May be a stupid question about transmission coolers but…

[72c20customcamper]

I’ve noticed when pulling that my trans stays about 150 to 170 most times on long hills and heavy loads it has climbed over that for brief periods . This is directly out of the trans . My water temps hover around 185-190 mechanical gage in the head . Again it’s climbed to 220 ish on long inclines . Both are not really a problem but if the trans is say 180 and climbing going into a 190 and climbing radiator would it not be beneficial to bypass the trans cooler in the rad since the trans fluid is always lower than the coolant . Small load pulled the hill going to my house 17% plus grade

I don’t use the truck in cold so no need to warm the fluid .

Edit: Forgot to mention I have a large auxiliary transmission cooler in front of the radiator

[Steeveedee]

I've had (before I got control of the cooling system) my engine temp to 260º and the trans right behind it at 230º, iirc. I don't smell burnt oil in either case. I do have a cooler (not well placed) at an angle under the bumper. It is plumbed in line with the integral cooler in the radiator.

I don't like the way the added trans cooler is mounted. It was OK when my PiL towed a 4k Lb trailer, but our 6k Lb (dry) trailer is challenging it. I'm thinking trying fans on it first. In my case, a by pass might also be better, Where I live it hasn't frozen in years.

[joedoh]

believe it or not, you should ALWAYS route the trans cooler through the rad if you have that option.

two reasons

1. the trans takes longer to warm up with an external cooler, and a cold trans is a sluggish trans. the engine warms up much faster and works as a trans fluid heater in warmup and freezing weather.

2. surface heat transfer works much better in fluid than air (yes air is a fluid, but a relatively weak one), the fluid allows conduction of trans fluid heat to the coolant through the body of the cooler, increasing the efficiency of the transfer. plate and fin external coolers rely on CONVECTION, convection is pretty inefficient which is why you need such a LARGE radiator or external trans cooler compared to the little tiny trans cooler mounted in the radiator.

transmission damage is exponential over about 300 degrees, and your radiator cooling system can do a tremendous amount of heat transfer before it gets to even 260. the best external only trans cooler will struggle in high humidity to shed enough heat by convection before the fluid goes back in the trans, this is called thermal runaway. when you are PARKED or STOPPED IN TRAFFIC an external cooler only cools by what it can radiate away, with no air movement. imagine testing bath water temperature by 1. holding your hand over the bath water (convection) or 2. by putting your hand in (conduction)

a lot of guys with heavy duty trans applications will ADD a plate style trans cooler to the existing rad cooler to keep the warmup/cold weather performance and help shed heat in heavy towing situations. my neighbor followed this advice on his tow rig and his trans temp never gets over about 200.
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[72c20customcamper]

I understand the properties of liquid cooling as apposed to air . Use it all the time with a plate chiller making beer .

My reasoning is the trans never gets warmer than the radiator even climbing long grades like the mountains in PA on 81. In fact it’s usually 20 to 15 degrees cooler than the engine . My system is line running to rad which has the sensor inline then exiting the rad to the cooler mounted directly in front of the radiator so it gets air from movement and the engine fan . It’s never gone over 210 but the engine has been at 220. This was towing my 68 to Carlisle last year in August . Running empty the trans never goes over 150 .

Guess I’m overthinking it and most likely leave as is.


My Cummins has a plate cooler with heater hose running to it if I’m not mistaken the fluid runs from a giant cooler in front of the rad back to the plate cooler then to the trans I believe it’s actually to warm the fluid a little . There is no cooler in the radiator itself

[LS short box]

On my LS/auto swaps I run a big stacked plate cooler in front of the radiator. So when the radiator warms up and the electric fan comes on it pulls air thru the radiator and the trans cooler.

[Tom]

Everything is good temps wise, I'd leave it alone.

[57taskforce]

Originally Posted by Tom

Everything is good temps wise, I'd leave it alone.

I was thinking the same honestly. 280+ is where I’d be worried. Fluid condition/life will tell you a lot about temps. If it looks and smells burnt fairly quickly after a fluid/filter change it’s running too hot. I’ve started using dex 6 in my older transmissions with really good success. I’m sure someone’s going to come on here and say dex 3 only for the older stuff but it’s not true in my experience. I’ve seen it drop trans temps 15-20 degrees in a couple of junky-ass 700R’s(I personally hate them) all with increased shift quality. I put it in my recently acquired IROC-Z with out hesitation.

[joedoh]

Originally Posted by 72c20customcamper

My Cummins has a plate cooler with heater hose running to it if I’m not mistaken the fluid runs from a giant cooler in front of the rad back to the plate cooler then to the trans I believe it’s actually to warm the fluid a little . There is no cooler in the radiator itself

if its got a heater hose connected to it, that coolant is making it to the radiator to shed the heat, its not just there to warm the fluid.

[Dead Parrot]

The OEM in radiator trans cooler is in the cool part of the radiator, post cooling, while your engine temp sensor is in the hot part of the engine. If the radiator system is working correctly, the trans cooler will always be in engine coolant that is a lot cooler then what the engine temp gauge is reading.

[72c20customcamper]

Originally Posted by Dead Parrot

The OEM in radiator trans cooler is in the cool part of the radiator, post cooling, while your engine temp sensor is in the hot part of the engine. If the radiator system is working correctly, the trans cooler will always be in engine coolant that is a lot cooler then what the engine temp gauge is reading.

This makes sense

[Tom]

Originally Posted by 57taskforce

I was thinking the same honestly. 280+ is where I’d be worried. Fluid condition/life will tell you a lot about temps. If it looks and smells burnt fairly quickly after a fluid/filter change it’s running too hot. I’ve started using dex 6 in my older transmissions with really good success. I’m sure someone’s going to come on here and say dex 3 only for the older stuff but it’s not true in my experience. I’ve seen it drop trans temps 15-20 degrees in a couple of junky-ass 700R’s(I personally hate them) all with increased shift quality. I put it in my recently acquired IROC-Z with out hesitation.

I've heard a lot of talk about dex 6 not being compatible with some older seals. Enough so that I made sure not to get it when I had my 4L60 rebuilt.

[57taskforce]

I’ve seen similar things online BUT… It’s completely backwards compatible with dex 3, 2 etc. there is no issue running it with older seals. It was designed and intended as the replacement to dex 3 etc fluids.

I’ve had really good results running it. There’s a lot of BS info on the inter webs on the subject. I’m going off of my real world experience.