Thermostat opening time

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richardabeattie

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Raw water 2 GM 20. If I start the engine from cold and run it at modest revs in neutral how long is it likely to be before the thermostat opens and I can start running fresh water through without it going through the bypass? Are we talking ten minutes?
 
richardabeattie said:
Raw water 2 GM 20. If I start the engine from cold and run it at modest revs in neutral how long is it likely to be before the thermostat opens and I can start running fresh water through without it going through the bypass? Are we talking ten minutes?
Click to expand...

I don't know that engine either but when I ran my RW engine yesterday in neutral, it took for ever to detect 35degC leaking through the (closed) thermostat when the temp. stablises. I.e it would never open the thermostat in neutral (Sea Temp about 12degC, I think)
To have the thermostat open the engine has to be run in gear. When the thermostat opens the temperature overshoots to 68degC and then slowly drops to 58ish. (Thermostat is set at 60degC)

I don't understand your reference to fresh water in a RW engine but that's probably more to do with my ignorance.
Cheers
Bob
 
richardabeattie said:
Raw water 2 GM 20. If I start the engine from cold and run it at modest revs in neutral how long is it likely to be before the thermostat opens and I can start running fresh water through without it going through the bypass? Are we talking ten minutes?
Click to expand...

Why do you want to know?? I really don't understand your question.
 
Fairly obvious I would have thought. It's raw water cooled. So I want to flush it with fresh water when I lay the boat up. But until the thermostat opens the fresh water will bypass the block. So I just want run the engine long enough to open the thermostat, then connect the freshwater leave the engine running to clear the salt.
 
I assume you want to put some antifreeze mixture through the system but don't want to waste it through the bypass.

When I do my Bukh, it doesn't take very long to get to temperature but generally I want it to run a good while before running the antifreeze through it.

I stick my hand in the exhaust water to find out how hot it is. I also catch it in a bucket and recirculate the increasingly hotter water.
 
Now seen your explanation.

I like to run the engine with fresh water for 20 mins or so after it's hot. During that period, using my hand test, the thermostat will be cycling through open and then closed then open again. I have a bucket with the antifreeze mixture in and top it up from the antifreezed exhaust water as it appears, then the thermostat stays open longer as the water warms up.
 
richardabeattie said:
Fairly obvious I would have thought. It's raw water cooled. So I want to flush it with fresh water when I lay the boat up. But until the thermostat opens the fresh water will bypass the block. So I just want run the engine long enough to open the thermostat, then connect the freshwater leave the engine running to clear the salt.
Click to expand...

Not at all obvious, we're not clairvoyants!:rolleyes:
 
"If I start the engine from cold and run it at modest revs in neutral how long is it likely to be before the thermostat opens". That was the question. No clairvoyance required. But it would be nice to get an informed answer.
 
richardabeattie said:
Fairly obvious I would have thought. It's raw water cooled. So I want to flush it with fresh water when I lay the boat up. But until the thermostat opens the fresh water will bypass the block. So I just want run the engine long enough to open the thermostat, then connect the freshwater leave the engine running to clear the salt.
Click to expand...
use a recirculating system, a bucket under the exhaust with a skin fitting & hose stuffed up the intake ( assuming the vessel is ashore ) then add antifreeze in the final moments
 
James_Calvert said:
I assume you want to put some antifreeze mixture through the system but don't want to waste it through the bypass.

When I do my Bukh, it doesn't take very long to get to temperature but generally I want it to run a good while before running the antifreeze through it.

I stick my hand in the exhaust water to find out how hot it is. I also catch it in a bucket and recirculate the increasingly hotter water.
Click to expand...

Circulating to and from a bucket is what we used to do with our 3gm30 before introducing anti-freeze.
 
Problem will be that the thermostat doesn't open at a set temperature and stay open. It will let a trickle of water through at a time, cycling open and closed. If it's to flush the engine with fresh only then I would run it for half an hour.
 
pagoda said:
Circulating to and from a bucket is what we used to do with our 3gm30 before introducing anti-freeze.
Click to expand...

And, of course, with the water constantly rising in temperature, the thermostat will be fully open much quicker. It seems that the OP is over-thinking this; it's not rocket science.:rolleyes:
 
richardabeattie said:
Raw water 2 GM 20. If I start the engine from cold and run it at modest revs in neutral how long is it likely to be before the thermostat opens and I can start running fresh water through without it going through the bypass? Are we talking ten minutes?
Click to expand...

My guess is that it will take at least 10 minutes , 20 perhaps at no more than a fast idle with no load.

Even then it will only have to open a crack and allow a very small water flow to keep the engine cooled. Most of the water will still go through the bypass and it'll take forever to thoroughly flush the salt water from the block

If I were doing this I would drain the cooling system first to get rid of as much salt water as possible.

I would transfer the pump suction to a bucket fed with fresh water from a hose and then run the engine until it was good and warm and then for a good bit longer.

If the boat has a self draining cockpit you can stand the bucket in the cockpit and let it gently overflow.
 
Yellow Ballad said:
Does the 2gm20 raw water cool direct through the head then? No heat exchanger?
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The seawater cooled version is directly cooled with sea water ..... The fresh water cooled version has a heat exchanger :rolleyes:

They are designated 2GM20(C) and 2GM20(F) respectively
 
Last edited:
black mercury said:
Problem will be that the thermostat doesn't open at a set temperature and stay open. It will let a trickle of water through at a time, cycling open and closed. If it's to flush the engine with fresh only then I would run it for half an hour.
Click to expand...

Bingo - we have an answer! And thanks also to Vic. How my original straight question about time could be descibed as overthinking beats me!
 
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