Recently it seemed to me that my glow plug light took longer to go out than it used to. Hadn't ever timed it, but just seemed to take more time.

Today I did time it. Took 9 seconds at 57 degrees with rain.

Is that about right?

Stock 2005 F250/6.0 with 31k miles

I'm not yet worried about it, just seems like a long time to me.
Thanks
dp

 

the light to the best of my knowledge is only a timed light and does not indicate the length of the glow plug "run" time. the best way to know how long the glow plugs stay on for is to install a volt meter gauge. it will linger around 12v until the glow plugs kick off then the volt meter will climb to around 13.5 to 14v.

but to answer your topic, yes they do.

 

I'm not sure how the glowplug timer is controlled, but mine is longer on colder days also. It's also been longer with the inductive heating flash, although I'm not sure that they're at all related.

Here's how to test a bank at a time: http://dan.prxy.org/Truck/6L_bible_h.../Page_068.html

and a little more about the system operation:
http://dan.prxy.org/Truck/6L_bible_h.../Page_066.html

The PCM will give a code for bad glow plugs according to this.

 

in short. glowplugs can and do go bad.

also, like was mentioned: the "wait to start" indicator light has nothing to do with how long the glow plugs are energized. they can stay energized up to 2 minutes AFTER the vehicle has been started.

 

The Pcm will read temp of the coolant once the key is cycled then depending on the temp of the coolant decides how long to run the glow plugs...and if suspected bad the rail has to be removed and each pulled out of the head. then use a OHM Meter put red lead on the small threaded end and the other on the GP body..OHMS should read low showing little resistance.

 

the gpcm reads oil temp not coolant temp.