Overfilled Engine Coolant Reservoir with Discolored Coolant

Some 2021-2022 Silverado, Sierra, Tahoe, Suburban, Yukon and Escalade models equipped with the 2.7L engine (RPO L3B) or 3.0L diesel engine (RPO LM2) and the 10L80 automatic transmission (RPO MQB, MQC) or 8L90 automatic transmission (RPO MQE) may have an internal leak in the automatic transmission fluid cooling exchanger. The leak may allow transmission fluid to mix with the engine coolant.

The cooling exchanger leak may result in discolored engine coolant with a strawberry milkshake appearance in the coolant reservoir. The coolant reservoir may be overfilled to the point where coolant is expelled from the overflow. (Fig. 9)

Fig. 9

In addition, the engine may experience an overheating condition; there may be possible degraded transmission performance, including a shudder, vibration or shift performance issue; and the transmission fluid level may be low.

If these conditions are found, confirm the presence of coolant in the transmission fluid following the procedure in Bulletin #08-07-30-035. Also refer to the bulletin for additional repair information.

In addition, replace the automatic transmission fluid cooling exchanger and thoroughly flush the engine coolant system to remove the contaminated engine coolant.

For additional information, refer to #PIP5845.

– Thanks to Terry Neuendorf

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One Comment


    Does there seem to be any sort of mileage threshold where confirmed coolers have failed? I see the PI has a specific almost 1 year long date range. Are most of them low mileage failures?

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