where it mixes with all the other oil draining down. So it cannot ever really be too cold. The oil going to the coolers is from the torque converter where it has the maximum amount of heat from the transmission so we really want this oil cooled down. We also don't want the most heat (remember the torque converter) dumped in front of your engine cooler (radiator) .

 

[cbear]

Stacked plate style coolers are supposed to be self regulating, going in to bypass when the fluid is to cold. Some transmissions also don't engage the cooler loop if the fluid isn't hot. I'm not sure about the TH400. If I was going to add a cooler, I'd also try to add a remote filter since I would be messing with the lines anyway. Something like the B&M 80277.

 

[rustystud]

Stacked plate style coolers are supposed to be self regulating, going in to bypass when the fluid is to cold. Some transmissions also don't engage the cooler loop if the fluid isn't hot. I'm not sure about the TH400. If I was going to add a cooler, I'd also try to add a remote filter since I would be messing with the lines anyway. Something like the B&M 80277.

There is no bypass on these coolers. The TH400 has no cooler loop either. It comes out of the torque converter and then to the cooler. This is also how we usually change-out the transmission fluid. After draining the pan and replacing the filter you would add about 8qts of fluid to the transmission. With the cooler inlet line off and pointed to a bucket you start the engine and watch the fluid coming out the line. (You can also take the inlet line off at the transmission if you want to crawl under the truck). You let it go until good clean fluid comes out or it starts to spurt. If it spurts you need to shut-off the engine and add more transmission fluid. Once you have the new fluid coming out the line you stop the engine and replace the line. Then you would remove the line where it comes out the cooler and start over again with the purge. After all the lines are clean you reinstall all lines and start the engine and adjust the fluid level in the transmission.
This way you completely remove all the old fluid including all the fluid in the torque converter.
I have also installed two extra oil coolers and a spin-on filter. Mine have the AN fittings so I have PTFE stainless hose on everything.

 

[M543A2]

All of my auxiliary cooler installations have been before the radiator. From my experience, the spin-on remote filter add-on is an excellent idea. I have one on a performance transmission. It keeps the oil looking noticeably cleaner and with nice bright color. I installed the filter before the auxiliary cooler. Chrysler automatics in the early years all had a replaceable inline filter in the cooler lines.

 

[MarcusOReallyus]

The way the factory installs them is really the best way.

The best way to do what?

There are many ways to do most things. Which way is the "best" way depends on what you are trying to do and under what conditions. Factory designs are "least common denominator" designs. They aim for the middle, the average use, and they aim to do it at the lowest possible cost consistent with their quality objectives. Chevy has different quality objectives than BMW or Ferrari or Yugo, so they will make different choices about designs and materials.

Conditions vary, too, and therefore, needs. For a guy in Alaska, overcooling the transmission is a real issue. For a guy in Panama, not so much. If you are toodling around town with only an occasional small load, your cooling needs are different than someone who is towing heavy loads long distances regularly. You had better make different choices than Mr. Toodler.

If you are going to have only ONE cooler, where it goes is a different choice than if you are going to have two. If your budget is small, you do the best you can with what you can afford. Bill Gates has a few more options. Maybe he uses a cooler from an F750, with its built in bypass and massive capacity. Maybe I can only afford a tube-type from Autozone.

Choices, trade-offs, and variables. There is no ONE BEST WAY.