DennisG01

Hi all, just a quick question (hopefully)... I've noticed that when the outside temp starts to dip (was in the mid 20's F recently), the engine turns over much slower. Quite a bit slower, actually. I'm aware of checking things like the battery, cables (poitive/grounds), etc. I really would just like to know if this is "typical" of this engine when it get's cold, or I do need to do some digging. I have an older, GM 6.5TD to compare it to - that turns over faster than the Merc. Although, I do have two batteries with that engine... but the engine is also twice the size.

joshd2012

Do you have a GL-320 CDI? If so, it's probably the glow plugs. That is normal wear and tear on a diesel.

alx

The om642 does turn over slower as the outside temp drops. Glow plugs have nothing to do with that. As long as it catches after 2-3-4 cranks it's alright.

DennisG01

Thank you, Josh, for taking the time to reply! Yes, it's a diesel. But as Alx mentioned, the glow plugs wouldn't affect how quickly the engine turns over. They could affect the ability of the engine to start (efficiently), but not to actually turn over. It's sort of like spark plugs in this sense (kind of) - if the spark plugs are bad, the engine will still turn over normally - it just won't fire off.

DennisG01

Thanks, Alx (is your name "Alex"?). Yes, about 4 cranks is what it takes to catch. I'm not sure if I can do this properly with words, but the first crank or two is very slow (like a low battery), then it speeds up. Sort of like: slow, slow, medium, fast, catch/fire.

Maybe this engine is right on the borderline of needing a second battery or not?

I've been thinking about adding an oil pan heater - maybe I'll do that. Although, maybe a battery blanket/heater would be a good idea, too?

EDIT: Come to think of it, running the electrical wire to the battery blanket may not be an easy thing to do...

Bimmer777

Its same for me. Freezing temps and first two turns are VERY slow (exactly like battery is low) but then it fires up every time after 4-5 turns. Due to another issue (stuck fuel indicator needle) I added Diesel 911 for the first time and that helped tremendously. Starts are much easier now.

DennisG01

Thank you - that's another affirmation that everything is OK... or at least it's "as it's supposed to be" . I do run a fuel additive, as well. I use FPPF Total Power, but have also used 911 and Stanadyne in the past, too.

I took a quick video this morning, just for clarification. But it seems as though I don't need it now. But I had already spent 20 minutes trying to figure out a way to upload it to a site and then insert it here... so I'm still gonna do it!

This was at 19*F, it was a bit slower when the temps were a bit colder.

http://vid768.photobucket.com/albums...psaukzgym2.mp4

Bimmer777

Thats what mine was like before 911. Also, on particularly cold mornings I cycle the glow plugs 2-3 times before cranking. Seems to help a bit.

DennisG01

Come to think of it... I think I forgot to put the additive in the tank the last couple times. Which is strange, because I'm usually pretty religious with the stuff.

I wonder if more glow time can be programmed in? When I had my engine computer reflashed for my Suburban (had to send the whole thing out for a '98 GM 6.5TD), I had the glow time algorithm changed. Before that, I would sometimes do just as you are saying and do a couple cycles... or even disconnect the ECT sensor (which would trick the computer into thinking it was -40*F and give max glow time).

I'll try cycling the glows - thanks!

Bimmer777

Temperature is definitely programmed in as the glow plug light stays on linger indicating longer warmup time. But I figure an extra cycle doesnt hurt.

DennisG01

Bimmer, just so I understand you correctly... When you use the 911, it allows the engine to physically crank at a faster speed? Or does it allow the engine to "start" sooner (with less cranks, so to say)? The only reason I ask is that I'm not understanding how the fuel side of things allows the engine to crank at a faster speed. Unless I misunderstood what you were saying?

Bimmer777

Per website description:

"The Winter Rescue Formula of Diesel 911 restores the flow of diesel fuel to an engine caused by gelled fuel or frozen fuel-filters."

http://powerservice.com/psp_product/diesel-911/

I got it because I had a problem with fuel indicator needle getting stuck at half full. One suggestion on this forum was that the fuel lever on the pump might be freezing up as there may be some moisture in the tank. Diesel 911 supposed to help remove water and defreeze, along with liquefying the fuel. So I got the extra benefit of easier starts.

In a nutshell, gelled fuel is tough to start motors on, while liquid is easy. So with 911 the engine has easier time starting on liquid fuel, so less cranks.

joshd2012

Hard start is symptom of bad glow plugs. It sounds like from your responses to others that the issue is that severe.

DennisG01

My issue is more of just slow (initial) cranking. If it was the plugs (which I tested recently, too), it would start rough and probably run rough for a short time till the cylinders heated up - also would likely have excessive smoke. In saying that, though, that's from my experience with bigger diesels like the 6.5TD I mentioned, along with some Duramax and Cummins (pickup truck, not OTR).

DennisG01

I was thinking only of cranking speed. Gotcha - I see where you're coming from, now.

alx

The om642 glow plugs go bad very rarely. The plug controller however is a consumable lol. It does not throw a code when it dies and the only indication is depending on the outside temps slower and slower catch by the engine when cranking.

If your engine has trouble catching when cold the controller is usually the culprit.

DennisG01

Ha! I like your comment about the controller being "consumable"!

I'm not getting any faults for glow plug circuits (nor any faults of any kind, even when hooked up to Star... pardon my terminology if that's wrong). When I tested my plugs (Ohm'd from controller plug to engine block) they all came back at 0 ohms. I read that they should be more like .4 Ohms (and based on my experience with other manufacturer's glow systems, those plugs always registered a small amount, too).

My meter is a decent one, but not top of the line - also they were warm when I did this. Possibly that's why I got the low reading? It is the same meter I use on my GM 65.TD, and a good plug there will register somewhere around .8 to 1.2 Ohms - which is correct according to the "specs" and what my meter reads. Those are 12V plugs, though, and I'm not sure if that makes a difference.

But since it was "0" (not open or infinity), I suspect they're OK. That, along with it doesn't seem to be a "catching" problem - it just needs the revolutions of the engine to speed up a bit before it catches... which according to the posts here, seems normal for cold temps. Once the engine actually starts, it runs very smooth (no cold cylinders from an bad plug).

Please correct me if I'm wrong on anything above!

alx

Stop digging nothing to see here. Move on

bha

In order of least likely to most:

1. Glow plugs rarely go bad. Don't start with these. They get replaced as they fail, not all at once like spark plugs.

2. Glow plug controllers do go bad and are a 'consumable' item for sure. The new replacement one is totally different than the original part, so MB obviously figured something out and fixed it.

3. Battery is most likely.

How old is the battery in your truck? Mine died at almost exactly 7 years old which your truck is right now.

First thing I'd do on your truck is replace the battery if you don't know how old it is, or it is older than about 5 years.

My guess is you have an original battery in your truck and that is the problem right there!

DennisG01

Thanks, BHA, for the comments! Yes, I would agree that a slowly dying battery is often an overlooked, but likely, culprit. I replaced the battery about 2 months with a new Interstate. I have not had the battery load tested, but nothing is getting "worse" as it would with a battery dying out. The engine starts, consistently, the same every time - given the same temperature. In other words, at starts in 60*F it starts the same every time... In 20*F temperature it obviously starts different than 60*, but at starts in 20* it starts the same way every time.

ALX, thanks again for the 2nd affirmation (3rd affirmation? ). I'm satisfied there's no issues, but am curious to learn more about the testing of the glow plugs. What are your thoughts on the 0 ohm thing? Is it just "the way it is sometimes"? I can't imagine how all 6 could be shorted to ground (plus I would have major starting issues, right?). Again, I'm satisfied there's nothing wrong - just looking for information for future use.