Let's Honestly Talk Glow Plugs Here...

[Mad Maxx]

Are they REALLY, HONESTLY, SERIOUSLY needed?

My Cummins doesn't have them, it just uses a Grid Heater (which the Duramax uses as well, along with Glow Plugs)

The only thing I could see by NOT having the Glow Plugs, is the occasional hard start when it is REALLY cold, and I mean around 0*.

Because even when it's REALLY cold, the Cummins will sputter a lil bit until it gets warmed up.

So with that being said, what could SERIOUSLY go wrong on the Duramax by NOT running Glow Plugs, that WOULDN'T go wrong on the Cummins since it doesn't use Glow Plugs? By seriously wrong, I mean Crack a Piston, Throw a Rod, Lift a Head, Burn a Valve, ect...

 

[btfarm]

I'm pretty certain they have something to do with not undergoing excessive cranking and subsequent overuse of the batteries and starter.

 

[Mad Maxx]

That's pretty much all I'm finding too.

Somewhat longer of a Crank & some people say they have an Emissions Function, but we know how we all feel about about Emissions BS.

 

[Will L.]

afaik, shortened crank time is it. On any diesel, as long as the air temperature is high enough it will fire. It is just a design choice to use heater strip, gp, or combo. If an engine is set up to heat the glow plugs while running for emissions , it can use the heater for the same task. It just takes a moment longer for the hot air to be pulled into the clylinder is all.

 

[THEFERMANATOR]

The bid thing you overlooking is the grid heaters in a CUMMINS are MASSIVE compared to the grid heater in a DURAMAX. The CUMMINS grid heaters draw about 90 amps a piece VS the DURAMAX grid heaters 50 or 70 amps. Until you get below freezing the glow plugs aren't really needed, but below freezing you should have them in there. Without them you would be putting alot of unneeded stress on the starter, as well as the problem of not firing on all 8 when cold and wet stacking.

 

[Mad Maxx]

The Cummins Grid Heater isn't really much bigger, when it's on, you know, because the Lights Dim and the Voltage drags down to about 12v...but same thing with the Duramax, especially when running the Glow Plugs & Grid Heater, it still drags the Voltage down.

I remember back when I deleted the Grid Heater on the Duramax, people said it wasn't gonna start when it was Cold, well guess what, there was no difference in the way it started or how long it cranked.

Now with both the Grid Heat and the Glow Plugs, sure, it may take longer to start, but an extra Crank or 2 isn't gonna Hurt anything or kill the Starter & Batteries by the end of the Week, IMO.

I'm talking about...is there a possibility of CATASTROPHIC ENGINE FAILURE due the to Glow Plugs not being there and Heating the Cylinders enough??

 

[Ed HD]

We have old diesel tractors that don't have glows, and they run year-round.

 

[btfarm]

Well the first really cold morning that you were counting on the truck to start and it doesn't because the batteries were juuuuuust on the ragged edge of not up to snuff is when you'll get your answer James. If you're not gonna depend on it in real cold conditions then give it a go... Firing a wet stack can make a pretty big mess if enough cylinders decide to take off that day at startup though.

 

[Mad Maxx]

Well the first really cold morning that you were counting on the truck to start and it doesn't because the batteries were juuuuuust on the ragged edge of not up to snuff is when you'll get your answer James. If you're not gonna depend on it in real cold conditions then give it a go... Firing a wet stack can make a pretty big mess if enough cylinders decide to take off that day at startup though.

See now, if you have Batteries that are on the Edge, to me, trying to Spin the Starter, Light the Glow Plugs, and Warm the Grid Heater would put a helluva lot more strain on them than the Starter alone having to Spin 2 or 3 more times.

But I dunno?

 

[Will L.]

You could eliminate both, replacing them with block heaters if needed for starting. It is harder to start without either, my question would be why not run at least the gp's though? I get the airflow for power thing but why gp's?

The electrical draw difference could be measured. Just need an ammeter on the starter while cranking, then on the gp and heater draw. The only thing is the difference in how long it has to crank to start with out them. My bet would be more draw cranking than preheating as needed. Shortened starter life would obviously result, but weight the cost of starter replacement vs gp & heater replacement.

 

[tanman_2006]

I think a pan heater and block heater would be a good start.

Are your gp's that bad? I don't live in salt like you but mine are holding up good.

 

[THEFERMANATOR]

The LBZ's intake heater is only there to prevent wet stacking, and does not run until the engine is running if I'm not mistaken. So it is not a starting aid for the DURAMAX i nany way. The LLY didn't even have an intake heater(the only DURAMAX that didn't come with one though), and they started fine. If it wet stacks severely enough, you risk hydrolocking the engine. Others eliminate tehre glow plugs all together on built engines, but usually resort to ether for starting in below freezing temps. As to the difference between the 2 grid heaters, the CUMMINS one is MASSIVE compared to the DURAMAX unit. The CUMMINS since 94 has used a dual element design whereas the DURAMAX uses only a single. And I would say it is a good 3 times the size of the DURAMAX element in heat output. For a truck you rely on to start when cold, I would keep the glow plugs around. The grid heater isn't that important as it is for emissions after the engine is running, and the glows have stopped there after glow cycles. The glow plugs do all of the work for starting and right after starting in a DURAMAX.

 

[Will L.]

For wet stacking? Wow, I thought common rail computer control for a non commercial commuter truck that wouldn't be a problem. I would expect they could build the tables to low enough fuel at idle to eliminate that for low temp readings. Guess I was expecting too much. Just cheaper to add the heater than cut back fuel and swing the timing or did I miss something there?

 

[THEFERMANATOR]

For wet stacking? Wow, I thought common rail computer control for a non commercial commuter truck that wouldn't be a problem. I would expect they could build the tables to low enough fuel at idle to eliminate that for low temp readings. Guess I was expecting too much. Just cheaper to add the heater than cut back fuel and swing the timing or did I miss something there?

With the 16.8:1 CR, wet stacking is an issue no matter what you do with the pressure, pulse width, and timing. The LLY didn't suffer from it, but it had 18:1 CR. The LB7 sufferred from it some, but it was due to how big the injectors were. Even the brand new 2015's still have a grid heater as well as glow plugs for starting and to avoid wet stacking on a cold engine(and emissions reasons, warm air burns cleaner with a cold engine to reduce NOX emissions).

 

[WarWagon]

It's all about the heat to start a diesel engine and it doesn't care where it gets it from: ether warming the cylinder up by burning before the injection event, intake air heaters (including the emergency hair dryer intake heater that the wife loves - NOT!), glow plugs, campfire under the engine, block heaters and 2200W+ from a current bush, propane coolant heaters, pre-chambers, brute force spinning the engine fast enough combined with high 22:1 compression to heat the air on a cold engine up enough to light the fuel. So to directly answer your question, no: Glow plugs are not required if you use something else for heat. You have other choices for heat and the downside is most other options take longer. I can't ether an engine as fast as the duramax glow plugs work never-mind other side effects. (Seriously get the cap off the can is slower!)

Improved extreme pressure injection systems and NOx emissions have lowered the compression of diesel engines. High compression gives you efficiency and ease of starting. Modern turbo's make up for low compression on current DI designs.

There are stories of people who start Cummins engines without the grid heater in really cold weather and claim the heaters are for emissions only. Older ones as I recall. Dodge/RAM trucks use massive batteries compared to the wimpy gas engines ones on the 6.5's. Duramax trucks do have larger batteries, but, I don't think they are as large as the Dodge/RAM ones. Correct me here as my Dodge experience is limited. :rolleyes5:

The "hard start" on cold mornings is really hard on the engine and starter. If the V8 doesn't use all 8 you get extreme vibration as the engine drives the dead cylinder, it dumps diesel on the cylinder walls, and then becomes even harder to light off from diesel diluting the ring sealing oil and lower compression. Let alone having to vaporize more diesel from the last missed firing. If it does fire cold and 'late' it can produce lots of soot and that winds up in the engine oil and fouls injectors. So even if you don't care about emissions the extra soot and unburned "wasted" diesel isn't doing your engine any good. (Wet stacking may have explained what I just said.)

The extreme vibration of missing and late firing is hard on everything like alternator brackets (may not apply to engine in question) flex plates, vibration dampers, crankshafts, and starters. Did I mention starters?

Hard on the starter isn't just grinding away on it till it melts down and batteries give it up. It is the hit-miss-miss-hit that will ruin the overrun clutch or worse on the starter. The hit and then miss is extremely hard on the overrun clutch where it can fail to unlock overspeeding the starter or fail to lock up and refuse to spin the engine over. Extreme cases are like the starter departs the engine as scrap metal regardless of what used to be bolts holding it on. I have ruined starter overrun clutches to where they don't spin the engine myself from bad 6.5 injectors.

Heat isn't just for starting FWIW. Older high compressions like our IDI 6.5 you can put the fire out on a hot engine. For example going downhill will cool the engine off from shutting off the fuel and cold air moving through the cylinders. I have to be careful with using cruise control as some grades can require a little fuel to maintain speed after cooling off the engine and this little amount of fuel is smoking white - while diesel washing the cylinders.

So at the end of the day the answer to the question is the more heat you have to start the engine the better chance that it starts smoothly. Smooth fast starting is easier on a lot of "expensive" things you don't want to change/fix/replace while in the nasty cold weather that finally overcame the brute force of fast cranking. Adding to this the colder the battery the less CCA it has while the engine needs more CCA the colder it is.

I see a pre-cranking grid heater "override" mod in your future... :hihi:

 

[THEFERMANATOR]

EARLY DODGE's with the CUMMINS used 1 group 31 battery, later models starting around 91 or so used a pair of group 34's which are the same size as a group 78, but with top posts instead of side posts. As for a CUMMINS starting in cold weather without the grid heaters, I can personally attest that even down here in Florida, a 12 valve CUMMINS will smoke out a parking lot at freezing temps without the grid heaters working. They will start, but the white smoking will be EXCESSIVE to say the least. I smoked out the shop one morning starting one to bring it in and put grid heater relays in it. Lets just say about 12 people were PISSED when an entire service department turned to white smoke when I finally got that thing lit off to pull it in, and that was a 35 degree morning. The 24 valves do start a bit better with the variable timing, but the 94-98 12 valves NEEDED the grid heaters, and came with 2 for a reason.

 

[WarWagon]

Pretty much sums up the need for heat while starting. Will start without it doesn't mean it's a good idea without it... :chairshot:

That reminds me another way to start a diesel and stop the smoke is going high load and throttle to generate heat. This is from starting scrapers (Cat Wheel Tractor-Scrapers) in Colorado winters 20+ years ago: Ether about 1/2 a can into the air cleaner, start engine after glow plug time, wait for oil pressure to come up, immediately drop in reverse with brake on and stomp the hammer clean to the floor. The engine would "unload" from a full load in a couple min. I don't recall why but neutral resulted in transmission oil pressures that would completely stall the engine out. Reverse had the lowest oil pressure. If it stalled you were in for a helva time getting it to re-start and stay running. Yeah, fully wound up turbo's and the massive yellow iron Cat engine would lug out and stall.

So when patch, the 1993, has trouble hitting all 8 after startup (well it doesn't start more like Booms to life) and smokes white I brake stall it and this clears up the white smoke... Literally sounds like a dump truck going through a nitroglycerin plant!

The 2003 Dodge's have Group 65's and I wasn't sure about the older stuff.

Group L" W" H"
65 12.10 7.50 7.60
34/78 10.30 6.80 7.90

 

[JayTheCPA]

It's all about the heat to start a diesel engine and it doesn't care where it gets it from: ether warming the cylinder up by burning before the injection event, intake air heaters (including the emergency hair dryer intake heater that the wife loves - NOT!), glow plugs, campfire under the engine, block heaters and 2200W+ from a current bush, propane coolant heaters, pre-chambers, brute force spinning the engine fast enough combined with high 22:1 compression to heat the air on a cold engine up enough to light the fuel. So to directly answer your question, no: Glow plugs are not required if you use something else for heat.

As usual, WW nails it :hammer:

There are two 'laws' in play here: physics' and Man's.

On the physics side, the diesel engine needs heat from somewhere for getting temperatures up to the fuel's flash point. Sure there are some conditions where just a single compression stroke is all that is necessary, but sometimes not. Personally, I'd not mess with this system as it typically is the least invasive on the motor.

On the other side, Man is playing with the equation by adding a configuration that only runs while the engine is still cold (or at a lower than optimal temperature) to control the type of emissions.

Owners quickly reverse-engineer the design and figure out which parts are necessary to comply with physics and then determine whether Man's add-ons are worth the cost.

To add some flavor to the discussion, I happen to know that the 7.3 PSD has both GP's and an AIH. The AIH only comes on when the ambient temperature is cool (IIRC 45 and lower) to avoid white smoke and possibly modify the emissions as the engine comes up to operating temperature. Seeing as the AIH also serves as an airflow restriction, it is common for owners to remove it and accept white smoke when the weather gets cold.

Back to the original question of truly needing a heat source, am in the camp that the laws of physics still call for it. Cummins seems to have the most elegant solution with the grid heater and if there was a way retrofitting, I would get the pre-heat that way as GP's can suffer from poor injection and lead to a death spiral.