Coolant flow diagram

[billmartin]

Originally Posted by listener

That's wierd, it looks as if two flows converge on the, I think the thermostat, from different directions that can't be right surely

The thermostat has an entry into the engine block (not shown in the diagram) so the cold water goes in there (near the dreaded stat) ,is heated by the engine and comes back out the top hose.

[T-Cut]

Yes, as explanatory diagrams go, it's not very - explanatory. In fact the flows look ambiguous throughout IMO.

TC

[HarryM1BYT]

Originally Posted by billmartin

The thermostat has an entry into the engine block (not shown in the diagram) so the cold water goes in there (near the dreaded stat) ,is heated by the engine and comes back out the top hose.

I agree it does look ambiguous. I think the idea is that the stat location is designed so as to have a constant flow of hot coolant past it, that which flows through the engine, heater, fbh etc., even with the sat closed - which makes the stat more much more sensitive to actual engine temperature, then when it opens it releases what ever flow is needed into the rad to maintain temperature.

That constant flow past the OEM stat, is the major disadvantage of the top hose stat mod.

[T-Cut]

The diagram will be rather different for a non-FBH system, which is probably more relevant to most owners.

Happy Christmas everyone!

TC

[HarryM1BYT]

Originally Posted by T-Cut

The diagram will be rather different for a non-FBH system, which is probably more relevant to most owners.

Happy Christmas everyone!

TC

Not really - instead of passing through the FBH, the pipe work is just linked together where the FBH would be located. To install an FBH, you break into the pipe.

[T-Cut]

Ah, OK. What looks wrong to me in the diagram is the cold flow from the bottom of the header tank. There is a bleed flow going in at the top and a flow out the bottom. As I understand it, the tank is simply a header without any 'flow' through it. The bleed pipe allows expansive heat soak from the head to be released via the cap as necessary. That's how the petrol systems work anyway and they all use the same cap.

TC

[man of kent]

All interesting comments which is why I asked the original question. There is something unusual about the coolant flow on the engine which is why the stat fails so often. Haven't a clue at this stage why! Until the actual flow and proximity of flow route changes and components is known we will not know why.

Doubt there is any better flow diagram in existance. I think it will only be answered when the forum becomes a classic car club and a technical meeting is held around a stripped down engine when you can actually see what is happening on the components. Unfortunately everything is packed in so tightly around the engine, like most cars now, its difficult to work out what is happening without stripping some of the engine compartment down.

In the meantime fit a top hose in line stat to raise the engine temperature and stop any incidental flow through the rad, if it exists.

[HarryM1BYT]

Originally Posted by T-Cut

Ah, OK. What looks wrong to me in the diagram is the cold flow from the bottom of the header tank. There is a bleed flow going in at the top and a flow out the bottom. As I understand it, the tank is simply a header without any 'flow' through it. The bleed pipe allows expansive heat soak from the head to be released via the cap as necessary. That's how the petrol systems work anyway and they all use the same cap.

TC

I've just been out to take a look - I fancy the small pipe up to the top of the header is just there to release any trapped air fro the top of the rad, I have never noticed an actual flow through the header tank nor have I have found it warm after a run.

Man of Kent - 'All interesting comments which is why I asked the original question. There is something unusual about the coolant flow on the engine which is why the stat fails so often. Haven't a clue at this stage why! Until the actual flow and proximity of flow route changes and components is known we will not know why.'

I don't really see how the flow could possibly cause any failures in the stat. I don't think the stats are failing that often, I replaced mine at 96K miles because it was opening at around 78C, at the start of my ownership and I was in the process of getting everything spot on.

The point which really needs to be investigated, is why these wax stats do gradually drift in opening temperature. I don't think there has ever been a reported issue of one which has been found to be stuck open (which is the normal failure mode of a wax stat), just simply that they all suffer the same problem of the stat gradually opening lower in temperature as they age - which can only point to some change in the properties of the wax cartridge with time. Leakage of the wax would not explain i either, because then the stat would fail to open. Someone suggested it might be the spring weaking, but the spring only has to provide adequate pressure adequate enough force to close the valve, as the wax contracts.

Since installing the FBH, I fancy the system is warming up very slightly faster than before - even when the FBH is not fired up. Maybe due to the FBH causing some restriction in coolant flow in the primary circuit?

[T-Cut]

Originally Posted by HarryM1BYT

- - - - which can only point to some change in the properties of the wax cartridge with time.

I agree, the wax changes its characteristics. Exactly what happens is a mystery to me. They typically contain a narrow melting range paraffin wax, which is about as inert as anything can be. Thousands of melt-freeze cycles can't do anything physically or chemically to a paraffin wax. That's the theory anyway, but the evidence suggests otherwise. Maybe OEM stats aren't based on natural paraffin wax, but something else, a synthetic wax perhaps. These may well be affected by long term heating/cooling, especially if trace moisture can penetrate the seal.

TC

[FrenchMike]

I wonder if among people having had thermostat problems, how many
have had fan issue previously ?
May be related ?

In my case,no overheating ,genuine thermostat...

Mike