What is a lower unit reseal and when is it necessary?

A lower unit reseal involves replacing worn or damaged seals that protect the gearcase from water intrusion. It becomes necessary if water is found in the gear oil, seals are leaking, or after propeller shaft damage. Resealing prevents internal corrosion and costly gear failure.

How do you pressure test a lower unit?

We perform both pressure and vacuum testing using professional tools. This allows us to detect even small seal leaks around the prop shaft, drive shaft, shift shaft, and drain screws. Testing ensures the lower unit is fully sealed before returning the boat to the water.

What happens if I keep running my boat with water in the lower unit?

Running with water-contaminated gear oil can quickly destroy bearings and gears inside the lower unit. This often leads to overheating, metal damage, and complete gearcase failure. Early resealing and testing can save thousands in rebuild or replacement costs.

Do you replace all seals or only the leaking ones?

In most cases, we recommend replacing all critical lower unit seals during a reseal service. This includes prop shaft, drive shaft, and shift shaft seals. Replacing all seals at once provides long-term reliability and reduces the risk of future leaks.

How long does a lower unit reseal service take?

Most lower unit reseal and pressure testing services can be completed within 1 to 2 days, depending on the engine type and seal condition. We prioritize accuracy and testing to ensure the unit is fully protected before returning it to service.

Is pressure testing included after the reseal?

Yes, pressure and vacuum testing is always included after resealing. This confirms that all seals are correctly installed and the lower unit is completely watertight. We never return a boat without verified test results.

Do you provide warranty on lower unit reseal work?

Yes, we provide a warranty on our reseal labor, typically ranging from 3 to 12 months depending on usage conditions. All replacement seals are OEM or high-quality aftermarket parts covered by manufacturer warranty. Full service documentation is provided.

Marine mechanic using a hand-held pressure tester pump connected to the drain hole of a Mercury outboard lower unit to check for seal leaks.

Lower Unit Reseal & Pressure Testing

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2147

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$150.00

Water in your gear oil is a disaster waiting to happen. We perform professional vacuum and pressure testing to find leaks, replace worn prop shaft seals, and ensure your gears stay lubricated and dry.

Details

Seal Integrity

Hold Pressure.
Keep Water Out.

Milky gear lube is the first sign of disaster. Water intrusion rusts gears and destroys bearings. We use precision pressure and vacuum testing to identify failing seals before they cost you a lower unit.

Pressure & Vacuum

We don't just guess. We drain the unit and pressurize it to 10-15 PSI to find leaks that let oil out. Then we pull a vacuum to find leaks that suck water in (cooling phase). If it holds, your gears are safe.

Complete Reseal

When a leak is found, we perform a complete teardown. We replace the prop shaft seals, drive shaft seals beneath the water pump, shift shaft seals, and all carrier O-rings with OEM quality parts.

Leak Detection

Using soapy water and UV dye, we pinpoint the exact failure point. Is it a fishing line cut on the prop shaft? A corroded shift seal? We identify the root cause so the new seals last.

The Reseal Procedure.

A rigorous defense against saltwater.

Drain & Pressure Test

We drain the old lube (checking for water/metal) and hook up the pressure tester. We inflate to 12 PSI and watch for a drop. A drop = a leak.

Disassembly

We pull the bearing carrier and water pump base. We inspect the shafts for grooving (which ruins new seals) and polish them if necessary using Speedi-Sleeves if needed.

Seal Installation

Using specialized drivers, we install new double-lip seals. We ensure the springs face the correct direction (oil side vs water side) for maximum protection.

Final Verification

Before adding oil, we re-pressurize the unit. It must hold 10-15 PSI for at least 15 minutes with zero drop. Only then do we fill it with synthetic lube.

Sealed Tight.

Quality components make the difference.

Pressure Testing Gauge Setup

New Prop Shaft Seals

Shift Shaft Seal Replacement

Test Specs.

We follow factory standards.

Pressure Test 10-15 PSI (Holds for 15 mins)

Vacuum Test 3-6 inHg (Checks water ingress)

Shaft Runout Checked to prevent seal wobble

Common Questions

What causes seals to fail?

The #1 culprit is fishing line wrapped around the prop shaft, which cuts the rubber. Age, heat cycling, and sitting dry for long periods also cause the rubber to crack.

Can I just refill the oil and ignore it?

Absolutely not. Water is heavier than oil and settles at the bottom, rusting the gears and bearings. Ignoring a leak guarantees a complete lower unit failure.