Yanmar thermostat not closing

[Uricanejack]

Oil, filters, antifreeze, impellors and thermostats are a lot cheeper than engines.

 

[nigelmercier]

I don't understand the Volvo thermostat system, either, and I've got one!

There is quite a good description in my VP 22 Series DIY manual:

The coolant in the closed freshwater system passes from the coolant tank to the suction side of the water pump. From the pump the coolant passes through the cylinder block and cylinder head to the thermostat housing. If the coolant is cold, it passes it via the by-pass channel and directly to the suction side of the water pump.

When the coolant temperature increases, the thermostat opens and the by-pass is closed, forcing the coolant through the heat exchanger. In the heat exchanger, the coolant passes over the outside of the pipes that are cooled by seawater running through them. The coolant leaves the heat exchanger and comes to the tank unit, where it cools the exhaust manifold which is an integrated part of the unit. The coolant then returns to the suction side of the water pump.

On MD22A-A and TMD22A-A , some of the coolant passes through an outlet in the tank unit's rear part to an oil cooler (for the engine's lubricating oil) and then to the suction side of the water pump. MD22L has no oil cooler. B and P generations have a seawater-cooled oil cooler, see further under chapter "Seawater system".

 

[ghostlymoron]

That isn't true of some raw-water cooled engines, including both Yanmar and Bukh. As the thermostat opens the upper part of it closes off the bypass, forcing water to pass through the engine block. If the thermostat is removed the water takes the path of least resistance, i.e. through the bypass, and the engine is likely to overheat. Volvo thermostats are a mystery to me: I have no idea how they control engine temperature, so the same may apply to them, or not.

Vyv, I bow to your superior knowledge - I've only ever had a Yanmar engine which, I think, operates in a different way.

 

[ghostlymoron]

There is quite a good description in my VP 22 Series DIY manual:

I need to draw a diagram of that to understand it.

 

[AntarcticPilot]

There is quite a good description in my VP 22 Series DIY manual:

Sadly, this is for a different engine - mine is a raw-water cooled VP 2003.

 

[pvb]

Sadly, this is for a different engine - mine is a raw-water cooled VP 2003.

Here's a very basic diagram, taken from a VP publication.

 

[richardabeattie]

I am now getting confused! I thought that when flushing fresh water through my raw watercooled engine whilst ashore at the winter layup the trick was to first remove the thermostat. My assumption was that the fresh water and then the added antifreeze would go round the whole engine without it having be to run for the much longer time it would take for the thermostat to open.

Oh and I promise that if the thermostat sticks open again I will use descaler on it rather than smacking it with a knockometer or Detroit Screwdriver.

 

[pvb]

I am now getting confused! I thought that when flushing fresh water through my raw watercooled engine whilst ashore at the winter layup the trick was to first remove the thermostat. My assumption was that the fresh water and then the added antifreeze would go round the whole engine without it having be to run for the much longer time it would take for the thermostat to open.

Yes, I think it would work, however the Yanmar manual suggests that you drain the water out of the engine for winter. If you want to add antifreeze, the Yanmar manual suggests putting it in through the thermostat housing until the water passages are full with antifreeze mixture.

 

[AntarcticPilot]

Here's a very basic diagram, taken from a VP publication.

Sorry - I can't make the leap from a fresh-water cooled engine to a raw-water cooled engine. I'm sure it's obvious to most, but I just can't see it.

 

[VicS]

Sorry - I can't make the leap from a fresh-water cooled engine to a raw-water cooled engine. I'm sure it's obvious to most, but I just can't see it.

The diagram is frankly not very helpful!

In very general terms:


With seawater cooled engines when they are cold, and the thermostat is closed, there is no water flow through the engine itself but there is a flow through an external bypass ( perhaps built into the thermostat cover) which allows water to continue to cool the exhaust.
When the engine reaches working temperature the thermostat opens and cooling water is then able to flow through the engine. In some/many/most cases the thermostat also closes the bypass as it opens to allow the main flow through the engine.

The system is different with indirectly cooled engines. Sea water always flows unhindered through the heat exchanger and into the exhaust.
While the engine is cold, and the thermostat closed, no engine coolant flows from the engine though the heat exchanger.
When the engine reaches working temperature the thermostat opens and coolant can then flow through the heat exchanger. In most cases there is a bypass, possibly internal, that allows engine coolant to circulate around the engine while the thermostat is still closed . When the thermostat opens to allow coolant to flow to the heat exchange it may/will also close this bypass .

 

[pvb]

Sorry - I can't make the leap from a fresh-water cooled engine to a raw-water cooled engine. I'm sure it's obvious to most, but I just can't see it.

Absolutely right, sorry, consider it a senior moment!

 

[vyv_cox]

This is a page from my yacht auxiliary systems course.

It shows a Bukh but a Yanmar is identical in principle.
In a Volvo water flows to the manifold down the perforated tube inside the head, which is effectively the bypass. The thermostat is at the inlet end of the tube. When the thermostat opens something persuades water to pass down the copper tube that is external to the head. This is the one that is broken into to supply a calorifier, photos on the website. I don't understand what happens and, up to now, nobody has been able to give me an explanantion.