2024 LZ0 transmission temperature and thermostat question.

[Green02z71]

Hey All, I've been combing through the forums looking for all the information that I can find on the LZ0 and it's transmission and the relatively high transmission temperatures. I just bought a 24 LTZ LZ0 and also think that the temperature is too high when just driving around. That said, it seems like GM has made an effort to make sure there is an elevated tranny temperature by (from what I've read) adding a transmission fluid heat exchanger that uses engine coolant to either warm up or cool down the tranny temp. depending on which is hotter. Now, if that's the case, deleting the transmission thermal bypass valve and adding a bigger cooler will certainly help to bring the temp. down but won't we still be fighting the engine coolant temperature that runs at 200ish F? Would it not be wise to lower the coolant temperature by replacing the thermostat with a lower temp. model? Then the ATF would only be exchanging heat with a 180ish F coolant temp. I wonder if anyone has replaced the factory thermostat with a 180, and if so, did the tranny temps. also drop as a result? 

Then of course there's the how cool is too cool question which goes back to the seemingly deliberate high temperature that GM has these trannys running at. Are they supposed to run above xxxF minimum temperature? UGH! Any help or answers would be appreciated. 

BTW, I have the PPE bypass block and tranny cooler ready to go in, just haven't pulled the trigger yet.

[newdude]

3 hours ago, Green02z71 said:

Hey All, I've been combing through the forums looking for all the information that I can find on the LZ0 and it's transmission and the relatively high transmission temperatures. I just bought a 24 LTZ LZ0 and also think that the temperature is too high when just driving around. That said, it seems like GM has made an effort to make sure there is an elevated tranny temperature by (from what I've read) adding a transmission fluid heat exchanger that uses engine coolant to either warm up or cool down the tranny temp. depending on which is hotter. Now, if that's the case, deleting the transmission thermal bypass valve and adding a bigger cooler will certainly help to bring the temp. down but won't we still be fighting the engine coolant temperature that runs at 200ish F? Would it not be wise to lower the coolant temperature by replacing the thermostat with a lower temp. model? Then the ATF would only be exchanging heat with a 180ish F coolant temp. I wonder if anyone has replaced the factory thermostat with a 180, and if so, did the tranny temps. also drop as a result? 

Then of course there's the how cool is too cool question which goes back to the seemingly deliberate high temperature that GM has these trannys running at. Are they supposed to run above xxxF minimum temperature? UGH! Any help or answers would be appreciated. 

BTW, I have the PPE bypass block and tranny cooler ready to go in, just haven't pulled the trigger yet.

 

 

So, lets start off with the temps are normal.  GM designed the LM2 and LZ0 10 speed to have a stock TBV of 194F opening temperature.  This is for fuel economy and transmission shift performance.  

 

The transmission cooler lines flow as follow on LM2 and LZ0.  ATF exits the transmission and immediately enters an oil to water heat exchanger.  From there, ATF exits and flows to the TBV.  If the TBV is not opened, ATF will direct back to the transmission. 

 

When the TBV opens up at 194F, ATF will then be directed through the TBV out to the oil to air ATF cooler at the front in the radiator packaging.  This aux cooler has no coolant in it and is used to further regulate ATF temps.  From the aux, it then flows back to the transmission.  

 

Why does it use an oil to water heat exchanger?  Multiple factors, it helps heat up the ATF faster as the engine coolant temps get hot faster and will help warm it, and then once up to temp the exchanger will then regulate those temps, with the aux cooler further aiding when under loads or the TBV is opened. 

 

Thermostat.  You cannot change a thermostat on the LM2 or LZ0 because they don't use one.  These engines use what GM calls Active Thermal Management.  The ATM system uses an engine driven water pump on these, the ATM water flow control valve and two water to oil heat exchangers (one for the transmission, the other engine oil).  ATM via the water flow control valve can infinitely target cooling flow to the block, heads and the heat exchangers as needed to warm or cool faster various components.  There is no swapping to a lower t-stat that can be done here.  

 

So.  All of that to then say...you can install the PPE bypass if you so choose.  What it will do is eliminate the 194F TBV and allow the transmission loop to be open at all times.  You will still be heating the ATF and regulating temps from the heat exchanger it passes through, but it will be able to hit the aux cooler out front immediately to slow down the temp rise. 

 

Are you going to see a 50F drop?  Nope.  "Maybe" all of 5-10 degrees up and running hot, otherwise its just slowing down the rate at which it takes to reach hot operating temp.  

 

[Grover67]

I did the PPE trans oil cooler first. It held the trans temp down some but its being regulated by the bypass. I changed out the bypass with the PPE and it runs about 40-50f cooler overall winter/summer. Just got back from doing some work today at our cottage about 2hrs away. Mostly highway running 80mph, it was 80f out today and once the trans temp stabilized it runs right around 158f. Winter driving here in Michigan it runs a little cooler to a little warmer due the radiator louvers shutting/ regulating. I would just run the bypass and if needed add in the cooler.

[Green02z71]

19 hours ago, newdude said:

 

 

So, lets start off with the temps are normal.  GM designed the LM2 and LZ0 10 speed to have a stock TBV of 194F opening temperature.  This is for fuel economy and transmission shift performance.  

 

The transmission cooler lines flow as follow on LM2 and LZ0.  ATF exits the transmission and immediately enters an oil to water heat exchanger.  From there, ATF exits and flows to the TBV.  If the TBV is not opened, ATF will direct back to the transmission. 

 

When the TBV opens up at 194F, ATF will then be directed through the TBV out to the oil to air ATF cooler at the front in the radiator packaging.  This aux cooler has no coolant in it and is used to further regulate ATF temps.  From the aux, it then flows back to the transmission.  

 

Why does it use an oil to water heat exchanger?  Multiple factors, it helps heat up the ATF faster as the engine coolant temps get hot faster and will help warm it, and then once up to temp the exchanger will then regulate those temps, with the aux cooler further aiding when under loads or the TBV is opened. 

 

Thermostat.  You cannot change a thermostat on the LM2 or LZ0 because they don't use one.  These engines use what GM calls Active Thermal Management.  The ATM system uses an engine driven water pump on these, the ATM water flow control valve and two water to oil heat exchangers (one for the transmission, the other engine oil).  ATM via the water flow control valve can infinitely target cooling flow to the block, heads and the heat exchangers as needed to warm or cool faster various components.  There is no swapping to a lower t-stat that can be done here.  

 

So.  All of that to then say...you can install the PPE bypass if you so choose.  What it will do is eliminate the 194F TBV and allow the transmission loop to be open at all times.  You will still be heating the ATF and regulating temps from the heat exchanger it passes through, but it will be able to hit the aux cooler out front immediately to slow down the temp rise. 

 

Are you going to see a 50F drop?  Nope.  "Maybe" all of 5-10 degrees up and running hot, otherwise its just slowing down the rate at which it takes to reach hot operating temp.  

 

Excellent information and it all makes sense. Thank you. I'm only looking for a more "reasonable" tranny temperature, not 140F all the time. What you say makes me wonder how the NHT max trailering people manage such low tranny Temps.? Thanks again.

[Green02z71]

12 hours ago, Grover67 said:

I did the PPE trans oil cooler first. It held the trans temp down some but its being regulated by the bypass. I changed out the bypass with the PPE and it runs about 40-50f cooler overall winter/summer. Just got back from doing some work today at our cottage about 2hrs away. Mostly highway running 80mph, it was 80f out today and once the trans temp stabilized it runs right around 158f. Winter driving here in Michigan it runs a little cooler to a little warmer due the radiator louvers shutting/ regulating. I would just run the bypass and if needed add in the cooler.

Thanks for the information. I worry about the ATF being too cold in the winter, but I'll probably throw the bypass in anyway. We'll see.

[newdude]

16 minutes ago, Green02z71 said:

Excellent information and it all makes sense. Thank you. I'm only looking for a more "reasonable" tranny temperature, not 140F all the time. What you say makes me wonder how the NHT max trailering people manage such low tranny Temps.? Thanks again.

 

 

NHT just has a larger main radiator for cooling enhancements.  The other parts (the heat exchangers and the aux transmission cooler) stay the same. 

 

I'd agree with Grover67 and start with the bypass kit.  If from there in your view its still too hot, then go for the larger PPE aux cooler.  

Edited August 14, 2024 by newdude