I would take that dealer comment about Quad Bosch plugs making a few ML's run hot with a grain of salt?! I wonder what other factors, such as timing -- could have produced that effect? I put the Twos in my 89 420SEL and they seem to run fine .... also put them in my 76 450SEL, same story.

It would seem that if you get full combustion from the Quads that the engine should run at a normal temp .... after all it is supposed to handle combustion heat as a norm, not an exception and the Quads may achieve X mpg at a lower gas usage rate, but not necessarily raise engine heat ? Also, perhaps a slight rise in engine temp means it is performing actually better -- without any detrimental effects?

I would have to see all the factors involved with those ML's running hot, before I could determine that the plugs were the cause.

Thanks for the update however; all knowledge is useful. Ben Carter

__________________
Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)