The Mercury Water Tube Seal Grommet 26-38970, also identified as Mercury 86027, is a small but essential component of the cooling system found on many Mercury, Mariner, and MerCruiser engines.
The Mercury 26-38970 water tube seal creates a watertight connection where the water tube passes between the water pump housing and the exhaust tuner plate cooling passages, preventing pressure loss before cooling water reaches the powerhead.
Although inexpensive, replacing a worn Mercury 26-38970 seal during routine water pump service can help maintain proper cooling system pressure and reduce the risk of overheating.
This seal is commonly used on numerous Mercury V6, inline-four (IL4), and inline-six (IL6) outboards, as well as many MerCruiser sterndrives equipped with compatible water pump housings and two-piece exhaust plates.
Where the Mercury 26-38970 Water Tube Seal Is Used
The Mercury 26-38970 / 86027 water tube grommet seals the cooling water tube at both ends of the cooling system. One seal is installed in the water pump housing at the top of the lower unit, while another seals the upper end of the water tube where it enters the two-piece exhaust plate or engine water outlet, depending on the application.
These Mercury 26-38970 grommets prevent cooling water from escaping around the tube, allowing the water pump to deliver maximum pressure and flow to the engine. A leaking seal can reduce water pressure, particularly at idle, and contribute to overheating or inconsistent cooling performance.
Why Replace Mercury 26-38970 During Every Water Pump Service?
Whenever the lower unit is removed to replace an impeller or rebuild a water pump, replacing the Mercury 26-38970 water tube seal is inexpensive preventative maintenance. Over time, the rubber hardens from heat, age, compression, and repeated lower unit removal.
Even if the original Mercury 86027 seal appears serviceable, it may no longer provide the tight seal required to maintain proper cooling system pressure.
Installing a new 26-38970 water tube grommet during every water pump service helps ensure the cooling system performs as Mercury intended.
Installation Tips
Before installing the new Mercury 26-38970 water tube seal, inspect the water tube for corrosion, burrs, or damage that could cut the rubber during assembly. Clean both sealing surfaces thoroughly and apply a light coating of waterproof marine grease to the inside of the 86027 seal to help guide the water tube into place without pinching the grommet.
After assembly, verify the water tube is fully seated before tightening the lower unit fasteners and always confirm proper cooling water flow during the initial engine start-up.
Final Thoughts
Whether you're servicing a Mercury V6 outboard, an inline-four, an inline-six, or a compatible MerCruiser sterndrive, replacing the Mercury Water Tube Seal Grommet 26-38970 (86027) is an important step in maintaining cooling system reliability.
The Mercury 26-38970 water tube seal is inexpensive, easy to replace, and helps ensure maximum water pressure reaches the powerhead.
Replacing the 26-38970 / 86027 seal whenever the water pump is serviced is one of the simplest ways to prevent cooling system leaks and extend engine life.
Included one (1) Small Tube Water Tube Seal Grommet for the Mercury Lower Unit.
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