Volvo 2000 series coolant flow

[vyv_cox]

Please can anyone inform me precisely how the coolant system on a raw-water cooled Volvo 2000 engine works? I am aware that when cold, water is pumped through the perforated tube inside the cylinder head and out through the double right-angle pipe to the manifold. As this is the bypass flow, I assume it is sized for the full flow rate of the pump.

Once the engine is hot, the thermostat opens and water now passes along the external pipe to the manifold. Why does this happen? I am at a loss to understand why it should, other than a bit of convection flow, which I would not have thought would be effective enough. Many owners have broken into this pipe to drive their calorifiers (photos on my website) so there is clearly plenty of flow.

 

[pvb]

Please can anyone inform me precisely how the coolant system on a raw-water cooled Volvo 2000 engine works? I am aware that when cold, water is pumped through the perforated tube inside the cylinder head and out through the double right-angle pipe to the manifold. As this is the bypass flow, I assume it is sized for the full flow rate of the pump.

Once the engine is hot, the thermostat opens and water now passes along the external pipe to the manifold. Why does this happen? I am at a loss to understand why it should, other than a bit of convection flow, which I would not have thought would be effective enough. Many owners have broken into this pipe to drive their calorifiers (photos on my website) so there is clearly plenty of flow.

I don't think the cold bypass is sized to take the full flow of the seawater pump. Therefore, the water in the cylinder head is under some pressure and, when the thermostat opens, hot water comes out.

 

[Dave_Seager]

I am not familiar with this particular engine but on most of them the thermostat does not just open to allow cooling water to flow. Usually, the movement that opens the main cooling path also closes the bypass.

This is often overlooked by people who remove the thermostat, thinking it will make an engine run cooler. On some engines, removing the thermostat will actually make the engine run hotter and probably guarantee overheating.

 

[vyv_cox]

I am not familiar with this particular engine but on most of them the thermostat does not just open to allow cooling water to flow. Usually, the movement that opens the main cooling path also closes the bypass.

That is true of the Bukh, and probably some others. On the Volvo it is as I described. Water into the engine is supplied by the perforated bypass tube, so it cannot be blocked by the thermostat.

 

[wotayottie]

I believe you have it the wrong way round vyv. I'm going from memory here ( and my memory is not 100% reliable) but I believe that the flow until the engine is warm does not go through the cylinder head. Instead the block and head are full or water but the flow goes through the pump and the gearbox and then to the exhaust injection point. When the engine gets warm the thermostat opens and a part of the flow then goes through the head and into the calorifier if fitted. However the flow through the exhaust is not reduced in any way which is the core issue for people who have a non working calorifier.

If you talk to volvo ( that is when they would deign to talk to a customer) they tell you that a calorifier on the raw water cooled engines will never work properly because the flow is low, and indeed at one time they supplied a restrictor you could put into the pipe feeding the exhaust to increase the flow through the head when the thermostat opened. It doesnt help that in northern europe with cold atlantic water it takes some time and some hard use to get the engine up to max temperature with a fully opened thermostat

 

[pvb]

I believe you have it the wrong way round vyv. I'm going from memory here ( and my memory is not 100% reliable) but I believe that the flow until the engine is warm does not go through the cylinder head. Instead the block and head are full or water but the flow goes through the pump and the gearbox and then to the exhaust injection point. When the engine gets warm the thermostat opens and a part of the flow then goes through the head and into the calorifier if fitted. However the flow through the exhaust is not reduced in any way which is the core issue for people who have a non working calorifier.

If you talk to volvo ( that is when they would deign to talk to a customer) they tell you that a calorifier on the raw water cooled engines will never work properly because the flow is low, and indeed at one time they supplied a restrictor you could put into the pipe feeding the exhaust to increase the flow through the head when the thermostat opened. It doesnt help that in northern europe with cold atlantic water it takes some time and some hard use to get the engine up to max temperature with a fully opened thermostat

Here's the coolant diagram from the workshop manual...

You'll see that the flow is as Vyv described.

There are lots of raw water cooled engines which successfully heat calorifiers.

 

[vyv_cox]

I believe you have it the wrong way round vyv. I'm going from memory here ( and my memory is not 100% reliable) but I believe that the flow until the engine is warm does not go through the cylinder head. Instead the block and head are full or water but the flow goes through the pump and the gearbox and then to the exhaust injection point. When the engine gets warm the thermostat opens and a part of the flow then goes through the head and into the calorifier if fitted. However the flow through the exhaust is not reduced in any way which is the core issue for people who have a non working calorifier.

If you talk to volvo ( that is when they would deign to talk to a customer) they tell you that a calorifier on the raw water cooled engines will never work properly because the flow is low, and indeed at one time they supplied a restrictor you could put into the pipe feeding the exhaust to increase the flow through the head when the thermostat opened. It doesnt help that in northern europe with cold atlantic water it takes some time and some hard use to get the engine up to max temperature with a fully opened thermostat

I have it the right way. Look at a photo of a Volvo, for example on my website. The pipework clearly goes from the pump into the head.

My website shows many raw water cooled engines running calorifiers, including Volvos. Several examples kindly provided by informed posters here.

 

[wotayottie]

Vyv. As I said earlier my memory of the precise flows is not that reliable but two things I do remember as clear as the day since I was at the time struggling to get the system to work in my then Moody.

The first is the Volvo tech dept comments about the lack of effectiveness of the system - surprising since they sold the system to boat builders ( the spilt pipes you show are the Volvo system) and they offered an exhaust flow reducer which is still in the parts book to try and make it a bit more effective. The second is that there is no flow through those split Volvo calorifier pipes until the thermostat opens and that even when it does open nothing reduces the bypass into the exhaust so the flow through the calorifier is small.

On a pals Moody 31 the system worked OK with very short runs from the engine to the calorifier, no doubt helped by my pals inclination to motor everywhere at as near 7kn as the poor engine can manage. On y bigger Moody it took half an hour or more for the water to get hand hot and yes, the calorifier and the feed pipes and the head were all good and clear - I stripped them

 

[skip50]

Well, the calorifier on my raw-water cooled VP2003 seems to work well, IMHO-never had one before. The calorifier is positioned over 2 metres from the engine.

 

[reeac]

My VP2002 once developed an overheating problem which only showed up above a certain rpm. - about 2500 IIRC. Turned out to be a thermostat stuck in the closed position. My conclusion was that the cooling water must always have been flowing through the manifold and exhaust system but it wasn't flowing thro' the cylinder head. This would have permitted normal running at lower power levels with the cylinder head being cooled by conduction to the manifold. i.e. the thermostat permits by-passing only of the cylinder head.