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

Re: Slow Crank when Hot
 

weak starter , but check all connections first

Re: Slow Crank when Hot
 

Thanks. If it were a weak starter, why would it crank fine with a fresh battery and weak after several drives?

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.

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.

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.

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

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.:metal:

Re: Slow Crank when Hot
 

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

Re: Slow Crank when Hot
 

Those mini starters with a heat blanket works good.

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.

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

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)

Re: Slow Crank when Hot
 

How is your timing? Just a thought.

Re: Slow Crank when Hot
 

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.

Re: Slow Crank when Hot
 

Thanks. I definitely do not have all of those ground points.

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

Re: Slow Crank when Hot
 

Not sure. It is new to me but only has 55k miles so my guess is original

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.

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.

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

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.

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 !!!!

:chevy::chevy::chevy:
:gmc2::gmc2::gmc2:

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!

Re: Slow Crank when Hot
 

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

Re: Slow Crank when Hot
 

Yes, true if you have a plain wire supplying full 12V to the distributor, to replace the original resistor wire. What do both sides of your positive battery cable look like, and both sides of the negative battery cable? Can you post pictures? I misdiagnosed a starter problem because of a bad battery cable on my truck last year. Other people on the thread have talked about their headers, but didn't ask you if you have headers.

Re: Slow Crank when Hot
 

Hmmm my battery grounds to the alternator body. Then I have one more (very old and beat up) ground from the valve cover to the body. I have no frame to fender grounds.

And thanks for the recommendations!

Re: Slow Crank when Hot
 

Does the truck have headers on it?

Re: Slow Crank when Hot
 

No headers.

Also noticed that the starter has a NAPA sticker on it. So assume its a reman and that is probably the culprit? In any case, just ordered 5 new ground straps.

Re: Slow Crank when Hot
 

Thanks. Cables are in great shape. Cleaned up the ends last night and still a tired starter after a drive.

Re: Slow Crank when Hot
 

Yep, not needed when HEI equipped...but make sure its not able to short out anywhere...tape off the end with electrical tape and secure it away from heat sources like headers etc.

:chevy::chevy::chevy:

Re: Slow Crank when Hot
 

Would suggest you replace the starter with a small format reduction style unit...new...not reman...

Grab a heat shield for it while you are ordering it...

Even without headers, the exhaust pipe will likely be putting too much heat onto older fat style starter...

Also...make sure there is a starter end support strap fitted and correctly in place...

GM part number is GM 23502557...most wholesalers carry them...even Amazon...

I have witnessed so many engine block damage scenarios with bolt holes stripped or broken out due to missing brackets...

:chevy::chevy::chevy:

Re: Slow Crank when Hot
 

Something like this? http://www.jegs.com/i/JEGS-Performan...2/-1#reviewTab

Re: Slow Crank when Hot
 

Just a little different perspective on it. If the truck is cold, it has a good battery charge / New battery and you drive it for a while.. It's hot, obviously and you shut it off. This is when you experience the sluggish starts. .. If the truck is hot when you try to start it back up.

If the truck sits for a few hours and cools completely off, will it start back up normally? .. or are you saying at that point, even cold it won't start back up until you charge / replace the battery?

Re: Slow Crank when Hot
 

Yes Sir, that one will do fine...

on that Jegs page, also grab the heat wrap and the shim kit to correctly space pinion teeth from ring gear teeth.

Also...make sure you use the correct knurled shank bolts to attach the starter to the engine.

:chevy::chevy::chevy:

Re: Slow Crank when Hot
 

Here is a link to my fight with this issue. I tried everything - long story short, nothing fixed it until I got a high torque mini starter.

http://67-72chevytrucks.com/vboard/s...d.php?t=729029

Re: Slow Crank when Hot
 

Had exactly the same problem you are having and did this to correct it. http://67-72chevytrucks.com/vboard/s...d.php?t=363603

Re: Slow Crank when Hot
 

My truck had the same issue ended up putting a thicker gasket in between the carb and manifold and the problem went away.This is a common problem just on the edelbrocks.

Re: Slow Crank when Hot
 

Post a pic of your engine ,

Does it look like this http://67-72chevytrucks.com/vboard/s...d.php?t=509243

or this http://67-72chevytrucks.com/vboard/s...d.php?t=457938

It all makes a difference , next time you have a hard to crank issue use a set of jumper cables and hook them directly to the starter + post and a solid ground - next to the starter , get in turn the key and if it starts fine its your battery cables/ connections , If it still starts hard it's your starter is suffering heat sink . you can't ground your system to a valve cover . why jump to parts suppliers like jegs when anyone of your local auto parts stores carry exactly what you need just down the street ? personally I'd just go buy a new mini starter and a new set of good battery cables and be done with it , :smoke:

So many get hooked on setting up their 50 year old truck by the numbers the book say 8 degrees timing BUT it just may run better at 6 or 10 . these aren't computer driven systems . It's called tuning for a reason ...

Re: Slow Crank when Hot
 

I'd put the big ground cable directly on the block, not the alternator bracket.
What exactly is the voltage across the battery with the engine off and running?
How many CCA is the battery rated at?
I'd also be looking at the positive and negative cables and make sure they're in good shape. Grumpy's suggestion with the jumper cables is good, but the wording is a little funny. Connect from the + battery terminal to the big cable connector on the starter, then crank. Similarly, connect to the - terminal and to the starter body, then crank.