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.

[texasclarks]

Glad you and son got her starting with no issues again. The time working on it together is probably better than money given to your mechanic who at least will ensure that this winter you won't have glow plug issues. 🙂

[HJGyswyt]

MARK VANDERBENT wrote:
does it start clean every start ?? or does it spin fast and not always pop off right away?? My 95 suburban 6.5 that I put a new starter on cranks fast but has a bit of a sloppy start at times. I do have new glow plugs. Truck runs awesome though.

Yes, pops off right away, no smoke, smooth idle. I hope it's good for a couple hundred thousand more miles. These old 6.5 diesels were the underdog of the big three, but aside from the injection pump issues, they are well built engines. I used to work that truck pretty hard, hauling a camper and towing a four horse trailer. All the Powerstroke, Cummins, and Duramax would pass me on the hills, but my 215hp never missed a beat and always got me home. I did remote my PCM on a heat sink to the front bumper and ever since that I've never had an injector pump issue. It's a good truck for my son, it gets him back and forth to college every day.

[blt2ski]

Hans,

Funny about your take on the dmax crew cab. My 05 did feel bigger than the 96 6.5td CC. BUT, I still wish I had the 96. I like that 88-00 body/interior for some reason over older and newer models. Maybe because I have had three of them?!?!?

Marty

[MARK_VANDERBENT]

does it start clean every start ?? or does it spin fast and not always pop off right away?? My 95 suburban 6.5 that I put a new starter on cranks fast but has a bit of a sloppy start at times. I do have new glow plugs. Truck runs awesome though.

[HJGyswyt]

mkirsch wrote:
Same here.

Unfortunately for us here in the lovely state of NY, they use road salt and lots of it because of the idiots who refuse to learn how to drive in winter. By the time most trucks are 10 years old, they're rotten beyond repair.

Oh don't say that, Washington State has just started using salt in addition to some kind of chemical de icer that is very sticky and pits aluminum terribly, even before it snows. My 19 year old daughter drove our 98 3/4 ton Suburban to Fairbanks this summer and is using it for her last two years of engineering school. Wonder how it will make out with all the salt up there.

MegaCab_PL wrote:
Any time I see a well maintained C/K 88-00, it's a joy.

That truck looks so nice.

I wish I kept my 99 Tahoe, it was so simple to work on it.

I remember feeling like the luckiest guy in the world, I had a 1998 2500 Suburban and our 1996 2500 Silverado pickup in my garage, paid cash for both, bought each one when they were used after 3 year leashes were up from the leasing company. Gave the pickup to my son and the Burb to my daughter, but I still have a hand in their maintenance and upkeep. And I think I liked the looks of them too. Love my newer Duramax crew cab, but the cab feels smaller, the windshield is a lot lower, and the seats really hem you in with the console that comes from the dash to the arm rest. Hard to spread your legs in the new ones.

[mkirsch]

Same here.

Unfortunately for us here in the lovely state of NY, they use road salt and lots of it because of the idiots who refuse to learn how to drive in winter. By the time most trucks are 10 years old, they're rotten beyond repair.

[MegaCab_PL]

Any time I see a well maintained C/K 88-00, it's a joy.

That truck looks so nice.

I wish I kept my 99 Tahoe, it was so simple to work on it.

[BobsYourUncle]

Glad you got it beat! Good work!

It's nice when the OP comes back and announces the solution to an issue.
It further helps those of us who offered input and shows us whether our thoughts on a problem were directed in the right direction or not.

Based on my wrench turning experiences I had the starter as the prime suspect.

Thanks for posting this.

[HJGyswyt]

Follow up on the starter issue if any of you subscribed to this thread.

We replaced one battery cable clamp, swaged, not bolted. Broke all the connections, cleaned and reinstalled with dialectic grease. Still no help.

Normal humans cannot get to the positive cable on the starter when it is bolted in. We tried extensions with crow feet, dog bones on extension, nothing in my professional rollaway tool box could reach, so we took the old starter out.

At almost a quarter million miles I would not put an old starter back in even if it was the cable connection, so I bought a brand new (not rebuilt) starter from NAPA, my lucky day, normally $240 but they had some kind of sale if you bought 3 other items you got 20% off. So I got the starter and 3 different light bulbs for $190.

Son and I enjoyed working on it though it took two of us to do the job. Two big bolts hold it in, but there is a third bolt and bracket you can't see easily holding it to the block. Any way, that motor spins so fast now, you don't even need glow plugs. Wow, it was such a gradual decline we both forgot what it was supposed to sound like when starting.

Thanks all for the help and the confidence to do this job. Your knowledge is appreciated. All the best, Hans.

[colliehauler]

2003silverado wrote:
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.

I had something similar happen 2 months ago. My battery was only 2 years old and top of line. I put in a new battery and had the same problem a week later. The 2 bolts that held the battery cable to the terminal, one bolt had pulled out of the lead and only had one bolt holding the wire on. I cleaned the wire and put on a new terminal. Fixed the problem under 5 bucks.

[mkirsch]

Don't be so harsh on the mechanic. After all he did find a legitimate problem with the truck, and he did not do anything that did not need to be done. Those dead glow plugs would've made for hard starting come winter.

Everybody thinks mechanics are these magical wizards that can read minds, know every detail about every vehicle ever made, and have x-ray vision. The days of dead simple vehicles that are all practically the same went away about 40 years ago friends. Even 20 years ago GM dealers were sending their mechanics to school to learn to work on that specific truck.

He found 4 bad glow plugs. Maybe he thought they were shorting and drawing the battery down? Like you said, everything else looks fine! How many hours at $75+/hr do you want him to spend chasing the problem? Sure he could pull the starter and have it tested... $150 labor just for remove and replace. What if it tested good (it probably will, because starter testers are USELESS)? Now you'd be complaining about the "crooked" mechanic needlessly racking up a huge labor bill.

[ktmrfs]

bad starter solenoid could be a problem as well. once the contacts start going bad any increase in resistance= much lower voltage to the starter= slow motor.

and the starter could have either a shorted winding or have worn out the bushings and rubbing against the case, or bad brushes, or just worn out.

Nothing much has changed since "Boss" Kettering realized you can get much more than continous rated power out of a motor for a short period of time and developed the starter motor. Same thing today, they are capable of high output for short time periods which means they are being run really hard and everything has to be up to snuff for it to work.

[rhagfo]

2003silverado wrote:
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.

X2!!

I don't know how many cars and trucks I have helped with a "dead Battery" by simply cleaning the battery connections!

That being done, yes a diesel needs to spin at a certain speed to start. If like my 2001 5.9 with mechanical injectors at the correct speed it takes about a half engine revolution to start.

[45Ricochet]

ksss wrote:
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.

Exactly! It was slow to turn over when hot also. So much for "trusted".