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Benz Tech
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I've gone through my third factory radiator in four years, damn plastic side tanks keep crapping out on me. I've been looking at some universal aluminum radiators but most of them do not come with a built in trans cooler like the factory one has. My question is, is it a bad idea to just bypass the factory cooler and run only an auxiliary cooler?
 
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I believe that you can recrimp the plastic tanks to get them to stop leaking. As far as bypassing the trans cooler you should be fine with just the aux cooler. Imo the only usefulness it has is warning up the trans fluid in the colder months.
 
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The good thing about running your trans fluid through your radiator is that it warms up quicker & stabilizes at a steady temp by not getting over cooled.

Heat is the number 1 killer of transmissions... the runner up (number 2 killer) is running the transmission too cool. If your running an Aux trans cooler, you may want to run that on a return system that is thermostatically controlled... this way you can adjust what temps the fluid goes to the cooler and what temp it goes back to the block...

I ran a similar cooling system for my oil cooler. The sandwich adapter only let the oil go to the cooler when it reached 190 degrees... at that temp it was sent to the cooler... if it dropped below that temp then it kept the oil flowing through the engine... This kept the engine temps extremely steady. I had planned to do the same system for the transmission cooler but sold the truck before I got to it.

The bottom line is that running a transmission too cool is also bad for it.

SPEED SAFE, AIR RAM
 

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Discussion Starter #4
What is optimal temp for trans fluid? Can you post a pic or link to the thermostatically controlled adapter you are talking about.
 

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This is the one I was going to use.



Its set to open at 180 degrees. I used a 180 degree sandwich adapter for my oil system .... having both the transmission and engine running steady at the same 180 degree temps is key for consistent performance. The cooling system was set at 180 as well...

SPEED SAFE, AIR RAM
 

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You live in Phoenix. You'll be fine bypassing the radiator altogether. No need to worry about heating up the fluid to temp. Both my 98 & 99 rigs bypassed the radiator with no issues. I lived in SoCal with the 99 and now live in Kingman (Ariz) with the 98 R/T. Get yourself a big B&M flat plate style cooler and you'll be set. See the chart below for tranny temps. Good luck!

 

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borg warner flat plate cooler the 11 x 11 one with 1/2 inch fittings
There is a picture in the EMPI catalog
run 1/2 inch "oil proof" hose to and from your trans
(there IS a reason the diesels use 1/2 inch)
install a filter between converter and cooler (transdapt adapter and full flow filter)
my 92 518 has 250,000 miles on it, So Cal, towing, radiator bypassed, 9 blade fan and aux pusher fans, 73 Chry Imperial 4 core radiator and Maxi van AC condenser (different body style than yours)
 

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I've been running with a bypassed radiator tranny cooler pretty much since I've owned my current truck. I'm running one of the tru-cool 45000GCVW coolers I got off Ebay. they are like $120 but well worth it. Will keep your tranny cool no matter what the circumstances and come with a thermocouple bypass to bypass the cooler until the fluid reaches operating temp. Even living in a warmer climate area like Phoenix, I'd still run the thermo bypass to help speed up the warm up of the transmission.

I'd also recommend a plate/fin style cooler(like I have) over a stacked plate, or tube/fin style.
 

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The tube fin is not sufficient
frontal area in sq in is the primary key for radiators, condensers, coolers
thickness is secondary
but you have to fit what fits
 

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The one I'm using fits perfectly behind the opening in the lower valance.

Search for Tru-Cool # LPD4739

They are used by a lot of diesel guys, so you know they work.
 

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website says
For use with 5/16" & 3/8" transmission cooler lines.
Do not use on 1/2" or larger lines used on some Chrysler diesels and Allison transmissions.
 

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The factory lines are pretty small and works fine. I can;t imagine the need to go to such a large line as 1/2" line. I plan on "upgrading my stuff to some -6AN braided lines from the tranny to the cooler eventually. Get rid of the stock hard lines that are a PITA.
 

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Let me jog your imagination
It's not only cool oil it's lubrication oil for your thrust plates
there is a reasons that diesels with he same trans run 1/2 inch lines
braided would be nice but 1/2 inch oil proof works well
when the trans is out you can open up the passages
we hung three gauges on the lines and checked the pressures and flow
both 1/2 inch lines and bypassing the cooler reduce your backpressure about 15 lbs each- 45 lbs total
 
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