Dont Kill Your Glow Plugs

[rl71459]

Hi Everyone
I recently (About a week ago) needed my Generator (Isuzu C201 powered) during a power failure.

When I tried to start it, It would not start, Odd... This thing always fires right up! It was cranking fine, but would not run.
I finally got it running. and it ran fine for the outage.

Today I set out to find the problem. I checked the Glow plug resistance first. All 4 checked OK. (None Open)
Then I checked the voltage to the Glow Plugs, It was also good?

So I attempted a start, Same result's, Sounded like it was going to start, But no luck. I cranked some more and suddenly
smoke began pulsing from the No. 1 cylinder Glow Plug. It was coming from around the insulator and stud.

I pulled the plug to inspect it. It was destorted from overheating. Thats when I remembered that the last time I used the
Genny I forgot to shut off the glow plugs after starting, When I finally realized what I had done, I shut them off, But they
had been on for approx 30 minutes while running. OOPS!

When I inspected the plug I found it was cracked at the point where the pencil meets the seat surface. So I dug out one of
old ones I kept when I replaced them years ago. It tested OK so I installed it in place of the cracked one.

Tried a start, And she fired right up!

So I Think I will install a timer on my Glow plug circuit to prevent this in the future.

Rob

[Ronmar]

OR put the glowplug circuit on a momentary switch contact, like that spring loaded part of the key switch on my tractor that powers the glowplugs one notch before the start location:)  I usually turn my key to that location for about 20 seconds, or untill I see the amp gauge come off the -30A peg(whichever comes first).  The drop in current draw from the plugs indicates they have reached full temp(resistance changes as plugs heat). Any more than that just cooks the plugs.  My key switch also maintains power to the plugs when I crank, so they wind up getting a few more seconds anyway...

[mobile_bob]

if it were me, i would replace them all!

reason being, i would not want the engine to digest a broken off piece of a glowplug

anytime they have been stuck on, and show signs of overheating, they are suspect and are known to break off or crack and a piece come off.

not worth the risk in my opinion.

fwiw
bob g

[thomasonw]

Maybe a cut-out relay tied to the oil pressure switch?  That way once the oil pressure comes up the plugs will be disabled -even if one forgets to turn off the switch...

[quinnf]

I used a momentary switch for the glow plug (leftmost switch in the pic of control panel) that must be held closed while the START switch is held.  There are other ways to do it, but simpler is better.

The wiring in the box below the control panel is to control the air valves and genny contactor. 

[rl71459]

Thanks for the responses everyone.

The reason I used a maintained contact switch was due to advise (Dont Remember from who) That with my engine (When Cold)
it is best to do a 2 minute pre-crank warm-up, And It really does start clean that way. Anyway, I did not feel like holding a Key or Button for 2 Minutes so I used a selector switch, I intended to install a timer, But ran out of "RoundToIts".

I do plan on replacing all of the glow plugs asap, I too have the same concern as MB about the potential for future failure/engine
damage, I did pull them all for inspection... Just the no. 1 cyl looked bad, The others did not show signs of distortion, This made
curious as to why they did'nt? My Plugs are connected together Via a "Copper Ribbon"(Isuzu Part I believe) My wiring connects
to the No. 1 Plug using a 10 AWG wire. I would think the Voltage Drop thru the ribbon would be insignificant. But when I
re-assembled it I connected The feed wire to the No. 2 plug position, Just in case.

I think a Timer will resolve the issue, and will fit in well with the existing controls.

Rob

[quinnf]

Two minutes is a long friggin' time to have glow plugs burning.  Their purpose isn't to heat the combustion chamber, but to provide a local hot spot to light off the fuel/air charge.  10 seconds should be all you need with most glow plugs.

Just for grins, you might want to pull a plug and connect it to your battery and see how long it takes to begin to glow.  If it's only 10 seconds or so, then you know the 2 minutes is excessive.  Glow plugs aren't meant to burn for very long and can be damaged by excessive heat, as you found out.  So I sort of wonder about the advice you were given.

Quinn

[Ronmar]

I would also question that advice.  2 minutes is way too long in my experience.  Every glowplug system I have ever dealt with has a caution attached to it about excessive glow plug use...

[Thob]

It depends on the glow plugs - some of the older plugs, 2 minutes isn't out of the question.  Newer plugs, and 15 seconds is about the maximum.  Also, some of the plugs are designed to run on 11V (assuming cold battery, long wires, switch, etc).  Once the engine starts and the alternator kicks in, you could be running 14V to the glow plugs.

Good advice on connecting one to a battery and see how long it takes to glow.  I did that on new plugs for my JD tractor, they started glowing in about 15 seconds.  The label on the machine indicates that 2 minutes can be used for below 0 degrees F, IIRC.  That would explain why the new plugs I bought didn't last very long, they were designed to be run for a much shorter time than the original plugs.  The only thing was I needed to replace all 4 of them so that all 4 would heat up quickly.

[rl71459]

Great discussion everyone, Thank you all

You made me think about it so much, that I wanted to find the source of the (COLD) 2 minute stuff, Just to make sure that I
had'nt lost my mind!

Well after some deep digging, I found it. It was in an message I received on the "LISTER ENGINE FORUM" shortly after I bought
the partially built genny, when I was asking for help. the source is also a highly respected member on this forum also.

I did "Glow Test" the plugs, But honestly I was not paying attention to time... Just Glow. (A "Glow"  "No Glow" test) 

I'm kinda glad I broke it now, It gave me a good reason to interact with you folks.

Rob

[mobile_bob]

the c201 engine's had a timer function, and some had a push button for the operator to
do the timing

the basic time under 70deg f was 45 seconds and if it was below freezing they called for up to 2 minutes of preheat.  so 2 minutes might not be a problem but...

longer times are very hard on glowplugs

and their ends have been known to fall off!

then they get caught on top of a piston, or under a valve, and you have problems

bob g

[Ronmar]

I'm kinda glad I broke it now, It gave me a good reason to interact with you folks.

Rob

You need a good reason?   

[cohippy]

the c201 engine's had a timer function, and some had a push button for the operator to
do the timing

the basic time under 70deg f was 45 seconds and if it was below freezing they called for up to 2 minutes of preheat.  so 2 minutes might not be a problem but...

longer times are very hard on glowplugs

and their ends have been known to fall off!

then they get caught on top of a piston, or under a valve, and you have problems

bob g

wish I could find a timer like that the refer i pulled my c201 did not have any controls like that for the plugs it was just a toggle with the starter switch

[mobile_bob]

my apologies
the timer function...

the timer was the operator!  my bad

there was a plate on the refer unit, that outlined the starting sequence
you flip on the switch, hold up the momentary switch for the prescribed amount of time and then you flip the switch down to start position and it would start

from memory above 70 deg F you preheat 30 seconds,  down to 40F you preheat for 60 seconds, down to 32F you preheat 90 seconds and below zero F, you preheat for 120 seconds.

if the engine failed to start you simply reheated according to the chart.

the oem glowplugs were very durable, but i am not sure they would do well under continuous operation, therefore the momentary toggle switch.

fwiw
bob g