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Old 10-04-2011, 21:24   #1
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Thermostat Housing: How important?

Hi,
I have a little raw water cooled Volvo MD5, which I built a new thermostat housing for.
Looking at the cooling circuit, I don't fully understand what controls the direction of water flow. Here's the system (picture would be best ofcourse), water enters via saildrive -> strainer -> impellor pump -> thermostat housing -> NOW, the water either goes straight out the other side of the thermostat housing and then back into the head (via a hole directly inline with the inlet hole), or it can go out the top of the housing to the exhaust, or it can go through the thermostat (when open - it opens inwards, in to the engine).
Seems to me that the water would always find the easiest path is straight out the exhaust....
The original housing is very corroded, but I recall the inlet and outlet (out to head) being linked to the thermstat chamber and exhaust outlet via a fairly small port. Is this intended to restrict flow and force it through the head? In that case the thermostat would be controlling water by restricting water exiting the head, not entering it.

In case your wondering, my engine is overheating!
Overheating Raw-Water Cooled Volvo

Thanks for your thoughts.
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Old 11-04-2011, 01:01   #2
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Re: Thermostat housing - importance?

Maybe the picture link below will help?

Volvo Penta Exploded view / schematic COOLING SYSTEM, INDUCTION- AND EXHAUST MANIFOLD: A MD5A, MD5B - MarinePartsEurope.com
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Old 11-04-2011, 04:29   #3
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Re: Thermostat housing - importance?

that is proper.

you need some restriction of the water in the engine. This slows it's flow speed down. Allowing the water to absorb heat from the engine. At the same time you need a little bypass water to keep the exhaust gas temperature down. This prevents the exhaust hose from melting / burning.
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Old 12-04-2011, 22:41   #4
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Re: Thermostat housing - importance?

Thanks - already seen that one. Unfortunately it does not indicate what the flow direction is, or how flow might be controlled.
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Old 12-04-2011, 22:56   #5
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Re: Thermostat housing - importance?

Quote:
Originally Posted by never monday View Post
that is proper.

you need some restriction of the water in the engine. This slows it's flow speed down. Allowing the water to absorb heat from the engine. At the same time you need a little bypass water to keep the exhaust gas temperature down. This prevents the exhaust hose from melting / burning.

I have not changed the restriction for water getting out of the engine, just in the circulation path. I hear what you say about absorbing the heat, but surely for arguments sake, twice the amount of water (so flowing faster) and absorbing half as much heat, has the same net cooling effect?

There's no problem with the water cooling the exhaust - in fact the water coming out is only warm at best under heavy load. The problem I have is that I don't think the water is circulating through the head in the correct direction - ie water is not getting warm because most of it doesn't even get in to the head.

Do other raw water systems have a control to prevent water from using the bypass circuit (and go through the head instead) when the thermostat is open?
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