I want to install an auxiliary transmission cooler on my 98 LeSabre. It already has the factory cooler in the radiator. I am looking at the TruCool line, like what willwren uses.

I have no blockages in the stock cooler. Main reason to add the cooler is that we use this car for towing a small popup camper through mountains in summertime.

It seems to me there are three install options: in series with the stock cooler, in parallel, or bypass the stock altogether.

So, what are the pros and cons of each option?

In a series, you will not cool as much as using the new one only. However in the winter, the series will gain you a little heat from the radiator to help bring the transmission up to temperature.

Keep in mind, WillWren is not driving his car much in the winter, but did provision for that with a thermostatically controlled cooler.

Thanks for the replies.

Bypass seems to be winning here. I am looking at the TruCool line specifically because it is the thermostatically controlled type.

What about parallel? That'* what most of the online research I have done suggests...

If you've ever had any type of transmission failure, bypass is the ONLY option. The core in the radiator will plug up with debris, restricting flow.

I bought the Tru-cool and installed it in series. Great product. In addition to greatly improving the performance of my old worn tranny, I realized an unexpected benefit of cooler engine operating temperatures. I like the idea of leaving the rad in the loop for winter heat up of the trans fluid. And the thermostatic design of the Tru-cool helps in cold weather by bypassing to the rad. My only regret was not purchasing the bigger $65 unit. That'* what I will buy next time.

I would leave the in-radiator cooler in all cases, for stabilization of the temp. If I lived where it was pretty cold routinely, I would put the aux cooler before the in-radiator cooler. That way, the cooler could take any REALLY hot fluid, and get it down to normal temps, which would then be stabilized by the in-radiator cooler. Since I live where it rarely freezes and is usually hot as hell, I put the biggest stacked plate cooler that will fit AFTER the radiator for maximum cooling benefit. I usually run the Hayden (parts store) cooler that is just over 10" square, and sometime put the 10" fan on it as well. The cooler is $50, and the fan is another $50.

Here'* my '97 SE...

Nice install pics there.

How'd you do the return from the aux tranny cooler to the steel tube...did you cut the steel tube shorter, then flare the end before adding the fitting?

And what kind of fittings are those (the yellow, plastic things)?

If you buy a Tru-Cool with the installation kit, you will get all the fittings you need to do the install as shown. (I know the one shown is not a Tru-Cool, but mine is installed the same way, except I have no fan.) I didn't have to cut anything. And, if you like, you can remove the cooler when you sell the car. The adapter fittings that come with the kit are brass and IIRC were provided for both 3/8" and 5/16" lines. These fittings are not easy to find at your local plumbing or hardware store, BTW. The kit also gives you a choice of a quick install using spacers and plastic barbs that push through the radiator fins, or bolting to the radiator vertical support. I had mine installed in less than an hour.

Good question. The brass fittings are made to screw directly onto the existing cooler lines, no cutting necessary. The yellow plastic part is part of the brass fitting. It'* just the "stop", where you push the hose all the way on until it hits the yellow plastic.

At Advance Auto Parts, they had a Hayden book where you could use make and model and get the fittings needed (5/8"?). The fittings come 2 per pack for about $12-14.

This was on my '97 that had TCC issues, and would surge when the converter locked, but it only did it when the trans was HOT, after sitting in traffic on 90+ degree days. After the cooler and fan, it never did it again. If you felt the metal feed line and the return line after driving, the feed line felt like touching the stove (ok, not really), and the return line was mildly warm to the touch. I'm in Texas with no chance of overcooling, but plenty of chances to overheat.

As for the fan, I used a relay that took the power directly from battery +. For the fan trigger, I used the driver'* side cooling fan, as there'* a place on the block where the factory wiring connects that allows you to put a spade connector (the female rectangle kind that will slip over a male spade, like connecting a speaker wire) to it. This is right on the driver'* side fan. What that did for me was to allow the fan to come on with the cooling fans. The way I see it, if the factory cooling fans were needed by either temperature or by the A/C being on, then the trans cooling fan would also need to be on. The ONLY scenario where that might be a problem is in extreme cold where you're using the defrost, thus the A/C and therefore the cooling fans would be on. Again, it'* not cold enough here for me to be concerned. Hope that helps. Here'* a shot of the cooler before the fan was installed, so it'* easier to see just how it looks from the front: