<VV> Maybe the starter.

[FrankDuVal]

You are confusing several comments.

1. A cold engine does turn easier than a hot engine. Now, a frozen 
engine, as in low temperature frozen, does turn harder! Cold for this 
discussion is 70 °F or 21 °C. For our California members! This frozen 
slow crank is mostly oil viscosity related for frictional loss.  Even 
the oil in he starter bushings, and anything else turned by the engine, 
like transmission input gears. Add to that the harder to move fuel, and 
harder to atomize fuel at frozen temperatures. Diesel fuel gets hard to 
move at 16 °F   (-8° C). BTDT. :)   And then if there is water in the 
fuel.....It doesn't move at all!  BTDT also....:)

2. A hot starter also turns harder than a cold starter (again, cold as 
in not yet running today, not winter time in Minnesota).

3. Worn parts like bushings in starters allow the armature to be out of 
position due to magnetic forces acting upon it. Hence the pole piece 
marks on armatures with worn bushings.

4. Worn bushings + drag of armature on pole pieces makes it harder to turn.

5. A mechanical piece of equipment that works OK when cold but not OK 
when warm is a temperature related problem. Worn parts change shape due 
to heat (as do perfectly fine parts), so a marginally OK starter 
suddenly becomes a not good starter because of heat. And as soon as it 
and the engine cool down, works fine again. But of course, it is not 
working fine, but does start the engine so it does not yet get replaced, 
even though it is worn out.

6. No one said the engine alone got so hot the perfectly fine starter 
could not turn it over. The starter is bad, the engine is not, just 
operating normally as a warm engine, needs more umph to turnover when warm.

7. Not mentioned yet, but related to worn bushings, is starter drive to 
flywheel clearance. It might be possible the magnetic forces on the 
armature cause it to shift enough in worn bushings to close the gear 
gap, causing more frictional loss. When cold, maybe that force is less 
due to the engine turning over easier. Starters are series wound motors, 
the more the load, the more current they draw, the more magnetic force 
increases inside on the armature.

8. The only proof is that just changing the starter fixes the problem. 
So, the proof of what is wrong with the starter is change a part at a 
time and retest! Who has the time and energy, so just put bushings and 
brushes in and call it a day! Ha!

I like having discussions.

Frank DuVal

On 8/8/2020 3:51 PM, Hugo Miller via VirtualVairs wrote:
> And the notion that a heavy diesel engine with over a million miles on 
> the clock would be so tight at normal running temperature that a 
> massive 24 volt starter cannot even turn it over - well that is 
> frankly laughable. I am equally certain that an engine at normal 
> running temperature will take less effort to crank than a cold engine. 
> I thought that was universal knowledge, so obvious that it wouldn't 
> need stating. The Wehrmacht found that out to their cost at Stalingrad.