by-pass hose

[classic225]

Hi,

I know I need the old style bellows thermostat or block the by-pass line with a 3 mm drilled plug. I went for the plug with drilled hole, but I just want to understand why this needs to be done. Would cooling in the head be affected if you run a normal thermostat and no plug??

Thanks,

Yves

[BlueTR3A-5EKT]

Bellows thermostats have a moving sleeve that blanks off the bypass hole when the thermostat is fully open. Modern wax type thermostats do not have the blanking sleeve.

 

Restricting the water flow through the bypass with the drilled plug as you describe means water from the pump will not take the shortest route possible, up the bypass and back to the radiator. Thus avoiding cooling the engine. The bypass is the same size as most jap/ euro box main radiator hoses.

 

Peter W

[classic225]

Thanks Peter !

[Fireman049]

Hi Yves ~

 

This is how I did it on my 3A. The hole is approx 1/8th diameter.

 

Hope it helps.

 

Tom.

 

[peejay4A]

Just for the avoidance of doubt, not all bellows type 'stats have a sleeve. Oh and don't be tempted to increase the poundage of the radiator cap. Above 7 psi a bellows 'stat won't open properly.