So my car Hyundai i20 has an overheating issue. Took it to a local garage and they have given me a quote saying it's a blown head gasket. The quote says, along with the report :

" Checked out vehicle, found high HC readings in cooling system indicating head gasket failure ."

Have been quoted £1236.

Does the high HC reading mean it's definitely as blown head gasket?

Thank you.

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    Welcome to Motor Vehicle Maintenance & Repair! Sorry for the bad news. Commented Jul 10 at 17:45
  • Thank you very much. The worst part is I bought it off a dealer 2 months ago. There seemed to be no issue when I bought it. This is my first car ever so during the test drive, I didn't have much knowledge on what to check really. :( Commented 2 days ago

1 Answer 1


High HC (Hydrocarbon) readings in the coolant system means exhaust gasses and or engine oil are getting in somehow, and the thing that normally prevents that is the head gasket, add in the overheating and I'd say it's a very strong indicator, not perhaps definitive proof.

That said, since most of most of the other options I can think of for how that can happen are worse than a blown head gasket I think, as strange as it might sound, you might have to hope that it's only the head gasket that's failed.

We don't really do shopping advice here (and I know you didn't explicitly ask) but the quoted price sounds a bit on the high side for just a head gasket replacement to me, but it depends on whether they're looking at replacing other bits (the i20 uses a timing chain so the normal "replacing the timing belt at the same time" doesn't apply here but it's safe to say a full change of oil and coolant would be sensible) or whether they're building in some headroom in case they need to skim the head due to warping.

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    As long as someone has not poured oil or fuel into their coolant, HCs in the coolant is considered definitive as to a head gasket issue. There should be absolutely no HCs in the coolant. As you said, adding in the overheating and I'd suggest it's a sure thing. I'd put it at a "5-nines" type odds. Commented Jul 10 at 17:44
  • I really appreciate the detailed inputs on the issue. Commented 2 days ago
  • Only thing I want to know now is, so I bought this vehicle on April 12th 2024. Couldn't identify any issue when I took it for a brief test drive ( this is my first ever car). It ran without issue the first month but overheated (after the car did 1500 miles under me) when I took it to the highway. Now I am taking dealer to court and I need a report that basically says the fault was there when I bought the car. The fault must've been there right? Did I cause it? The dealer absolutely doesn't want to accept responsibility. Stuck with this car with no money to buy another one. Nightmare ! Commented 2 days ago
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    Yeah it probably did have the issue then, assuming you're in the UK (from your use of £) then since the fault has occurred within 6 months of purchase the Consumer Rights Act 2015 covers you and the fault is considered to be pre-existing unless the dealer can prove otherwise. This would obligate them to either replace or more likely repair the car. Commented 2 days ago
  • Yes, I'm currently in the UK. I have already provided the car to the dealer for repair. He said the issue was with temperature sensor that prohibited fan from running and he has replaced it. Now that the issue has reoccured, he blames me and does not want to take any responsibility. I have sent him a letter of rejection and he has refused to receive it. I'll have to wait 14 days before proceeding any further. Commented yesterday

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