1989 Buick Century 3.3

Was replacing my radiator and all the associated rubber and realized I didn't know which transmission cooling line was which. One runs to the transmission cooling unit in front of the radiator and the other runs directly to the top of the radiator. When I look at the transmission itself there are two lines coming out, one on top and one on bottom. Which (top or bottom) goes to the radiator and which goes to the transmission cooler? If you can't be sure can you at least tell me which line from the transmission is an outlet and which is an inlet?

Does't really matter. As long as it starts from point A and gets back to point B. That sounds custom anyway. You don't normally find external trans coolers installed on FWD cars.

It'* original. From what I understand you want to feed the output from the transmission to the top of the radiator and feed the return to the transmission from the transmission cooler. Something like this: https://www.etrailer.com/faq-about-e...n-coolers.aspx. I would just need to know which is the output from the transmission and which is the input. I've got two lines, one directly above the other, coming out of the transmission. Other GMs have the output on the bottom and the input on the top. I'm just not sure about this one.

Forgot to mention earlier that this is a three speed auto, no overdrive.

Funny, I didn't see any mention that it HAS to be in that specific order.

There is one way. Have both lines disconnected from the trans, have someone get in, start it, and watch for what port fluid comes out of. Voila. Just make sure the person starting the car knows to SHUT IT off right after it starts.

I've seen elsewhere that people seem to think it makes a difference. That was just the best diagram I could find.

In the winter time I could see that. The warm coolant warms the trans faster. But then again, in the winter time, why would you be using an external trans cooler? It defeats the purpose. If your not towing anything, I wouldn't even bother with the external one.

I agree with Mike on finding the source by starting it for a moment.

You'll end up with cooler fluid if the external cooler is in front of everything else (radiator, AC condenser, etc.) and is last in the fluid path before return to transmission. Depending on how far North or South in the country you are and how tired your transmission is could decide which way you want to go on this. Some marginal transmissions do funny things when too cold so put the external cooler first and radiator cooler second or skip the external altogether. Some don't care about being cool so run the external cooler second.

Personally, I've almost never had a transmission become sad about being too cold, even in below zero. The exception being one time on my 1981 Bonneville'* GM Metric 250C (never-touched including fliter change with 149,000 miles on it) when it was 2 minutes running after being ice cold for a week. I gave it a pass on that. And later when my parents gave it to me I dropped the pan and found out how plugged up things were.

Others may have different experiences.