I`ll keep it simple and quick!
Is the tranny line comming out of the lower radiator hook-up the "return line"?
Just want to make sure, as I`m installing a tranny cooler this weekend!

Thank you in advance for your assistance.

Cheers, Rick (R.P.)

 

You're going to get different answers here. My tranny cooler is in series with my bottom radiator line and works flawlessly. My tranny temps rarely if ever get above 169-170* and I don't baby it either. However there are some who are going to tell you to use the top line.



I hope this helps.

 

Let me be the first one to say it.

Fluid goes from the transmission to the lower connection at the radiator then it exits the radiator at the top connection and goes back to the transmission.

 

Cooler goes in the return line the top line

 

My two cents, you should install the cooler in the return line to the transmission. It makes no sense to cool the fluid , then run it through the radiator that has hot water in it. Alway installed mine on the return line.

 

Since we're talking about it, my trani. usually runs around 200 temp. once it's warmed up, is that normal for big city dirving...

 

200* is normal for an A4. When you pass 225* it is too hot.

 

All, thank you for your replies!
Based on the replies so far I`m still not sure if my original question has been addressed corectly.
According to a "very reputable" West Coast vendor/builder/tuner, the lower tranny/radiator line is the return line! I`m just double checking this info to be correct, as It`s my nature! (measure/check twice execute once)
Obviously I`m intending to run the tranny cooler aft of the radiator, just need to verify that the lower line is indeed the return line!
Thank you again for your assistance.

Cheers, Rick (R.P.)

 

That is exactly what I was told. That it was the bottom line which was the return line and I got this information from my tuner as well. I argued with him up and down that it was not and based my argument on the information I had gotten here. I was very upset that he had installed it using the bottom line. We consulted a reputable transmisson specialty shop in my area and the owner of the transmission shop said that it was really a moot point.

Well all I know is that he (my tuner) installed it on the bottom line and my tranny cooler works great. Can't argue with success.

This question shows up from time to time on the forum. I get a kick out of it because I rarely if ever see above the 170s and my usual operating temps are 169* almost like clockwork.

I even went to the track and on the way back from the track, on the interstate, one evening in about 60* outside temps, I had tranny temps in the high 150s low 160s after traveling about 15 miles from the track at highway speeds. My tranny temps are generally in line with and somtimes slightly lower than, my coolant and engine oil temps.

Once I remember someone commenting that people in the northeast tend to install transmission coolers on the bottom line and people in hotter climates on the top. Accept that FWIW.

Good luck whatever you decide.

 

 

I just recently had mine installed. I used to get up to and a little over 200 during normal operation. Now I have to drive it hard in 3rd to get it over 170 other wise it stays below 160.

I will check which line was used.

 

Let me put this to rest for you. On a C5 the upper radiator A4 cooling port IS the return line. If you want maximum cooling this is where you need to splice in your cooler. Come out of the upper radiator fitting, go to the cooler and then to the trans.

The late model cars, 2003 and 2004 I know for sure use a coupling at the radiator GM calls a quick connect fitting. It is anything but. If you decide to use AN fittings to hook it all up this can make things very difficult.

I have a Doug Dewitt’s radiator and I ordered it with NPT (National Pipe Thread) at the radiator which is how the earlier C5’s were configured. DTE has a special fitting which is made for them by a local machine shop that will fit the male GM quick connect fitting on the line and adapt it to NPT. That will allow you to adapt to almost anything. DTE uses it when they install a BeCool radiator in a customers car. BeCool radiators use NPT threads at the radiator and this lets them install a BeCool for customers without cutting any lines.

However if you run the stock late model radiator you will still have a problem connecting to the female connection point on the stock radiator. For late model cars it’s a PITA to hook all this up unless you use hoses and clamps or change the radiator like I did. And by the way, the GM cooling lines are 3/8 but the fittings are metric, go figure.

On a stock late model application the only way I know of to get hard fittings into this system is to remove the upper line from the car, cut it a few inches past the quick connect fitting and weld AN fittings on each end of the pipe. However, this requires that the line be removed from the car and that requires the removal of the front undercarriage. If you decide not to use hose clamps, and I will not use them, it’s involved on a C5 that uses the stock quick connect type of fittings.

Perhaps by now someone has come up with a fitting that will convert the female outlet in the radiator to NPT or something you can connect to.

I researched all of this last summer

Now, here is how sure I am that the upper line is the return on a C5 A4. I will give $1000 dollars to anyone who can prove me wrong. The upper line on a C5 is the return line.

If you do it backwards (via the lower line) the trans cooler will drop the temps and then the radiator will reheat it when it passes through the radiators cooler. This will render the trans cooler ineffective. Don’t ask me how I know.

 

I'd like to see you prove it right. Please show us some documentation or point us to where there is documentation that it is indeed the top line on a C5 which is the return line.

No one is here to try and take $1000.00 off of you. If you have reliable information, diagrams, etc that demonstrate what you say then please show us, share the knowledge and keep your grand.

http://corvetteactioncenter.com/foru...mission+cooler
In this thread c4c5specialist makes mention of using a power steering cooler as opposed to a transmission cooler for a "factory look" and going into the BOTTOM line.

"......On vehicles NOT equipped with the Z51 power steering cooler, I simply add the PS cooler and plumb the lines, from the lower pipe, going to the lower half of the radiator.
This works very well, and looks factory."


The reason why I ask is because my tuner referenced the C5 shop manuals when I argued with him that it was the top line.

My cooler is quite effective. All I know is that it works and my transmission temps are rarely above 169*. And thats after driving around well long enough to reach operating temperatures. My coolant temp is usually slightly higher than my transmission fluid temps. So if the radiator is warming the transmission fluid back up and "reheating" it, it is doing a very poor job.

My Hayden transmission cooler was installed in May '04. I can drive to the track from my house about 20-30 miles away, make several 1/4 mile passes and never see tranny temps pass 175* the whole time I am on the way to the track, at the track, or coming home from the track.

Plus, I am not running a stock torque converter. If I were going to have a problem, I'd have had it already. . I drive with my tranny temps displayed on the DIC.

Again, thats exactly what my tuner told me.

 

Some people love an argument and others can't take a hint, then there are those who do not understand that money talks and BS walks.

OK, you didn't understand the hint so here it is. I have done it both ways on the same car and we did it backwards the first time. When we got it right temps dropped drastically. Now up north where it gets really cold some people like to hook it up to the lower line. This is because during the winter they can't get the trans fluid up to normal temps, at least that's the rumor. If it were me I would simply cover the trans cooler during the winter. Truckers have done this for a long time.

Now, if you still don't believe me get under your car. Remove the cross over pipes and the tunnel cover plate. Find the point where the cooler lines enter the trans. I don't remember which but they are either labeled on the trans or in the manual for in and out. I don't remember which. Find the input port on the trans and follow the line back to the radiator.

Your tuner would not be the first shop to get this wrong. I am happy for you that your trans stays cool but none the less, on a C5, from the factory, the upper line is the return. When you live in a location that sees ambient tempratures frequently exceed 100 this becomes critical information. Been there, done that, know that.

 

And some people are going to need more than just your word for it. Show us proof.

http://corvetteactioncenter.com/foru...mission+cooler

Why is this guy talking about "lines, from the lower pipe, going to the lower half of the radiator" ??? You saying that he is installing them wrong too?

Why pray tell would I do all of that when mine works and the c4c5c6 mechanics, ASE certified w/L1, Chevrolet Professional service guild, NCM#7993 over on the other forum, plus my own professional tuner, plus the original poster's professional tuner says this is the way to install it?

"A BM cooler I usually mount to the front AC condenser, and pipe to the lower outlet. Hoses and lines run to the passenger side of the vehicle."

You better go over there and set him straight.

OK

 

Seems like this would be pretty easy to verify. Drive the car and get everything nice and warm. Simply measure the temp of the top and bottom lines and the cooler one is the return line......

 

Only problem with that is that the underhood temps get up and heat both lines up. I have tried this. Both lines warm up due to the temperature of the radiator and it being in close approximation to the lines themselves. As the radiator heats up the lines heat up.

And due to the underhood temps if you drive the car for a couple blocks in an attempt to heat up one of the lines, they'll both heat up.

Also I don't like reaching into the engine bay with the engine running and pulleys turning anyway. Try doing it with the engine shut off and you still get two warm lines after the car has warmed up a bit.

For the record I really don't know with 100% certainty which one is the return line. About the only thing I can tell you is that mine is into the bottom line and it not only works, but it works GREAT. And anyone who says that :

is incorrect. Mine is quite effective.



My tuner insist that the return line is the bottom line. A well respected transmission specialist, with a chain of very successful transmission shops in my area said that it really did not matter which line the cooler was hooked into. It works, my tranny temps are great, so I don't care which line is which.

 

You and I have had this discussion before, back during the summer when I researched this. I am sorry to have to tell you this but you are wrong and should refrain from handing out bogus information.

Sure, you can connect the cooler to the lower line if you want to. But,
the original question was, which line is the return line, upper or lower?

The answer is the upper. You want proof? Take a look at this link:

http://www.photohost.org/gallery/upl...ans_cooler.jpg

Its a page out of the GM service manual that details how to test the transmission for fluid flow rate after you have flushed the system. It is a test to see how much trans fluid will flow through the trans and cooling system in 30 seconds. If you can't read it here is what it says:

"1. Disconnect the hose from the oil cooler pipe. Connect the oil cooler feed pipe, bottom connector, to the transmission for normal flow."

"2. Clip the discharge hose (1) to an empty oil container."

The diagram clearly shows that the oil cooler feed pipe, which is the oil output line for the trans, to be connected at the bottom of the trans. In the diagram this line feeds into the bottom of the trans cooler. The discharge from the cooler then returns from the top of the cooler to the upper port on the trans which, in the picture, goes into the can so that the volume can be measured to check the flow rate.

You are entitled to your own opinion as to where in the line the best place to connect the cooler would be. But you are not entitled to your own set of facts. The cooler return line is the upper line.

 

A few points:

1. That diagram does not look like any C5 engine/ transmission assembly that I have ever seen. Is this a service manual for a C5? A "Y" platform manual?

Of which cars? ????? That does not look like a C5 Vette's engine and transmission.


2. Say...........is that a transmission cooler hooked in series with the bottom line in that diagram? If so, then thanks for proving my point.


3. You said that "If you do it backwards (via the lower line) the trans cooler will drop the temps and then the radiator will reheat it when it passes through the radiators cooler. This will render the trans cooler ineffective." That is incorrect apparently according to your own diagram.

4. One more time, is that a transmission cooler in series with the bottom line in your diagram??? Is it hooked up wrong too???

Not according to your diagram. If that is an auxilary cooler, in series with the BOTTOM line, then the fluid is going into the bottom or limb of the auxillary cooler. The discharge from the auxillary cooler exits at the top of the cooler to the rejoin the LOWER transmssion line BEFORE going into the RADIATOR and the stock transmission cooler. And then heads back to the transmission.

This was a configuration which you told us was "backwards" and would not work, remember????? Yet this is the way it is described in your "GM Manual".


5. I have been saying that all along. Mine is and it works. And it is described that way in your own reference material. But I thought you said: "If you do it backwards (via the lower line) the trans cooler will drop the temps and then the radiator will reheat it when it passes through the radiators cooler. This will render the trans cooler ineffective." Thats not true.