External transmission cooler add on

[OR VietVet]

On my girls 1990 K2500 with the 5.7 and 700R4 transmission, we are going to get a smaller 2 axle trailer for weekends, either a conversion or from a manufacturer. The radiator is like new and I did just run all steel transmission cooler lines. With the trailer weight of approximately 5k to 6k loaded, I plan to give the transmission every chance I can. It is not the original transmission. It was replaced by a GM dealer in state of Washington, in 2012 at approximately 110k miles. It is close to 123k miles now.

When I took over work on this truck about 20 months ago, I did a transmission filter and fluid change. I did not do a flush and it all looked pristine in there. I now want to install an external transmission cooler and am reaching out to members here to get ideas of a good made cooler, fit and function, and if there is anything special I need to know. It all looks very straight forward but there is a reason I am a member and I will use info from you all.

 

[Marky Dissod]

Wait. It's a 2500? with a 4L60, not a 4L80?
Does it NOT already come with a separate external ATF cooler?
Does the radiator have at least one ATF sidetank?
What's the axle ratio?

 

[OR VietVet]

Wait. It's a 2500? with a 4L60, not a 4L80?
Does it NOT already come with a separate external ATF cooler?
Does the radiator have at least one ATF sidetank?
What's the axle ratio?

You must have missed what I said. It is a 1990 K2500 with a 5.7 engine and a 700R4 transmission. It does have the transmission cooler in the radiator. The same one I explained that I ran new steel lines to. The 4L60 and 4L80 were not around in 1990. The 4L80 came about the next year in 1991 and then the 4L60 came about 2 years later in 1993. I had to look that up. The 1990 K2500 truck, my girl owns, does not have an external transmission cooler. The axle ratio is 3.73.

 

[Marky Dissod]

What you call a THM700R4, IS a 4L60.
I do not call radiator sidetanks 'coolers'. No sidetank will EVER let ATF get any cooler than the adjacent engine coolant.
That's why I recommend a 180F thermostat for the L05 (not a 195F) for towing 6000lb.
If the external ATF cooler is not rated big enough to cool for more than 6000lb of towing, a fan attached to the cooler is a great idea, especially if you have control over that fan.

Is 3.90 or 4.10 possible? That'd help out your 4L60 too.

 

[Eman85]

If you want a quality cooler a B&M stacked plate cooler with threaded fittings is a good cooler.

 

[strutaeng]

@Marky Dissod : He's got a "2500" 6 lug...which is closer to a 1500 (with a few upgrades) than a 8 lug 2500 of that era.

IIRC in 1990 the 8 lug trucks were still getting the TH400, because as @OR VietVet quoted, the 4L80e started hitting the streets in 1991...it had to do with gvwr. 7200 lbs vs 8600 lbs(?) something like that...

Sorry, I don't have anything to add, but there are a lot of threads on adding the aftermarket auxiliary coolers.

I would probably tow that on "3" and avoid using OD... fingers crossed.

 

[OR VietVet]

To all that replied. I guess I should clarify a few things. The RPO code says is a 700R4 transmission, so I am going with that for all future references. I do know to tow in 3rd and not OD. I do know there is a cooler immersed in the coolant of the side tank of the radiator and that is not much of a cooler and that is why I will install a separate external transmission cooler. I had forgot about running a cooler thermostat but would have likely remembered somewhere along the line. I would install a new fan clutch, just to be sure and I had been thinking about a switch controlled electric fan but had not decided yet. I will update along the way.

 

[exp500]

To all that replied. I guess I should clarify a few things. The RPO code says is a 700R4 transmission, so I am going with that for all future references. I do know to tow in 3rd and not OD. I do know there is a cooler immersed in the coolant of the side tank of the radiator and that is not much of a cooler and that is why I will install a separate external transmission cooler. I had forgot about running a cooler thermostat but would have likely remembered somewhere along the line. I would install a new fan clutch, just to be sure and I had been thinking about a switch controlled electric fan but had not decided yet. I will update along the way.

A Stacked plate 14000 cooler is a great choice, with several good manufacturers. Also be aware of different fans and radiators-7blade and a wider / thicker rad. Shrouds important too.Larger Radiator rubbers and holders sometimes tough to find.
I don't forsee problems towing up to 12000# With your combo. Good luck and keep us updated.

 

[Marky Dissod]

The RPO code says 700R4 ...

... In 1990, the Turbo Hydra-Matic 700R4 was renamed the 4L60.

Not a 4L60E - a 4L60.
So yours was likely built in '89 for sale in '90.
ANYWAY
IFF you upgrade to 4.10, you may get away with using 4th on flat level ground.
Anything under 4.10, yes, absolutely avoid 4th gear.