Transmission cooler questions

[Cubey]

Looking at big aftermarket transmission coolers for my soon rebuilt C6.

I'm thinking I might bypass the radiator connections and put a cooler with "bypass" built in.

I'm usually not in very cold climates but maybe i should keep the radiator connections and also get a bypass one?

Or no bypass and no radiator connections?

My thought is keeping the water heat separate from the trans heat might be a good idea since it's ALWAYS under a heavy load, and I'm rarely in below freezing temperatures for very long, usually only overnight lows.

 

[IDIBRONCO]

Someone may end up correcting me on this, but since you're almost never in cold temps, I think it would be a good idea to keep them separate. If you have trouble keeping the trans fluid temps down, you could try to double them up. Are you planning to install a trans temp gauge?

 

[Cubey]

Someone may end up correcting me on this, but since you're almost never in cold temps, I think it would be a good idea to keep them separate. If you have trouble keeping the trans fluid temps down, you could try to double them up. Are you planning to install a trans temp gauge?

Yeah, I will put a gauge, just dunno when. I'll probably put it on the input line to the cooler so it shows the max temp before cooling.

I'm looking at one of these. It's massive vs the factory one:

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• Size is 3/4 inch x 11 inch x 11-5/8 inch

The factory one is about 11 x 3".

 

[gandalf]

I'm not familiar with running a cooler attached to a C6, but more so attached to an E4OD. On the E4OD it is recommended to run the lines through the radiator and then the cooler. The E4OD must reach a certain temp to run more efficiently. Running the line through the radiator helps in that. Once it reaches that temp the cooler help from letting it get too hot. That being said, I would suggest the largest cooler you can fit.

 

[Cubey]

I'm not familiar with running a cooler attached to a C6, but more so attached to an E4OD. On the E4OD it is recommended to run the lines through the radiator and then the cooler. The E4OD must reach a certain temp to run more efficiently. Running the line through the radiator helps in that. Once it reaches that temp the cooler help from letting it get too hot. That being said, I would suggest the largest cooler you can fit.

Yeah, I was thinking that, and get a cheaper non-bypass cooler (it always full flows, doesn't ever bypass internally based on temperature).

The 11x11 one above (Hayden 679, premium tube/heavy duty) also says:

• Class "A" motor homes, large travel trailers, 5th wheel trailers
• GVWR up to 30,000 pounds, towing up to 10,000 pounds

Sooo yeah that would be more than enough cooling, even with the radiator hooked up I'm guessing.

It's $66 from O'Reilly or $53 on Crapazon. I'll probably pay the bit more and go with O'Reilly since one is in walking distance (2.5 miles round trip) and shows in stock.

 

[chillman88]

I think that's the same one I put in my truck. I don't have a temp gauge though so I can't say how it's working.

 

[Cubey]

Well I went with Crapazon anyway. Money is so dang tight right now. $15 less is $15 less.

I'll have to drive a tiny bit more around Yakima to pick it up, but I also plan to ask a small RV shop there if they'll store my cargo trailer for me for a week while the RV is being worked on, so the trans shop don't have to try to store it in their insanely crowded lot. Since my reverse is going out, that might be a problem parking it at the trans shop's yard. The RV place would need it backed up too but maybe their own vehicle that could back it up for me if I drop the trailer and hitch it to theirs. An extra 10 miles total in the city in 1-2 will probably be fine on this dying trans since 3/R are what's going.

 

[Brian VT]

I thought C6s were bullet-proof?
But I guess yours does get worked pretty hard.
I'm no transmission specialist but it seems to me that too cold is almost as bad as too hot?

 

[Cubey]

I thought C6s were bullet-proof?
But I guess yours does get worked pretty hard.
I'm no transmission specialist but it seems to me that too cold is almost as bad as too hot?

Well it's 37 years old, the seals are probably what went bad and are causing temps to be too high or something since the fluid has turned dark very fast. It could be a clogged cooler too, who knows? I have never put any trans repair additives into it, but can't speak for past owners. And maybe the clutches have just gone bad from age too.

I have heard that too big coolers can be a problem, but I'll see what the trans shop guy says when I drop it off. If he thinks the one I got is too big, I can send it back (free returns) and just have him get one he thinks is a better size. I'll have him remove the factory cooler and install the new one, despite the probably extra $100+ labor, so that way everything is fresh and clean for the new transmission.

That's another reason I'm thinking about bypassing the radiator, so any nasty old crap in the trans portion doesn't end up in the new trans, if it's not clogged up even.

Plus in case of a rad internal failure, water can't mix into the trans. That's a thing that can happen, I think? It is the original radiator, after all, and leaks a tiny but externally, but not enough to justify replacing since it still cools fine and only needs coolant added a couple times a year. (maybe a gallon per year at most).

But yeah, I'll see what the shop guy says about it once I'm there.

 

[gandalf]

If you're worried about running the transmission too cool you can have a temp sensor in the line. It will cut off flow to the cooler and return the fluid to the transmission until the fluid temp hits a certain point. That will eliminate the possibility of running the transmission at a temp below it's optimum operating point.

I'm running a Long Tru-Cool Max, model LPD 4739, with a GVW rating of 40000. It came with the inline sensor I mentioned. Picture below. The Costco card is there for size.

 

[Cubey]

I'm guessing that it would be hard to run it too cold on this setup. This is always loaded down, unlike a pickup that can drop a trailer and empty the bed. I do 2500-3000 mile oil changes because 2500 is the dusty/heavy load OCI for IDIs. I do run the PSD filter so a bit over 2500 is probably ok filtering wise.

But I will keep that in mind. It wouldn't be hard to add in if needed later.

 

[Black dawg]

With no locking converter, c6s dont have any issue getting warm.....and will be worse with the GV.

 

[Cubey]

With no locking converter, c6s dont have any issue getting warm.....and will be worse with the GV.

Well, something turned the fluid dark in short order in this dying one, but slipping could be why? I'm no expert on such things.

(edit: oh i think i see what you meant, they get hot fast you mean?)

The fluid I removed in 2020 didn't look that bad, but I had no idea how old it was so I felt it was a good idea to change it. I drained the torque converter too.

I noticed reverse beginning to slip I think around last October in a place that requires backing into RV spots but it wasn't drastic. Only in the past few weeks did 3rd begin slipping into gear and now reverse slips very badly. 1-2 seem ok still, so I'm staying in 2nd gear at 35mph now, on back highways where I pulled onto the shoulder when it was safe to let people pass easily, and the next/last 17 mile stretch is a dividend highway with 2 lanes both ways so people can pass me all they want. I just put on some music and toodle along.

 

[chillman88]

I'm guessing that it would be hard to run it too cold on this setup. This is always loaded down, unlike a pickup that can drop a trailer and empty the bed. I do 2500-3000 mile oil changes because 2500 is the dusty/heavy load OCI for IDIs. I do run the PSD filter so a bit over 2500 is probably ok filtering wise.

But I will keep that in mind. It wouldn't be hard to add in if needed later.

If that is the same one I have, it has an internal thermal bypass so it won't run too cold. It's supposed to bypass until the temperature gets hot. That's one of the reasons I picked the one I did.

 

[trackspeeder]

Leave the radiator in the cooling circuit. Specially with a C6.
This is the primary cooler, it does most of cooling in slow speed and reverse.

Don't bother with a bypass valve unless you are in extreme cold. You will not need it.

As for dark fluid, one or more clutch packs are failing. Clutch material will make the fluid dark.