Thermostat replace

[jonathanhsm]

I have just bought a new thermostat because mine was sticking open and overcooling engine. In the picture you can see the 'old' one on the left has a bleed hole which various instructions say should be at the 12 o clock position. The new thermostat doesn't have a hole. Is that a problem? The engine is a Perkins Perama M20 - virtually the same as the Volvo MD2020 and parts interchangeable.

 

[Boater Sam]

The tiny hole, often with a jiggle pin, is a bypass but primarily to let air through so it vents. I would drill a 2mm hole before fitting the stat.

 

[jonathanhsm]

Thanks - there is a bleed hole in the thermostat seat pictured ... but that is mostly covered by the 'skirt' of the thermostat when it is inserted - so I guess drilling a small hole is a belt and braces approach. I am assuming the hole should be oriented at 12 o clock when thermostat is installed ... as per advice I have seen in various threads ? Still cant quite work out why replacement doesnt have a bleed hole and original did - they are both the same make.

 

[Boater Sam]

Perhaps the hole fell out of the box in transit?

Position hole at the highest point when installed.

 

[Refueler]

Maybe someone drilled the hole in your old one ?

 

[jonathanhsm]

Maybe ... but if you look at thermostats online - which I have nerdily done - most appear to have a breather hole some with a 'jiggle pin' and dire warnings about the overheating consequences if you don't install it right way up! I shall be obeying the rule and drilling my own hole because I never want to replace the thermostat on a Perkins Perama M20/Volvo MD2020 again. Ludicrously it involves taking off the alternator, starter motor, exhaust elbow and whole heat exchanger assembly. Then you need new gaskets/ thermostat/ spring etc. etc. And cream for skinned knuckles !