It is relatively warm here in So Cal. My 85 300sd starts easily without waiting for the glow plug light to turn off AFTER it is warmed up to 85 degrees C. Is this a good practice or will problems happen? Does starting without waiting for glow plugs make any difference. Did not find anything in a search. Thanks.

No issues. Glow plugs assist with cold weather / engine starting. Once warm feel free to fire it up anyway you chose.

Once its been warmed up, glowplugs don't make much of a difference until its been off for 20minutes or more.

With a 617 in So Cal you will probably never need GP's. A good one should like right off to at least 50 without them.


Just remember if you ever do drive someone cold, that you are screwed.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

It is harder on your battery and will shorten its life. But other than that it's fine.

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'79 300SD
'82 Chevy Chevette diesel

The owner's manual for my '96 says to not wait for the lamp if the engine is warm, but to immediately crank the engine; yours may differ so read it. It's harder on the battery to glow if you don't need it.

It's hardest on the battery to do a partial glow.
If you don't need to glow don't glow at all, that's easier on the battery.
If you must glow, make sure you let it go long enough for the light to go out.

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'79 300SD
'82 Chevy Chevette diesel

That could be; I'm not sure. However, a partial glow on my '96 triggers a code and MIL, unless the engine is warmed up.

And then the dealer harasses you when they read the code: "You're not glowing long enough!" Bad as the dentist and flossing!

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I doubt it's a problem as long as you glow long enough for it to start immediately. When mine is warm I turn it to glow, put on my seat-belt, then start it (maybe 5 seconds). If you have to crank on it, you didn't wait long enough.

With an upgraded GP relay, it relay wouldn't matter (from what i understood from the convo) because it keeps the GP's on for 20 Secs after the light goes off to reduce smoke, and to have a smoother start. So i doubt it will put to much strain on the battery, plus those things are a monster. thought the one on mine had finally given out when the cold first hit, but charged it up and its been good. (lack of summer driving :-( )

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1983 Euro 240D 277K
2016 Mazda 6
Coming Soon, 2013 Mercedes E350 Bluetec
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Would not using the glow plugs at all cause them to carbon up around the plug from not being used? most newer cars don't even turn the gp's on if the temps above 60, of the DI variety

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2004 Infiniti G35 3.5L 6mt Coupe 73K miles 25.6mpg ytd
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1982 300D Turbo 231K 120hp? 28.1mpg YTD

If your car is warm enough it won't hurt your engine to do a short or partial glow, but it will wear out your battery.

This is because the GP's build up resistance as they get hotter and thus draw less amperage from your battery. So if you crank while they're still drawing a lot of amperage, your putting that amount PLUS the starter draw on your battery.

The amount of time you should glow depends on how "fast" your GP's get hot.

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'79 300SD
'82 Chevy Chevette diesel

On my cars the glow plugs stop glowing as soon as you try to start the car. I believe all 123s are like that unless modified. If your car starts right away and you don't have to grind for a while then your good.

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1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C

All of the above is false.

You will not wear out your battery.

While it's true that the GP's will draw more current when cold, waiting for 15 seconds for them to heat up will not offer any benefits to the battery. The battery is providing current for the entire 15 second period and, after 15 seconds, it can be proven that the battery is in a slightly weakened condition as compared to the capability of the battery at 3 seconds.

Furthermore, the glow plugs draw a maximum of about 100 amps.........briefly. The starter can draw upwards of 400 amps. So, the relative effect of the glow plugs is minimal as compared to the starter.

Starting the engine immediately when warm is considered standard practice.