2,0 DCI M9R glowplug preheating time?

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2,0 DCI M9R glowplug preheating time?

Post by Axa » 14 Sep 2017, 07:56

Is there any good reason there is no indication light on preheating on modern diesel engines?
Morning temps are getting down towards zero and I suspect I notice a bit difference if waiting with engine on or not. But all the plugs are very low on recistance when measuring ohm. So I have new coming in the mail..
I know the 1,6hdi in our C5 are doing up to or close to 60sec of preheating when egnition is turned on. I can't find any info about this on the M9R. YM2008.

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Re: 2,0 DCI M9R glowplug preheating time?

Post by ekjdm14 » 14 Sep 2017, 20:33

Not sure on the Renault, but I suspect the PSA engines do in fact have a glow plug light it's just that the DI engines require little to no preheating in order to start from cold. (our 206 very rarely shows it's glow lamp, and even on cold mornings down to -5c it only comes on for about a second.)

If the Renault DCi is similar then you may not get a glow warning until much colder than freezing, and glow plugs DO have a very low resistance by their very nature so is it possible that the plugs are in fact good? I should imagine a faulty plug would throw a diagnostic code as it does on PSA cars, so in the absence of an engine light or codes I'd tend to assume all's well electrically at least.

So what ARE the glow plugs for in modern common rail engines, if not primarily for cold starting? Simple answer I believe, is emissions control. Even if they're not needed to allow the engine to start, they're likely used in a post-glow capacity to allow the engine to run cleaner when cold and (again based on PSA workings) to raise exhaust gas temperatures and thus aid in particulate filter regeneration...

P.S. I don't know why your 1.6HDi would be preheating for up to 60 sec in such mild conditions unless there's a temperature sensor fault causing the ECU to think it's -40 but it's entirely possible they would post-heat (after starting) for this long. Am I right in thinking you see no glow lamp on the C5 either? I believe it does have one also, just won't need to warn you to wait until ambient temps drop much lower.