Has anyone heard of glow plugs becomming less effective with age. Someone told me that they should be replaced from time to time. I was under the impression that they either worked or they didn't. Comments?

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85 300TDT 456,000 orig. miles

Funny you should mention this. My '85 300 TDT was starting a bit harder on cold mornings and I was concerned that I might have problems getting her started when I go to the mountains skiing so this weekend I replaced my 8+ year old glow plugs. It made a noticable difference. If I had a bad plug there was no indication of it but it now starts more easily and runs smoother after a cold start. I know PEH will think less of me for this frivolous act but if it helps me avoid a AAA call in the Sierras to me it was worth it.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

I thought that they could get covered with carbon deposits, reducing their ability to heat up the prechambers, but more or less, unless they short out or break off, they tend to get to the same peak temp throught their lifetime, its just how well that goes out into the rest of the engine...

But now I can rethink this.

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

A couple of my plugs did have some carbon on them. Not a real heavy covering but maybe enough to hurt the heating. Maybe that's what made the difference. I wonder if these should be cleaned up once in a while. I recently did my periodic "Italian Tuneup" so what carbon was on there stayed on through that.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

For what its worth, in my experience....

Glow plugs will fail suddenly (one day it starts, the next it doesnt), so every diesel owner should have a few extras on hand.

Also, in my experience the glow plugs will also lose their effectiveness with age.

All else being equal (assume good starter, new battery) try starting a 123 diesel when it is zero deg. F with 3 year old glow plugs, then try with new glow plugs...I believe you will have much better cold weather starts with new glow plugs. Yes, carbon buildup may be a factor, but when I take out old glow plugs, I don't see so much carbon to effect the function of the plugs...if the engine is running well, (not burning oil, etc.) then carbon buildup on glow plugs should not be a big factor.

Also, because in cold climates you will occasionally have to crank the engine for an extended period (10 seconds or more) in order to start the car, you also need a good battery in these cars...not one that will fail after the first or second try.

For the above reasons, being in New England, I replace my battery and glow plugs every three years, even if they have not failed. That comes to about $35 a year for a good battery, and $20 a year for good glow plugs...well worth it to me. In warmer climates, I dont think this would be necessary.

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Do you Rheem out the glow plug holes when you replace the glow plugs? Is it necessary?, or can you just replace them?

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85 300TDT 456,000 orig. miles

When I have removed glow plugs, I have never seen significant carbon buildup on the tips, and the plugs were very easy to pull out....once unscrewed, they wobble in place and almost fall out. In such cases, I dont believe it is necessary to ream.

But if you see heavy carbon buildup, or worse, if after unscrewing, the plug is still held in tightly by heavy carbon around the tip, then reaming is necessary.

There is a special tool which screws into the glowplug socket and reams the glow plug hole while it is spinning. I dont think this is really needed....I don't see why you cant use a hand-held drill bit about the size of the glow plug pin, or slightly larger to do this (it is only carbon that you want to remove). While I havent seen any formal procedure for reaming, I would think that the way to do it is remove both the glow plugs and injectors, and vacuum out the pre-chambers via the injector holes allowing air to flow in through the glow plug holes...this will insure that no solid chunks remain in the prechambers.

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)