no juice

[vso737]

Hi,

Need opinions on my dilemma.  Actually had........since I just sold it.

I have a BIG BLOCK motor, which on occasion, will NOT turn over after a one hour trip.  It acts like a complete dead battery but after a 15 minute cool-down, it will start with plenty of juice.
I suspected a bad ground and even replaced the battery for more cranking power when the engine got hot.  Still does it.

The thing is that it will start all day long after turning it off and on numerous times when driving around town.

It is just the long constant extended drive that will cause the issue of not turning the motor.

I suspect it has to be the starter/solenoid that is heating up.

Any suggestions extremely welcomed.

Thank you in advance,
Mike

[wayne petty]

heat roasts the starter and the solenoid windings..

there are a few tricks...

installing a 70 dodge dart starter relay... but using 10 gauge wire back and forth





i have had GM starter solenoids pull 50 amps of current on the starter tester when trying to pull the plunger in..

the load dropping relay really makes small and big blocks start quick also..  takes all the starter solenoid load off the ignition switch and wiring.. as the dodge solenoid only takes an amp or two..

let me explain the starter solenoid wiring GM starters..

from the S terminal.. the windings are grounded to the solenoid output stud.. where the starter motor winding is actually attached..

when you turn the key.. the electrons have to flow in from the engine block to the starter nose to the motor housing to the negative brush.. thru the armature and the positive brush before it comes up in the conductor to connect to the solenoid lower stud..

this creates enough magnetic field to PULL the plunger in hard enough to engage the drive with the lever and bottom the plunger out into the solenoid and push the contact disc out and across the heads of the 2 big studs in the cap of the solenoid...

once that contact is made.. there is now voltage at the lower stud.. but because of voltage drop  as the starter is using a significant amount of current.. the solenoid winding still has enough hold in power to keep the starter engaged..

with HEAT SOAK.  the copper windings can expand and contract overtime to wear thru the varnish on the windings.. this reduces the amount of magnetic field it can create and prevents the solenoid from pulling in on the plunger..

this is one of the reasons that when you change the solenoid.. the heat soak issue sometimes goes away...

other times its the field windings or the armature windings..

the load dropping really really helps..  once you install it.. you just won't believe how fast the starter engages..

all new cars since around 1996 use a starter load dropping relay.. as its far easier on the ignition circuit..

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[vso737]

VERY, VERY INTELLIGENT ANSWER............

THANKS a million Wayne.

I will be looking for a 70 Dodge relay to use with my SBC in the Model A.

I passed on your solution to the new owner of my past '40 Chevy.

LG,
Mike

[unklian]

Electrical Resistance increases with heat.