Th400 transmission cooler for towing

[89_C3500_Larry]

I have a 1998 c3500, motor swapped from a 350 tbi to a 454 with a demon 600. It's got a th400 with a 4.10 rear gear. The radiator has a built-in transmission cooler. Would it benefit me to add a fan driven external transmission cooler? I'm consistently towing 11,000 fully loaded and my transmission temps start rising quick after I get off the highway.

One other question about the carburetor. Is a demon 600 enough for a 454 tow vehicle? I average 5.5mpg loaded. 9-10 unloaded city. If I went with a larger carburetor, would it improve mileage? It seems like it falls flat a little at the top end when I go balls deep in the throttle. Would a bigger carb fix that?

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[stutaeng]

I don't know anything about carburetors, but regarding your transmission cooler: get the largest external cooler you can find. I don't think the external cooler needs it own fan though. They are less than $100, and installation takes a few hours. What temperatures are you seeing? How fast are you going and what are your RPMs?

Did your truck have the larger radiator? I can't seem to recall if the CK3500s had the larger radiator, or only the ones with the BBC. Might want to looking into that.

Nice truck and travel trailer BTW!

 

[kennythewelder]

That carb is to small. Thats a stock 350 card and its a little small for that. You need about a 780 carb on a 454. At least well over 700 CFM. And trans cooler is always a good thing.

 

[89_C3500_Larry]

It has the large 4 row radiator with the transmission lines going thru it. Belt driven fan. My theory is. After Travel about 75 miles at 55mph on country roads, with intersections every 10iles or so. I get to my site, and there are some trees, and it taking time to get situated, my coolwnt temperature went from 170 to 210. Which means that my transmission was at 210, and I believe the reason my coolant temperature rose up because the hot transmission no longer had the high rpm fan + wind. If I'm not towing, it never gets over 185-190.

 

[89_C3500_Larry]

I have a 1998 c3500, motor swapped from a 350 tbi to a 454 with a demon 600. It's got a th400 with a 4.10 rear gear. The radiator has a built-in transmission cooler. Would it benefit me to add a fan driven external transmission cooler? I'm consistently towing 11,000 fully loaded and my transmission temps start rising quick after I get off the highway.

One other question about the carburetor. Is a demon 600 enough for a 454 tow vehicle? I average 5.5mpg loaded. 9-10 unloaded city. If I went with a larger carburetor, would it improve mileage? It seems like it falls flat a little at the top end when I go balls deep in the throttle. Would a bigger carb fix that?

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Correction #### 1988 C3500,. Not 98

 

[Supercharged111]

I'm having a difficult time fathoming a dually that didn't come with an external trans cooler stock. Your trans will run hot as it has no lockup feature. Your mileage sounds spot on to me. Is the 454 a GenV or GenVI?

 

[kennythewelder]

Electric fans are a grate swap, but like everything else, they need to be big enough to do the job and a little extra is a plus. I have a set of Cadi Deville fans on my truck. Grate swap. That 350 never over heats. 454 s have always been known to run hot. More colling is a good thing.

 

[kennythewelder]

Oh, and yes add a trans cooler.

 

[stutaeng]

So 1989?

You need to install a tranmission temperature gauge.

I thought for heavy duty towing the mechanical fan was favored? I think the temperatures you are seeing are normal.

 

[89_C3500_Larry]

I'm having a difficult time fathoming a dually that didn't come with an external trans cooler stock. Your trans will run hot as it has no lockup feature. Your mileage sounds spot on to me. Is the 454 a GenV or GenVI?

Gen V