A head gasket ha a seal, but when the engine severely overheats it ruptures the metal ring around the piston and the antifreeze will leak in. This is a blown head gasket.
There are a few things you can do to test if you have a head gasket leak or not
- Are you constantly adding coolant to the radiator. If you're constantly losing coolant but don't have any leaks on the ground (related to anything else you've tested - if it's an oil leak, you shouldn't confuse the two).
- White smoke or steam coming out of the tailpipe. As antifreeze gets in, the piston will be pushing water/coolant right up into the spark plug which will end up firing out of the tailpipe as steam, which will look like white smoke.
- Check engine light will be on. If your electronics work correctly, it should pick this up.
If you notice these yourself, you can take it to a shop and see if there's a non-head gasket repair solution like a valve job where they can rebuild your cylinder head, which is MUCH cheaper than a full on head gasket replacement. If that's not the case, and you have a car that's not a newer high end car, it's worth a shot using a sealant product. There are many on the market, one of the most popular being from Blue Devil. If you read the reviews on sites that sell this product (third party, these are legit) you'll see the success rate is quite high. If you've got a care with plenty of miles on it, you really don't need to spend more than it's worth to fix a blown head gasket when you can buy a cheap can of product and potentially fix it. No, I'm not recommending you try this out on your 2013 BMW, but there's definitely a place for this and it can certainly save you money.
If you've had luck with this product or similar products, please let me know, I'm always looking for other methods to help our readers save a few bucks.