TC lockup


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TC lockup

Postby disallow » Tue Aug 24, 2010 7:01 am

Hey all,

I was thinking about all this nonsense we have going on with faulty radiators, and bypassed trans coolers and got to wondering:

How would the trans cooler bypass affect the ability of the TC to lock up? As stated in other posts, many doubt that the cooler in the rad actually cools the trans fluid, and in most cases probably heats it up.

Would this action of heating up the trans fluid (or cooling if the fluid is hotter than 180-200) help keep the trans at the right temperature for proper torque converter lockup?

Not being a transmission expert, wondering if anyone out there knows what the criteria are for the Pathy auto trans to reach TC lockup?


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Postby richardekirby » Tue Aug 24, 2010 7:55 am

Good question. The trans performs it's best when in a certain temperature range, somewhere around 160*. My concern with removing the rad/cooler from the loop is the fluid may have trouble warming up in cold weather. Personally, I would rather spend a few extra minutes warming it up than spend a few thousand dollars fixing the trans.

How difficult is it to install a temp gauge on a Pathfinder? I installed one in my Lightning and it was fairly easy. I had to remove a plug from the body of the trans and replaced it with the sending unit. I had the highest temp reading ever the other day. It reached about 195*. Could be due to it being over 100* outside and I was getting on it pretty good.

Anybody here install one and have data of pre/post mod temps?

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Postby GbayPathfinder » Tue Aug 24, 2010 5:20 pm

Let me start this by stating that I am not transmission expert but I have an idea (and it could be the wrong idea) as to what will allow the converter to lock up;

1) The fluid has to be at or near the manufactures pre-determined temperature, which is about 60 Celsius (140 Fahrenheit) in most vehicles and I believe it is actually higher in the Pathfinder
2) The ECM has to determine from various sensors that the transmission is able to lock up, ie; RPM/Wheel Speed sensors and grade as well as throttle input.
3) If the vehicle is in manual mode as selected by the driver the converter is always locked, which gives the rock/pulse kick if you are on and off the gas in a certain gear

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