Aftermarket trans cooler - run it through radiator first?

[motorguy222]

There was a I beleive a question in Popular Mechanics that covered this.When adding an external trans. oil cooler,it is best to put the external cooler ahead of the factory radiator cooler.By doing this the trans. fluid will be a lot cooler but it will also warm up to the proper temp. faster in colder weather and at start up.In other words,splice into the trans lines,place the external cooler on the intake side of the radiator cooler and then hook the radiator cooler up.By doing it this way the trans. fluid will go into the external cooler first and then into the radiator cooler and then on to the transmission.This way the trans. fluid will run much cooler but it will also be closer to the normal opperating temperature without getting to hot.If the fluid does not get up to the proper temp.,the trans does not opperate quite as it should.Just as an engine needs to be at a proper temp. to run correctly so does a transmission.Remember,transmissions also have some of the problems that motors have with condensation etc. getting into the oil.An external pump alone may keep the fliud to cool,this could eventually cause damage.

 

[mechtech]

I've installed a number of trans coolers at my shop, and follow the instructions, and common sense.
EVERY manufacturer indicates that the supplemental cooler should be installed after the fluid EXITS the stock radiator cooler. No one recommends bypassing it. They warn against it.
I wouldn't own an automatic without a supplemental cooler, BTW.

 

[QuadDriver]

2 schools of thought and 1 warning:

warning: unless you are usign a very large external, do not ditch the rad cooler. you may end up with reduced or barely over stock capacity.

school 1:

Install after the rad. The radiator will cool the fluid and the aftermarket will really cool it. This is the ONLY acceptable position for severe duty (which includes towing)

school 2:

Install before the rad. This has been a recommended position for GM vehicles in extreme cold climes for a while now that are NOT used for towing and excessive idling. This way the radiator will actually re-warm overcooled fluid in the winter. It is not as efficient as it could be for the summer when towing or when idling and water temps climb to the max.

In all cases, overfill the transmission by at least 1/2 qt to make up for the extra volume.

 

[QuadDriver]

Oh btw, I noticed a lot of posts about installing filtering systems on the cooling lines. DO NOT, (repeat) DO NOT do this unless you have rebuilt and/or modified the transmission. Factory transmissions are not 'full coolers' - i.e. the fluid pumped does not all enter the cooling circuit - but rather a small bleed hole (and to add insult to injury on most e-models - a termo switch) allows appx 10% at normal pressures to enter the cooling circuit.

During a rebuild, most transmission shops will enlarge the hole or add others and in some cases add xfer tubes to route much more of the fluid to the cooler. With a filter, you are increasing the resistance of the cooling circuit and hence decreasing flow....this could be fatal.

(you could never route 100% of the fluid - the flow rate will easily overwhelm the tiny cooler lines)