its a popular mod - at least in this part of the tropics - to replace the thermostat with one that opens at a lower temperature. Don't ask me why, this is what I'm told at my parts shop.

Anyway, this is fine with an older cooling system with a partially blocked radiator as the engine temp stays in spec. However, if you change out your radiator for a new one and replace the visco fan, as I did, the effect is that your engine never actually reaches operating spec and consequently runs rich all the time. Mine sat at just below the 80 deg mark whereas it used to be pegged exactly at 9-o-clock before the rad change.

Took me a while to figure it out but replacing the thermostat with the correct part sorted the mixture out.

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1987 300e manual 250,000 km (sold)