Why You’re Experiencing Cavitation In Your PWC

Have you noticed your personal watercraft (PWC) feeling a bit shaky when you try to take off? Or it feels like it wants to go, but doesn’t?

Well, that could be due to a common issue known as cavitation. I’ve noticed that sometimes, people mistake it for other common jet ski problems or will say the pump is “slipping gears.”

Cavitation is so interesting, it’s the water boiling around the impeller blades due to the pressure difference and thus wearing them out. When it comes to PWCs, cavitation is also used to explain a loss in power because you sucked something up. This is because when you suck something up, you damage the jet pump and that causes the cavitation.

How To Know You Have Cavitation?

The most common signs of cavitation you’ll see is…

• You give the PWC gas, and it doesn’t want to move.
• It feels like it “slipping” gears.
• Makes loud noises when the engine is on stemming from the rear.
• Overheating warnings or check engine lights.
• You’re not getting the top speed you used to get.
• PWC is shaking a lot, especially when giving it gas.

Most people mistake cavitation in a PWC for “slipping gears” or a slow take-off. You may eventually catch, and the PWC can reach top speed, but it takes forever as it feels like the engine is “spinning its wheel’s”.

Note: PWCs don’t use “jet engines”. A PWC engine is more similar to a motorcycle engine, and the jet pump is more similar to the prop on a boat. I get this a lot, compared to jet engines, a PWC engine is a lot more simple.

You’ve Sucked Something Up!

When you suck up debris such as rocks, sticks, ropes, and even unusual items like snakes (yes, it’s happened to me), that creates cavitation in the jet pump.

Cavitation can occasionally be caused by manufacturer defects or worn-out components, like a misaligned driveshaft leading to impeller imbalance. However, most cases I’ve encountered arise from debris being ingested into the PWCs intake, damaging essential parts such as the wear ring and impeller. So don’t expect warranty to cover it.

This disruption in water flow typically results from user actions, such as operating in shallow waters or areas with rocks, sand, or weeds. In other words, cavitation is rarely due to equipment flaws, but is almost always the result of external damage caused by improper use or poor maintenance.

How To fix cavitation

The most common cavitation problem you’ll run into is that you sucked something up, this means you’ll need to remove the item that was sucked up and repair the damage.

Steps:

1. It’s important to get the damaged watercraft out of the water and on a trailer or stand.
2. Secure the PWC so it doesn’t move and have the engine off.
3. Look into the intake grate to see if you can see anything out of the ordinary. Use a flashlight as it will be hard to see.
4. Look at the rear into the pump to see if you can see anything. You may need to raise the iBR or reverse bucket systems.
5. Remove the jet pump to fully see if any debris is hiding or stuck – best to let the repair shop do this. A lot of the debris won’t be easy to spot unless the pump is removed.
6. Check the driveshaft and carbon seal for any damage because if they’re off by a lot it can cause cavitation. A bent driveshaft will cause the PWC to shake like crazy when trying to take off.
7. Check the seal where the driveshaft goes through the hull. A damaged seal can cause air to leak in, causing cavitation problems. A damaged through-hull seal is an expensive fix, but a very rare problem.

You need to inspect what is stuck in the impeller and assess the damage to eliminate cavitation. If the wear ring or impeller is damaged, the PWC’s pump must be removed and these items repaired. It’s advisable to have the local repair shop handle it for you, as you may require a special impeller removal tool, and wear rings on some models can be tricky to work with.

Even though some things need special tools, you can get them online. You won’t need the dealership computer to fix this kind of damage, as the ECM on the PWC doesn’t know or understand jet pump damage… yet.

Note: You CAN NOT get to the pump from the inside of the bilge, the pump is on the outside!!! I've had several people start to rip their engine apart to get to the pump, and it only makes things worse for themselves. 

The Easy Cavitation Fixes

Sometimes it can be an easy fix of simply knocking the rocks or sticks loose, as it may have not done enough damage to cause the impeller and wear ring to cavitate constantly. Other times, rocks can cause significant damage, necessitating the replacement of the impeller and/or wear ring.

If you observe cuts or a generally non-smooth impeller, replacement is necessary. Even “slight barbs” and cuts will cause it. The impellers are metal, often aluminum or stainless steel, so they can be cleaned up with the right tools. You can only clean the impellers so much before you throw off the weight of the impeller and cause it to cavitate for that.

But There Is Nothing In The Pump?!

It is possible to take out the jet pump and notice nothing be stuck in it, but damage was still done and there’s horrible and excessive cavitation.

Often, it only damages the wear ring, which is what it is designed to do. It’s important to understand that these things are powerful, so the item that was once stuck is now blown out, but the damage to the pump has been done and it cavitates.

Is Cavitation A Common Thing?

An impeller is always experiencing some kind of slight cavitation, but the manufacturer designs it so that it’s so small it’s not an issue. The only time it can become an issue is if you suck something up or the pump is damaged.

There are the few times something in the pump or connected to the pump fails and starts cavitating, but from my years in the field, the most often it’s because of someone sucking something up.

Cavitation Repair Cost – $100 to $1,000

The repair cost varies based on the damage, ranging from $100 to $1,000 or more, depending on what needs fixing and your machine’s type.

DIY is an option, particularly for models like the Sea-Doo Spark without iBR, which is straightforward.

Some models may be more challenging but still manageable. Proper tightening and alignment are crucial to prevent cavitation and other issues. Failure to tighten the proper bolt in the pump area correctly can cause some to sink.

Cavitation is Not Covered Under Warranty

Unless it was a manufacturer defect, it won’t be covered under warranty.

Let me be blunt: it’s usually not a manufacturer defect, so don’t expect warranty coverage to help.

This may not be what you want to hear but, the cavitation that most riders experience is often done by someone sucking something up, so it’s NOT a warranty item. You need to be careful while operating in shallow water, as covered in this post.

How To Avoid Cavitation?

Avoiding cavitation involves a combination of proper riding habits, routine maintenance, and awareness of environmental conditions. Here are several key steps to minimize the risks:

1. Avoid shallow or debris-filled waters: One of the most common causes of cavitation is debris like rocks, sand, seaweed, sticks or other objects being sucked into the intake. To prevent this, avoid running your PWC in shallow water or areas with visible debris, like avoid riding after a bad storm.
2. Throttle control: Be mindful of how you use the throttle in low water or murky areas. Abrupt acceleration can kicks up debris and increase the chance of something getting lodged in the intake.
3. Inspect and maintain the wear ring and impeller: The wear ring and impeller are critical components for the smooth operation of your PWCs propulsion system. Regularly inspect them for damage, as worn, grooves or damaged parts can create gaps that disrupt water flow, leading to cavitation. Replace the wear ring or impeller as needed to ensure optimal performance.
4. Rinse and clean your PWC: After each use, especially in saltwater or murky environments, rinse the intake and other critical areas of your PWC to remove any debris that may have been caught during your ride. This prevents buildup that could lead to performance issues over time. Keeping your PWC in the water will also build a scum on the bottom of the hull and rob you of top-end speed.
5. Avoid overloading the PWC: Overloading your PWCs with too much weight can put excess strain on the engine and drive system, making it more susceptible to cavitation. It’s more of a problem with pull sports like tubing as they create a lot of drag and make the PWC work harder. Stick the max seating capacity for everyone on the craft and tube combined.

Sum Up

Cavitation is an interesting thing to experience, not only for boats, but other vessels experience it as well.

The most common reason your jet pump will cavitate is due to sucking something or an imbalance with the impeller. Most of the time, replacing the impeller or wear ring will fix the odd take-offs you’re seeing due to cavitation.