99438A1 Mercruiser Heat Exchanger | Genuine Used Part

🔧 Product Description

Genuine MerCruiser 3.7L Four-Inch Heat Exchanger - Part Number: 99438A1

A genuine MerCruiser four-inch-diameter heat exchanger for selected 3.7-litre and 224 CID inline four-cylinder sterndrive engines.

The exchanger separates the engine's closed freshwater coolant circuit from the raw-water circuit. Coolant flows through one side of the exchanger while seawater or lake water removes heat through the other side before being discharged into the exhaust.

The larger four-inch assembly is commonly used as the upgraded replacement for the earlier three-inch heat exchanger fitted to some MerCruiser 470-family engines.

⚙️ Key Features

• Genuine MerCruiser closed-cooling heat exchanger
• Correct service part number 99438A1
• Approximately four-inch shell diameter
• Used on MerCruiser 3.7L / 224 CID engines
• Verified Lenco direct replacement available

🚤 Compatibility

Commonly used on

• MerCruiser 3.7L closed-cooling systems
• Later 470-family engines and earlier engines upgraded to the four-inch exchanger

Typically suits

• Engine models:
• MerCruiser 165 3.7L
• MerCruiser 170 3.7L
• MerCruiser 180 3.7L
• MerCruiser 190 3.7L
• MerCruiser 470
• MerCruiser 488
• MerCruiser 3.7L
• MerCruiser 3.7LX
• MerCruiser installations whose cooling diagram specifies 99438A1
• Engine Type: MerCruiser 3.7-litre / 224 CID inline four-cylinder petrol sterndrive
• Cooling Type: Full or engine-side closed cooling, depending on installation
• Year Range: Approximately 1980s production

🔌 Function

The heat exchanger removes heat from the closed engine-coolant circuit without allowing corrosive raw water to circulate through the aluminium engine block.

⚠️ Common Signs of Failure

• Engine temperature rises under load
• Coolant level falls without an external engine leak
• Raw water and coolant mix internally
• End caps or tube bundle leak
• Internal scale restricts raw-water flow
• Coolant appears at the exhaust outlet

🔄 Supersession & Cross Reference

OEM Supersession Chain

• 99438A1 documented four-inch MerCruiser heat exchanger
• 77319 earlier three-inch heat-exchanger reference commonly replaced by the larger assembly
• The change from 77319 may require the matching mounting and hose arrangement

OEM / Related Numbers

• 99438A1
• 99438-A1
• 77319
• Related heat-exchanger end caps and gaskets
• Related coolant filler neck and pressure cap
• Related raw-water inlet and outlet hoses
• Related mounting brackets and straps

Aftermarket / Verified Equivalents

• Lenco: LE-99438
• Lenco LE-99438 is catalogued as a direct replacement for MerCruiser 99438A1

📦 Condition

• Genuine used part
• Removed from running engine where applicable
• In good working condition unless otherwise stated