Hot engine - slow cranking starter

In my non-scientific experience…

The innards of starter motors (and anything else on a car that conducts electricity) don’t like heat; it adds resistance. Normal, and harmless enough, until and unless degradation elsewhere (voltage supply, battery cables, and connections mostly) can no longer overcome the additional resistance.

But with age and use starter problems develop, typically worn bearings. The armature naturally expands with heat which, again, is harmless enough…until and unless worn bearings allow the now-expanded armature to drag against the field coils. Now you have an inoperative or very draggy starter. No problem when cold… but a definite problem after absorbing engine heat.

Cheers
DD

After much research, you are correctish about the oil viscosity that’s what you get for preaching what you read on a forum once! But it’s much more than 10 times a 15w50 at cranking temp is 3500cP and at 100°can is 3.7cP you learn something every day! All from this ifor i’m wrong again!

I just noticed that I never responded back on this issue: The problem was the starter motor. The bearing of the motor shaft was completely messed up. Starter replaced - Case closed.
Thanks again for all advice.

Stephan