How cold is considered "cold" for a diesel truck?

[mwechtal]

Re: How cold is considered \"cold\" for a diesel truck?

BGL990,
Don't be too confidant in you dealer's ability to work on diesels unless they do that a lot. A friend took a Ford 1 ton dually w/diesel to a dealer, and they had no idea how to fix it. It started fine, but wouldn't make much power. Well, the dealer put in all new glow plugs, and that was about all they could think of. If it wasn't starting, glow plugs would have been a good guess, but in this case, a few calls to Ford, and a trip to another dealer located a problem in the injection system (it's been a while, so I don't remember the details).

He sold it the next day, and bought a Dodge. He thought that at least he could pull into a Cummins dealer and get it fixed if the Dodge garage couldn't fix it. It turned out that he loved the Dodge and had zero problems with it, so he never had to test his theory.

Mike

 

[BGL990]

Re: How cold is considered \"cold\" for a diesel truck?

I agree about dealers - in general I don't trust them to work on anything. The place we had the injection pump replaced and who supposedly checked the glow plugs was actually a diesel specialty place that is also a Stanadyne injection pump distributor, so one would presume they know what they are doing.

One possibility is the injector timing. My dad's cousin (who owned the truck before us) heard from some other diesel mechanic once that the factory specs for the injection timing on this truck are not what it should really be set to for best performance. He had the original pump re-timed to what this old guy said and it did indeed have much better power. When we had the pump replaced we told the place about this and they agreed and said they would time it accordingly. After getting it back, however, it feels like it has a bit less power and off-the-line pickup than before. I suspect it just got passed to someone in the back to do the pump replacement and they just went by the book. *Maybe* this has something to do with the harder starting now. We'll have to confirm the timing at some point but haven't had the time to take it in yet.

I still think fitting some sort of intake air pre-heater would help a lot with the temperatures we get up here.

Thanks for everyone's comments (keep 'em coming if you want ...)

 

[BGL990]

Re: How cold is considered \"cold\" for a diesel truck?

Just thought I'd update everyone on the hard starting issue (which I've now solved)

First, some stuff I found out about the GMC 6.2/6.5L diesels. Apparently several different glow plugs were used over the years and many (or most) of them were actually 6 volt plugs. They were still run on 12V, the idea being that you don't have to wait so long for them to heat up. The glow plug controller accordingly had a short-ish glow time - 9 seconds. This worked OK if everything was in good order AND you had the correct glow plugs. At some point GM decided to change to 12V positive temperature coefficient glow plugs because the 6V ones had a tendency to burn out and in extreme cases they distorted at the tip making them very difficult to get out of the engine. The currently spec'd plugs (AC Delco 60G) have a positive temperature coefficient, meaning that their resistance increases as they get hotter, thus drawing less current as they heat up. At some point they reach an equilibrium where they won't get any hotter. In essence they are self regulating and are supposed to be quite burnout resistant, no matter how long you hold the power to them.

As I said, the truck is a 95, but has a newer engine (actually a 2000, not a 98 as I previously said). The glow plug controller is original, but the new engine has 12V glow plugs, so they don't get hot enough to start the engine well in cold weather. To make things worse 4 of the glow plugs were burned out! (they were not 60G's, so I don't know if they had a PTC or not). So much for trusting a shop to check things out.

I decided to toss the factory glow plug controller and just put a manual button on the dash. I replaced all the plugs with brand new 60G plugs (which by the way took a day and a half and required disassembling a ton of stuff just to get at two of them on the turbo side of the engine - stupid layout). I also built new wiring harnesses and a box with 4 relays to switch power to the plugs (2 plugs on each relay - 12A per plug, 24A per relay, almost 100 amps total).

Now we can just push the button on the dash for however long we like. 20 to 30 seconds has the plugs bright orange from the tip almost down to the threaded base. The original 9 seconds only gets them dull red at the very tip. We haven't had any really cold weather yet, but so far the truck starts instantly with almost no smoke at all. Before I started this endeavor it would take cranking for about a minute on and off, belching white smoke the whole time to get it to stay running. That would obviously have been much better if there weren't 4 plugs burned out, but I still think the manual button paired with the burnout resistant plugs is much better.

 

[2458n]

Re: How cold is considered "cold" for a diesel truck?

We are very lucky to have a young man in the area that fools with the diesel trucks. this is one trick that has helped his rep spread. he would by-pass the old controler and give your truck the push button set-up. I took a 7.3 IDI ford to him with the same hard starting in cold weather. I asked about different glow plugs and he said none were avaiable at that time. He said the GM plugs would run the battery down before they distorted. Made alot of believers after they spent big money at the dealers and still had cold start problems. The ford required new glow plugs and a couple of new batteries to spin it faster.