white smoke after the car has been running for a while.

I have a 2003 Polo and the engine keeps losing power. I've taken it to mechanics and they can't find the problem. Every time I go, they charge me a lot... since they've already given me the correct answer to the problem the Opel had...

Son, check that the car isn't leaking brake fluid; it happened to me with a Fiat I had and it was the brake fluid pump that had bad seals, the fluid leaked into the brake booster and from there into the engine, when I took apart the brake booster it was full of brake fluid;

It's important to provide vehicle information so we know what we're talking about. White smoke at startup is normal. If it happens afterward, check the coolant level. If it mysteriously drops, you might have a gasket or cylinder head problem. Another thing you can do is remove the spark plugs and check their color.

The problem is with an Opel Corsa 1.7 Eco.

If it's diesel, then the problem could be faulty injectors.