I have a 1987 Mercedes 300D Turbo....and according to the E-class Bible, the ready light does not glow as long as it should on older relays and there is no "afterglow". Is there any truth to this and if so, can a later relay that has afterglow be retrofitted to this model or should I consider a new relay for this car.

Are you having starting issues and how do you know for sure that there's no afterglow? On colder days like now, I wait until I hear the click from the relay before starting and mine starts smoothly. Once warmed up on restarts I only wait for the light to go out and I still hear the click from my relay after it's running.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

That is correct, the afterglow relays first appeared in the 90's. Try letting the glow plugs glow another 15 seconds or so after the light goes out before starting the engine. If it's still rough and all your plugs are working, I'd get a new relay (which will have the afterglow).

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL