I am about to fit an external trans cooler to my AWD and well..... here we go, another external trans cooler question.

The general consensus is to run the external cooler in line after the radiator cooler. I fail to see the advantage of using the radiator cooler if the external cooler is plumbed inline after it.

Would it be better to just bypass the radiator cooler altogether?

Before, after, instead of. All valid options.

Run inline thus the temp of the trans will come up to temp sooner as a cold trans will do just as much damage as a hot one

Run inline thus the temp of the trans will come up to temp sooner as a cold trans will do just as much damage as a hot one

On that basis put the cooler in front of the radiator cooler, so the trans gets heated fluid as soon as the radiator warms up.

If you're in a cooler climate, put the extra cooler before radiator - radiator can re-heat the fluid a little.
If you're in a hotter climate, put the extra cooler after the radiator's - that way the radiator can cool the fluid a bit first and the new cooler finish the job.

If you're new cooler is a big ass mofo, then bypass the radiator's cooler to keep the number of connections down.

Would it be better to just bypass the radiator cooler altogether?

I don't believe so.

I'm a qualified mechanic of many years and I can tell you about when I worked at a custom radiator place. I used to remove radiators and do the aircond repairs there.

Anyhow, I owned a VE Valiant with a 383 Big Block Chrysler in it. There was not one day in that motor's long life it didn't get turned 6500rpm :2cool: The only auto for those things is a 727B (B for Big Block) and I had 2 external trans coolers on it and bypassing the inadequate 2 row CL/CM radiator.

While I was employed there, I decided I was going to fit an R-134 air cond system to my Val from new and secondhand parts after work. I planned it carefully as I lived 80kms away and the car had to stay mobile.
I already had 383 air cond brackets and pulleys, I used a secondhand York compressor I retrieved from the Dump-Master and fitted a new R-134A seal kit to it, bought a new R-134 condenser, condenser fan, a 3way switch for compressor and hi/low clutch cut out and fan cycling, a secondhand under dash unit and an R-134 TX valve. All the pipes were as much as possible metal, and any rubber hoses were new and made up by me.
I also got them to build me a 3 core radiator. I used the large 7 blade Chrysler fan and matching fan shroud with a new Commodore V8 fan clutch (same mounting pattern as Chrysler and cheaper). I did the job properly, it worked faultlessly for years and the car never overheated.

So getting back to the install, after work they're all pissing on and they see me fitting the condenser and radiator as all the grille was out of it. They see the "agricultural" transmission cooler arrangement. They laughed at my reasoning of running 2x externals and I do believe they were right to, mumbling things like "stupid bloody mechanics think they know everything about cooling systems".

They show me OEM radiator heat exchangers for auto transmissions from several different radiators. I can say that these heat exchangers are of a well thought out and highly efficient design - often being hollow with a coiled fluid circuit and quite large too so as to maximize the surface area.

As was pointed out, a liquid to liquid heat exchanger is going to be more efficient than liquid to air only arrangement. They always recommended an external cooler be placed BEFORE the internal radiator cooler so to maximize transmission cooling (which is why the external is being added).
On balance for Australian conditions I believe they are absolutely right. They were very knowledgeable on cooling systems by my estimation.

What they showed me, and the reasoning behind it, makes a great deal of sense when you get thinking about it. I am surprised at my naivety with hindsight.

I hope this helps.

Sorry but comparing a VE Val Auto to a much more advanced auto of now day is like comparing a T model ford to a current model XR8 and has no significance at all in this discussion.

The Magna Auto gets very hot under some pretty normal conditions, it has been proven many times that although the in radiator cooler does work to an extent, it is simply not enough especially with the 5sp auto's

Putting a cooler that is too large can do just as much damage as no cooler however the smaller air coolers together with the in radiator cooler is perfect for these cars. IF you are going to go overboard and use an over size cooler use an inline thermostate / bypass set up as well so the new cooler is only in use when the temps get to a certain level and higher thus you do not run the risk of over cooling the trans especially during winter

Mal, has the science behind heat transfer changed in the last 50 years or something?
I know you might be busy, but seriously you amaze me sometimes with your attitude.

What Victa posted is a relevant story and something that bears thinking about - if the OP bypasses the original cooler, thinking his air cooled radiator is better, then think about what happens after putting some heat into the trans oil and then getting stuck in traffic with no air flow. Only the liquid cooling in the radiator and it's big fan will keep the transmission temp down.

So IMO with the above in mind, it might be very bad to bypass the factory cooler.

Madmagna, what would be a good size cooler for the 5 speed in a sedately driven car which might tow 1,500kg once or twice?
And would it be a good idea to cover the cooler with cardboard or something during winter?

Mal, has the science behind heat transfer changed in the last 50 years or something?
I know you might be busy, but seriously you amaze me sometimes with your attitude.

What Victa posted is a relevant story and something that bears thinking about - if the OP bypasses the original cooler, thinking his air cooled radiator is better, then think about what happens after putting some heat into the trans oil and then getting stuck in traffic with no air flow. Only the liquid cooling in the radiator and it's big fan will keep the transmission temp down.

So IMO with the above in mind, it might be very bad to bypass the factory cooler.

Really??? well be prepared to be amazed as my attitude does not care what you think.....

So the story about a car some 30+ years old is comparable to a Magna, be real

The cooling needs of a 30+ year old 3 speed governor basedl auto is totally different to a 5 speed auto which is all electronic AND is jammed in a case half or even smaller than that of the old school trans. Those old transmissions were bullet proof, ours are not. Our transmissions generate a whole lot more heat and this has been shown with so many failures. Further to this the Magna in rad cooler is not that big, have you even seen one.

If you bothered to read my post, was not attitude, was simply a reply and my stating my opinion that the comparison made was rubbish is it was rubbish. Totally different cars, totally different technology and totally different cooling needs

Sorry if you dont like my attitude but I state it as it is, if you dont like that dont read my posts, simple really ??

Spetz, the DER13101 is an ideal size for the average Magna, plumb it inline with the factory cooler and you get the best of both worlds so to speak

Sorry but comparing a VE Val Auto to a much more advanced auto of now day is like comparing a T model ford to a current model XR8 and has no significance at all in this discussion.

This statement is irrational. There is no comparison to a 727 "VE Val Auto" and a 5sp Mitsubishi auto. I suggest you re read it with an open mind to get the spirit of my post.

There is a discussion on the relative merits of bypassing auto transmission radiator coolers (or otherwise) as imparted to me by a radiator specialist; my car being the impetus for the information I gained.

My experience at that place was 8 years ago BTW.

Unremarkably, 727 transmissions do run hot and are effected similarly by heat as any other transmission. Thermodynamic principals don't alter because of your misreading of my post.

This statement is irrational. There is no comparison to a 727 "VE Val Auto" and a 5sp Mitsubishi auto. I suggest you re read it with an open mind to get the spirit of my post.

There is a discussion on the relative merits of bypassing auto transmission radiator coolers (or otherwise) as imparted to me by a radiator specialist; my car being the impetus for the information I gained.

My experience at that place was 8 years ago BTW.

Unremarkably, 727 transmissions do run hot and are effected similarly by heat as any other transmission. Thermodynamic principals don't alter because of your misreading of my post.

I like this a lot. It's about going back to basics and understanding a cooling system and how it actually works. Pretty interesting stuff.

FWIW, I've run two 2nd-gen tranny coolers on my TW AWD for around 70,000km, nearly 27,000km of which has been towing a ~1500kg caravan around Australia. Towing the van, I've encountered temperatures in the high 30s and, without the van, temperatures as low as -5. To cope with the extremes I run the coolers before the built-in one. That way, if the coolers over-cool the fluid, the built-in one will warm it up again; conversely, if the coolers don't cool the fluid enough, the built-in one will cool it a bit more. Either way, the fluid temp ends up being closer to the 'correct' temp, which is the same as the water temp. Since I live in the ACT, which gets fairly cold in winter, I have also installed a thermostat to bypass all cooling until the fluid temp reaches about 80-85 degrees. 100% reliability to date.

Great to see someone taking the proper approach with a thermostat kit to ensure fluid does not get too cold, while I would not personally use second hand coolers the thermostat will bypass anytime fluid gets too cool

I am about to fit an external trans cooler to my AWD and well..... here we go, another external trans cooler question.

The general consensus is to run the external cooler in line after the radiator cooler. I fail to see the advantage of using the radiator cooler if the external cooler is plumbed inline after it.

Would it be better to just bypass the radiator cooler altogether?

Hey Craig, Let us know how you go and what you decide to do.

No advantage to remove the trans cooler from the radiator, it is needed especually in traffic when there is no airflow over the external cooler and also when cold you can do just as much damage with fluid too cool as you can too hot