I have a 92' Ford Ranger XLT with 201,000 miles. Original engine and original transmission. For the last few years I have noticed that the starter motor has to crank longer to start the engine. It only does this in the warm or hot weather. If it is cool or cold, it starts up right away. Now the current starter is only four months old, and it's already doing it.

I notice I have had a slow oil leak for a while. I have heard from 3 different people that oil leakage can very gradually seep into the inside of the alternator and gum it up making it difficult to start. Right now my alternator cranks strong, it just takes more time for it to start the engine.

What is causing this? Could it be old wiring to the starter?

 

I wan to make a correction to my post about it taking longer for engine to start in hot weather. I inquired about oil leakage possible seeping into the alternator.

I mean to say oil leakage seeping into the starter motor.

 

Don't think oil seeping into the starter going to hurt it.
Maybe the slow starting has something to do with the Coolant temp sensor?