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MRP

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  • Name
    Mike
  • Location
    Labrador
  • Drives
    2019 GMC 1500 Elevation

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  1. MRP
    While I was searching for info on flushing and changing transmission oil on the 8 speed (going from Dexron HP to Mobil 1 LV ATF HP), I found this GM technical service bulletin that is specific to the flushing and changing fluid on the 8 speed 8L90 transmission in various applications. Although one would not have the special tools/equipment that GM has, it gives you a solid guideline on the procedure to follow as well as torque specs. Hope this helps the DIY guys out there. 8L90 flushing proceedure.pdf
  2. MRP

    Hi Newdude

     

     

    Grumpy Bear suggested that I have a chat to you about my questions on the 8L90 transmission that I have in my 2019 Sierra 1500.  I have been following the threads on the pill flip that is being done on the 6L’s and am looking to do the same on my truck for the same reasons – help it warm up quicker in the winter and run cooler in the summer.

     

    Considering the above, I did a trip into the nearest town on Friday, which is 250km away.  The ambient temperature was 36F and I drove for 2 hours and covered 190km before the transmission fluid got to 169F and stayed there for the rest of the trip.  Sat at the same temperature on the way home, with the ambient temperature up slightly.  Would it still run at the optimum temperature in summer and winter?  Not sure if that would be the 130f to 160F, same as 6L’S?

     

    Do you happen to know what the trigger temperature is for the thermostat on the 8L90?  Would it be close to the 170F mark if that is where it sat once eventually warmed up?

     

    Based on what I have tread about the issues with the 8L90 transmission, I see that there is a new fluid from GM, the Mobil LV ATF HP that has superseded the Dexron HP.  I have 30000km on the truck now and the gm planned maintenance transmission oil change is at 70000km.  Would it be worth changing to this new fluid now proactively to try and avoid or limit problems down the line? I plan on keeping the truck as long as possible.

     

    I have also read about Lubegard being recommended for adding two bottles to the transmission to help improve things even with the new oil.  Some just saying add Lubegard to the Dexron HP that is in there and run it to the 70000km mark and then change.  What is your take on this?  Especially if there is still some warranty period left.

     

    Your thoughts and insight would be appreciated.

     

    Thanks Mike

     

    1. Show previous comments  7 more
    2. MRP

      MRP

      I hoped under the truck today to do the pill swap.  Thought I would have a look at the flow of the transmission cooler lines first.  Interestingly enough, the transmission cooler fluid does not go through a cooler in one of the the radiator tanks, but only an external cooler in front of the AC condenser.  I wanted to get you opinion from a technical point of view, if I may, with regards to the temperature of the transmission oil especially in winter with the pill swap in place. 

       

      I can see in warmer temperatures, having the oil flowing through the cooler all the time would be beneficial.  My query is in winter, if the oil was running through the external cooler all the time (pill swap in place);

      1. would it warm up slower than it is now in re-circle mode? (currently 190km in 37F weather to get to 169F and then it stays there)

      2. would it get to a suitably warm enough operating range temperature?  Presently in cold weather I sit at 169F.

       

      The truck does have louvers in the front grill that remain closed in very cold temperatures.  Not sure at what temperature they open.

       

      Any input/gut feel would be welcome.

    3. newdude

      newdude

      In the winter it will run cold.  You might not even break 100F.  My truck on my route to work runs 90-110F.  If I goose it, 120F in the winter.  It might shift slightly more aggressive as well at times or at least feel firmer.  It will warm slower, yes.  Even in the summer time the warmup is nowhere near as fast as when the thermostat is installed.

       

      Trucks prior to the thermostat being added ran quite similarly in the winter, albeit slightly warmer as the cooler lines went trans to the radiator, then aux cooler then back to the trans.  These 1500's as of about 2016 just go direct to an external cooler and back so they will run cooler than through the rad style setups.  

    4. MRP

      MRP

      Thanks, you have confirmed my thoughts although good to get temperatures from you.  My gut feel is to hold off for now with the pill swap until the truck starts to work harder on an ongoing basis or if we move to a warmer climate.  Here in Labrador in northern Canada we get to between -4F and -22F on a regular basis in the winter. Sometimes even colder.

       

      Today I did a 500km round trip with ambient temperatures between 39F and 68F and the transmission fluid never went over 170F.  So the thermostat would not have opened the whole trip.

       

      What is the minimum temperature that you need for the TCM etc. to function properly?  Also what is a good running temperature range for the transmission?

  3. MRP
    Hi Grumpy Bear, I have been following you posts about the thermostat delete. Tried to find the exact posts again, but could not by managed to find the thread. I have a 2019 GMC with the 8L90 box. 30000km on the clock so far and no issues. Wanting to keep the truck for as long as possible, I have been following threads about the problems experienced with this transmission. I came across your threads on the thermostat delete and have been going through them with interest. Having originally come from Africa where keeping transmissions cool whilst working them hard was a top priority. I found it interesting that GM put a thermostat in the cooler lines. It just so happened that yesterday I had to take a trip to the nearest town, 250km away so I thought I would watch the transmission fluid temp in line with what I had read in your posts. The ambient temp was 35F. Transmission was 64F when I took the truck out the garage. I had driven for 2 hours and covered 190km before the transmission temp reached 169F. It stayed there for the remainder of the trip. The trip on the way back was pretty much the same with the ambient temp having gone up marginally to 40F. Transmission temp remained the same. In this case, the thermostat would not have even opened? I was surprise that it did not build more heat, and was even more surprised, as you have said previously how long it takes to get to running temperature. With thermostat removed I can see how it would warm up more quickly pulling heat from the radiator as you mentioned. Under the conditions above, what do you recon the truck would run at with the thermostat removed? Something else that I have been doing some research on is the proactive upgrading of the oil from the current Dexron HP to the improved Mobil 1LV ATF HP now rather than the planned 70000km based on the problems experienced with these boxes. Speaking to GM they are sort of downplaying it. Have you any thoughts or experience with transmission oils and any thought on additives like Lubeguard that are meant to improve oil and transmission performance? Although I still have three years left on the drivetrain warranty, I do not want to allow a problem to start now, that I will have to live for for the life of the truck. Similar to your outlook on longevity of the vehicle and doing that's right now to ensure this. Any insight greatly appreciated
  4. MRP
    Anybody have any experience with weather tech window deflectors?
  5. MRP
    Hi Patrick I have my JLT catch can on the way for my 2019 Sierra. How is your catch can working since you installed it? You still running it?
  6. MRP
    Thanks for your thoughts and feedback
  7. MRP
    Thanks for your input
  8. MRP
    Been reading up and researching on the coating etc. of upper engine parts/component with oil etc. over the longer term. If what people say is true about catching half a can between oil changes, not sure that would show up on the dipsticks? What are your thoughts?
  9. MRP
    My Sierra 1500 has 26000km on the clock now and I have not noticed any oil consumption. Although the dealer is still doing the oil changes at present as the truck came with two years worth of free oil changes, I check the oil regularly and before long trips and all good. I am looking at the JLT 3.0 unit
  10. MRP
    I am looking at the JLT 3.0 air/oil separator catch can. It looks like a really great until and good quality https://www.jlttruecoldair.com/jlt-3-0-oil-separator-2019-2021-chevy-silverado-gmc-sierra-1500-5-3l-6-2l-2021-chevy-tahoe-suburban-gmc-yukon-yukon-xl-5-3l-6-2l/
  11. MRP
    So is anyone running the Flowmaster American Thunder cat back system that can give feedback on sound and drone? One gets a good feel for sound on the the video but not drone?
  12. MRP
    What Fllowmaster system did you install? I am looking for more of that V8 sound but worried about drone.
  13. MRP
    Any particular name, model or part number for the Gibson system you used?
  14. MRP
    Did you end up getting the American Thunder Cat Back system? Been considering this for my 2019 5,3 elevation. Just worried about drone.
  15. MRP
    I was looking at the Flowmaster but they are the 409. Started to look at the Borla due to it being 304 stainless. Also need to look at what I can get shipped easily to where I live. Borla easy as well as can get from GM. Thanks for all your feedback

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