MT643 question

Cameronbraaap · 10-02-2019, 03:04 PM

92 tc2000, 5.9 Cummins with an mt643. I live in the mountains, so much of my driving is up grades. My tranny starts heating up when climbing. I keep a close eye on it and drive accordingly.... but it's a concern. Obviously heat is the enemy, so I'm wondering if anyone has experience with, or can recommend a specific aftermarket tranny cooler for the 643? I've found quite a few posts in reference to coolers for the 545 but not much on the 643. It's not an issue yet, more preventive than anything. A couple hundo and a little elbow grease seems a better choice than cooking a tranny. And it would be nice to be able to stay in the throttle a bit more in some of these hills. I'm going nowhere fast, but it would be nice to keep going. Lol thanks

EastCoastCB · 10-02-2019, 03:58 PM

I can get the part number later on but I got a beefy Earl's cooler off Tango. They're around $400.

bigskypc50 · 10-02-2019, 04:23 PM

What kind of temps are you seeing? In mine with a DT466 and MT643. On a 90 plus degree day pulling heavy hills, I was seeing about 220-225.

Cameronbraaap · 10-02-2019, 05:23 PM

Awesome. Thanks

Cameronbraaap · 10-02-2019, 05:31 PM

Quote:

Originally Posted by bigskypc50

What kind of temps are you seeing? In mine with a DT466 and MT643. On a 90 plus degree day pulling heavy hills, I was seeing about 220-225.

I'm running in the same temp range typically but itll start climbing if I let it. I keep my R's below 2400 when pulling grades. The engine stays cool with no issues but the tranny will climb pretty quickly if I let it. I'd like to try and keep that temp down for longevity and it would be nice to be able to keep up a little more momentum on longer pulls.

o1marc · 10-02-2019, 05:49 PM

The coolers are seldom specific to the trans. Most are an extra radiator on the stock radiator. One that works for a 545 would also be correct for a 643

Cameronbraaap · 10-02-2019, 07:37 PM

Quote:

Originally Posted by o1marc

The coolers are seldom specific to the trans. Most are an extra radiator on the stock radiator. One that works for a 545 would also be correct for a 643

Correct me if I'm wrong, but I believe the 643 lines are larger than the 545. The cooler that I've seen people run on the 545 has 1/2" lines and inlets, which look considerably smaller than what's coming out of mine. My concern then would be restricting flow with the smaller inlets.

o1marc · 10-03-2019, 12:29 AM

Quote:

Originally Posted by Cameronbraaap

Correct me if I'm wrong, but I believe the 643 lines are larger than the 545. The cooler that I've seen people run on the 545 has 1/2" lines and inlets, which look considerably smaller than what's coming out of mine. My concern then would be restricting flow with the smaller inlets.

While this is true, I think you just need to know what size fittings you have and get the appropriate kit. The radiator will probably be the same, just different fittings. I doubt you'll find a specific model for a Cummins 643. You can get them in barb fitting or AN fitting.

https://www.flex-a-lite.com/transmis...r/coolers.html

bigskypc50 · 10-03-2019, 08:05 AM

Did you cut out an remove your inside heaters?

Although not for the trans but it helps cool everything down, I still have a spot in coolant system where I connect the hoses together after I removed the inside heaters. At times I have thought about adding a radiator and fan from like a Geo Metro or Honda Civic, the hosing sizing has to be close, I would assume and with a fan you could mount it vertical under there. I am far from a expert on the laws of thermodynamics but it seems to me it might help.

cadillackid · 10-03-2019, 08:39 AM

the line sizes are bigger on the 643 vs the 545.. on the trans itself it uses a #12 ORB fitting, you can adapt that down to any number of different sizes.. if the manufacturer stays true then the line size will be 3/4 on the 643..

ny 545's both had 5/8 line running to the radiator..

if you are making your own cooling lines you can adapt different sizes, however larger lines move more fluid...

if you install a monster cooler than its a good idea to install a thernal limiting block as well.. an ice cold transmission is hard on them as well.. driving in winter with your cooler wide open wont allow the trans to warm up properly.. this is less of an issue on 545s as they make a lot of heat.. but the 643 once locked up doesnt make as much heat esp on flat ground..

if you dont plan to drive your bus in ice cold weather or are using the stock radiator cooler warmup is less of an issue..

o1marc · 10-03-2019, 11:19 AM

Quote:

Originally Posted by bigskypc50

Did you cut out an remove your inside heaters?

Although not for the trans but it helps cool everything down, I still have a spot in coolant system where I connect the hoses together after I removed the inside heaters. At times I have thought about adding a radiator and fan from like a Geo Metro or Honda Civic, the hosing sizing has to be close, I would assume and with a fan you could mount it vertical under there. I am far from a expert on the laws of thermodynamics but it seems to me it might help.

While it does give more places for heat disappation, it is not a fix for a separate overheating issue. If your system is working correctly the heaters becaome a burden when maximizing floor space. Generally these builds lean towards stationary use, rather than than on the road use.

You may also like: