Bigger RV trans cooler: how big?

[Cubey]

I'm considering upgrading the rather small factory(?) trans cooler on my RV since I will be pulling a small enclosed trailer behind it now:

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The Valvoline Merc/Dex fluid is fresh right now with maybe 10 miles on it since I changed many months ago and test drove to get the level correct. What came out was slightly dark (without me towing). It wasn't totally brown yet, but it was due for a change since the age of the fluid was unknown. There was a 4WD filter it, so at least I know it wasn't 35 year old factory filled fluid, like the rear axle oil probably was.

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How big of a cooler do I need? I could get a BIG one that's about 11x11" for about $50 tax and all, which says it's good for Class A motorhomes. My Class C is basically as big, if not bigger, than the smallest compact Class As.

This exact one seems to be sold under a ton of other brands, including Hayden (O'Reilly, Amazon) and Imperial (Advance Auto) but the Napa price I'm seeing based on the local store selected is the best price ($45.49) beating Amazon by $5. https://www.napaonline.com/en/p/ATP17508

Would that be too much cooling? Or is there even such a thing as "too much cooling" on a 27ft motorhome that is always loaded and pulling a 5x8 enclosed trailer?

 

[Cubey]

Maybe the cooler I have is JUST enough to get by without it being too small. The factory cooler is roughly 11x7 based on rough measurements from outside the grill.

Hayden says this in their catalog PDF under models of trans oil coolers:

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Source: https://www.haydenauto.com/media/5475/oil-cooler-brochure_individual-pages.pdf

So my factory cooler is kind in between those two, with an 11k GVWR chassis that will be pulling maybe 1500lbs a most. The trailer is so tiny, it won't much in the way of wind resistance behind that brick of an RV.

I might take a trip to the you-pull-it salvage yard and have a look around for a cooler since money is very tight right now. They charge $24 tax and all for trans oil coolers, according to their website. They have tons of trucks, so I can probably find a good one.

Or, just put it off until spring when I should we WAY better off money wise again. I'm probably not gonna be seeing temps higher than 80-85 degrees anytime soon and I won't be crossing any mountains. I might be heading to the CA/AZ state line area, but I'll be taking the I-10 route, not I-40.

 

[chillman88]

There IS a such thing as too much cooling. The cooler I put in my truck is the 11x11 Hayden. It is supposed to somehow have a built in thermostatic bypass so it won't overcool.

Can't tell you exactly why overcooled transmission fluid is bad, but I know it's not good if it doesn't get up to temp.

 

[gandalf]

This is the transmission cooler I have: TrueCool Max. I have never had a problem with the transmission running hot. My last tow was a 6x10 trailer, loaded waist highwith mostle paper and books, north to the Canadian border, 1000 miles, and then back with household goods. Granted, it will cost more than the $50 cooler you mentioned.

Warnose also has a thread going currently, Hot Transmission, you might want to follow.

Here is the truck and trailer for the run to Canada.

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[Cubey]

There IS a such thing as too much cooling. The cooler I put in my truck is the 11x11 Hayden. It is supposed to somehow have a built in thermostatic bypass so it won't overcool.

Can't tell you exactly why overcooled transmission fluid is bad, but I know it's not good if it doesn't get up to temp.

That's a different line of coolers from the one I was looking at. This should be yours, #699: https://www.amazon.com/Hayden-Automotive-699-Transmission-Cooler/dp/B01N8S3X3L

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[chillman88]

That's a different line of coolers from the one I was looking at. This should be yours, #699: https://www.amazon.com/Hayden-Automotive-699-Transmission-Cooler/dp/B01N8S3X3L

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Just checked in my email and yes, the 699 is the one I used. I can't really comment on it other than it looks nice, as I don't have a gauge to monitor temps.

 

[Cubey]

Just checked in my email and yes, the 699 is the one I used. I can't really comment on it other than it looks nice, as I don't have a gauge to monitor temps.

The one I was eyeing, #679, looks like yours but lacks the internal bypass system. Not sure I'd want one of those without a trans temp gauge. If it stops working when closed, you'd overheat the trans.

I'd rather go with #678 below that is listed for Class C motorhomes without the bypass. I don't live in the midwest or Alaska, so I don't really need that feature in winter. The factory cooler is still tied in to the radiator, so it can get heat from there still if I leave it set up that way. I also don't drive around in 100+ degree temps, so I don't need the biggest cooler possible. If I was towing a car behind it, then I'd probably want something that big.

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[chillman88]

That's a fair thought. But I drive in the winter and I don't think the cooler is needed at 15 degrees for a 15min drive, but it definitely is when it's 95 degrees with a trailer in tow. I figured it was the best of both worlds for me. I doubt yours will stay cold very long, unless you end up spending a winter up north, which I'm sure is not in your plans!

 

[Cubey]

This is the transmission cooler I have: TrueCool Max. I have never had a problem with the transmission running hot. My last tow was a 6x10 trailer, loaded waist highwith mostle paper and books, north to the Canadian border, 1000 miles, and then back with household goods. Granted, it will cost more than the $50 cooler you mentioned.

Warnose also has a thread going currently, Hot Transmission, you might want to follow.

Here is the truck and trailer for the run to Canada.

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Yeah, that thread got me thinking about it. I didn't want to hijack their thread since it wasn't about a motorhome. It's a different beast due to how tall it is right up front. You can't add a wind deflector to the cab like you can on pickups pulling a trailer/5th wheel too.

I don't have a pic of the RV with the trailer hitched up yet since it hasn't been attached to the RV yet (I pulled it home with my F250) but here is a rough mock up in photoshop of how it'll look. Yeah, it's gonna be a bear to back up when I can't see it at all. Thankfully I won't have to hardly ever do that.

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I am tempted to haul around a HFT trailer dolly in case I ever have to move the trailer easier than with the RV. Or bolt a hitch receiver tube to the front bumper and "back in" the trailer by pushing it with the front of the RV so I can see where it's going.

Generally though, I stay in big enough places where it's either a pull through or big enough of an area that I can probably back it in ok. Maybe a caster on the tongue jack would be enough to move it around without a dolly, but it needs to be pretty smooth ground for that.

Another option would be to have a camera mounted up high on the rear so I can see the trailer and the area around it from the driver's seat, like a rear view mirror.

 

[Cubey]

That's a fair thought. But I drive in the winter and I don't think the cooler is needed at 15 degrees for a 15min drive, but it definitely is when it's 95 degrees with a trailer in tow. I figured it was the best of both worlds for me. I doubt yours will stay cold very long, unless you end up spending a winter up north, which I'm sure is not in your plans!

It gets mighty cold in that RV when it's 12-15 degrees even with two 1500W heaters going. The water lines froze up last fall one night in the TX panhandle under that situation, because they run down in a space under the cabinet where the hard wired 30A cord is fed into when stored away. A mini hot water bottle stuck down in there thawed it out enough to get it flowing again within a few mintues, so it was just arely frozen. It burst any thankfully. Pretty sure I had the water hose outside turned off (and unhooked), the water pump turned off, and the faucets open to help avoid that, but of course the water in the line still froze. So no, I won't be spending winters in the frozen tundra of the north.

 

[spg]

Put the biggest trans cooler you can fit in addition to the factory cooling. Heat is the number one enemy of an automatic transmission. Towing generates a LOT of additional heat.

 

[Dirtleg]

Here is what I have been running for the last 13 years.

Pulling a 14k trailer it's never gotten over 210 on the gauge. My transmission has never been the healthiest but without this cooler I'd have lost it years ago.

I am not saying to buy from them specifically just found it in an easy to view format. Rated 40K.

https://cpaddict.com/tru-cool-4739-...AROzIMnu2lLteMadF9NTwzmjDKI3nrV8aAlepEALw_wcB

 

[gandalf]

The Tru-Cool 4739 is what I have. It has never let me down. It's mounted in front of all other coolers by the radiator. It may cost more than you wish to pay, but it's so much less expensive than a new transmission.

 

[Cubey]

Put the biggest trans cooler you can fit in addition to the factory cooling. Heat is the number one enemy of an automatic transmission. Towing generates a LOT of additional heat.

I'd have to probably remove the added factory ("tow package"?) trans cooler shown in the first post since it's right in the middle of the grill. Of course, I can leave the trans connected up to the radiator like it is from the factory, since that provides some cooling too.

Since money is very tight right now, I'm gonna wait. It's got fresh, name brand trans oil and a new filter, so it should be good for a while.

The new trans pan I put on about 6 months ago with a drain bolt allows draining without dropping it, so I can replace about 3/4 of the trans fluid as easily as an oil change now. There is no excuse not to drain and replace every few years, since it's one bolt and not messy. The filter is just a screen, so it matters less about replacing it that often. I put a magnetic drain plug in it to catch any bits of metal. The factory pan had no magnet at all, so that's an improvement right there. The new pan has some dull "fins" which might help with cooling a degree or two more than the completely flat factory pan.

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I'm sure someone towed something early in the RV's life, since it has a 1980s brake controller. Plus someone put in a fuse+breaker (i guess they wanted to be sure) under the hood for the +12v for on a 7 way trailer connector (which is gone, but the wiring is still there). I know that's what it's for since they wrote on the hood's ledge with a sharpie saying it's for "trailer", with an arrow pointing to it. (No fuse in it since it's a bare wire back there right now with no connector)

The RV itself would probably cook the trans before that little trailer would. I'm not sure the trailer will matter much heat wise. The RV is many feet taller and at least a couple feet wider, so it's not really gonna add much head wind resistance. It's also not gonna be that heavy, maybe 1500lbs when fully loaded.

Towing it home 85 miles from where I got it, my NA F250 with 3.55 gears could feel it back there taking off from stops, despite the trailer being totally empty. The old rotten car/truck tires it had though with flimsier side walls might have been to blame for that. It has Maxxis trailer rated tires now. Come to think of it, it did feel like it towed better with the F250 recently since it got the trailer tires. It had about 300lbs of stuff in it too. The RV, being turbo with 4.10 gears, might not notice it at all.

Keep in mind also, this is the original, 35 year old transmission with 35 year old seals in it. So far so good with it. Seals might go before the clutches do. It IS low mileage (about 70k original I suspect) but yeah. On the plus side, it looks super easy to pull a C6 on these vans since you can reach the top of the bell housing from the dog house. The rear support has a big cross member with a single bolt on each side at the frame, so labor might not bad too bad at a shop. Assuming of course, that I can find a trans shop with a big enough garage bay and lift to work on this thing.