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#1
08-04-2017, 05:07 PM
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Correct spark plugs?
Hi all,
Apologies for posting what seems to be such an easy question to answer, but I can't seem to nail it down...I want to put new spark plugs into my '71 280se 3.5 coupe (Euro model, w116 engine). The plugs I pulled out are Bosch W7DC ( Super RO 969). They have been in there a long time. It's easy enough to find W7DC plugs, but I can't seem to definitively say that they are correct. Could someone please let me know what the correct plugs are for that engine, thanks. Dave
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1971 W111 280se rhd coupe (The Duchess) 1959 Bristol 406 (Monty) 1970 Volvo Amazon 131 (Lola) Lives in Cornwall, UK. 
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#2
08-04-2017, 05:41 PM
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It's not that easy to answer. Plugs in owners manual probably no longer exist!
Surprised you can get W7DC plugs. Not so easy it seems in NA. Most these days are the resistor version WR7DC. For non resistor plugs, we can get NGK BP6ES or BP7ES. This chart suggests W7DC or W6DC Bosch plugs or BP7ES NGK plugs. 
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Graham 85 300D  ,72 350SL, 98 E320, Outback 2.5
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#3
08-04-2017, 06:06 PM
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Thanks Graham,
Those W7DC plugs seem easy enough over here. The chart (which is really helpful, thanks) seems to suggest W5DC (280 typ 108,111) 3.5Ltr. Unless I'm reading it wrong of course. That cross references with the NGK BP7ES. My car is often a sod to find in these charts as it was made for a short time. The w7 is a hotter plug than the w5, not sure how that affects things with todays fuel etc?.. thanks again. d
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1971 W111 280se rhd coupe (The Duchess) 1959 Bristol 406 (Monty) 1970 Volvo Amazon 131 (Lola) Lives in Cornwall, UK.
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#4
08-04-2017, 08:18 PM
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The 5 in the Bosch number and the 6 in the NGK number represent how "hot" the plugs are. With Bosch, bigger number mean hotter plugs. With NGK bigger number mean colder plug. The Bosch W7DC and the NGK BP6ES are more or less equivalent. And W5DC and BP7ES are equivalent.
Not sure why a 3.5L M116 in a 280 108or111 would need a colder plug than same engine in another chassis. The heat range of the plug has a lot to do with how the car will be driven. Lot's of slow speed riving, then use hotter plug. (This link may be of interest) If you have the original owners manual, it may have the recommended plugs listed in the car specs. Those plugs will be obsolete, but you may find equivalents using this site: Spark plug cross reference
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Graham 85 300D ,72 350SL, 98 E320, Outback 2.5
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#5
01-31-2019, 04:52 PM
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Thank you, Graham
For the very helpful chart.
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Charles Cleaver 1975 350SE + 1992 300CE-24 SportLine 5-speed + 2002 SLK320 6-speed + 1974 W114 280 1986 190E 2.3-16 (Decomm rear self-leveling suspension; Euro-code headlamps) sold 2004 Audi S4 6-spd - sold 1969 (2) and 1980 Porsche 911T, S, and SC - alas gone 1987 300SDL - Graf Spee; Euro-code headlamps; 16-inch 8-hole wheels - sold 1994 E420+(E500 suspension/E-code headlamps/PAD chip) sold 1968 250SE 4-speed (NICE car) - long gone 1962 220S 4-speed/column mount - long gone
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#6
01-31-2019, 07:37 PM
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How do the old plugs look from a heat range perspective? Short of being able to nail down the exact number, the state/read of the current W7DC's could be your guide.
Good luck!!!
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"Rudeness is a weak man's imitation of strength" - Eric Hoffer
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#7
02-01-2019, 04:25 PM
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Quote:
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Linear Mode
