Auxiliary trans cooler, thermal bypasses and such.

Buddha.

Lurker
During normal driving my scan gauge2 was indicating my trans temp was getting up to 220-225 everytime I drove it if it was over 80f ambient temps. Didnt matter if I was parked, in stop and go, or cruising down the highway. I wonder how the trans has lasted ten years like this if this is the way its alwsys ran.
I bypassed the stock in-radiator cooler and installed a 24k cooler in front of the condenser and to make sure it was getting up to operating temp i installed an oil thermostat that's not supposed to send oil through the cooler untill temps are about 180 instead it sends the fluid back to the trans. Seemed like a good set up.

Installed it today before work pretty trouble free. Huge differance. I let it idle for ten minutes before heading out and the fluid was only 90 degrees f. It would have been twice that temp before the change. Driving to work 30 minutes it only got to 155 degrees after slowly climbing to that. Again much cooler than before. Granted its an unseasonably cool day of 60f today. I was expecting the temps to quickly rise as before but then top off at about 180.

Is the thermostat malfunctioning? There are only three oil bypasses on the market i may try another but they are $50.
 

rayra

Expedition Leader
Do the late edition Blazers / midsize trucks have their trans cooling lines routed thru the radiator tank, as the full size trucks do? Is it possible you have some sort of line blockage there? If routed that way, did you delete that portion when you plumbed your new trans cooler?

I ask as my C-10 is plumbed to the tank with no additional cooler, while our Tahoe & Sub with the tow package have both that AND an external cooler in series.

Too, if plumbed thru the radiator tank for cooling, a trans is going to pretty much run same as your coolant temp, unless it's really working hard.
 

Buddha.

Lurker
Yes the factory setup is just the in radiator cooler. Im not using that cooler at all right now. The coolant temp ranges from 195-210 depending on ambient temps. The trans was 220-225 in the same conditions. Ive read 170-190 is a much healthier range.

Im concerned its going to run too cold in the winter. I installed the thermostat to keep minimum temps up but im not sure its working.

This is the unit.https://www.amazon.com/dp/B008BTJFJ4/ref=sr_ph?ie=UTF8&qid=1440025807&sr=1&keywords=tru+cool+bypass
 
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VanIsle_Greg

I think I need a bigger truck!
I used a B&M Supercooler for my trans cooling duties. It has a built in low temp bypass so it does not overcool, and is supposed to keep the temps closer to 170* as I recall (cannot locate any data on this)? I added it inline with my factory Jeep transmission heat exchanger on the rad. I did this for 2 reasons:

1. In winter it will help heat up the trans fluid that is likely too cold to function properly (too cold is also not good)
2. To keep things simple and still get some cooling from the rad

In about 5 years of use it has performed very well. In the process of installing it I also added a B&M Trans Temp gauge to keep an eye on cooling efficiency, but the ODBII gauges on my tablet also will tell me what is going on. It is all working as it should and I never see temps even close to 250*.

You might be right about the overcooling in winter. I would re-introduce the factory heat exchanger into the mix, as it should help warm the cold fluid.
 

Buddha.

Lurker
I thought about keeping the factory cooler in the loop but its on the cold side of the radiator so i wasn't sure if itd add anything
 

rayra

Expedition Leader
I thought about keeping the factory cooler in the loop but its on the cold side of the radiator so i wasn't sure if itd add anything
. Heh. 'cold side' is a relative term. There's nothing 'cold' about it. When at operating temp it won't be any cooler than your engine thermostat rating, typically 180F-195F. Keep that in mind too, GM thought that was a fine operating temp for your trans.

Too, the electric fans on our Tahoe and Sub don't even kick on until their sensor hits 230F, that too might be contributing to a higher trans temp in your stock config.

I'm still suggesting a possible blockage of the in-tank trans cooler, about the only thing that explains such a wide disparity in temps. blowing it out from the lower connection would be a messy proposition.
 

Buddha.

Lurker
I could try back flushing it with some air and a rag i guess and put it back in the loop. Still seems like the 180 degree oil thermostat should keep the fluid from going through the cooler untill about 180. Or maybe it is and the transmission just generates that little heat on its own.
 
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Herbie

Rendezvous Conspirator
On the Astro/Safari vans (which have a lot in common with the Blazer), the stock tranny cooling is similarly anemic. Standard practice for our guys is to plumb in a secondary cooler after the stock in-rad tranny cooler. We haven't found that bypassing is necessary, and it makes the plumbing very easy. Nobody has used (or needed) a thermostat on that system, so far as I know.
 

1stDeuce

Explorer
. Heh. 'cold side' is a relative term. There's nothing 'cold' about it. When at operating temp it won't be any cooler than your engine thermostat rating, typically 180F-195F. Keep that in mind too, GM thought that was a fine operating temp for your trans.

Too, the electric fans on our Tahoe and Sub don't even kick on until their sensor hits 230F, that too might be contributing to a higher trans temp in your stock config.

I'm still suggesting a possible blockage of the in-tank trans cooler, about the only thing that explains such a wide disparity in temps. blowing it out from the lower connection would be a messy proposition.
Rya, you're correct that cold is a relative term, but the "cold" side of the radiator should NOT be at the same temperature as the engine thermostat... The engine thermostat keeps the coolant coming out of the engine at 195-ish, but once that coolant hits the radiator, it begins losing heat, and cools a significant amount, or your engine would overheat. What Buddha is saying is that most modern radiators are set up to flow left to right, or top to bottom, and there is a "cool" side tank opposite where the hose at the thermostat dumps into the radiator. That side of the radiator should be at least 30F cooler than the opposing side if the system is working correctly. You're right that it's not really "cold", but it's certainly not at the temperature of the thermostat, or the engine will begin to overheat.

As for your question about function of the new cooler/bypass, it makes sense to me that the trans is now taking longer to warm because there's no heat going in from the radiator, as there was before. Unless you're slipping the converter a LOT, a trans generates MUCH less heat than an engine, which is why many people leave the factory cooler inline when adding an aux cooler. If you add the aux before the factory radiator cooler, you'll get faster warm-ups because the radiator can then help warm the trans, at least until it reaches the temperature of the "cool" tank. But because the cool tank shouldn't be getting over 170-180F in normal driving (Usually lower than that when the radiator has good airflow) it won't really add enough heat to make a difference. You'll then have the best of both worlds: Faster warmup with the engine helping out, but much improved cooling with the added aftermarket cooler. And you don't need the bypass anymore, and you can just flow trans fluid through both coolers all the time. :)
Chris
 

rayra

Expedition Leader
I used to think such things, with my old C-10. Our Tahoes and now my Sub however have 195F thermostats and I found out that the electric cooling fans on my radiator are thermo-controlled to not even come on unless the temp reaches 230F. I'd always considered a vehicle operating temp above 212F/boiling was a Bad Thing. Apparently for these newer computerized wonders it's a design criteria. Hence my comments about 'cold' being relative. Maybe 'less hot' or 'sub-boiling' is a more accurate phrase. But I agree with the structural logic of what you posted. The missus' current Tahoe routinely operates at an indicated temp of 205F and nothing I've tried so far makes it run any cooler. somethings she comes home from her highway commute and the heat coming out the grill at rest in the driveway is blistering.
My Sub on the other hand runs an indicated 205F (same engine / trans combo as the Tahoe) and I just recently ran a torture test during our big heat wave, flogging it over and back on our local vehicle-killing I-5 'Grapevine' mountain pass grade. just over 4000', ~1300' at both ends, and a very steep incline coming southbound. Ran it with a heavy foot and both ACs running and my temp never budged. Glorious. But I was worried the whole time, by years of conditioning in other vehicles.
Can't really say what's happening to make that even possible. 'great engineering' is the closest guess I can make. I don't seem to understand it anymore. These newer heavily computerized engines don't do what I expect them to.
 

IdaSHO

IDACAMPER
Yes, there are many 200+ degree t-stat equipped vehicles now days.

And for very good reasons.

The overall efficiency of the engine goes up as the temp goes up. To a point, obviously :Wow1:


My 7.3 Powerstroke has a 203 degree t-stat. And normal operating temp when working hard is in the 210-225 range.

That said, I have a large trans cooler in front of the radiator, and the trans temps rarely get above 200
 

Buddha.

Lurker
I Installed lS1 fans on the truck for no good reason. The fan controller is a very good unit and turns on the fans 0-100% based on how hot the engine is. In the process of this install I carelessly popped a hole in the radiator. So now I have LS1 fans and a new radiator. The engine temp hovers around 200F plus or minus 5 degrees, I have a 195F thermostat. Engine temps are much more stable than before. I introduced the in-radiator trans cooler into the circuit when I installed the new radiaior. The trans temps dont seem to warm up any faster than when the radiator was out of the circuit. The temps only hit about 140 on my 25 minute commute. The other day however doing errands, driving around for a couple hours with an ambient temp of 75F the trans temps hit 180-185ish. This seems excessive for a vehicle that is not towing and has extra cooling. The auxiliary trans cooler is appropriate size for a midsize truck pulling 5,000lbs(my tow rating) or for a full size with a smaller load.

I suspect the trans temps wont get much higher during towing, fingers crossed. I have to chase wires for the trailer harness before I can test that out though.
 
There are a lot of variables between vehicles, but on my truck (yes, a Dodge) I'm only using a engine mounted water cooler for the trans. It's a water to trans heat exchanger mounted on the side of the block. The temps never go past 120-125 (PAN temp) on the road, but will reach 180 after more than 30 minutes of idling in 90+ heat. So how 190 degree radiator coolant doesn't heat up a transmission on the highway I have no idea. Just FYI.
 

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Buddha.

Lurker
Driving to work Christmas day at 6am I noticed a fog was forming on my windshield but only on my passenger side, this seemed like it might be a problem. I thought maybe my heater core had let go and steamy coolant was coming up on my windscreen. I was only ten minutes from work so I tried to make it. When the engine rpm's started to rise rapidly but my speed was dropping fast I knew it was the tranny. I coasted up a nearby off ramp and a couple of cops pushed me into a parking lot where I waited for a tow.

The rubber tranny line popped off the bypass valve and dumped all the fluid. I put the line back on, filled it back up to full (about 6 qts, half its fluid), and it's been running and driving fine ever since. What a PITA though!

I used fuel injection clamps because they looked better constructed than regular hose clamps. I'm going to swap them out for the latter, and double them up.
 
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