Can You Run an Outboard Motor Without a Thermostat?

Outboard motors run with a thermostat to help regulate the temperature as you use the motor, but they can break or fail after use, leaving you, your passengers and your boat in a difficult situation – wondering whether you can run your outboard without a motor.

Yes, you can run an outboard motor without a thermostat but it is bad for your outboard and should not be done for more than a few minutes at most to avoid permanent damage or degradation to the motor.

If you must run your outboard without a thermostat, there are several things you should do to minimize the damage it will have on your outboard – let me explain below.

Running Outboard with a Broken Thermostat vs Without a Thermostat

Before going further, let’s be sure about one key distinction here.

An outboard with a stuck thermostat is more likely to overheat and cause all of the issues we discuss in this post which will permanently damage your motor. Running without a thermostat altogether, however, will likely have the opposite effect, causing your motor to run cooler.

With that in mind, let’s have a look at some of the key points around this.

Primer on How an Outboard Motor Thermostat Works

The video below has a great explanation of how these thermostats work for an outboard, this one taken from an Evinrude, but most are similar in design:

It also shows you how to test whether your outboard thermostat is faulty by simply putting it in water to see if it still functions properly.

Does a 2-stroke outboard motor have a thermostat?

All outboard motors have a thermostat, so both 2-stroke and 4-stroke outboards have these as a key part of their design to keep the motor running a

You can also buy replacement outboard motor thermostats on Amazon for under $20, so it’s worth getting one as soon as you can.

The video below shows you how to change the thermostat on your outboard quickly and easily using a few common tools – it’s a very handy guide.

Run an Outboard Slow Speeds With a Broken Thermostat

Keeping your outboard motor to a low speed is essential if you must run it without a working thermostat because this will reduce the chance of it getting dangerously hot, which could permanently damage your machine.

While running your motor at this time, just take it easy go for short bursts rather than the all-out blasts of the engine you might do normally.

Getting from A to B slower is better than not getting there at all and having to pay out for another motor!

Use a Restrictor If You Do Not Have a Working Thermostat in Your Outboard

Using a restrictor plate on your outboard will slow the motor down and keep it running cooler, making for a much safer run while you are without a thermostat and reducing the risk of overheading

They even use restrictor plates in Nascar car engines to do just that – restrict the speed and temperature of the engine, having been used since the late 80s to try to reduce the risk of high-speed crashes.

That said, many outboards come with a restrictor plate, so you should check your model to see if it already has one.

Hot Spots Can Develop in the Outboard Engine Without a Thermostat

No thermostat means no timed temperature mechanism for your motor when it has been running for a while, which can shorten the life of your outboard and excessive heat can cause fractures or cracks to develop in the engine. You may not see these at first but they cannot be reversed once they happen.

The overheating happens because a working thermostat on your outboard motor would normally let in water to the chamber around the pistons when it starts to run hot, managing the temperature of the right parts of the engine at the right time.

Hot spots can develop since the air flow inside the engine will be so different that it can have some very weird and unwanted consequences and, without getting bogged down in the technical details, will be bad for your outboard!

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