Outboard Motor - running without thermostat

[thatsshallot]

Hi,

I have a 1987 Honda 8 outboard, and I have a feeling the thermostat has stuck.

I have considered running the engine without a stat until I can get a new one, but have been advised that doing this can cause overheating?

Any advice guys?

Thanks,

That's shallot

 

[Rum_Pirate]

Running it without a thermostat will cause the engine to run cooler, not overheat.

Not sure if this would result in additional or greater wear.

Running the engine with a STUCK thermostat could damage the engine (incl overheating) depending at what temperature the thermostat stuck.

 

[VicS]

It is always advised that you do not run without a thermostat.

one argument goes that the pistons still get to their normal temperature but because the cylinders are being over-cooled the clearance is reduced and could lead to trouble!

Suggest then that if you must run without you do so at moderate speeds rather than full chuff.

Over time running too cool will also lead to a build up of moisture in the oil and perhaps condensation in parts of the engine.

But why do you feel the thermostat has stuck?
Overheating? When was the last time the pump impeller was renewed? Might the water passages be clagged up with corrosion or scale? Water intake screen blocked?

Easy enough to check that a thermostat is working once you get it out. Heat slowly in pan of water. It should just start to open at the specified temperature ... maybe marked on it.

 

[Lakesailor]

It depends where the thermostat is in the water system. Whilst it would seem that the obvious answer is that it would run cooler, sometimes the backpressure caused by the restriction of the thermostat causes scavenging which pulls hot water from the far reaches of the water passages. So without a thermostat there may be hot spots developing. Bad thing.
Many car tuners fit a plate with a restricted hole in to replace the thermostat when wanting to run without one in order to retain the scavenging effect.

 

[rafiki_]

I agree with LakeSailor, that you should run with a restrictor if no stat. Have you taken the stat out to check it?

 

[RayOz]

I have an Evinrude Elan 35, great for our lake, and the thermostat is new, but when the thermostat is in it goes into limp mode without it, and the engine runs, we are opting to just run it without, I can not see a problem but understand its best to idle the engine first, thoughts, please. Also, In Australia it's not as cold as U.S., our water is cold at 11-15C (the U.S. gets to -20C or more in the water) being a US engine I think it's designed for your frozen environments. Please give thoughts

 

[snowbird30ds]

(the U.S. gets to -20C or more in the water) being a US engine I think it's designed for your frozen environments. Please give thoughts

If the water gets to -20C you are not going boating anywhere as it's solid!

 

[Boathook]

I have an Evinrude Elan 35, great for our lake, and the thermostat is new, but when the thermostat is in it goes into limp mode without it, and the engine runs, we are opting to just run it without, I can not see a problem but understand its best to idle the engine first, thoughts, please. Also, In Australia it's not as cold as U.S., our water is cold at 11-15C (the U.S. gets to -20C or more in the water) being a US engine I think it's designed for your frozen environments. Please give thoughts

11 to 15C is cold for the US southern States as well.
Either the thermostat is faulty, even though new, or the water cooling channels in the engine are restricted or even the water pump is on its last legs.

 

[Fire99]

I have a 1991 Mercury 10hp (2-stroke) which was missing its thermostat when I bought it. I ran it for quite a long time before I noticed and bought a thermostat. To be honest, I wouldn't intentionally run without one long term. The outboard will take longer to warm up and may ultimately run cool which isn't great for an engine long term. That said older generation outboards are pretty basic in function and mine didn't show any complaint from its time without one..So for me, ok for a little while but not best practice. I wouldn't do such things on a modern outboard since everything is much finer tuned.