Glow plugs

[vipra]

I've been in this Sprinter for 3 years and I drove trucks OTR for 7 years before that, and I just learned about something very basic to diesel engines: glow plugs. I know practically nothing about engines (obviously), but I'm probably not the only one who never heard of glow plugs, so here's some info:

Recently the 'engine control unit malfunction' light on my Sprinter's dashboard came on. My shop said one of my glow plugs was bad and it would cost $500 to replace, but he also said that glow plugs aren't vital and that the engine would run fine without them, so I told him not to fix it. I just searched the web to find out what glow plugs are, and found that they are heating elements inside the cylinders of diesel engines that warm up the cylinders before the engine starts to make it easier for the engine to start, especially on cold mornings. You should turn the key to the 'On' position and leave it there for 10-20 seconds which fires up the glow plugs so they can warm up the cylinders, turn the key back to the 'Off' position and then start the engine.

I just checked my Sprinter's Owner's Manual, and sure enough, there it is right in the Starting The Engine section. There's a light on the dash called the Preheater Indicator Lamp which lights up during that 10-20 seconds I mentioned above, and it goes out when the glow plugs have heated the cylinders enough, letting you know when to start the engine. The Manual says, "If the engine is at normal operating temperature the Preheater Indicator Lamp will only light up briefly." I just turned my key to the 'On' position and that's exactly what it did, which isn't surprising since I turned my engine off 2 hours ago and it's 80 degrees outside.

Now I have a question: I don't remember if the $500 my shop quoted me was for one glow plug or all of them, but either way, is it worth that much to get one or all of them replaced? It seems like if the glow plugs aren't working the only problem created is that the battery will have to work harder to start the engine. I put in a new battery last winter and it was $100, which is a lot less than $500 glow plugs.

 

[OntarioVanMan]

My thinking would be on a real cold day and Sprinters not having a block heater unless one installs one would be hard to start. History being what it is that 500 is prolly only one glow plug.

 

[talkinghorse43]

From the '03 servica manual:

"DESCRIPTION
The glow plug relay supplies battery voltage to the
glow plug through a timed cycle that is related to
coolant temperature. The glow plug relay is located
under the battery. The purpose of a glow plug system
is to improve combustion for low emissions and to
achieve easy starting at low temperatures.
OPERATION
When the ignition key is turned to the ON position,
the glow plug output stage and pre-glow indicator
lamp are actuated by the ECM. The duration of the
signal depends on the coolant temperature. The glow
plug relay has processing that communicates with the
ECM. If no data exchange occurs at the triggering
stage, the preheating is switched off after 2 seconds.
Start glowing is initiated when the key is in the
start position. The glow plugs (R13–R17) continue to
be supplied with voltage. This makes it possible to
stabilize the cold starting speed. (After glowing is initiated
when the starter reject speed is reached).
After the engine starts, the ECM determines the
afterglow period in line with coolant temperature. If
no signal is received from the coolant temperature
sensor, afterglow is maintained for thirty seconds.
The following aims are reached by the afterglow :
² Improvement in warming-up properties
² Prevention of white exhaust smoke after cold start
² Stabilizing of the cold starting speed
The glow plug output stage constantly signals the
current operating state and faults. The following are
faults detected and transmitted to the ECM :
² Open circuit at one or several glow plugs
² Short circuit in the glow plug circuit
² Relay fault
If the Glow plug relay detects an open circuit at a
glow plug, it is stored and indicated only once the
engine is running by the preglow indicator lamp coming
on for about one minute and a fault is stored in
the ECM. If a short circuit, a glow plug output stage
faulty or a temperature related switching off of output
stages is detected, the fault is stored and indicated
immediately by the preglow indicator lamp
coming on. Once the fault is no longer current, the
indicator is immediately switched off, but the fault is
stored in the ECM. If the fault is constantly current,
the preglow indicator lamp remains on until the ignition
is switched off."

 

[RLENT]

>Now I have a question: I don't remember if the $500 my shop
>quoted me was for one glow plug or all of them, but either
>way, is it worth that much to get one or all of them
>replaced?
I think I priced a glow plug (single) from the dealer for my son's 2004 when it was acting up ..... turned out it wasn't actually the glow plug. The price IIRC was around $180 for the part only ..... which is way, way expensive in my book.

I'd look for an aftermarket replacement but it may not be available.

>It seems like if the glow plugs aren't working the
>only problem created is that the battery will have to work
>harder to start the engine. I put in a new battery last
>winter and it was $100, which is a lot less than $500 glow
>plugs.
Not entirely correct - in the winter time, in very cold temps, the engine will be very cold itself if it has sat for any length of time not running, and pulling in very cold air on every intake stroke.

In order for combustion to occur in a diesel engine the intake air must be compressed and heated to a point where the fuel will combust when it is injected. Normally when the engine is warm and running this isn't a problem - the high compression ratios on diesel engines raise the temp in the combustion chamber enough for that to happen. But if the engine and ambient air temps are low enough the engine will have to (theoretically) crank longer to fire ..... and the whole time it is cranking it is pulling in more cold air on the intake stroke - which complicates things a bit .... enough that the engine needs an assist - hence glow plugs.

A battery might only be $100 ..... but the starter is around $400 List Price ..... and cranking a starter for extended periods isn't good for it.

I don't know the exact location of the glow plug (be in the cylinder head somewhere) and how hard or easy it is to reach but I would bet you could replace it yourself without too much trouble. Finding the bad one can usually be done fairly easily with just an ohm meter (check the service manaual for the exact procedure)

 

[greg334]

You can find them for around $35 to $45 each, real Bosch - look around. Don't buy the cheap Chinese knockoffs, they will last maybe 6 months.

It is always a good idea to keep a set with you if the engine has turned 150K. The start/heat cycles do where the tips as do high exhaust temps.

They should screw into the head around the injector but I am not sure and I don't carry my sprinter manual with me. When I worked on the 5 Cylinder car engines, I think I used either a 10mm or 12mm long socket.

The mercedes as with others like them, you really should have no problem removing them BUT there could be a number of issues if it is stuck. The one thing I learned the hard way is that if I, as a mechanic, break off the thing in the head (which is possible depending on the condition of the head), I am responsible for removing the head and repairing it. As an owner, you're on your own.

I don't know if this still applies, but when I replace them, I used a very good conductive anti-seize compound on the threads. It has to be conductive, not the cheap cr*p that you get for $11 for a big can.

Oh, usually if the mechanic tells you to replace all of them, either get the actual code or go to another mechanic. If you burned all 5 of them out, you have other serious problems but I would venture to guess that the possiblity that the glow plug realy is bad and he is padding the bill. ALSO with these parts, ALWAYS ALWAYS get them back so you can be sure. There is no core or exchange for these parts, so you are entitled to them - tell the mechanic up front.

 

[x06col]

Been driving, (diesels I presume) TEN!!!! years, and , just heard of glow plugs???? What DO??? you pay attention to???? I'm perplexed, frankly.

 

[greg334]

x06col,
Not to beat up on anyone with this, but I do agree with you in part.

Glow plugs are not all that important on many trucks, in my case my engine has none to speak of, so I would expect a few not to know about them.

But with that said and trying to be clear not to beat anyone up here, I think that every drivers license test should have some mechanical knowledge in it and the higher the license, the more info you should know and be tested. The tests now are too simple and too easy, my cat can get by passing the CDL tests.

I have run across people who could not check the oil, who did not know where the batteries were and a few who were clueless on how to check the tire pressure or read the tire or the tire gauge.

As much as I try to help some out, I feel that we would be a lot better off in this profession if the ones who can't do simple things like what I describe above would just stick with flipping burgers for a living.

 

[x06col]

Greg: You cannot even begin to fathom how much I agree with you. The flipp'in burgers part. Beat up on em??? If we don't, someone else will, with way more dire results than hurt feelings. Seems no one has any interest in learning (things) about their profession. It's gotta be a hum drum world, when you can keep on humming whatever makes you happy at the moment, I guess. Thank God for this forum to keep me awake.

 

[x06col]

Sorry but I gotta continue. I read he spent (or someone spent) 40K for a sprinter, and, THREE years later we read the owners/operators manual? How foolish can this be?? If I were so hard up for drivers that I had to hire someone that can't read, and had spent 40K for a vehicle, I'd read the manual to them myself, no matter how broke they were, or, how big a hurry they were to get on the road. If it took a week. It is no wonder this country is in the shape it is in. Keep it up folks and you'll be pikk'in crap with the chickens.

 

[Deville]

Man, the first thing I was taught about Diesels is that they dont have saprk plugs cap rotor or wire & they have glow plugs & you ALWAYS WAIT FOR THAT WAIT TO START LIGHT TO GO OUT B4 STARTING, NOMATTER HOW WARM THE TRUCK IS! LOL it was driled into me over & over again!

 

[lanier1]

I started to respond as well but decided to let x06col take the reins on this one. I was just hoping you didn't miss the post.

 

[Moot]

x06col what brand diesels do you run in your fleet and do you know how many glow plugs each engine incorporates?

 

[bryan]

Hi

That should be parts and labor.But if you can change spark plugs then you can replace the glow plugs.Just remember to disconnect the batteries because if you accidently touch the wires while your grounded against the truck it will shock the crap out of you.I always change them as a set for the simple fact that if one is worn out the rest aren't far behind.

 

[silverdollar]

Well, I think that I have waited long enough, I am going to sit down and read this manual on How To Tie Your Shoes.:9

 

[Moot]

Hey x06c0l have you figured out how many glow plugs each of your truck engines has? Glow little glow plug, glimmer, glimmer. Glow little glow plug, glimmer...

 

[Moot]

x, how goes the glow plug counting? Instead of counting all those pesky little glow plugs, get a total cylinder count. Then divide the total number of cylinders by 3.14159. That should get you in the ballpark. Otherwise ask one of your drivers how many glow plugs each truck engine is equipped with. You may be surprised with the answer!