bad head gasket if you saw sludge and smoke, similar thing happening to me except no signs of a bad head gasket/smoke.

 

is that very serious? expensive?

 

yeah, u need to do a leak down test ....and yes it can get expensive unless ur mechanically inclined and do it yourself...another way to make sure its head gasket is check ur oil if it has water in it, and check the exhaust if it has white smoke while idling...

 

If you drove it while it was in the red, you most likely warped the head and possibly did more internal engine damage. Your engine's not starting now most likely because any compression is blowing out from between the head and the block.

 

Pull the dipstick.. if it looks like fudge on the end of the stick, you are all done my friend...

 

This dude probibly just pooped alittle after these posts, I would of. They may be right though.

Is your car under warranty? Call Hyundai if it is, they will usually tow it for you. If not, Do what these guys are saying. Of course checking for white smoke while idleing can't be done. Check for fudge on the dip stick, and check your oil for water. Acually, theres ways you can tell water is in your oil. Here's something I dug up for you from "Poor Man's Oil Analysis" search on Google.

The Blotter Spot test

This test reveals oxidation products, sludge formation, dispersancy failure, glycol contamination, water contamination, fuel dilution, and high levels of particles.
You want to place a drop or two of used oil on the surface of chromatography paper (good heavy white card stock works pretty well too). Lay the paper or business card flat, but so that all but the very edges of the paper is suspended. For a fairly stiff business card, placing two pencils down on a table and laying the business card so that the ends are resting on the pencils would work well.
You want to wait for the paper or card to absorb the oil drop(s) which might take awhile. Once all of the oil has been drawn into the pores of the paper you can begin evaluating the condition of your oil.
- A colorless spot or slight yellow outer ring - "good" oil.
- A dense, dark deposit zone – Dispersancy failure
- A black, pasty zone – Glycol (Antifreeze) in your oil
- A dark center with distinct outer ring – Severely oxidized oil
- A dark center with surrounding rings – Fuel in oil

 

The Crackle Test

This test is useful for establishing water ingression into your oil from condensation problems. Typically, you'll be most susceptible to water in your oil if you are a short trip driver and/or if your vehicle sits for long periods without being run.
If you have fuel in your oil, this can cause some disruption of the test, so do the blotter spot test first to see if you have any fuel dilution. If so, that is already a problem, so the crackle test is a moot point.
To perform the crackle test, you place a very small quantity of oil onto a hotplate of some sort which is set to a temperature high enough to boil off any water in the oil. Since most oil isn't volatile until it gets up around 375 degrees F or higher (synthetics much higher than that), you could set the plate to a temp anywhere between 250 and 350 degrees most likely.
At that temp, when you place the oil on the plate, you'll hear a crackle as the water boils off. Should occur very quickly as long as the amount of oil you use is small.
If there is no crackling, then you know there is no water present. An oil analysis is more precise in that it will tell you if the level of water in the oil is a problem and what that level is, but the crackle test is a good cheap way to establish water ingression.

 

The mud was coming from the radiator? what kind of coolant do u use?, i had an Impala with the eco friendly **** in it and if oxygen hits that stuff it turns to mud and screws your whole coolant system up, so if there was a leak in the radiator then that is a good possibility.