The Mercury Water Pump Inlet Guide Tube Sleeve, commonly identified as 23-29804 or 29804T, is a small plastic alignment sleeve installed at the top of the water-pump housing. Its job is simple but important: it helps guide the engine’s copper water tube into the pump outlet during lower-unit installation so the cooling-water path is properly connected.
Mercury parts catalogs identify 29804T as “SLEEVE, GUIDE – WATER INLET TUBE” and show it as the current replacement for the earlier 29804 number. Older parts listings also associate 52928 with this same guide-sleeve family.
Why This Sleeve Matters
When the lower unit is installed, the copper water tube must enter the water-pump outlet and seal correctly. The guide sleeve helps center the tube and prevents it from catching the edge of the housing or seal.
If the sleeve is missing, cracked, deformed or heat-damaged, the water tube can be difficult to align. A misaligned tube can prevent the cooling system from sealing correctly and may reduce water delivery to the powerhead.
The sleeve itself does not create water pressure, but it helps ensure the connection between the pump and the engine’s water tube is assembled correctly.
Common Failure and Service Conditions
Because this guide is plastic and sits directly above the water pump, it can become brittle or distorted with age. Severe overheating, a failed impeller, dry running or prolonged high temperatures can also damage the sleeve.
Typical problems include a sleeve that is warped, cracked, partially melted, loose in the housing or missing entirely.
Whenever the water pump or impeller is serviced, inspect this guide sleeve along with the water-tube seal, pump housing, impeller and driveshaft slinger. If the guide is damaged or no longer holds the water tube squarely, replacement is inexpensive insurance against a difficult or incorrect lower-unit installation.
Mercury and Mariner Outboard Fitment
The 29804 / 29804T water inlet tube guide was used across a very broad range of Mercury and Mariner gearcases for many years.
Factory parts diagrams confirm use on older inline and V-series outboards, including applications such as 85 HP 4-cylinder, 115 HP 6-cylinder, V-135 and many other classic Mercury two-strokes.
The same guide-sleeve family also appears across numerous later Mercury gearcases used with 2.0L, 2.4L, 2.5L and selected 3.0L outboards, depending on the exact gearcase and water-pump design.
Because Mercury reused this guide on many different lower units, fitment should be verified by engine serial number, gearcase family or original sleeve number rather than horsepower alone.
MerCruiser Sterndrive Applications
This sleeve is not limited to outboards. Mercury parts diagrams also show 29804T in MerCruiser gear housings, including older R/MR/Alpha-style and related sterndrive gearcase assemblies.
In those applications, it performs the same function: guiding the water inlet tube into the pump assembly so cooling water can move from the drive into the engine cooling circuit.
Part Number Cross Reference
The strongest verified Mercury references for this part are 23-29804, 29804 and 29804T. Mercury parts listings show 29804T replacing 29804. Older catalogs also list 52928 as a superseded or associated guide-sleeve number in this family.
A common aftermarket cross-reference is Sierra 18-3109.
Buckshot Racing #77 Installation Tech Tip
Before reinstalling the lower unit, make sure the sleeve is seated fully in the water-pump housing and that the copper water tube enters the guide squarely.
Do not force the lower unit upward if the water tube is not aligned. If the gearcase stops short of the midsection, lower it slightly and verify the driveshaft, shift shaft, and water tube are all entering their respective locations correctly.
Also inspect the water inlet tube seal, because a new guide sleeve cannot compensate for a hardened, damaged or missing seal.
The Mercury 29804T Water Pump Inlet Guide Sleeve is a small part, but it makes lower-unit installation easier and helps ensure the cooling-water connection is properly aligned. It is a smart item to inspect or replace anytime the water pump is being rebuilt on compatible Mercury, Mariner or MerCruiser gearcases.