Slow Crank when Hot

[71rehab]

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

[harpo231]

weak starter , but check all connections first

[71rehab]

Originally Posted by harpo231

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?

[azle]

What he said and add a heat shied to your starter. You can also duct some fresh air to starter.

[sick472]

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.

[HO455]

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.

[paul blair]

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

[custom10nut]

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.

[71rehab]

thanks for the info guys. will clean connections then look to a starter.

[panhead59]

Those mini starters with a heat blanket works good.

[DT1]

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.

[Boog]

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

[demian5]

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)

[Jcfcamaro]

How is your timing? Just a thought.

[71rehab]

Originally Posted by Jcfcamaro

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.

[71rehab]

Originally Posted by demian5

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.

[Tiger Joe]

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

[71rehab]

Originally Posted by Tiger Joe

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

[SJLenz1340]

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.

[CG]

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.

[andrewpclayton]

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

[brown7373]

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.

[AussieinNC]

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 !!!!

[71rehab]

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!

[71rehab]

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