Does fuel type affect MOT pass rate? Petrol beats diesel in 83% of models

We compared petrol against diesel in 276 models with enough tests of each. Petrol has the higher first-time MOT pass rate in 229 of them, 83 percent.

MOT DATA · 5 min read

A third cut of the same dataset

Our age and mileage pieces both found pass rate does not move in a straight line with either. Fuel type is the other variable on every listing, so we ran the same DVSA data against it: 33,321,407 first-time tests split by fuel type, across every model with enough of a given fuel to count.

The controlled comparison: same model, similar age, different fuel

Comparing model against model removes most of the confounds a straight national fuel-type comparison cannot, body style, market segment, typical buyer, but only if the petrol and diesel versions of that model were actually registered in similar years. We isolated 276 models with at least 1,000 first-time tests of both petrol and diesel, close enough in average registration year to compare directly. Petrol has the higher first-time pass rate in 229 of them, 83 percent. Diesel wins in the other 47. The average gap is 3.5 points in petrol's favour.

What that looks like on real models

Volkswagen Polo: petrol passes first time at 72.6 percent against 62.6 percent for diesel, both averaging a 2010 to 2013 registration, a 10-point gap. Ford Fiesta: 73.5 percent petrol against 63.6 percent diesel, 2013 against 2012. Nissan Qashqai: 77.5 percent against 68.6 percent, 2015 against 2014. Volkswagen Golf: 80.3 percent against 74.7 percent, both from an average 2012 registration. Nearly 2.4 million first-time tests sit behind the four petrol figures alone, so this is not a small-sample artefact.

Why diesel tests worse is not fully explained by this data

The DVSA result tells you pass or fail, not which fuel-specific system caused it. Diesel-only components, the particulate filter, EGR valve and injectors among them, are a reasonable explanation given how often they turn up as expensive MOT-time repairs in practice, but this dataset cannot confirm that mechanism directly. What it can confirm is the gap itself, repeated across almost every mainstream model sold with both a petrol and a diesel option.

Hybrid and electric test far better, but age muddies this part of the picture

Weighted across the whole fleet, hybrids pass first time at 90.1 percent and electrics at 88.2 percent, against 77.6 percent for petrol and 74.6 percent for diesel. Unlike the petrol-versus-diesel comparison above, this one is not well age-controlled: the hybrid fleet being tested averages a 2018.5 registration and the electric fleet 2020.1, against 2012.9 for petrol and 2013.4 for diesel, and for most individual models the petrol and hybrid versions were not sold across the same years either, the Toyota RAV4's petrol test fleet averages a 2006 registration against 2019 for its hybrid. Where the ages do line up, the gap survives but shrinks: the Toyota C-HR's petrol and hybrid versions average a near-identical 2018 and 2019 registration, and the hybrid still tests better, 91.2 percent against 88.7 percent. Take the fleet-wide hybrid and electric numbers as a snapshot, not a like-for-like verdict on the powertrain.

What this means for a salvage buyer

Choosing between a petrol and diesel version of the same model at a similar age, the data says petrol is the safer bet on first-time MOT reliability, sometimes by a wide margin. That is a generalisation across the whole fleet, not a prediction for the specific lot in front of you, so check the model's own pass rate and the individual reg's MOT history before you price repairs, particularly on a diesel where DPF or EGR failure can be an expensive surprise.

Run the actual lot through the Analyzer

Fuel type is one more input, not the whole picture. Paste the Copart lot in, let the Analyzer read the real damage from the photos, and check the reg's own MOT and mileage history free before you decide what it is worth bidding.

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