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Does my thermostat engine circuit need a restrictor?


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Sorry for the weird title. Thanks to some helpful pointers earlier for my old engine I am now the owner of a thermostatic housing to direct hot water away from my engine and towards the calorifier. 
 

However I am not sure whether I need something to restrict the flow back into the engine. Let me try and explain 

 

When cold - the engine thermostat will be closed and water will exit the engine and run directly through the pump intake and straight back into the engine with no restriction on the flow. 
 

When hot the thermostat will open and allow water towards the calorifier and skin tank. HOWEVER there is nothing stopping water flowing through the original circuit and back into the engine. I estimate most of the water will flow back into the engine. After all - it can either flow direct back into the engine unrestricted or push through the thermostat and round the calorifier coil and through a skin tank and back to the pump. 
 

Surely I need just a bit of resistance in the original engine bypass circuit? Some sort of fitting that increases the pressure build up behind so that when the thermostat opens it will prefer the longer route. 
 

Does any of that make sense? Or am I over complicating something very simple? 
 

Many thanks in advance

 

 

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Without seeing the whole circuit, I can't be sure.

 

First off, have you got instructions from Redsaws for the correct way to pipe the housing. I say this because the calorifier/cab heater circuit is sometimes used as the bypass.

 

What type of thermostat is fitted. It could be a bypass stat (two types) which will shut off the bypass when the engine is hot. A photo would identify it.

 

The bypass port/hose on engines so equipped often has an i.d. of perhaps 5/16 to 3/8 of an inch, so naturally controls the maximum flow through the bypass.

 

 

 

 

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1 hour ago, Tony Brooks said:

Without seeing the whole circuit, I can't be sure.

 

First off, have you got instructions from Redsaws for the correct way to pipe the housing. I say this because the calorifier/cab heater circuit is sometimes used as the bypass.

 

What type of thermostat is fitted. It could be a bypass stat (two types) which will shut off the bypass when the engine is hot. A photo would identify it.

 

The bypass port/hose on engines so equipped often has an i.d. of perhaps 5/16 to 3/8 of an inch, so naturally controls the maximum flow through the bypass.

 

 

 

 

I didn’t specifically ask because I couldn’t remember the exact setup. The calorifier is 15mm tube which I don’t think is enough for it to be included in the bypass circuit. Although again a restrictor pipe would help ensure that the calorifier is the favoured route. 
 

The thermostat does not shut off the bypass - it simply opens an additional 1” bsp pipe. However if this is going straight down to a 15mm pipe that doesn’t seem ideal? 
 

 

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9 hours ago, Doodlebug said:

I didn’t specifically ask because I couldn’t remember the exact setup. The calorifier is 15mm tube which I don’t think is enough for it to be included in the bypass circuit. Although again a restrictor pipe would help ensure that the calorifier is the favoured route. 
 

The thermostat does not shut off the bypass - it simply opens an additional 1” bsp pipe. However if this is going straight down to a 15mm pipe that doesn’t seem ideal? 
 

 

 

If your original diagram is correct, then you say the flow goes from the engine to the calorifier and then through the skin tank. If so, the full coolant flow has to pass through a 15mm tube in the calorifier. That is far from ideal in my view. Fine for canals, but likely to cause overheating when pushing current on rivers.

 

About a half inch bore (15mm o.d.) tube seems a bit large when compared with other bypass port, but it really is suck it and see. At least a 15mm bypass is more restrictive than what looks like 22mm on your original photo.

 

Your description does not clarify the arrangement to me, in fact it seems to confuse things more.

 

Hopefully someone with more knowledge and one of these engines will be along to help you.

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The 15mm take off before the thermostat goes to the cali. And returns back to the return from the skin tank I believe. The main cooling then runs through the skin tank when the thermostat opens. 

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Thanks, Jon, in that case the calorifier is acting as the bypass circuit, much as I suspected it might, but it seems as if the OP's boat is different, or he has not understood it.

 

Edited to add. Although the calorifier take off is on the thermostat housing it is on the engine side of the actual thermostat valve, so is effectively an identical circuit to the vast majority of other engines.

Edited by Tony Brooks
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