Plugs - Peter
Is there any advantage in changing the spark plugs from say WR7DC down to WR6DC or in fact upwards to WR8DC. I am going on a long touring holiday with a Volvo 740 and anything to improve the mpg would not go amiss. Buying another car is not an option.

Thanks
Plugs - Pete F
Unless you are suffering plug fouling and consequent misfire, I would say no. If WR7DC are recommended then there are dangers in going either way from this. Maybe someone else has tried this.......
Plugs - Chas{P}
The number in the middle of the part number (Bosch in this case) refers to the heat range of the plug.

There is no economy advantage in putting plugs in of a different heat range and it could cause the symptoms already stated by PeteF.

Best way to achieve maximum economy IMO would be to make sure the car has been serviced properly before going on holiday and avoiding a roofrack or towing if at all possible.

HTH

Charles
 

Value my car