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Old 02-13-2018, 04:49 PM   #1
71rehab
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Slow Crank when Hot

All, my C20 cranks slowly when the engine is hot. I have a new battery and when I charge it cranks rapidly. But after several drives I get a slow crank.

Any ideas on where to check first?

thanks
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Old 02-13-2018, 05:09 PM   #2
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Re: Slow Crank when Hot

weak starter , but check all connections first
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Old 02-13-2018, 05:13 PM   #3
71rehab
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Re: Slow Crank when Hot

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weak starter , but check all connections first
Thanks. If it were a weak starter, why would it crank fine with a fresh battery and weak after several drives?
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Old 02-13-2018, 05:14 PM   #4
azle
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Re: Slow Crank when Hot

What he said and add a heat shied to your starter. You can also duct some fresh air to starter.
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Old 02-13-2018, 06:21 PM   #5
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Re: Slow Crank when Hot

Overheated starters seem to crank less than desired when compared to cold starts, and bad wire connections when overheated will transfer less electrical power.

Slightly off ignition timing can also effect the crank rate of a motor that is up to temp. Don't ask me to explain that one, but I have found that a cold motor that starts fine with the timing a little off will have a harder time starting once it's warmed up.

Make sure all your wiring connections to the starter and battery are clean and shiny as mentioned, then look into shielding the heat from the system, and/or have your starter checked out. You should check your timing too, maybe retard it a bit when up to temp and try the starter right away.
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Old 02-13-2018, 08:46 PM   #6
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Re: Slow Crank when Hot

Starter solenoids are part of the draw on the battery when starting. When they get old and the wiring inside starts to break down they draw more current due to increased resistance, this in turn leads to a slower turning starter. Heat causes the resistance to increase and the problem is more pronounced. The same problem can occur with the windings inside the starter.
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Old 02-13-2018, 09:02 PM   #7
paul blair
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Re: Slow Crank when Hot

How is the alternator output? 14.2 volts or so. If you know the starter is ok...maybe the charging system is not keeping the battery up. Easy to check...just my 2 cents. Loose connections a possibility. Good luck
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Old 02-13-2018, 09:45 PM   #8
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Re: Slow Crank when Hot

The new starter will help for a while, but the core problem will return. Heat soak on the starter motor. I was having the same issue with numerous starters, but then I put one of those Kevlar heat blanket on, and fabbed a heat shield that I attached to the header. Haven't had an issue since.
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Old 02-13-2018, 11:47 PM   #9
71rehab
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Re: Slow Crank when Hot

thanks for the info guys. will clean connections then look to a starter.
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Old 02-14-2018, 09:07 AM   #10
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Re: Slow Crank when Hot

Those mini starters with a heat blanket works good.
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Old 02-14-2018, 10:12 AM   #11
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Re: Slow Crank when Hot

This has happened with my 71 before and it turned out to be the starter. I replaced mine with a Vette starter of the same period and now it cranks like a beast. It could also be too much timing advance.
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Old 02-14-2018, 10:59 AM   #12
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Re: Slow Crank when Hot

There are plenty of threads about hot start issues over the years. Heat soak is the usual culprit. There are also plenty of ideas of how to fix it.
Start with the basics.
fresh battery
clean cables
charging up to parr
engine in good tune
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Old 02-14-2018, 12:45 PM   #13
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Re: Slow Crank when Hot

Take a set of battery cables and do this:

Hook one end to the engine block, the other end to the frame.
For the other cable, connect one end to the body and the other to the frame or engine block.

If this helps, you have a ground problem where the existing ground isn't enough. Should be:
Cable between battery and engine (alternator bracket, water pump bolt, or bolt on front of block by fuel pump)
Cable between battery and vehicle body (inner fender usually)
Cable between engine and vehicle body (firewall and valve cover bolt usually)
Cable between engine and chassis (valve cover bolt and frame)
Cable between chassis and vehicle body (under cab)
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Old 02-14-2018, 01:37 PM   #14
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Re: Slow Crank when Hot

How is your timing? Just a thought.
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Old 02-14-2018, 03:58 PM   #15
71rehab
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Re: Slow Crank when Hot

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Originally Posted by Jcfcamaro View Post
How is your timing? Just a thought.
I'm sitting at +8 initial timing with HEI. I've had the issue when the timing was both retarded and advanced so I dont think thats the issue. The commonality is always heat.
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Old 02-14-2018, 04:00 PM   #16
71rehab
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Re: Slow Crank when Hot

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Originally Posted by demian5 View Post
Take a set of battery cables and do this:

Hook one end to the engine block, the other end to the frame.
For the other cable, connect one end to the body and the other to the frame or engine block.

If this helps, you have a ground problem where the existing ground isn't enough. Should be:
Cable between battery and engine (alternator bracket, water pump bolt, or bolt on front of block by fuel pump)
Cable between battery and vehicle body (inner fender usually)
Cable between engine and vehicle body (firewall and valve cover bolt usually)
Cable between engine and chassis (valve cover bolt and frame)
Cable between chassis and vehicle body (under cab)


Thanks. I definitely do not have all of those ground points.
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Old 02-14-2018, 04:19 PM   #17
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Re: Slow Crank when Hot

how old is your starter? what kind is it- original AC delco starter, or a cheap parts store rebuild?

We have a 79 C30. used to have a 350 in it and no matter what we could only get a few years out of a rebuild starter. We tried everything- checking grounds, new battery, even put the relay kit in to get the starter max juice. none of it helped. Finally we put a NEW starter on, not rebuilt, and never had an issue with it until we pulled the motor. Think it was just cheaper quality parts in the rebuilt starters
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Old 02-14-2018, 04:21 PM   #18
71rehab
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Re: Slow Crank when Hot

Quote:
Originally Posted by Tiger Joe View Post
how old is your starter? what kind is it- original AC delco starter, or a cheap parts store rebuild?

We have a 79 C30. used to have a 350 in it and no matter what we could only get a few years out of a rebuild starter. We tried everything- checking grounds, new battery, even put the relay kit in to get the starter max juice. none of it helped. Finally we put a NEW starter on, not rebuilt, and never had an issue with it until we pulled the motor. Think it was just cheaper quality parts in the rebuilt starters
Not sure. It is new to me but only has 55k miles so my guess is original
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Old 02-15-2018, 01:46 AM   #19
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Re: Slow Crank when Hot

Had the same problem on my 67 with a 327. Ultimately found the battery cable to have a pretty good voltage drop. Replaced cable, cleaned all connections and symptoms have not returned. My 2 cents worth.
And FYI, I have what appears to be an original starter.
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Old 02-15-2018, 02:12 AM   #20
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Re: Slow Crank when Hot

Ive forgotten what year but Chevy put a high torque mini starter on the trucks, sorry its been awhile since I dealt with this issue. I had long tube headers and they were very close to my stock fatty starter. Made a big difference when I switched.

Of course check all the other things mentioned here.
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Old 02-15-2018, 02:38 AM   #21
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Re: Slow Crank when Hot

I have the same problem... even if its been a few hours, the second start of the day is way worse than the first. I will try the heat shield and check grounds also.

I love this community so helpful... thanks everyone
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Old 02-15-2018, 10:46 AM   #22
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Re: Slow Crank when Hot

Are the cables the right gauge? Heavier cables are better than lighter ones. A 2 gauge will carry 10 times as much current as a 4 gauge. If a lighter cable was used, It will have too much resistance when hot and won't crank properly. Same goes for all the connections.
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Old 02-15-2018, 08:04 PM   #23
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Re: Slow Crank when Hot

Good old heat soak...

1/ Wrap the headers in heat wrap tape at least a foot in front of the starter and six inches behind the starter. Make it a double wrap thickness and secure it with hose clamps or wire.
2/ Replace the primary starter cable with a #2 cable, making sure it has totally clean connection ends.
3/ Replace the ground cable between engine block and battery ground, again, make sure contact surfaces are really clean.
4/ Check and clean all other ground cables making sure all connections are really clean.
5/ Double check battery charge rate is at least 14.2 volts at the battery itself with the engine running around 1500 rpm.
6/ Check static timing and set at 8 degrees at idle,,,idle being 650 to 700 rpm.
7/ If above fails, replace starter with small format reduction gear style starter that also has a heat shield built into its design.

Above all...have FUN !!!!


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Old 02-15-2018, 08:45 PM   #24
71rehab
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Re: Slow Crank when Hot

So I climbed underneath to look at the starter and found that the yellow cable coming from the starter led to nowhere. Any ideas what it is for and where to plug it? Thanks!
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Old 02-15-2018, 08:57 PM   #25
71rehab
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Re: Slow Crank when Hot

I figured it out. I have an HEI and i'm reading that yellow wire isn't needed anymore.
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