Thermostat yes/no with raw water cooling

[pwilletts]

The issue here is the degree of cooling effectiveness in a raw water system that can be run with or without a thermostat...It happens to be a small 1 cyl Farymann Lets forget about ambient water temp and whether the engine runs better hotter or cooler.
My observation is that with the thermostat in place and open, that there is a certain amount of restriction created by the thermostat which allows the water to "linger" around the cylinder and thus absorb more heat. Versus the non thermostat system where the water flows through much quicker and at a higher volume....but does not linger . Is there more heat transfer with the open or the restricted system???

[charliehows]

If the engine was designed to run with a thermostat, it should have the appropriate thermostat fitted.
The principle is very simple – a raw water cooled engine has to maintain a fairly cool running temperature to avoid heat precipitation of salts from sea water. But running any engine dead cold is problematic, so the purpose of the thermostat is to allow the engine to heat to its operating temperature as quickly as possible and then maintain that temperature without exceeding it or falling back to a too cool temperature. Running the engine without a designed thermostat is not going to have any short term effect on a raw water engine but it'll probably slightly shorten the long term life of the engine. If you have any sort of reasonable maintenance schedule on your engine, occasionally checking or replacing the thermostat is a pretty simple matter. If you cant manage that, the engine will probably die from some other type of neglect before the thermostat becomes a problem.

[denverd0n]

Originally Posted by pwilletts

Is there more heat transfer with the open or the restricted system???

Short answer: the open system.

But the real point is that every engine is designed to operate at a particular temperature. The idea of the thermostat is to bring it up to the correct temperature fairly quickly, and then keep it there. If your cooling system cannot keep the engine at the designed temperature with a thermostat in place, then something is wrong. You need to fix the cooling system. Not just remove the thermostat.

Despite what some people seem to (mistakenly) believe, it is NOT good for an engine to run cooler than its designed operating temperature. When you do so you only serve to lower its efficiency, and shorten its life.

[pwilletts]

As I stated in the opening...this engine is certified to operate either with or without the thermostat....I find it much cooler w/o the thermostat

[Lepke]

If I had a raw water cooled engine I'd buy a pump and heat exchanger before the engine rusts out...

By heating the engine to 160°F (usual raw water cooled thermostat) the engine runs more efficiently and the warm oil evaporates out some of the water it has absorbed. The compounds formed at low temp ignition are not burned off and eventually gum up the rings.
If you can't keep your engine below 160° with a thermostat, you have other problems. Pump, plumbing, etc.

[roverhi]

The 160 degree temperature has to do with the salt in the water. With temps above 160 degrees salt/mineral deposits develop eventually blocking water passages and ruining the engine. With the compression ignition of the diesel you have to run them warm enough that they will fire efficiently but not too hot where they will have deposit issues.

[a64pilot]

Originally Posted by pwilletts

The issue here is the degree of cooling effectiveness in a raw water system that can be run with or without a thermostat...It happens to be a small 1 cyl Farymann Lets forget about ambient water temp and whether the engine runs better hotter or cooler.
My observation is that with the thermostat in place and open, that there is a certain amount of restriction created by the thermostat which allows the water to "linger" around the cylinder and thus absorb more heat. Versus the non thermostat system where the water flows through much quicker and at a higher volume....but does not linger . Is there more heat transfer with the open or the restricted system???

There is supposedly truth to what you say, that is water can move through the system too quick to pick up the heat.
It doesn’t sound right, but circle track race cars don’t run thermostats due to it being something else that can break and they want to run as cool as possible cause the cooler, the higher the Hp due to increased air density. But engines were running hot, until a washer was installed where the thermostat goes, restricting the water flow, just like a thermostat does.
It seems that maybe the engine designers designed a system taking into account the thermostats restriction and that Jim Bob the shade tree mechanic messed things up by “improving” the cooling system.

Now interestingly it’s the engine, specifically cylinder head temp that was running higher, not the water, the water was not overheating.
Heat, especially cylinder head heat, robs power, something that a race car driver doesn’t want.

[sailorchic34]

I would consider a 160 degree F thermostat to be too hot for a raw water cooled engine. Minerals start precipitating out of water (fresh or salt) at temperatures over 140 degrees F ( really starts at <>135F, but close enough). The higher the temperature the more minerals precipitate out The danger of course is letting the cylinder walls get too hot.

For heat to transfer from one surface to another there has to be a difference in temperature. So if the water temp is set at 160F, the cylinder wall might be 162-165F. Way too hot for Raw water cooling.

I would recommend a 140F thermostat for raw water. A hotter engine is more efficient, but it's only a few percent drop loss in efficiency from 160 to 140 degrees F.

[Wotname]

Originally Posted by pwilletts

The issue here is the degree of cooling effectiveness in a raw water system that can be run with or without a thermostat...It happens to be a small 1 cyl Farymann Lets forget about ambient water temp and whether the engine runs better hotter or cooler.
My observation is that with the thermostat in place and open, that there is a certain amount of restriction created by the thermostat which allows the water to "linger" around the cylinder and thus absorb more heat. Versus the non thermostat system where the water flows through much quicker and at a higher volume....but does not linger . Is there more heat transfer with the open or the restricted system???

I not familiar with the Faryman but most raw water cooled (RWC) Yanmar engines will overheat if the thermostat is removed . They will run hotter when there is no restriction but not because the water is travelling too fast. Rather it is because the water does not past around the cylinder when the thermostat is removed.

In many RWC engines, thermostat is more like a switch that diverts the water into the engine when it is hot enough to open and blocks the bypass (which is open to the raw water when the engine is cold). This action allows full flow of water to the exhaust and almost none to the block when the engine is cold and as the engine is warmed, some of that water is now forced though the block until full operating temperature is reached. At this time, all the cooling water is directed though the block before reaching the exhaust.

Note: as sailorchic34 posts, 160F is way too hot for a RWC engine for the reasons she mentioned.

[Wotname]

Originally Posted by Lepke

If I had a raw water cooled engine I'd buy a pump and heat exchanger before the engine rusts out...

......

Crikey, you will be waiting a long time. A properly designed RWC engine will last as long (or longer) as any other engine if you keep the zincs up to it. My 2GM20 (RWC) is now 15 years old with no internal rusting and I recently pulled down a 40 year old YSE-8 with no real rusting or wasting of metal.

It isn't a simple job to convert a RWC engine to fresh water / heat exchanger; of course it can be done but you have provide a new (separate) thermostat etc for reasons posted above regrading thermostat design aspects of the RWC engines.

[Pete7]

Originally Posted by Wotname

Crikey, you will be waiting a long time. A properly designed RWC engine will last as long (or longer) as any other engine if you keep the zincs up to it. My 2GM20 (RWC) is now 15 years old with no internal rusting and I recently pulled down a 40 year old YSE-8 with no real rusting or wasting of metal.

It isn't a simple job to convert a RWC engine to fresh water / heat exchanger; of course it can be done but you have provide a new (separate) thermostat etc for reasons posted above regrading thermostat design aspects of the RWC engines.

Indeed, ours is now 30 years old, when should I start to notice problems?

Good advice from SC and Wotname about the thermostat diverting cooling. Compared to a car thermostat they seem to be an outrageous price but I would still fit one.

Pete

[Wotname]

Originally Posted by Pete7

Indeed, ours is now 30 years old, when should I start to notice problems?

........
Pete

When you forget to replace the zincs

[SSgtPitt]

Where are the zincs on a Perkins 4-108?

[SVTatia]

Originally Posted by Pete7

...

Compared to a car thermostat they seem to be an outrageous price but I would still fit one.

Pete

I did find this to be true when I had to replace mine. I still don't know why... any specific reason?

[Pete7]

Originally Posted by SVTatia

I did find this to be true when I had to replace mine. I still don't know why... any specific reason?

Probably because people keep buying them. Lets be honest there is nothing special about them. The last one I fitted in my VP 2003 was a mix of yellow and silver metals which probably fizz quite nicely in saltwater. The problem is the time it takes to track down what car parts the manufacturers have fitted.

Pete