Can I Run My Outboard Without A Poppet Valve?

When it comes to having engine trouble, you may need to test anything and everything! Even a poppet valve!

Can You Run An Outboard Without A Poppet Valve? Yes, you can run the engine for a short period of time without the poppet valve for testing purposes. If you run for too long without the poppet valve, you may experience over-cooling or overheating conditions with your engine.

There are a couple of things that you should understand about a poppet valve and what it does, so here’s what you need to know!

What Is An Outboards Poppet Valve Function?

An outboard poppet valve is basically an assembly of parts. With the most important parts being a spring and a piece of plastic that acts as a valve.

This valve and spring sit in a housing. In between where the cooling passages that are coming from the engine.

Meet the passages that enter into the exhaust system. The purpose of the poppet valve is to regulate coolant water pressure.

Or more specifically, the amount of cooling water that is running through the engine block.

This helps to regulate the temperature at different operating speeds of the engine.

Generally, at idle, the poppet valve stays closed because the pressure from the water pump impeller isn’t strong enough to open it.

And the engine temperature is more regulated by your thermostats. (Here’s a lot more information about running an outboard without the thermostats here!)

Then at higher RPM, the water pressure will open. Allowing more water to flow through the engine.

Which will help cool the engine down, keeping the correct temperature.

Here is a video from our Youtube channel about an outboard that is overheating, and some poppet valve diagrams!

What Happens When The Poppet Valve Is Removed?

With this understanding of the poppet valve function. Hopefully, it should be more clear of what would happen if you completely remove the poppet valve!

Without this valve in there, you will have a massive water leak from the cooling passages. To the exhaust passages.

Leaving your engine with not enough cooling water at lower RPM. Which is most commonly going to result in an engine overheat issue at idle.

But, at the same time. You probably won’t notice anything at wide open, because the valve is usually open at that RPM range anyway!

So your engine should run fine at wide open, but, again, could run too cool or too hot. Depending on if you have other stuff going on.

As well as the fact, that without the poppet valve in there at all. You will be flowing way more water than normal.

This means that you should really only run the engine without the poppet valve. When you are in the process of troubleshooting your systems!

If you are having a water cooling issue. Here is another video that you will find helpful when it comes to a lack of water flow.

Or when you don’t see a tell-tale coming from the engine.

Outboard Poppet Valve Symptoms & Problems

Poppet valves aren’t too hard to diagnose though. The symptoms that you will usually see will depend on what kind of issue you are having with the valve.

As well as, making sure that you aren’t dealing with any other issues at the same time! If there are other issues, you might be chasing your tail with a poppet valve.

But, when a poppet valve does fail. You will find that when it is stuck closed. You won’t have any issues at idle.

The engine temp and water flow should operate as normal because the valve is normally closed at idle.

But, once you get up to speed, even at around 2-3000 RPM and up to WOT. You will usually see an overheat condition.

Because the engine can’t get enough cool water into the engine to cool it down. Seeing that it is lacking the volume flow that it should get when the valve is open.

You can tell a poppet valve like this by inspecting it. As well as by looking at your water pressure gauge as you increase RPM.

The pressure should drop a little whenever the valve opens up. Then when we are dealing with a poppet valve that is stuck open.

You can have an overheat at idle because all the cooling water is dumping out through the valve into the exhaust.

Not allowing the engine to cool down! Depending on other factors like the actual temperature of the water you are in.

You can experience over cooling issues as well.

Some other symptoms that you might find are going to be fouling issues. From running rich based on the engine temp.

Or condensation build-up in the crankcase, creating water in the oil. Or lean running conditions, that will show in fuel consumption and spark plugs.

Here is another video that you should watch about fuel economy and how to lower your outboard fuel consumption!

Poppet Valve Replacement

When it comes to the poppet valve replacement. That is going to differ based on what brand engine you are working with.

But it will only differ in the sense of where it is located. And what kind of parts you are going to be changing.

Most poppet valves come in individual pieces. They do not come as an assembly. So you will have a spring, the valve, some gaskets, and if you need, the housing or cover.

When replacing it, you probably won’t know what parts you need. Until you pull the old one out and inspect it.

But, by in large, if you are having trouble with the poppet valve, it’s best to just change the gasket, the spring, and the valve. All at once.

If there are diaphragms or other parts to the valve. Then go ahead and change those too.

It’s a lot easier to just change out the majority of these parts while you are there. Then to have to take it all apart again and change out the ones that you didn’t!

Usually, you shouldn’t need to change out the housing or the cover. Unless it is a decently older engine and the housing is corroded or broken.

Check Us Out!

We hope that this has helped you understand more about running your outboard without the poppet valve.

And what exactly the poppet valve does, as well as what you can do to change it out!

If you have more questions or want to learn more about your boat and its different systems. You should consider joining our Boating Academy where we have created HUNDREDS of video courses teaching you basically everything about your boat!

There are also even more helpful videos on our Youtube channel where we create even more boating videos!

You can also save some money by using our coupons when you need to buy stuff from your boat by using any of these coupons here at Partsvu!

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Here are some other super helpful articles that you might find interesting!

Aaron Hilligoss

Aaron has been working in the Marine Industry for over a decade and holds certifications for Yamaha and Mercury Marine. It is not uncommon for him to own and be working on at least three different boats at any given point in time!

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