The V8 Owners Forum -

This is just for my own understanding really.

Does anyone know how the bypass cooling circuit works (pre remote thermostat housing) There is lots of talk about this bypass cicruit and its obvious that its needed to allow flow around the engine when the thermostat is closed, but what I can't understand is how this flow diverts through the rad when the thermostat opens? This was a question I mused about with my old 3.5 when I had some cooling issues, I was unsure if I was geting all my coolant flowing through the rad?

With the later rover v8's and I think most modern engines (rover K for example) there is a seperate thermostat housing which also has a plate/diverter attached to the end of the thermosat. When the stat starts to open it gradually shuts off the bypass circuit so all the coolant flows through the rad, we actually it will bleed/mix the cool rad outlet with the hot bypass flow so there is no sudden input of cold fluid so helping reduce thermal stress on the engine.

This is the route I have taken with my 4.6 although I can't comment on how effective it is as it is yet to be started!

Tom.

Hi
It relies on the bypass pipe being smaller diamiter than the main circuit, when the thermostst opens the coolent followes the path offering the lowest resistance to flow, ie down the big pipe and into the radiator, the flow through the bypass becomes stagnent as the open thermostat reduces the pressure difference across it.
Best regards
Mike

kiwicar wrote:Hi
It relies on the bypass pipe being smaller diamiter than the main circuit, when the thermostst opens the coolent followes the path offering the lowest resistance to flow, ie down the big pipe and into the radiator, the flow through the bypass becomes stagnent as the open thermostat reduces the pressure difference across it.
Best regards
Mike

And therein lies the problem.

Have a look at the size of the opening on a thermostat - further reduced by all the "gubbins" to make the thermostat open and close and compare it to the bypass hose diameter

Not too much difference.

add to that the heter matrix that can also bypass the radiator and suddenly you get no flow through the radiator and "cooling" problems

For the best cooling as much flow as possible shoukld be directeed through the radiator.

Keep your system as simple as possible and you should have fewer problems

Of course this is all just my opinion but google MGB V8 cooling and you can read for days. (Makes good bedtime reading and helps you fall asleep)

I do know at first on the GT40 I had the heater matrix on permanent loop - full flow and the temperature rose really quickly when idling in traffic. (Remember my rad is on the nose and the engine in the boot! so going to and from the radiator takes a lot out the waterpump)
It now has a loop but with a restrictor in it (Actually made with 15mm plumbing bits with a "pipe end" - drilled with a 1.5mm hole to allow air to be bled through and yet have mimimal flow. Works a treat!.


Ian

That's interesting, I had though it may be something like that.

This also means that with these engines being fitted in all sorts of cars with different radiators with different resistances to flow there's potential of not getting full flow if needed through the rad!

Tom.