Both of my ' Cadillacs have the same problem When...
Both of my '69 Cadillacs have the same problem. When they are cold, they start great. But if I turn them off when the engines are hot, it's hard to get them started again. The battery seems almost dead at first, then a moment later, the engine starts to move and finally turns over. One of the cars has had three starters in the last year. The other has had two. That's five starters! What's wrong?
TOM: You need five more starters, James. You just need to hook them all up in tandem.
RAY: Actually, it sounds like you have a classic gas-guzzling-old-heap-hot-starting problem. What happens is that, over time, carbon builds up on the pistons. And that carbon build-up makes the pistons, in effect, "bigger" than they're supposed to be. That increases the engine's compression, which makes the car harder to start.
TOM: But more importantly, when that carbon gets hot, it retains heat, and that heat makes the fuel in the cylinder explode early; while the piston is still on its way up. And that's why the engine is hard to start; the piston is trying to come up, and the "pre-ignited" gasoline is trying to push it back down (the same thing happens when your timing is too advanced). That's where those five starters would come in handy.
RAY: Then, when the car has been sitting for a long time, and the carbon on the pistons cools off, the engine starts again with a lot less effort.
TOM: So, what do you do about it? There are additives you can try that are supposed to remove carbon from inside the engine. And you should try one of those first, because it's relatively inexpensive. It probably won't work, but, as I say, it's relatively inexpensive.
RAY: And when that doesn't work, you'll have to have the engine taken apart and de-carbonized (they actually scrape the stuff off the pistons). That'll cost you a few hundred bucks, but think of all the money you'll save on starters, James! 1951