After a long drawn out process in dealing with our Chevy four speed transmission running hotter than I liked (lots of discussion about it on the forum) I probably became hyper-sensitized to the cooler makers exaggerated claims, ratings based on who knows what real data, and confusing descriptions of their "benefits" over other brands and styles.
I am now looking at a plain old add on cooler for my 1996 Roadmaster so am looking at the lower end of the product lines compared to the large, more race capacity coolers I was for the van.
I have always been a fan of the the thermostatically controlled bypasses for trans coolers, as IMO things like transmission oil just plain work the best between certain limits of temperature, as do the clutches and bearings etc in the trans. It appears lots of the newest transmissions have internal temp control now, as people report seeing relatively high and very consistent temps in them.
Looking at coolers I mainly go by the BTU removal rating, although they never seem to mention the conditions or any standard they rated too. Size and design will mostly track the btu rating between brands, too.
What I am finding is not any of the above different than in the past, but what I am seeing is many more of the coolers claiming to have "automatic internal thermal bypass" built into them to aid in warmup time and cold weather oil flow. Great, I thought, but when I looked at what it really is I think it is not very great, and costs you hot cooling capacity compared to using an external bypass on same size and style cooler.
What the "thermal" internal bypass does is just bypass some of the oil through lower restriction tubes through the cooler so it goes straight through with minimal cooling but easier flow in the cold. They claim that as the oil warms up the flow "automatically" shifts to the small tubes that go through the efficient cooling area. This simple doesn't make sense based on how fluid flow works. The flow will split between all the tubes, all the time, based on the resistance to flow of the tube and the viscosity of the oil, AFAIK. So you get enough cold flow through the bypass tubes and some flow through the cooling tubes when cold and save the trans from oil starvation in cold weather or an overpressure. When the oil heats up you would get more flow in the bypass tubes from reduced viscosity and also more flow in the cooling tubes so, yes, the cooling capacity of warm oil is higher than it is cold, but you are still wasting cooling capacity by sending more oil through the bypass tubes when hot. This means to get the same trans cooling, you would need a bigger cooler and also more transmission oil flow to compensate for the bypass.
It all got pretty clear to me when I looked at the Tru-Cool coolers. They were one of the early pushers of the internal bypass as I remember, and still are. But, they also have a line of coolers called Max that come with an external thermal bypass and they have significantly higher cooling vs area. My guess is that to get the better cooling they got rid of the internal bypasson those coolers, but I haven't heard back on my inquiry to them yet.
I think the bottom line on all this is that manufactured have figured out that big coolers and cold climates were giving starvation when cold issues and they are putting in the bypasses to address that issue. This is good, but it should be stated that it costs you cooling capacity at any given size cooler. I do believe the cold flow needs to be addressed, but an external thermal bypass is a much better choice, IMO. This is true for both standalone coolers and if you run through the regular radiator cooler after and addon cooler as we are talking about oil starvation when cold, although the oil will run warmer as the engine warms up. The external thermal units seem to hold about a 15* range when using the higher than necessary flow capacity of the run of the mill engine oil bypass units. I have read dozens of rave reviews for the internal bypass units because they the hold the temps down very low in cooler weather in the 100*F range at freezing for instance, but they run warmer in warm weather and not much different than before the cooler was put in. Most them are plumbed to the radiator so that makes sense. It also points out that the addon cooler is not thermally controlling anything in reality.
An external bypass can be installed to bypass both the addon cooler and radiator cooler for much faster warmup in most cases as the water temp will lag some, although it will vary by engine and vehicle. It can also just bypass the addon cooler, which puts you back to be very much like a stock setup when cold, with the radiator affecting the oil returned temps. I prefer bypassing both, but the plumbing is often easier just to put the bypass right at the cooler. I would guess you get a bit more oil flow cold with both bypassed.
Our vans tend to need as much trans cooling, with least air blocked to the radiator and AC condenser as we can get, so it seems like it just wouldn't be a good idea to leave capacity lower to get the ineffective for temp control but effective for addressing cold oil starvation when you can keep the capacity and control temp better with a regular cooler and external thermal bypass.
Any and all input welcomed and appreciated as this is kind of a new thing, I think to throw into the selection process.
Of course if you live in the deep south where it rarely even freezes, you will not have any issues with cold flow with any system.
But you will probably need more cooling in the summer time.
I am now looking at a plain old add on cooler for my 1996 Roadmaster so am looking at the lower end of the product lines compared to the large, more race capacity coolers I was for the van.
I have always been a fan of the the thermostatically controlled bypasses for trans coolers, as IMO things like transmission oil just plain work the best between certain limits of temperature, as do the clutches and bearings etc in the trans. It appears lots of the newest transmissions have internal temp control now, as people report seeing relatively high and very consistent temps in them.
Looking at coolers I mainly go by the BTU removal rating, although they never seem to mention the conditions or any standard they rated too. Size and design will mostly track the btu rating between brands, too.
What I am finding is not any of the above different than in the past, but what I am seeing is many more of the coolers claiming to have "automatic internal thermal bypass" built into them to aid in warmup time and cold weather oil flow. Great, I thought, but when I looked at what it really is I think it is not very great, and costs you hot cooling capacity compared to using an external bypass on same size and style cooler.
What the "thermal" internal bypass does is just bypass some of the oil through lower restriction tubes through the cooler so it goes straight through with minimal cooling but easier flow in the cold. They claim that as the oil warms up the flow "automatically" shifts to the small tubes that go through the efficient cooling area. This simple doesn't make sense based on how fluid flow works. The flow will split between all the tubes, all the time, based on the resistance to flow of the tube and the viscosity of the oil, AFAIK. So you get enough cold flow through the bypass tubes and some flow through the cooling tubes when cold and save the trans from oil starvation in cold weather or an overpressure. When the oil heats up you would get more flow in the bypass tubes from reduced viscosity and also more flow in the cooling tubes so, yes, the cooling capacity of warm oil is higher than it is cold, but you are still wasting cooling capacity by sending more oil through the bypass tubes when hot. This means to get the same trans cooling, you would need a bigger cooler and also more transmission oil flow to compensate for the bypass.
It all got pretty clear to me when I looked at the Tru-Cool coolers. They were one of the early pushers of the internal bypass as I remember, and still are. But, they also have a line of coolers called Max that come with an external thermal bypass and they have significantly higher cooling vs area. My guess is that to get the better cooling they got rid of the internal bypasson those coolers, but I haven't heard back on my inquiry to them yet.
I think the bottom line on all this is that manufactured have figured out that big coolers and cold climates were giving starvation when cold issues and they are putting in the bypasses to address that issue. This is good, but it should be stated that it costs you cooling capacity at any given size cooler. I do believe the cold flow needs to be addressed, but an external thermal bypass is a much better choice, IMO. This is true for both standalone coolers and if you run through the regular radiator cooler after and addon cooler as we are talking about oil starvation when cold, although the oil will run warmer as the engine warms up. The external thermal units seem to hold about a 15* range when using the higher than necessary flow capacity of the run of the mill engine oil bypass units. I have read dozens of rave reviews for the internal bypass units because they the hold the temps down very low in cooler weather in the 100*F range at freezing for instance, but they run warmer in warm weather and not much different than before the cooler was put in. Most them are plumbed to the radiator so that makes sense. It also points out that the addon cooler is not thermally controlling anything in reality.
An external bypass can be installed to bypass both the addon cooler and radiator cooler for much faster warmup in most cases as the water temp will lag some, although it will vary by engine and vehicle. It can also just bypass the addon cooler, which puts you back to be very much like a stock setup when cold, with the radiator affecting the oil returned temps. I prefer bypassing both, but the plumbing is often easier just to put the bypass right at the cooler. I would guess you get a bit more oil flow cold with both bypassed.
Our vans tend to need as much trans cooling, with least air blocked to the radiator and AC condenser as we can get, so it seems like it just wouldn't be a good idea to leave capacity lower to get the ineffective for temp control but effective for addressing cold oil starvation when you can keep the capacity and control temp better with a regular cooler and external thermal bypass.
Any and all input welcomed and appreciated as this is kind of a new thing, I think to throw into the selection process.
Of course if you live in the deep south where it rarely even freezes, you will not have any issues with cold flow with any system.
But you will probably need more cooling in the summer time.
