Thermostat failure: which cars, and at what mileage

What thermostat failure means here

Complaints are assigned to this mode by matching the owner's own description against a phrase list held in the failure-mode catalogue. The match is made on the text, never on the part number, because owners describe symptoms and not components. It is accurate in bulk and fallible one report at a time.

Where it has to be repaired rather than lived with, $250–$900 is the range this site publishes for an independent US shop. It is an editorial estimate, not a figure from NHTSA, and it does not include diagnosis or the labour a dealer would add.

The catalogue classes this mode as moderate, which is what decides its weight in every risk score it contributes to.

Where it starts earliest

Ranked by median reported mileage instead of by rate, the earliest onset is on the 2017 Hyundai Elantra. Sorted that way the leaders are 2017 Hyundai Elantra at 10,000 miles, 2012 Chevrolet Sonic at 10,000 miles and 2015 Jeep Cherokee at 35,000 miles.

Early onset and high rate are different findings. A car that reports this failure rarely but at 40,000 miles is a warranty problem; one that reports it often at 140,000 miles is closer to wear. Both belong on the page, and neither answers the other's question.

Which vehicles report it most

The table below ranks 40 model years by reports per 1,000 vehicles built rather than by raw count, which is the only way a ranking like this stays honest: a model that sold two million copies will out-report one that sold thirty thousand even if it is the better car.

At the top, the 2001 Holiday Rambler Holiday Rambler shows 486 per 1,000 with 17 reports on file.

Chevrolet accounts for 33% of the worst-affected entries on this list, which usually means a shared part, a shared platform, or a shared supplier rather than 13 separate faults.

How to read this page

Nothing here is a defect investigation. It is a count of what owners chose to write to a federal agency about, sorted so that the sales figures do not decide the order. 2,348 reports is a floor: for every owner who filed, some number simply paid the bill and moved on.

If a specific car matters to you, the useful page is the model-year one, where this mode is shown against every other failure reported on the same vehicle. A single failure mode read on its own always looks worse than it is.