What are the symptoms of a failing circulation pump or thermostat?

Common symptoms include engine overheating, fluctuating temperature readings, poor cabin heater performance, alarms, or reduced water flow at the exhaust. A failing circulation pump may also leak or make unusual noises, while a stuck thermostat can cause slow warm-up or sudden overheating.

Can you test the circulation pump and thermostat without replacing parts right away?

Yes. We perform full diagnostic testing before recommending replacement. This includes temperature verification, flow testing, thermostat opening temperature checks, and inspection for leaks or internal wear. Only faulty components are replaced, helping you avoid unnecessary costs.

What happens if I keep running the engine with a bad thermostat or pump?

Continuing to operate the engine can lead to severe overheating, warped cylinder heads, blown head gaskets, or internal engine damage. Early testing and repair of the circulation pump or thermostat can prevent major and expensive engine failures.

Do you test both raw water and closed-loop cooling systems?

Yes. We service both raw water–cooled and closed-loop (freshwater) cooling systems. We verify proper coolant circulation, thermostat operation, hose condition, and overall cooling efficiency based on your engine type and manufacturer specifications.

How long does circulation pump and thermostat testing usually take?

Most inspections take between 1 and 2 hours, depending on engine access and configuration. If replacement is needed, we provide a clear estimate before starting any additional work. Our goal is minimal downtime and reliable results.

Do you replace marine thermostats and circulation pumps if needed?

Yes. We replace marine-grade thermostats and circulation pumps using OEM or high-quality equivalent parts. All installations follow manufacturer torque and sealing specifications to ensure proper cooling system performance and long service life.

Do you provide service reports or recommendations after testing?

Absolutely. After testing, you receive a clear report outlining system condition, test results, and recommendations. This documentation is useful for maintenance planning, warranty records, and resale value. Service is available in Newport Beach and Long Beach marinas.

Marine technician using an infrared laser thermometer to check the temperature of a thermostat housing on a running marine engine to diagnose overheating issues.

Cooling System: Impeller & Thermostat Service

SKU

2145

Rating:

100 % of 100

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$150.00

The #1 killer of marine engines is overheating. We perform preventative surgery on your cooling system, replacing worn rubber impellers and testing thermostats to ensure your engine runs at the perfect temperature.

Details

Prevent Overheating

Stay Cool
Under Pressure.

Heat is the enemy. A \$40 rubber impeller is all that stands between your engine and catastrophic failure. We perform comprehensive cooling system maintenance to ensure reliable flow and consistent temperature.

Impeller Service

The "heart" of your raw water pump. Rubber impellers dry rot and lose vanes even when sitting still. We replace them annually to prevent broken rubber bits from clogging your heat exchanger.

Thermostat Testing

A stuck thermostat can cause rapid overheating (closed) or prevent the engine from reaching operating temp (open). We remove and test them in a heated bath to verify opening temperatures.

Circulation Pump

The engine's internal water pump. We inspect the weep hole for leaks and listen for bearing noise using a stethoscope to catch failures before the pump seizes and throws the belt.

The Cool Down Protocol.

Verification before replacement.

Infrared Scan

We run the engine and use a laser pyrometer to measure temperatures at the thermostat housing, risers, and manifolds to identify hot spots.

Pump Inspection

We open the raw water pump. If the impeller vanes are set (curved permanently) or cracked, we replace it. If the housing is scored, we resurface or replace it.

Thermostat Check

We inspect the housing for salt corrosion (common in saltwater boats) which can jam the thermostat. We install new gaskets and seals.

Flow Verification

After assembly, we verify water flow at the exhaust. A strong, steady stream indicates a healthy pump and clear passages.

Vital Components.

Keeping the flow moving.

Worn vs. New Impeller

Thermostat Housing Clean

Laser Temp Check

Service Intervals.

When to service your cooling system.

Raw Water Impeller Every 1 Year / 100 Hours

Thermostat Every 3 Years / 300 Hours

Coolant Flush Every 2 Years (Closed Cooling)

Common Questions

My engine gets hot at idle but cools down when running. Why?

This is the classic sign of a worn impeller or a scored pump housing. The pump can't move enough water at low RPMs but catches up at high RPMs. It needs immediate service.

What happens if an impeller breaks?

The missing rubber pieces travel downstream and get stuck in the heat exchanger or oil cooler, blocking flow. We have to "go fishing" to find all the pieces, which adds labor.