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Old 20-08-2015, 02:15   #1
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Do I need a thermostat in Fiji?

We have a Perkins 4-107 and the engine overheated. The local mechanic tested the thermostat and said it was no good. I have heard that in warm tropical water one can get away without a thermostat. Is this OK? . Water temp in the Marina is 81 F. Can't find a replacement locally, so can I do without at least temporarily ? I will be ordering a new one, but it will take awhile.
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Old 20-08-2015, 03:00   #2
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Re: Do I need a thermostat in Fiji?

You should ALLWAYS use a thermostat. Some engines won't get warm without them, and some will overheat. If they were not required, they would not be there! Get another one ASAP.
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Old 20-08-2015, 06:03   #3
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Re: Do I need a thermostat in Fiji?

Can you "get away with it?" Yes, temporarily. "Is this okay?" No, not really. The engine will take longer to warm up, and may never warm up as much as it should. That is not a good thing. Over time it can cause serious problems. Over-heating is unlikely, unless there is something else wrong with your cooling system.

If you HAVE to move the boat, and there is simply no way to get one right away, then you don't really have much choice. But you should replace it as soon as you possibly can.
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Old 20-08-2015, 06:27   #4
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Re: Do I need a thermostat in Fiji?

As a better than nothing fix for now, you could cut the center / moving bit out of the one you have and refit that, Will be a bit closer to original flow restriction/turbulence,
Tim
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Old 20-08-2015, 06:47   #5
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Re: Do I need a thermostat in Fiji?

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Originally Posted by Neptune's Gear View Post
You should ALLWAYS use a thermostat. Some engines won't get warm without them, and some will overheat. -----
How would the lack of a thermostat cause an engine to overheat?
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Old 20-08-2015, 07:42   #6
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Re: Do I need a thermostat in Fiji?

Many cooling system designs use a thermostat which employ a "block off plate".
When the coolant warms up and the thermostat opens, the block off plate simultaneously closes a cooling water bypass opening, thereby directing the coolant thru the open thermostat and to the heat exchanger.

Removing the thermostat in such a system allows a large portion of the coolant to return to the circ pump without having traveled thru the heat exchanger and the engine will overheat.

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Old 20-08-2015, 08:15   #7
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Re: Do I need a thermostat in Fiji?

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Originally Posted by Alan/Rhapsody View Post
We have a Perkins 4-107 and the engine overheated. The local mechanic tested the thermostat and said it was no good. I have heard that in warm tropical water one can get away without a thermostat. Is this OK? . Water temp in the Marina is 81 F. Can't find a replacement locally, so can I do without at least temporarily ? I will be ordering a new one, but it will take awhile.
The thermostat is there to get you to operating temperature as quickly as possible. Most engine wear occurs when running cold.

The thermostat also regulates the cooling system temp in response to changes in engine load and raw water temp. They act more like a switch in that they are either closed or open so you will see some running temperature variation.

You can replace it with a suitable sized washer to get you out of trouble. But some experimentation is usually necessary to determine the right size orifice. I can usually guesstimate by looking at an opened thermostat.

Leaving it out allows the coolant to circulate too fast and therefore heat transfer is impacted. Your gauge may show cool but your engine may be running too hot. Oil temp or head temp will confirm.

My background is motorsport. We would always replace thermostats with a disk with a right sized orifice. Thermostats are not reliable in highly modified engines. I wont bother explaining the failure modes.

I do run an oem thermostat in our Perkins 4-236. We carry spares and a disk as an extra backup.

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Old 20-08-2015, 09:15   #8
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Re: Do I need a thermostat in Fiji?

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How would the lack of a thermostat cause an engine to overheat?
Theoretically, the water moves through the engine too fast to pick up all the heat required to cool it to the proper operating temperature. I've never seen it though...
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Old 20-08-2015, 09:54   #9
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Re: Do I need a thermostat in Fiji?

If you do have a recirculating hose and do not have a thermastat in you can pinch it off to avoid water from bypassing going through block or exchanger.
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Old 20-08-2015, 13:06   #10
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Re: Do I need a thermostat in Fiji?

If it's typical Brit engine design, you can run without a thermostat. Better to have one for quick warm up and long term operating at proper temperature, however. Without a thermostat engine could run colder than it's designed for which will mean burning more fuel inefficiently. For short term use, shouldn't be a problem. Have run many Brit. car engines without thermostats, one for a fairly long time, without any issues.
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Old 20-08-2015, 13:18   #11
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Re: Do I need a thermostat in Fiji?

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Originally Posted by jimbunyard View Post
Theoretically, the water moves through the engine too fast to pick up all the heat required to cool it to the proper operating temperature. I've never seen it though...

The dirt track car racing guys use what looks like a washer where the thermostat goes, theory is the water in fact does not overheat, but the engine, specifically the heads do, based on the water moving too quickly through the engine if not obstructed.
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Old 20-08-2015, 13:23   #12
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Re: Do I need a thermostat in Fiji?

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Originally Posted by roverhi View Post
If it's typical Brit engine design, you can run without a thermostat. Better to have one for quick warm up and long term operating at proper temperature, however. Without a thermostat engine could run colder than it's designed for which will mean burning more fuel inefficiently. For short term use, shouldn't be a problem. Have run many Brit. car engines without thermostats, one for a fairly long time, without any issues.

My old MG had what they called a pump assisted thermal siphon cooling system, and had two different thermostats called for. One Winter, the other for Summer.
Most of our engines coolant first enters the block and exists the head, which is actually backwards, but it comes from the old days of the thermal siphon, which relied on convention to circulate water.

I agree, best to have a thermostat, and I'd order one, but wouldn't change my travel plans on not having one
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Old 20-08-2015, 19:40   #13
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Re: Do I need a thermostat in Fiji?

Perhaps a little lesson for all of us.
It could pay to carry a spare thermostat on board.
Easy to replace no long wait for it to arrive when ordered.
When replaced,sit back, relax with a cuppa and enjoy peace of mind.
Fair wind, happy and safe sailing to all of you.
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Old 20-08-2015, 19:57   #14
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Re: Do I need a thermostat in Fiji?

Where are you? The 4-108 engine is a very common engine so you just might be able to find one in a truck repair facility if there is one near you.

That idea of using a washer like disk is a new one to me. Thanks for that tip.
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Old 20-08-2015, 20:01   #15
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Re: Do I need a thermostat in Fiji?

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How would the lack of a thermostat cause an engine to overheat?
Lots of interesting info, thanks guys.
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