Truck slow to crank when warm

I have a 97 3/4 ton Chevy truck with 136K miles on it. The problem I have is that the truck is slow to crank when it is warm but when the engine is cool like in the morning or when it has cooled after 2hrs or so the engine turns over fine. I put a new battery in it last summer. I was just wandering could it be my starter.

Have the starter checked.

I agree. It sounds like a bad starter. If this truck does not have a starter heat shield then the problem could be compounded.

Sometimes people say “slow to crank” when it is cranking just fine, but actually takes quite a bit of cranking to get it to run.

So please clarify. “Slow to crank” would mean that you turn the key and it sounds really sluggish - as if there isn’t enough power to really get it going. Is that what you mean? Or do you mean you turn the key, it sounds like a good healthy crank but it takes a lot of cranking before the engine will fire up?

In the old days of engines with carburetors, sometimes the piston tops would get a coating of carbon. The carbon would retain heat and the fuel mixture in the cylinder would pre-ignite when the engine was hot. This prignition would force the piston down and rotate the crankshaft in the opposite direction that the starter motor was turning the engine over. However, this would be unlikely in a vehicle with fuel injection.

When the engine is hot, have a mechanic check the current draw of the starter as the engine is cranked. Then have the mechanic disconnect the ignition and check the starter current draw again. If the current draw is the same, it eliminates the possibility of the engine being “carboned up”, and points to a starter problem. This assumes that you mean that the engine cranks slowly when hot.

I mean the it is sluggish when turning over and after about 3 or 4 turnovers it cranks.

Start by just pulling all of your cable connections at the battery and the starter. Clean them all up really well and put them back nice and tight. If that doesn’t help check out how the cables look underneath the insulation and replace if necessary. After you know the problem isn’t in cables or connections then move on to worrying about more expensive things like starters.

A heat shield can be made with a sheet of steel and a muffler clamp. I use heatproof gasket goop and gasket material to cover the metal on the starter side. You have to drill two holes in the steel. You don’t need the gasket material.

Probably a worn starter motor…When they start to go…when warm or hot they require a lot more voltage than normal to spin the engine over at the proper speed. Thats my guess for now…aside from incorrect (too far advanced) ignition timing which is unlikely in this vehicle.

Id go with a dying starter myself