Slow turning over 6.5 GM Diesel

[HJGyswyt]

Looking for some help with my 20 year old 6.5 GM Diesel.

Just recently it started turning over real slow when starting. We replaced both batteries, same results. Checked connections at battery again and tested new batteries.

Took it into trusted mechanic, they diagnosed four glow plugs that were bad. Replaced all eight, it still turns over real slow, hot or cold, but always starts.

Do starter motors slow down with age? It has 260,000 miles on it now. What is my trusted mechanic missing? What am I missing?

Are these older GM starters the kind that get 24 volts at starting through a relay? I thought the actual starter was 12 volt.

Ideas for this old truck please.

[wcjeep]

Have you used the jumper cables to bypass the factory battery cables to verify their integrity?

[2003silverado]

I don't want to beat a dead horse about connections, but...one of my work trucks is a 1987 6.2 diesel. Last fall into winter I had a hell of a time with slow cranking. I thought I checked all pertinent connections, but still had to jump it at times. I thought that since it wasn't used too often we compromised the batteries that were only 2 years old. I replaced the batteries but that did not fix the problem. Prior to this problem I also converted the truck to top post batteries from side post batteries. However, when checking connections I neglected to check the connection between the cable and the top post terminals which is tightened with 2 bolts per terminal. Those 2 bolts were very loose and slightly corroded on all terminals. After I cleaned and tightened those connections The truck started like new.

Not saying this is your problem, but I want to make sure you exhaust all cheap solutions before you replace the starter.

[time2roll]

+1 for a new starter. Get new or lifetime warranty. No cheap rebuild.

[ksss]

The starters were notorious on these trucks. I am not sure why they stuck you with new glow plugs, if it cranks hard and doesn't start, ok check the plugs, but not if the cranking power is low, that obviously is not a glow plug issue. I would pull the starter and have it rebuilt if you can handle it down for a couple days. As mentioned don't go cheap, or you will become very good at pulling it out.

[MARK_VANDERBENT]

I have a 95 suburban 6.5 diesel and my starter was cranking slow then it pooped out. I put a brand new one in . Did it myself , and went well. Not she cranks fast!! still a bit of a sloppy start though like 6.5 s do sometime. Runs awesome though!!

[HJGyswyt]

Thanks for the replies. For clarification, I gave the truck to my son 2 years ago, and the last two years of that trucks life have been the absolute hardest years of it's life. He lives on our farm in his own trailer and is a full time college student, so we are still helping with the big bills.

We replaced one battery cable end that was bad, the cables had been converted from side post to top post by the original owner (I bought it used a couple years old).

In defense of my mechanic, he did show us how he checked the Glow Plugs and found ones that weren't functioning, but I too was skeptical that had anything to do with the rate at which the motor turns over. And after spending $380 for the glow plug repair I thought we were good, my son said it was OK.

Then we traded trucks for a day, and I realized my old truck is not OK, and I don't like that my 22 year boy said it was OK and I don't like that my home town trusted mechanic may have lined his pockets with a repair that should have been secondary to what I brought it in for.

I'm at an age where I don't really enjoy wrenching under trucks like I used to. But I will throw a little more $$$ at it and replace the starter with an new, not reman, starter.
All the best, Hans

[BobsYourUncle]

I had the same issue with a truck I had many years ago. Same thing you describe.

It was the starter. The field windings had a short in them somewhere causing a partial bypass of the current. This effectively reduced the magnetic strength thus causing a slower starter RPM.

Replace the starter and don't buy a cheap junk thing from China. Get a good reman from a reliable company such as Bosch. Or get an OEM - AC/Delco.

Replacing the glow plugs won't make anything turn over faster except your trusted mechanics bank book.

And ditto on the connections. When they look good take them apart and clean them anyways.
Don't forget the one where the battery cable connects to the starter! That's a suspect too. I had that happen once myself.

[2003silverado]

I agree to double and triple check all connections. Although starter motors can get weak over time, it would be so gradual that you wouldn't be able to say it started recently.

[Bill_T]

My recent hard start problem was dirty battery cable connection on the engine block. Removed cables and shined them up, put some dielectric grease on them and she fired right up. You might want to check them even if they look clean.

[lc0338]

Don't take it back to "trusted mechanic". it is well known that diesel engines need to turn over a certain RPM in order to start. Had same issue with my Dodge RAM... it was starter that needed replaced. In my case the truck started just fine when cold but when hot it would not always start. Let it cool down and it started just fine.

[Turtle_n_Peeps]

Yes the starters start to drag when they get older. And yes the 6.5 is notorious for this because the high compression they have.

Don't buy cheap junk from Kragen or whoever or you will be sorry.