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What is considered "hard to restart" when hot?

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urbex

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My new-to-me 6.5TD definately takes more cranking when hot than cold, but as this is my first GM diesel, I don't know what's "normal" and what isn't...

Truck is a '96 K2500. Fires up no problem when cold - turn key to on, wait for WTS light to go out, and it fires right up, usually in less than a second of cranking. Drive it around for an hour, stop at a gas station just long enough to grab a soda and back out, truck is sitting for less than 5 minutes, might take 2 or 3 seconds of cranking, but always fires right back up.

But same scenario, but let the truck sit for an hour, and now it takes 10-15 seconds of cranking to fire up. Zero signs of life other than cranking. No diesel smell/smoke, no sputtering, just cranking. Then it suddenly lights off, and runs great.

Let the truck sit for 3 or 4 hours, and it's right back to firing right up again.

I recently put two brand new batteries in it, as I found that it only had about 30 seconds of cranking in it before the batteries went flat. They definitely made an improvement in cranking speed, and decreased hot restart cranking time, but it still seems abnormally long...but again, I don't know what's "normal" or not on these trucks either.

I haven't noticed any running issues at all while it's running, has never stalled out on me. PMD has been relocated to the driver's side fender between battery and master cylinder (I'm planning on relocating it again, outside the engine bay). I put in a new electric lift pump and fuel filter under hood a few weeks ago (lift pump was intermittent when I bought the truck) Pouring water over the IP and PMD when hot doesn't make a bit of difference in cranking time. After putting new batteries in, it hasn't failed to restart, just seems to take longer than I think it should.
 
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Some diesel owners add a quart of 30W motor oil or two cycle oil to the fuel tank (preferably just before filling it )--this supposedly helps seal up any excess clearances in the injector pump and improves hot restart issues..

It also lubes the pump ,helps make up for the low sulfur fuel's lower lube qualities..some say the injector pump is on its way out when hot restarts become harder or impossible,this is one way to delay replacing it ,and a way to "test" it--if hot restarts improve,then its likely the pump is getting worn internally..

It could well be something else too though,so don't condem the pump right away..perhaps the engine has cooled off enough to need the glow plugs activated for a few seconds ,but they aren't coming on ?..
 
The "wait to start" light does come on, hot or cold, for a few seconds. Given the voltage drop on the guage with the light on, and the voltage rise when it goes off, I'd assume the plugs are operating on some level. Plus, as I said, this thing lights off almost immediately when cold. My experience with IDI diesels have been unless it's 95+ degrees F outside, you can forget about these engines lighting off when cold if the glow plugs aren't working, lol.

When hot, if I cycle the key a few times without starting the truck, the WTS light is on for shorter and shorter periods of time each cycle. Usually after 3 cycles, the light goes out immediately after coming on.

At this point, I'm not condemning anything at all. As I said earlier, I just don't know what is "normal" for these things. I may well be chasing a problem that doesn't exist..I just don't know. I have a ton of 2T oil here for the boat...tossing some in the next tank isn't a big deal.
 
To be fair, I guesstimated, :whistle:, and the only other frame of reference I have is my 7.3 turbo. It's like the exact opposite of the 6.5 - a bunch of cranking when cold to light off, but that sucker will light off almost faster than I can turn the key when hot.

With the 6.5, I'll crank it for a bit, turn the key off, on, let the glow plugs cycle, then start again and it'll usually fire on the 2nd go-around within a few seconds.

Next time I drive it where I can let it sit a bit and get back to it, I'll pull out a stop watch too to get a more accurate measurement on the cranking time.
 
My 6.2 needs some cranking to get fired from a cold start,especially when it dips below 40 degrees F...right now when its about 80 degrees it'll fire up after 6-10 revolutions cold as long as the glow plugs were activated for about 10 seconds..

I have the glow plugs activated by a push button,and usually use AC 60G glow plugs,but I have a few 9G's in it now as some had died and that was all I had,I have a bunch of Autolite 1110's too,but don't like them because I had one fail and get munched in the cylinder..and the 9G and Autolites will swell up if used with a manual switch if left activated long enough..

I should go buy more AC 60G's and keep them all a "matched set" because I've read mixing various brands may result in one getting more amps and hot enough to make it melt or swell up..

I recently added about half a quart of SAE 30 to my fuel tank,it did make a noticeable difference in the noise level of the clatter at idle and lower rpms,but it still rattles like always at cruising speed..

I am hesitant to add much oil,because it starts hard enough when it is cold out and when it gets colder,the high flash point of motor oil may make it tougher to get "lit" in the morning..

My engine starts with one revolution after its warmed up without using the glow plugs,so I think the injector pump is still OK..

I like the idea of added lube to keep the injector pump lubed good,but SAE 30 I'd only add in summer,like now when it'll be in the 90's for high temps..two stroke oil may "burn" better and provide the same level of protection (TC-3 is what most say to use),and may not affect cold starts as much..
I had used Marvel Mystery Oil in the fuel in the past,but I read it has a very high flash point,higher than most motor oils,so that might affect cold starts too..

Urbex is right about 6.2's not wanting to even fart without the glow plugs activated,even if was 100 degrees out I bet mine could be cranked until the batteries died and it wouldn't even fire once!..
But once you got it started and warmed up,it'll fire up all day long even after sitting several hours,and if you need the glow plugs they only have to be activated for like 5 seconds for it to fire right up..
It's the first start after sitting in winter overnight or longer that is the toughest..
 
diesel4me said:
Urbex is right about 6.2's not wanting to even fart without the glow plugs activated,even if was 100 degrees out I bet mine could be cranked until the batteries died and it wouldn't even fire once!..
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No no, I really meant a 7.3, wasn't a typo, lol. My other diesel truck is a 1990 F350 with the 7.3 in it. Yeah yeah yeah, I know...heresy to have a Ford :eek1::rotfl: But everything about that truck is bigger and heavier duty than the Chevys, and it's what I normally use for heavy hauling/towing. On the other hand, I HATE the Ford interiors, and that truck is anything but comfortable to drive long distances. My '59 International 2.5 ton truck is more comfortable than that Ford, and I could easily do a 1000 mile day in the Chevy.

So it sounds like whatever is going on with my Chevy isn't really a big deal at the moment, just something I should keep an eye on....if it starts taking longer to fire up when hot, then I'll start budgeting for a IP rebuild.
 
Simple test. Next time it's nice and hot and been sitting for about an hour or so. Before starting, dump a bottle of cool/cold water on the injection pump. If it fires up right away. You know the pump in on its way out.

This test will work on your idi 7.3 also.
 
urbex said:
Pouring water over the IP and PMD when hot doesn't make a bit of difference in cranking time.
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KirsL said:
Simple test. Next time it's nice and hot and been sitting for about an hour or so. Before starting, dump a bottle of cool/cold water on the injection pump. If it fires up right away. You know the pump in on its way out.
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Seems to be common dilemma in my posting....if I don't post details, it seems people think I haven't done jack for troubleshooting, expect spoon fed hand holding, and the only people that respond are those without a clue. If I post details, people don't read them, and suggest the same things I've already done.

I can't win :haha:
 
urbex said:
Seems to be common dilemma in my posting....if I don't post details, it seems people think I haven't done jack for troubleshooting, expect spoon fed hand holding, and the only people that respond are those without a clue. If I post details, people don't read them, and suggest the same things I've already done.

I can't win :haha:
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My bad :doah:. I wrote that after a long hot day, I was a little:weld:.:haha:
 
PO relocated to the driver's side fender, appears to be replacement, black case. I was planning on moving it to the front bumper area, in the air flow. Originally I was thinking of putting it inside the cab, but the AC isn't working right now, and it's getting hot inside the cab with little air movement as well.

Did some stop watch testing yesterday. On the way home from work, I stopped for fuel, and it took 6 seconds of cranking to restart after WTS light went out. 2 minutes later I made a stop at Autozone for about 5 minutes. 4 seconds of cranking on restart. Later I stopped at Lowes for about 30 minutes. 10 seconds of cranking, cycled the key, waited for WTS light to go out, and another 2.5 seconds of cranking to start.

Went home, let it sit for 2.5 hours, and it took 1.5 seconds of cranking to restart.
 
urbex said:
My other diesel truck is a 1990 F350 with the 7.3 in it.
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That engine uses a mechanical DB2 injection pump, yes? That would have a different set of problems than the electronic DS4 pump on your 6.5. Even though the engines are otherwise similar(ish).
 
Yep, that one is straight up mechanical. I wasn't bringing it up to diagnose any issues with it, just saying it's the only other frame of reference I have as far as diesels go.
 
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Well, turned out my issue was a starter..mostly. Came out of the auto parts store yesterday after 5, 10 mins, tops. Engine was cranking over noticeably slower, and just barely got it started. Instead of being intelligent and going home, I made another stop at Lowes for 30 minutes, and came out to a starter that cranked, slowly, for 10 seconds before giving up the ghost. Was seizing up internally, would BARELY turn over the engine, and wouldn't spin at all on the bench once I got it out.

Had the truck towed home, changed the starter out this morning, and took it for a drive. Stopped for fuel and lunch, truck was sitting for about 20 minutes. Hit the key, and immediately noticed the difference - engine is spinning over MUCH faster when hot. Fired up in about 5 seconds, though it did sputter a bit before fully starting.

But hey, progress! I'm adding in checking all the major power and ground wires/connections on my to-do list now as well when I dive back in next weekend to add a bunch of stereo wiring.
 
Glad you found the issue :waytogo:.

Not that it was your issue but the support bracket was there when you changed the starter out? It's a little piece of angle iron that goes on the back end of the starter. Without it you will break one of the starter bolts.

If it's there, all good!
 
It was there, and if it wasn't, I would have fabricated one for it, lol.

I've run a few more times as tests, and it's firing up nice and quick every time now. Not quite as quick as on a cold engine, but enough to get it fired within 5 seconds when hot. A PO has done some janky stuff on the electrical side that I still need to go through (such as using the universal clamp style battery terminals, where the bare wire end gets clamped down in the terminal), and I think once I fix those properly, all should be well.
 
Yea that little starter brace doesn't look like much but it makes a big difference haha. The 6.2 that was in my wrecker actually took part of the block off with it when it had been started without that brace (had studs welded into the block because of it).


While your at it upgrade the starter cable to 00. Common upgrade to help the slow cranking and give the starters a longer life.
 
The OEM cables GM used were an aluminum/copper alloy that often get gangrene inside,or build up excess resistance after years of use--sometimes if they get heated up from a short circuit they'll become resistors more than conductors....

I have been meaning to replace all of the cables on my '82 GMC,but haven't bothered too,it still seems to crank fine as long as I have decent batteries..but my Suburban had all its cables replaced with welding cables twice as thick as stock ones with much more fine copper strands,that does spin over faster than my pickup with good batteries..
Both trucks now have gear reduction starters,that made the biggest improvement next to replacing the batteries..the old "direct drive" Delco ingot draws more amps and wont spin up as fast..but good cables are important too..
 
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