Trans Coolers - External Vs Internal

[KrazyKong]

I'm currently having to replace my now dead/cracked radiator. Since I have an auto there's an internal trans cooler in the bottom tank. There is also a small rectangular shaped external trans cooler radiator that sits in front of the ac condenser radiator. So there are two points where the trans fluid is cooled.

As for radiator replacements there is virtually nil aftermarket ones for autos. The only ones I've seen are OEM replacements that are identical to the stock one.

But I have heard some people with autos still put in a manual radiator, and thus bypass the internal trans cooler and just use their external one.

So I'm wondering is this actually ok? is the trans fluid going to be cooled enough, or do I still need my two points of cooling for the trans fluid. I don't race or track my car, and apart from the odd cruise, just use it as an everday car.

This is my stock? external trans cooler.

[W0rp3D]

You will actually find that the fluid goes through the radiator after being cooled as it needs to be heated to running temp, just having an external cooler on its own may cool it too much and the auto will not be at its full running temp.

[KrazyKong]

Brett, that's interesting. I was told today the internal cooler was important if you did alot of stop/start driving. Like being in a traffic jam is a good example.

I had thought the fluid went into the internal cooler, then out to the external, then back into the trans. But what you're saying is it comes from the external, to the internal, then to the trans?

[W0rp3D]

that is correct, seemed odd to me when i was told so i checked it out on a few standard cars (non skyline) and they were all configured like that.

[wlspn]

Running only an external cooler is fine.

I have worked on transmissions for around 5 years & never had probelms with running too cold...

Very common to do on all sorts of cars, not just high-performance or tow vehicles.

If you are really paranoid you can get a B&M thermostat but really its not needed.

[KrazyKong]

Just got back from a few radiator repair places and also a transmission shop after taking my unit into them for advice.

The trans guy said if it's a toss up between a cooler engine, or a cooler transmission, go for a cooler transmission.

The radiator guy said also that rather than a 42mm or 52mm radiator cooling the engine better, it would in fact only cool better if there was a significant amount of air flowing past it. So if no tracking, or racing the car, the 25mm stock radiator was actually more efficient for everyday driving. Plus a stock/oem unit also has the internal trans cooler as well which the 42/52mm ones do not have.

So at this point, I'm thinking an oem auto replacement is the way to go. I've found a Koyo one for around $300. It's more than I want to pay, but with so few options concerning what is available for autos, I don't have much of a choice as this is the cheapest I've found one for.

[KrazyKong]

that is correct, seemed odd to me when i was told so i checked it out on a few standard cars (non skyline) and they were all configured like that.

I wonder why they have larger aftermarket external trans coolers then. They would only cool the trans fluid down even more wouldn't they?

[mad082]

not if they have a thermostat. also it depends on whether the box is modified or not. things like a higher stall converter would raise temps, as well as just putting decent power through the box would too. or if they tow with the car then you need one. when dad got a towbar put on his subaru outback the towbar came with a trans cooler