Thermostat Bypass Pipe

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garrycol
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Thermostat Bypass Pipe

Post by garrycol »

On the early Land Rover 3.5 V8s (Strombergs) there is a bypass pipe/hole in the bottom of the thermostat housing that has a s rubber pipe that connects to the back of the timing cover - it allows coolant to pass between the inlet manifold and water pump while the thermostat is still closed. It allows the circulation of a small amount of coolant from the water pump into the engine and back through the inlet manifold, thermostat housing to the water pump so helping warm the engine.

I have a 4.6 in my vehicle with the 4.6 timing housing and water pump but at this stage still have the original 3.5 carbs and manifold fitted. The issue I have is that the 4.6 does not have the pipe at the back of the water pump to allow the thermostat bypass pipe to be fitted so I just have it blanked.

My simple question is this an issue?

Older engines never had a bypass and the coolant in the engine just heated up until the thermostat opened and all was good.

Thanks

garry



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ChrisJC
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Re: Thermostat Bypass Pipe

Post by ChrisJC »

No, I believe what happens is that some heaters are always 'hot' and use ducting and flaps to change air temperature. In this case, there is no need for a separate thermostat bypass because the heater circuit does that job.

If your heater shuts off the water flow, then you do need the bypass.

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garrycol
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Re: Thermostat Bypass Pipe

Post by garrycol »

Thanks Chris - no flaps or vents. Old style heater with a tap control to turn it on and off. The heater plumbing is separate to the thermostat bypass - there is a heater outlet pipe at the rear of inlet manifold as per all older Landrover V8s.

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Garry

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Re: Thermostat Bypass Pipe

Post by ChrisJC »

If I recall correctly, the heater outlet at the back of the manifold and the thermostat bypass outlet at the front are both equivalent.

As long as one of them has a permanent return path back to the water pump inlet (radiator bottom hose), then all will be OK.

If you have neither open, then the water will not be able to circulate until the thermostat opens, which is bad news as it means the thermostat will probably never open as it won't get any hot water coming past it to warm it up!

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garrycol
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Re: Thermostat Bypass Pipe

Post by garrycol »

Thanks Chris - you input is appreciated.

I am going to run some heater hose from this outlet in the thermostat housing to the lower radiator hose so that irrespective if I have the heater on or off there will be a flow past the thermostat even when it is closed.

Cheers

Garry

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Re: Thermostat Bypass Pipe

Post by DaveEFI »

The heater on my SD1 EFI is of the air blending type - but shuts a valve in the heater coolant circuit when the AC is in use.
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Re: Thermostat Bypass Pipe

Post by minorv8 »

I have my heater valve closed in the summer and do not have a bypass hose. I have drilled a couple of 6 mm holes in the thermostat allowing some water to bypass. Works nice and there is less hose connections.

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Re: Thermostat Bypass Pipe

Post by ChrisJC »

minorv8 wrote:
Fri May 08, 2020 10:58 am
I have my heater valve closed in the summer and do not have a bypass hose. I have drilled a couple of 6 mm holes in the thermostat allowing some water to bypass. Works nice and there is less hose connections.
So that is not quite the same. It will keep water circulating when the thermostat is closed, but of course that circulation is going through the radiator.

This means the warm-up time will be longer than if the bypass coolant wasn't being cooled.

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Re: Thermostat Bypass Pipe

Post by minorv8 »

Mine is strictly a summer car so warm-up time is irrelevant :D

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