Thermostat

[Tim Bell]

Why do boats need thermostats?
I have a MerCruiser 5.0 and do not know why it needs a thermostat.

Tim Bell

 

[Maclin]

Re: Thermostat

I am curious why you think heat regulation is not needed in a boat, a water cooled engine in a boat or any vehicle or other industrial usage needs their heat regulated. In the cooling water circuitry there is always a thermostat or other thermo activated mechanism that can vary the cooling flow to stay within the preset heat limits. Engines are designed to work in varying environments and conditions, and proper heat for those running conditions is part of the economy and power and long life parameters it is expected to deliver.

 

[Another retired guy]

Re: Thermostat

If your engine didn't have a thermostat it would never reach correct operating temperature. This would result in inefficient fuel use; loss of power; plug fouling; rough running, and a shorter life span.

 

[Boomyal]

Re: Thermostat

If your engine didn't have a thermostat it would never reach correct operating temperature. This would result in inefficient fuel use; loss of power; plug fouling; rough running, and a shorter life span.

Not to mention excessive cylinder wear. Clearances of engine parts are calculated at normal operating temperature ranges. If the temps are too low you get insufficient expansion and wear increases.

 

[Tim Bell]

Re: Thermostat

I did not say that I did not need a thermostat. I was just curious why an engine couldn't run cooler. I know back in the old days engines ran at 160 degrees. Now they run over 200 degrees. I just never knew why the change.Thanks for the replies.

Tim Bell

 

[Maclin]

Re: Thermostat

Not all boats have the same type of cooling systems.

Closed systems, aka Fresh Water cooling, use a heat exchanger and circulate a captive anti-freeze coolant mix over and over thru the engine, giving up the heat in the heat exchanger which has raw water coming in and exiting all the time, like air thru a radiator.

Open systems, or raw water cooled, have "different" water coming in and going thru the engine as governed by the thermostat and the heat goes on out as new water comes in.

Closed cooling and Open cooling systems have different operating temps and different thermostats. Closed systems with heat exchangers will run 180-190 or so while open systems are more like 140 or 160.

When there is no thermostat, but should be, then the cooling water sometimes flows thru too fast and the engine can actually run hotter as the metal does not have as much time to give up the heat.

 

[matt167]

Re: Thermostat

As engine technology has increased, we have discovered that hotter engines run cleaner. With this, there is less carbon and low tension rings give excellent wear characteristics.. Raw water cooling has to run a little colder because of the temp differential. If you think about a heat exchanger or even a radiator. Thermostat opens, coolant flows to the heat exchanger, thermostat closes and the coolant in the exchanger might get 10-20* colder before the thermostat reopens and sends that coolant into the block. Raw water cooling, the water temp might be 50-60*, so if that cold water was introduced into a block at 180*, then the cold water can stress the cast iron.

 

[generator12]

Re: Thermostat

"When there is no thermostat, but should be, then the cooling water sometimes flows thru too fast and the engine can actually run hotter as the metal does not have as much time to give up the heat."

Uhh, what...??

 

[matt167]

Re: Thermostat

The fast running coolant simply does not have enough time to absorb the heat out of the metal in some cases. That is why in some auto racing ( Nascar, IMCA ect... ) they don't run thermostats, but they do run restrictors to slow the coolant to absorb the heat.

 

[Another retired guy]

Re: Thermostat

I did not say that I did not need a thermostat. I was just curious why an engine couldn't run cooler. I know back in the old days engines ran at 160 degrees. Now they run over 200 degrees. I just never knew why the change.Thanks for the replies.

Tim Bell

You may be comparing an open "raw water" system with a closed "fresh water" system. The closed system is pressurized (and may have antifreeze added) which raises the boiling point of the coolant thus allowing it to operate at higher temperatures.
If a high temp thermostat is used in an open system it could result in localized boiling around combustion chamber "hot spots" causing thermal damage to the block/heads.

 

[Maclin]

Re: Thermostat

Matt,

"Raw water cooling, the water temp might be 50-60*, so if that cold water was introduced into a block at 180*, then the cold water can stress the cast iron. "

Very good point, and yet another reason to control the rate of water introduced, good stuff, thanks for adding that