What would happen if the glow plugs come on while the engine is running?

[Big Red Suburban]

This is probably a stupid question, but what would happen if for example, one of my kids presses my new manual glow plug button while the truck is idling (after warmed up)? Is it of no consequence or does the extra heat cause the fuel to ignite sooner which could...?

It hasn't happened yet, but I know exactly what they will want to do once they see the new button ;)

[moondoggie]

Good Day!

Probably nothing immediately. If you have 9's or 11's, shortly thereafter they'll burn out; if you have 60's or KD's, likely no problem.

Blessings!

Brian Johnson, #5044

[DmaxMaverick]

No damage to the engine. It may cause the plugs to fail prematurely if it happens too often. Looks like you have JK's Quick Heats in there, which may not be an issue. JK would be better to respond to that question.

The heat caused by the glow plugs is well below that of compression heat on a hot engine. With a normally operating glow system, "after glow" is part of the program under most conditions.

[rjschoolcraft]

In cold weather, the computer sometimes cycles the glow plugs on and off after the engine is running to help combustion right after start. The only real concern is if they stay on indefinitely and burn out. The AC60G's and Kennedy's Quick Heats have been shown to cure that problem. With those, there should be no detriment whatever.

[Big Red Suburban]

Thanks for the replies. I feel better knowing it won't damage anything.

[DmaxMaverick]

Another issue you may make note of is....

If by chance you are out of the vehicle (or nappin' in the back seat), and the kid finds the switch, unbeknownst to an adult, or older kid that has headphones on.... The glow plugs draw a lot of current, and wouldn't take long to leave you with a dead battery or two (insert mental picture here)....."Wow, Dad! That light comes on when I push that button....Hold my bottle and watch this...."

There are ways to safeguard this. Use your imagination. Wire a relay through the brake switch (Step on brake, glow it, start it. I know a guy that did that. It worked fine.), ignition switch, or some other creative method.

The push-button I have wired to the relay on my '85 is too stout for a 7 year old to manage, at least for any concernable amount of time. The switch is a no-relay starter button (read--h e a v y d u t y!), but I used a relay anyway. Why the suspenders and a belt, you ask? I have holey underwear. But, you didn't hear that from me (or anyone else, for that matter).

[Big Red Suburban]

I wired it up such that the key must be on for the switch to have juice. Thankfully, I never leave the kids in the vehicle with the keys in it or with it running. The brake switch is a very good idea though!

[DmaxMaverick]

You did use a relay, didn't you?

If you wired it direct through the ign. switch, it won't carry the load for very long. Ignition switches aren't cheap, and are already a weak link.

[Big Red Suburban]

I didn't use a relay. I used one of the terminals (on the firewall by my left foot) which is hot when the key is on. This feeds the yellow wire going to the glow plug relay. This yellow wire is pretty small, I don't think it is carrying much load. From what I understand, normally the PCM supplys 12V to the yellow wire (it can't be pulling very much current can it)?