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New Impeller Not Pumping Water

New Impeller Not Pumping Water

If you’ve recently replaced your boat’s impeller and it’s still not pumping water, you’re not alone. Many boaters have faced this issue for a variety of reasons. This article will provide a detailed guide on how to troubleshoot and solve this problem based on the collective wisdom of the boating community.

Understanding the Problem

The issue begins when, despite replacing the impeller, there’s no water flow through the engine. This can be alarming, especially if your boat’s engine has always functioned well with the use of muffs. The problem could be due to various reasons, including remnants of the old impeller blocking the flow, packed sand in the vertube, or a problem with the coolant tube or thermostats.

Possible Causes and Solutions

  1. Old Impeller Remnants or Sand Blocking Flow: If parts of the old impeller were missing when you removed it, they could be blocking the cooling passages. Inspect the original impeller to ensure it was all in one piece. If not, you may need to check the cooling passages for blockages.
  2. Issues with the Coolant Tube or Thermostats: Check the coolant tube for any build-up. Also, inspect the thermostats to see if they are stuck or if there’s build-up there. A stuck poppet valve could also be the culprit.
  3. Problems with the Lower Unit: Ensure the hose is properly connected to the water pump when you put the lower back on. Some engines take a while to start pumping water, so give it some time.
  4. Engine Issues: If there’s air coming from the indicator hole, it could be a symptom of a bad head gasket or bad cylinder head. Pull out your plugs and look for one that is abnormally clean or has the presence of water on it. This could indicate water turning to steam in the chamber, which is a sign of a bad head gasket.


Troubleshooting a new impeller that’s not pumping water can be a complex task. It requires a systematic approach to identify and address the root cause. Remember, every boat and engine is unique, so what works for one person might not work for another. Always refer to your engine’s manual and consult with a professional if needed.

If you’ve encountered this issue and found a different solution, please share your experience in the comments. Your insights could be invaluable to other boaters facing the same problem.

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Steve Momot

Steve is an accomplished professional photographer and marketer who specializes in the Fishing, Yacht, and Boating industry. With a strong presence as an influencer and marketing expert in the Marine Industry, he has made a significant impact in the field. Additionally, Steve is the original creator and co-founder of Sportfishtrader. Prior to his career as a marine photographer, he gained extensive experience as a licensed boat and car dealer in South Florida.

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