To bypass or not to bypass stock transmission cooler.
 

I will be installing a b&m transmission cooler. I live in Long Beach, Ca so cold weather isn't an issue. I had already made up my mind to bypass the stock transmission cooler as the aftermarket should be more than enough.

I did lots of searching and found a post where he says that in stop and go traffic the aftermarket will not be enough. Is this true?

I've ran a test to see how how the stock cooler will heat up the fluid. I started the car and let it idle for 40 minutes (I forgot). The temp got as high as 160 just from idling.

I want to make sure that there isn't any other reason besides over-cooling your fluid that would encourage installers to install an aftermarket cooler in series with the stock tranny cooler. This isn't needed in my weather at all.

I ran both in-line on my old auto Maxima. Only problem was long warm-up periods on cold mornings due to over-cooling since I live in PA and the cooler I had didn't have a bypass valve. I can't see why you would want to bother disconnecting the factory one, especially since it's extra volume you can have more fluid in for better cooling.

I've driven mine with my B&M inline for about the last 6 or 7 years and no issues with overcooling. When I lived in MA, it would take a little time (warm up time) for my OD to kick in with the cold temps up there but now that I live in NC, it's prime for the hot weather we get here. My tranny hasn't missed a beat and it has almost 300k on it. Still shifts smoothly.

I also ran mine in-line with the stock cooler. Using the B&M took out any worries for overcooling, even as I ran it with synthetic ATF for further lower temperatures.

Unless you lived in a cooler climate and used an oversized plate/fin style like the Hayden don't bypass the factory unit.

I've been having problems with ATF weeping from both lines on the cooler the hose clamps that came with it don't provide enough clamping force might be worth replacing those with better quality clamps.

I forgot to add, the B&M should have the thermostat mechanism that closes off flow until the fluid is at the right temp so that would prevent overcooling anyway.

Overcooling isn't going to be an issue here. I'm just wondering if it will run cooler by bypassing the stock cooler and just running only the B&M cooler.

I know that it holds more fluid but that fluid will be preheated to 160 degrees and I would like to run closer to 150 if possible.

I bypassed the stock cooler and I mounted it to the bumper (not the outside bumper cover for those of you who think I just stuck this thing on the front of my car lol) rather than placing it up against the hot radiator.
http://forums.maxima.org/album.php?a...ictureid=10119
http://forums.maxima.org/album.php?a...ictureid=10118
Are you using synthetic fluid?

Yes, sir. I will be running Mobile 1 synthetic.

When I opened my B&M cooler box it had a bag full of stuff. The rubber caps that came on the cooler inlet and outlet I put onto the stock cooler nipples and ziptied each one on. I also noticed the temp gauge didn't go up as high with the stock cooler not being used now.

Great, that is what I wanted and was hoping to hear. I'm sure that the extra heat of the hot coolant will negate the cooling effects of the extra fluid and cooling surface.

What was the difference in temperature between bypassing the factory cooler and running it in-line? I haven't come across any cooler install that insists on bypassing the factory cooler.

The ones I've seen said to use the stock cooler with the new one. Wish I had extra money to test this with dual temp gauges.

I have one of the big Hayden ones on my car. It's on the return side of the factory cooler. I've never checked the temps.

Which one are you using?