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2018 Sierra 1500 Transmission Fluid Change - What's the Recommended Interval?

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Mike T. · rep 0 · May 25, 2:40 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Sierra 1500 SLT

My 2018 GMC Sierra 1500 SLT is approaching 75,000 miles. I've been reading conflicting information online about when to change the transmission fluid. Some sources say it's 'lifetime,' while others suggest every 50,000-100,000 miles.

I occasionally tow a boat during the summer, which I know can put extra strain on the transmission. What's the official word for this model year and usage, especially with towing in mind?

Should I just do a simple drain and fill, or is a full transmission flush recommended at this mileage? Any advice on fluid types would be great too!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:40 AM

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ClearTheCode admin answer:

For your 2018 GMC Sierra 1500 SLT, especially with occasional towing, adhering to a more frequent transmission fluid service interval than 'lifetime' is highly recommended. GM's service schedule often specifies fluid changes for vehicles used for heavy towing, commercial use, or extensive idling.

  1. Recommended Interval: For normal driving, GM might suggest around 97,500 miles (150,000 km) for transmission fluid and filter. However, for severe duty (which includes frequent towing, hauling, or driving in mountainous terrain), this interval typically drops to 50,000-60,000 miles. Given your 75,000 miles and towing, a service is definitely due.
  2. Fluid Type: Always use the specified DEXRON-VI automatic transmission fluid. Using an incorrect fluid can lead to premature wear and transmission issues.
  3. Drain and Fill vs. Flush:
    • Drain and Fill: This replaces only the fluid that drains from the pan (typically 4-7 quarts), leaving a significant amount of old fluid in the torque converter and cooler lines. It's less invasive and can be done more frequently.
    • Flush: A full flush uses a machine to exchange nearly all the old fluid with new. While more thorough, it can sometimes dislodge debris in older, neglected transmissions, potentially causing issues. For a well-maintained vehicle, it's generally safe.
    • Recommendation: Given your mileage and towing, a pan drop with filter replacement and fluid top-off (a more comprehensive drain and fill) is a good start. If the fluid looks very dark or smells burnt, a full flush might be considered by a professional, but only after careful assessment.
  4. Causes of Wear: Towing increases transmission heat, which breaks down fluid faster. Regular fluid changes remove contaminants and replenish additives that protect internal components.
  5. When to See a Shop:
    • If you're experiencing any shifting issues (hard shifts, slipping, delayed engagement) before or after the fluid change.
    • If the old fluid appears metallic or contains large debris, indicating internal wear.
    • If you prefer a full transmission flush, as it requires specialized equipment and expertise to perform correctly without damaging the system.
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