Debate me. Separate oil and trans coolers or in radiator.

One of the things I'm going to have to deal with on the K30 is the oil cooler. My diesel radiator doesn't have an oil cooler built in so I was planning on an external oil cooler. In my mind it seems better that way. Truthfully I'd rather the trans cooler to be dedicated also. The other side says well it was designed to be all in one. I've never heard of a radiator failing by mixing the fluids or just for trans or just oil. Added bonus is I can use factory lines to connect everything.  I like that there would be off the shelf replacement parts.  What are your thoughts?

I like them together. When done right they all buffer each other and keep temps where they should be. Packaging is good. The downside is when you have maintenance which requires pulling the radiator and that means a huge mess of lines and fluid. 

Separate coolers. With thermostats. 

There is plenty of history of cooling systems mixing fluids.  But that is another thread.  Part of the reason for coolers built into the radiator is (besides simplicity)  to maintain the correct operating temperature of the transmission. 

Dusterbd13-michael said:

Separate coolers. With thermostats. 

Wrong!!!!!!!! Cold oil or transmission fluid will arrive at a stable temperature when combined with coolant.  Cold oil is thick oil and takes longer to get to critical spaces same with trans fluid. 
On race cars they are separated for packaging purposes  and carefully brought up to temperature prior to  use. Maybe even preheated separately. 

In reply to frenchyd :

If the thermostat doesn't open until say 180 wouldn't the oil be warmer first inside the radiator?

If you need additional cooling for the trans, run a trans cooler in series with the cooler in the radiator. Should go: Transmission > Radiator cooler->Trans cooler-> Transmission. 
 

I've successfully run an in-line oil cooler with a remote filter mount in the past. It's not a bad way to do things. 
 

The key is to remember that fluids can be too cold as well as too hot...

I will not run my trans fluid through the radiator, not since i had an internal cooler fail and fill trans with coolant and kill it.  

Mixing fluids in one heat exchanger is bad.  It can lead to intermix.  Heck the Russians have a few submarines at the bottom of the ocean because they thought liquid sodium / water heat exchangers were a good idea.  I've always hated mixing fluid systems.  But yes, there is a buffering effect. 

I know my parent's Van was having trans overheat issues with the cooler/radiator combination.  An external cooler fixed the issue. 

Stampie said:

In reply to frenchyd :

If the thermostat doesn't open until say 180 wouldn't the oil be warmer first inside the radiator?

If the transmission is -23 and the water temp is -23. The trans mission will remain -23 while the water in the radiator quickly warms up as the engine warms up. If they are combined in one unit temps will be up to say 50 for both the transmission and radiator/engine/ heater. 

 

As a separate unit the fluid in the transmission won't start warming up until put in drive and started working. 
Now that is a bit of a extreme example to make the principle easy to grasp.  To those who think 40 degrees is freezing  it still applies.  Would you start your car rev it to redline and slam your stone cold (40 degree) transmission into drive? 
Of course not. Too cold/ thick of oil is just as bad as too hot. 

What you’re missing is the heat transfer from the engine coolant to the oil. It’ll speed up the warming of the trans or engine fluid. OEs put oil/water heat exchangers on cars from the factory for exactly this reason. It might slow the coolant temperature rise slightly but overall it’s better for the vehicle. 

Separate heat exchangers is always going to make more efficient use of the available airflow.  Combining multiple fluids into a single unit is for packaging reasons, plus the cold-start benefits that Keith mentions.

Depends on application... if you have only a small amount of heat to remove, combined is fine, reduces complexity and therefore the likelihood of problems.  If you are towing or racing, extermal.

You could probably use the Diesel oil cooler that GM used on the trucks. One in my 93 is fairly compact and would be easy to fit, plus cheaper than a lot of aftermarket ones.

My thoughts...

Oil (either trans or engine) needs to be at the RIGHT temperature.  Drivers too often think that cooler is better, but that is not the case.  Trans fluid is hydraulic fluid as well as lubricant.  The whole transmission is designed to operate best in a certain range of temps.  Too hot and things burn.  Too cool and the thicker properties of the fluid can't properly operate the hydraulics as they were designed.

Engine oil is the same way.  Too cool and it can't flow into the gaps like it should and you aren't lubing properly.  If you go way too cool, you risk spiking oil pressure and opening the bypass valve which means you're not filtering.  It also wants to be hot enough to evaporate/burn off things like blowby hydrocarbons and condensation.  Of course, too hot has drawbacks as well.  Oil too thin to properly suspend bearings, lower pressure, and cooking additives and hydrocarbons.

The benefit to having a radiator circuit for the transmission is that it helps get the transmission up to temperature as much as it sheds heat from the transmission.  People fight me on this a lot, but I get so irked at people who insist on going crazy with cooling.  Drivers like cool.  Engines like hot.

I will also say that transmissions don't like complexity.  An inline thermostat is a big no-no, especially for some transmissions.  Many transmissions (including the one in your K truck) rely on the cooling circuit as part of the lubrication circuit.  Simply stopping the flow of fluid can fry that trans in short order.  You might be thinking a bypass stat would be better, but it's just an extra failure point waiting to happen.  Unless you install a trans temp gauge and monitor it religiously to make sure the temps don't spike (stuck closed) or never get warm enough (stuck open), just skip it.

The real answer here is to get a radiator with a circuit for the trans.  If you want additional cooling (and by that I mean only if you NEED additional cooling), then install a secondary cooler.  Put it in front of the radiator, oversize it, then send it back through the radiator circuit.  Don't fight me on this, I'm right.  This has all kinds of benefits.  If you just randomly send all the fluid through an external cooler, you have no control over the fluid temps.  Did you oversize and it's too cool?  Did you undersize it and it's too hot?  Not to mention, it will be vastly different temps if you're stop and go, highway, towing, etc.  Putting the extra trans cooler FIRST means that you can't oversize it.  Let's say you're sending 230 degree fluid from the trans.  If you send it through the radiator first, then the external, you are dropping the temps to 200 in the radiator, then randomly dropping them to whatever bulk heat gets shed in the external and sending back a big question mark to the transmission. If you do the external first, you can drop it to whatever you want... 180 maybe? Then sending it back through the radiator will bring it back up to the proper temperature. (and draw some heat out of the coolant as well instead of adding).  Always put the known entity last in the circuit... in this case the radiator circuit.

For oil cooling, I would verify that you need it first.  Randomly adding cooling can be a bad thing.  Install a gauge, hitch a trailer to it, wait for a 90 degree day, and go climb a mountain with your foot to the floor.  If the oil temps don't get over 230, you don't need an oil cooler.  If they don't get over 250 for synthetic, you don't need an oil cooler.  The oil in an engine spends a considerable amount of time on the other side of water jackets. and is pretty good at cooling itself.  Ford 460, not so much.  B and RB mopars, not so much.  Chevys... pretty good.

Recon1342 said:

If you need additional cooling for the trans, run a trans cooler in series with the cooler in the radiator. Should go: Transmission > Radiator cooler->Trans cooler-> Transmission. 
 

I've successfully run an in-line oil cooler with a remote filter mount in the past. It's not a bad way to do things. 
 

The key is to remember that fluids can be too cold as well as too hot...

I agree with everything, but you contradict yourself with the flow of trans fluid.  If you send it to the radiator then the external, you have no idea if you're making it too cool.  Use the heat transfer to your advantage.  External first, THEN radiator.

In reply to Curtis73 :

You're right. I have a hard time and cannot brain well when I am tired...

Haa... can't brain well.

In reply to Curtis73 :

Comes from a saying in our family when someone pulls a stupid or goofy mistake-

"Sorry, I cannot brain today, I has the dumb"

It's our way of saying oops...

I can only say this. My land rover has a separate trans cooler instead of built into the Radiator. No doubt they thought that divorcing the two would be better for the type of activity a Land Rover is supposed to engage in. For your normal every day car, by all means combining them is probably the best idea, for a vehicle that might see any kind of extremes in usage or environment, I would prefer them to be divorced.

Patrick said:

I will not run my trans fluid through the radiator, not since i had an internal cooler fail and fill trans with coolant and kill it.  

See 2005-2008 nissan xterra/frontier/pathfinders. Many a replaced transmission.

mad_machine said:

I can only say this. My land rover has a separate trans cooler instead of built into the Radiator. No doubt they thought that divorcing the two would be better for the type of activity a Land Rover is supposed to engage in. For your normal every day car, by all means combining them is probably the best idea, for a vehicle that might see any kind of extremes in usage or environment, I would prefer them to be divorced.

Yes, however they have millions of dollars of R&D, and if I'm not mistaken they use an inline thermostat and a trans cooler circuit that doesn't require the circuit for lubrication.  At least the Jatcos didn't.  Just copying their idea isn't something you can do with a SWAG.  That's kind of like saying "NASA uses shuttles instead of rockets, so my next space vehicle will be a shuttle."

MrChaos said:

Patrick said:

I will not run my trans fluid through the radiator, not since i had an internal cooler fail and fill trans with coolant and kill it.  

See 2005-2008 nissan xterra/frontier/pathfinders. Many a replaced transmission.

Or Mopars that had a check valve in the cooler line that gunked up and killed it.  We hacked out every single one when we did a rebuild on a Mopar.

I will say, however, that billions of cars out there use a radiator circuit and they're perfectly fine.  I don't think a manufacturing or engineering flaw on one or two models of vehicle constitutes the need to try and re-engineer the whole world.

frenchyd said:

Dusterbd13-michael said:

Separate coolers. With thermostats. 

Wrong!!!!!!!! Cold oil or transmission fluid will arrive at a stable temperature when combined with coolant.  Cold oil is thick oil and takes longer to get to critical spaces same with trans fluid. 
On race cars they are separated for packaging purposes  and carefully brought up to temperature prior to  use. Maybe even preheated separately. 

If you stack the coolers, they can still provide that buffering effect. 

We used two pass radiators with a built in oil cooler on our stock cars for years.  It seemed to be the preferred way of doing it so both fluids stayed the temperature they should be.