Glow Plug Preheat Time

JcGilmour · **Posted:** Mon Jan 04, 2010 2:17 pm

Hello,
My first post:
2005 Liberty 2.7 CRD.
The manual states that glow plug preheat time is inversely proportional to coolant temperature (see data)

Engine Coolant Temperature, Key-ON-Wait-To Start Lamp-(Seconds), Pre-Heat-Cycle-(Glow Plugs On Seconds), Post-Heat Cycle(Seconds)
-30C 10 SEC. 35 SEC. 200 SEC.
-10C 10 SEC. 23 SEC. 180 SEC.
+10C 1 SEC. 21 SEC. 160 SEC.
+30C 1 SEC. 20 SEC. 140 SEC.
+40C 1 SEC. 19 SEC. 70 SEC.
+70C 1 SEC. 16 SEC. 20 SEC.

Out of this I get that at -10c, I should have to wait 10s for the light to go off. Well "if" I had to wait 10s for the light to go out, how could the preheat time be 23s? I am either missing something or the service manual data is incorrect. Could it be that they are saying that the light will go out in 10s but if I wait an additional 13 s before starting, I will get more heat time?
The other question I have is: my glow plug light never seems to stay on longer than 2s. Does anyone else see this?

Confused in Fort Erie (Near Niagara Falls ON)
John

dgeist · **Posted:** Mon Jan 04, 2010 3:16 pm

Not sure about the data in the chart, but I know my glow plugs (or at least the light) come on a LOT less than that. I don't ever see them come on in ambient temps of greater than 30F. When it's colder than that, it's only for a second or two.

Dan

Rich · **Posted:** Mon Jan 04, 2010 3:30 pm

After reading this thread I started allowing my GP's to sit for ~10 full seconds before cranking the engine. I cranked about half the time before the first cyl fired off, than would happen if I started cranking when the wait-light turned off.

Thanks for posting this info... helps a ton!

Joe Romas · **Posted:** Mon Jan 04, 2010 4:20 pm

Rich wrote:

After reading this thread I started allowing my GP's to sit for ~10 full seconds before cranking the engine. I cranked about half the time before the first cyl fired off, than would happen if I started cranking when the wait-light turned off.

Thanks for posting this info... helps a ton!

Exactly! the glow plugs stay on even after the engine is running as the "post" time indicates. I've also found that waiting a few seconds after the light goes out makes for quicker cold starting :lol:

But as we know Chrysler has changed the glow plug timing for reliabiltity. To me this means so they won't have to replace as many under warranty or to recall the ceramic ones and replace with metal ones as VW has done

Since they have changed the timing maybe these times are not totally valid now :roll:

Rich · **Posted:** Mon Jan 04, 2010 5:13 pm

How much does a set of GPs cost from chrysler?

ac5501 · **Posted:** Mon Jan 04, 2010 5:43 pm

Rich wrote:

How much does a set of GPs cost from chrysler?

Last time I checked you could order one through AutoZone for about 40 bucks.

mikey1273 · **Posted:** Mon Jan 04, 2010 6:51 pm

My glow plug preheat times are about 2 -5 seconds when the tempatrature outside is 20°F or colder. I notice that if I get impatient and dont wait it is very hard to start then I realize I'm being stupid, stop and wait.

grywlfbg · **Posted:** Mon Jan 04, 2010 7:14 pm

One of the benefits of the 7V glow plugs we have in our CRDs is that they can continue to heat even while the engine is cranking. In the "old" days of 12V GPs once you engaged the starter the battery voltage drops and can't run the GP's.

The flip side is that a lot of diesel mechanics are used to testing GP's by hooking them directly to the battery. That will fry our GP's.

JcGilmour · **Posted:** Mon Jan 04, 2010 7:42 pm

dgeist wrote:

Not sure about the data in the chart, but I know my glow plugs (or at least the light) come on a LOT less than that. I don't ever see them come on in ambient temps of greater than 30F. When it's colder than that, it's only for a second or two.

Dan

Thanks for all the input here.
My GP light never deviates from the 2-3second routine. The last few days the temp has been down to -10c and the light still only stays on for 2-3 seconds, just like it does in the warmer weather.

I have only had my Jeep since November 09 and it is my first diesel. I do have 15 years experience in the trade as a certified mechanic but that ended back in the 80's when I switched occupations from this to electronics.

If I can muster up the energy to connect my volt meter to one of my GPs, I will see if in fact there is voltage applied after "light out" but pre cranking. At the moment I doubt it, as this morning I let the light go out and then counted another 15s or so before cranking. The result was a no start; not even a hit. I cycled the key off and back on and waited just until light off, It started as usual in cold weather, about 2-3seconds of cranking before sounding like a coffee can with marbles in it for the first 1/2second or so.

Just as an aside, I have found running brand name fuel (Sunoco), from a large volume dealer to deliver much quieter operation. The engine hums rather than rattles under light acceleration.

John

mikey1273 · **Posted:** Mon Jan 04, 2010 8:54 pm

I got mine in the summer and never owned a diesel before this. I kept looking for the GP light then. I discovered in the summer mine is on and off so fast I was missing it. I then begain starting it like a gasser cus it didnt seem to need any preheating untill it got cool out.

as for buying brand name fuel I realy can't that often. there are no local brand stations close by me that sell diesel, sometimes I can get BP. I find mine runs smoother and queiter or bio blend of about 20% or more.

JcGilmour · **Posted:** Mon Jan 04, 2010 9:51 pm

I haven't tried the bio blend thing. Don't know anything about it. Do you purchase blended fuel or add filtered used cooking oil to regular diesel?

J

mikey1273 · **Posted:** Mon Jan 04, 2010 11:42 pm

JcGilmour wrote:

I haven't tried the bio blend thing. Don't know anything about it. Do you purchase blended fuel or add filtered used cooking oil to regular diesel?

J

No cooking oil unless you process it into bio diesel first. you can buy bio blends at some stations if your lucky to find it where you live. I got bio from a local place called Soy energy. they sell b100 and b99. the number after the B is the precentage of bio diesel in the mix. what I did was get it in fuel containers I bought and some in my tank and splash mix it in the tank.

Try this site to find a bio retailer near you
http://www.biodiesel.org/buyingbiodiesel/retailfuelingsites/

Biodiesel can also be made from used filtered cooking oil. to do that you need to preform a proccess with a catylist like methanol and lye, this creates transesterfied lipids (biodiesel) and glyserin (soaps) remove the soaps and ur good to go. thats the basics I am still learning about it.

WolverineFW · **Posted:** Tue Jan 05, 2010 1:17 am

In the last month or so I have seen temps from -7C to 8C and my light has been lit up for about 3-5 seconds. I usually wait a few more seconds and it will fire right up. As mentioned previously the manual is probably out of date because Chrysler modified the cycle times in a flash. When it is warmer, if I blink I miss the light even coming on.

dirtmover · **Posted:** Tue Jan 05, 2010 9:30 am

Rich wrote:

How much does a set of GPs cost from chrysler?

I got mine from RockAuto for $120 for 4 and, of course, the local stealers wanted almost $300/set for the exact same Bosch part. Interestingly RockAuto no longer stock this part and my local diesel injection specialist doesn't even see it listed in his Bosch literature. I'm wondering if it's been dropped altogether

liberty2.8 · **Posted:** Tue Jan 05, 2010 1:43 pm

Quote:

I cycled the key off and back on and waited just until light off, It started as usual in cold weather, about 2-3seconds of cranking before sounding like a coffee can with marbles in it for the first 1/2second or so.

Is there anything being damaged or stressed during the "coffee can with marbles" mode?
Mine sounded like that this morning in the coldest weather my Libby has ever seen (12F) and unplugged overnight. Just wondering because when it first started, it sounded like it was only running on 1 cylinder for a short time with lots of white smoke that smelled like unburnt diesel.

JcGilmour · **Posted:** Tue Jan 05, 2010 2:58 pm

I don't believe any damage is being done by cold starting (no block heater). The noise is pretty standard across the diesel industry and likely due to abnormal combustion.

Running on less than all cylinders is what got me started on this subject of glow plugs, as mine will run on 2 or 3 for the first few seconds in very cold weather. In an older, conventional diesel, missing at cold start would likely be due to a defective glow plug. In other words, the only cylinders firing at startup are the ones with the functioning glow plugs. The others simply fail to run until RPM's come up enough to cause sufficient compression heating to fire the fuel.

rjmaype · **Posted:** Tue Jan 05, 2010 10:49 pm

Just for reference, my 7.3 liter Ford diesel wait to start light is lit about 30-40 seconds at 20 degrees.

The glow plugs remain on for over 2 minutes after starting.

The current amperage drain is noticeable since the headlights become brighter after the glow plugs turn off.

JcGilmour · **Posted:** Tue Jan 05, 2010 11:42 pm

rjmaype wrote:

Just for reference, my 7.3 liter Ford diesel wait to start light is lit about 30-40 seconds at 20 degrees.

The glow plugs remain on for over 2 minutes after starting.

The current amperage drain is noticeable since the headlights become brighter after the glow plugs turn off.

This is what I would expect for preheat times at colder temperatures for most engines and have seed this in the field.

Apparently the Jeep 2.7 uses a ceramic glow plug that heats quicker than a metallic version but I would still would expect to see preheat times proportional to coolant temperature as described in the service manual but I don't see this in my jeep.

I guess if it starts (and it has so far) I shouldn't worry about it.

Glow Plug Preheat Time

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