TAke a good look at the insulator tips when you change them. If they are nice even gray or tan, you have the correct heat range. If they are dark brown, you are either rich or too cold, if blistered too hot.

Chances are what you have are working fine and I would not change heat range.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!