Transmission Cooling Line Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

78SilveradoSWB · 08-28-2003, 07:53 PM

On my TH 400 Tranny there 2 lines coming out and were connected originally to the radiator. On the radiator are 2 ports for the tranny line. One is the upper and the other the lower. Which one is the incoming and which one is the return?

Second question is a transmission cooling routing question. Does the tranny fluid travel to the tranny cooler mounted up front first, then through the radiator tranny cooler and back to the tranny or to the radiator tranny cooler through the tranny cooler mounted up front and then returned to the tranny?

82 Silverado 4X · 08-28-2003, 08:05 PM

Mitch,
I can't help on which line goes where on the TH400, but my opinion would be that it should flow from the trans to the radiator and then into the tranny cooler and then back to the tranny.

Doing it this way, it allows the fluid coming out of a radiator which has coolant that normally runs at 180-210 degrees to further cool the fluid as it passes through the tranny cooler before returning to the tranny.

*rage'nrat638* · 08-28-2003, 08:25 PM

the lower one

is out

78SilveradoSWB · 08-28-2003, 09:39 PM

Thanks George, looks like the guy who had the truck before me had it the same way, going to the radiator cooler, then to the aux. cooler, and back to the tranny.

Thanks Mark for the location of the radiator output.

**swervin ervin** · 08-28-2003, 10:04 PM

On the trans, the upper fitting is return, lower fitting is out to cooler. On the radiator, the lower fitting is in from tranny, upper is out to tranny.

From all my research, it seems it's best to route this way for best cooling.

Come from tranny to aftermarket cooler, out to lower fitting on radiator, out of top fitting on radiator back to tranny.

Reason is if you go to radiator first and then to cooler, back to tranny, it will cool the fluid too much. If you go to the cooler before the radiator, it lets it warm up just a tad first.

This is the way I have mine routed and believe me, it works very well. I have a trans temp gauge so I know for sure it does and not just hearsay.

78SilveradoSWB · 08-28-2003, 11:36 PM

Thanks for the input Mike! Where is your temp gauge located for tranny temperature?

**swervin ervin** · 08-28-2003, 11:58 PM

You have to braze a brass fitting in the pan for the temp sender.

78SilveradoSWB · 08-29-2003, 12:01 AM

Now I remember...You even had to have reworked it because of a leak, right?

08-28-2003, 07:53 PM	#1
78SilveradoSWB Senior Member Join Date: Apr 2002 Location: Beaverton, OR Posts: 1,615	Transmission Cooling Line Question On my TH 400 Tranny there 2 lines coming out and were connected originally to the radiator. On the radiator are 2 ports for the tranny line. One is the upper and the other the lower. Which one is the incoming and which one is the return? Second question is a transmission cooling routing question. Does the tranny fluid travel to the tranny cooler mounted up front first, then through the radiator tranny cooler and back to the tranny or to the radiator tranny cooler through the tranny cooler mounted up front and then returned to the tranny? __________________ Mitch 1978 Chevrolet Silverado C 10 454 BB, TH400

08-28-2003, 08:05 PM	#2
82 Silverado 4X Genuine Chevrolet Join Date: Feb 2003 Location: South West Pennsylvania. Posts: 582	Mitch, I can't help on which line goes where on the TH400, but my opinion would be that it should flow from the trans to the radiator and then into the tranny cooler and then back to the tranny. Doing it this way, it allows the fluid coming out of a radiator which has coolant that normally runs at 180-210 degrees to further cool the fluid as it passes through the tranny cooler before returning to the tranny. __________________ George 82 Silverado LWB 4x4 350 SM465 NP208 77 Chevrolet Blazer Chalet 400 TH350 NP203

08-28-2003, 09:39 PM	#4
78SilveradoSWB Senior Member Join Date: Apr 2002 Location: Beaverton, OR Posts: 1,615	Thanks George, looks like the guy who had the truck before me had it the same way, going to the radiator cooler, then to the aux. cooler, and back to the tranny. Thanks Mark for the location of the radiator output. __________________ Mitch 1978 Chevrolet Silverado C 10 454 BB, TH400

08-28-2003, 10:04 PM	#5
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	On the trans, the upper fitting is return, lower fitting is out to cooler. On the radiator, the lower fitting is in from tranny, upper is out to tranny. From all my research, it seems it's best to route this way for best cooling. Come from tranny to aftermarket cooler, out to lower fitting on radiator, out of top fitting on radiator back to tranny. Reason is if you go to radiator first and then to cooler, back to tranny, it will cool the fluid too much. If you go to the cooler before the radiator, it lets it warm up just a tad first. This is the way I have mine routed and believe me, it works very well. I have a trans temp gauge so I know for sure it does and not just hearsay. __________________ Mike 1985 Chevy C-10

08-28-2003, 11:36 PM	#6
78SilveradoSWB Senior Member Join Date: Apr 2002 Location: Beaverton, OR Posts: 1,615	Thanks for the input Mike! Where is your temp gauge located for tranny temperature? __________________ Mitch 1978 Chevrolet Silverado C 10 454 BB, TH400

08-28-2003, 08:25 PM	#3
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	the lower one is out

08-28-2003, 11:58 PM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	You have to braze a brass fitting in the pan for the temp sender.

08-29-2003, 12:01 AM	#8
78SilveradoSWB Senior Member Join Date: Apr 2002 Location: Beaverton, OR Posts: 1,615	Now I remember...You even had to have reworked it because of a leak, right? __________________ Mitch 1978 Chevrolet Silverado C 10 454 BB, TH400

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