[Help] 04 Hyundai Sonata Head Gasket Replacement!

Hello, first off I would like to say that I am new to this forum and hope to find some help to my questions so that I can sleep in peace.
So basically, I have an 04 Hyundai Sonata V6 Engine (2 head gaskets) with 170,000 miles on the engine. I have had the radiator and timing belt replaced 40,000 & 10,000 miles ago. I also do believe that the car has had/does have a coolant leak some where in the engine. With this said, I have also been told that the head gasket is loose and thought it was time to replace it. I am getting the job done by a friends relative who is a mechanic in Mexico and therefore I am able to get the job done for ~$600 versus $1600 quote from the shop I usually go to. Now, you can see why this makes me uneasy and a little skeptical about what can happen with a faulty repair especially with a job like this. I have read horrifying stories of people of rods going through engines, oil bursting out engines, liquids seeping into parts they should not be in and causing corrosion that led to ultimate death of their car, and new head gaskets being unable to support their counterparts. I believe that this guy is a good mechanic, but everybody makes mistakes. What are some questions/confirmations that I should ask him about how he replaced my head gasket BEFORE I drive the car out of the garage and back to US. For example, was all the oil/coolant drained prior to repair, etc. Please throw me ANYTHING you might think would be helpful in this scenario and avoid the costly damage that a faulty head gasket repair could have on my engine. Thanks so much! Hope the community can save me on this one and make my car live a long, happy life! :slight_smile:

Update: The parts being replaced are the head gaskets, new seal, new radiator hose (apparently it was bad, was soft when engine was running), and a new thermostat. He also mentioned he will be pulling the entire engine about because it is a 6 cylinder and there is not enough room to be working inside the engine bay.

When a vehicle reaches the 170K mark, and the head gaskets come into question. unless you’re able to do this repair yourself, you’re better off replacing the vehicle with something newer.


I do understand that and thought heavily before proceeding with this repair. I had gone with it in hopes that it’d be the last major maintenance I’d have to do and that it give me atleast 30,000 more miles. Since it is already being repaired, do you have any insight on weaknesses/or checkpoints i should look into for a head gasket replacement on an older vehicle like mine?

What I’m exclaiming is what I would tell you if you came into my shop with your vehicle.

I don’t want to waste your money or my time.


There really is nothing you can say. Mechanic has done his job and gives you his keys. It is insulting for you to question if he did all correctly. If you had those thoughts, why would you ask them to care for your vehicle.

Plus, if you didn’t like his answers to your supposed questions. What are you really prepared to do? Nothing is likely the answer. So moot point questioning them.


Are you quite sure the headgasket(s) are “loose” . . . ?

I’m thinking the headgasket(s) are worn away or blown, and that is why you’re using coolant, without seeing any external leakage

Normally, when a headgasket is replaced, the mechanic will place a straightedge on the block and head to make sure warpage . . . if any . . . is within acceptable limits. If the head is warped beyond acceptable limits, it will need to be machined

On many engines, the head bolts are torque-to-yield

Translation . . . play it safe and replace them

On some engines, it’s also recommended to replace the intake bolts

After replacing the headgasket, before starting up, you’ll want to replace the engine oil and filter, and the coolant also

Thanks all for the great answers, has definitely eased my mind a bit. I dont plan to interrogate the man but I do see now how it can be insulting to his profession. I may take a different approach and maybe ask him in a way to educate my own self about the proper maintenance of my engine. (PS. I kinda just did the repair because of the price/cannot afford to replace vehicle atm.)

Right, I believe i used the wrong terminology, it is more likely that my headgaskets are worn out. I will ask about the warpage and replace oil&filter before driving home!


As long as the vehicle is in pretty good shape, well maintained, and not rusty, I think you’ll get a few more good years out of the old warhorse

Have you serviced the automatic transmission . . . I assume that’s what you have . . . every 30K . . . ?

Cooling systems are filled with water in Mexico. Don’t expect fresh coolant and oil from this repair, the cost doesn’t allow for normal procedures including machine shop inspection or resurfacing. Expect to have the oil changed at the at the first opportunity and check for the presents of coolant after you get the vehicle to your house.

At that price I would not even count on the head and block being checked for flatness. I mean why bother to check if there is no money to get them milled. Unless he adds this on later.

When such a laborious job like this is done, it’s always worth trying to examine why the gaskets blew in the first place. You don’t want to be doing it again in the near future.

Again, I could not thank you all enough for this wealth of information. I am heading out in a few hours to pick up the car, I will have the oil and coolant change first thing when I return to the US and will post an update on how the procedure went. Bless you all!

too late now. Job is done. New headgaskets with no head/block maching might get u down the road. But for how long? New valve cover gaskets, cam seals, intake manifold gaskets? No loose exhaust clamps? Misplaced vacuum line hoses? 200-300 mile drive thru rural Mexico is no sweat.

It’s all water under the bridge now but there’s a number of things that could go wrong along with a lot of “should have…” and so on.

It’s all going to depend upon why the head gaskets were bad along with the competency of the guy doing the job.

Right, I do believe the headgaskets went bad due to an overheating incident, coolant was leaking and had to replace radiator. I did mention this to him. I also plan on taking the car into my licensed mechanic here in the states for a full inspection and see if he’s able to identify any problems or if the car is good to go

If I was your licensed mechanic and you asked me to check the work done by someone else in Mexico I am going to charge you twice my usual fee or tell you to go fly a kite.

@"VOLVO V70"
Is that a ridiculous question to ask a mechanic? I am being serious here, this is my first car and I’m only 19, so I am a bit blind to the proper etiquette of autoshops…I was just going to ask him to run diagnostics on things like compression, leaks, other stuff pertinent to the function of a head gasket.

If I asked you for a price on mowing my yard and I had someone else do it and then asked you to look at it to see if it was done right how would you feel?

One of the problems that] might surface after head gasket failure due to overheating is oil consumption.
This can be caused by seized oil control rings, fried valve seals, or both. The former is more common than the latter.

Until the car is checked over by someone else I would advise monitoring the engine oil level regularly just to make sure.

Take the proper coolant and oil with you when you pick up the car, and have them install that in the car now, before you leave the shop. Unless they’ve already done that, don’t drive it until you have the correct oil and coolant already in the engine. Besides that, here’s what I do

  • Before starting the car, while the engine is cold, check the oil dipstick, and the coolant level. You need to check both the plastic bottle and the radiator, so ask the shop to remove the radiator cap for you. If you have an auto-transmission, check the fluid level in that too. If a manual, I’d ask the shop to double check the level in that for you.

  • Make sure all the dashboards lights that are supposed to light up, including the check engine light, do, with the key in “on” but the engine not started. Next, make sure all of them go out once the engine is started and all the seat belts are on. If any dash lights remain, don’t remove the car from the lot. Ask that they fix whatever is causing the light to stay on. Probably something simple, like they forget to connect up one of the connectors.

  • Now look under the car. Any signs of something leaking? If so, ask them to fix it.

  • Next, assuming the engine is already started, let it idle in their parking lot. Watch the dash coolant temp gauge. It should go up to around mid-way, then the radiator coolant fan should turn on. After that, the gauge shouldn’t go any higher. The fan will cycle on an off, but the gauge shouldn’t move much beyond around the 1/2 mark. This will take 10-15 minutes, so check under the car for leaks again. And again for the dash lights.

  • Now take it around the block, and check for leaks and the dash lights again.

  • OK? Now take it for a longer drive on the freeway or the like. Make sure the engine coolant temp gauge doesn’t go beyond the midway mark. It should hover around the mid-way mark once the engine is warmed up, neither going much up or down from that.

  • Back at the shop, again check for leaks. Leave the car there at the shop and go have some lunch. Bring some snacks back for the guys at the shop. Once the engine is cooled off, again check for leaks, the dash lights, etc. Then remove the radiator cap and check to see that the radiator remains fully filled, and the oil dipstick is ok.

You might want to take a look at this too.