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2018 Suburban transmission
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Monkatom
New User
Apr 22, 2023, 4:15 PM
Post #1 of 5
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2018 Suburban transmission
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Hello just had the transmission replaced one month ago on my 2018 suburban. Today was the first hot day (90) since replacement and I got a message transmission hot idle engine. I turned the car off waited 10 minutes and checked the transmission fluid temperature and it was 268 degrees. Waited until it got to 200 to check levels and they were normal. Any idea why a new transmission would be running hot? Taking it back to mechanic on Monday. I am actually 40 miles from home so letting it cool down more before trying to get home.
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Hammer Time
Ultimate Carjunky
/ Moderator

Apr 22, 2023, 4:18 PM
Post #2 of 5
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Re: 2018 Suburban transmission
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The old transmission may have plugged up the cooler in the radiator when it failed. They probably should have changed the radiator and flushed the lines when they did the transmission. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Monkatom
New User
Apr 22, 2023, 9:59 PM
Post #3 of 5
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Re: 2018 Suburban transmission
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Thanks. I let it cool for about three hours. Drove home and luckily it only hit 224 right when I got home.
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Hammer Time
Ultimate Carjunky
/ Moderator

Apr 23, 2023, 3:22 AM
Post #4 of 5
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Re: 2018 Suburban transmission
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That will destroy the new transmission if you drive it that way. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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gsferraro
Veteran
Apr 28, 2023, 5:02 PM
Post #5 of 5
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Re: 2018 Suburban transmission
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Hello, If this transmission is a 6L80 or 8L90 (depends engine size) There is a thermal element that the cooler lines hook up to, it is right at the transmission bellhousing, these tend to go bad. I put a bypass valve in to eliminate the thermal element. How i tell if it is bad, i touch the cooler lines and sometimes they are just warm when the trans is hot. Gary
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