Duramax Service Tips: Allison Transmission fluid color

Updated Oct 26, 2023

_BS25958Duramax Transmission Service Tip: Let color and smell be your guide

Here’s a money-saving tip when it comes to Duramax pickup’s automatic tranny service: Let your eyes and nose be your guide as to when the fluid needs changing.

Although GM recommends the Allison 1000 trans fluid and external filter be changed when the HD’s oil monitor says – or every 25,000 miles for HDs used in severe service – Rod Halsten, a GM master technician in Tuscaloosa, Alabama, says let the trans fluid color and smell be the fluid-change indicators.

“The trans fluid should be reddish and not have any hint of a burned smell,” says Halsten.

“If it’s reddish and smells like ATF fluid, it’s probably good to the next scheduled filter change interval.

But if it’s off-color or smells burnt, flush the transmission system, change the internal filter and spin-on filter, and replace the fluid.”

Halsten also reminds service techs and DIYers to not over-tighten the filter.

Inspect and clean the drain plug magnet as well as the magnet on the filter itself.Inspect and clean the drain plug magnet as well as the magnet on the filter itself.

Another service tip: Inspect the drain plug magnet for any signs of metal. Any obvious bits or chunks of metal on the magnet would signal some serious internal problems brewing.

The same holds true for the filter magnet: “Make sure the magnet on top of the filter is cleaned and replaced on the new one,” Halsten says.

”I’ve seen some owners forget to put it back on the new filter. That mistake can come back to haunt you later.”