Engines · Subaru
Subaru EJ25 2.5 turbo flat-four (EJ255 and EJ257) common problems
The 2.5 turbocharged flat-four replaced the 2.0 in the UK Impreza WRX and STI from late 2005, as the EJ255 in the WRX and the higher-output EJ257 in the STI, which used it until 2018. Buying guides find little in the way of major problems on well-kept cars, and much of its reputation comes down to how individual cars were treated and tuned.
Common problems and what to look for on the EJ25
The known issues most worth checking when you view a car with this engine. None of them means a car is a bad buy, but they're worth knowing about before you buy, and a good history often shows they've been dealt with.
Ringland failure
What to look for: Watch the exhaust on start-up and on the drive for smoke, and feel for a lack of power or boost. Listen for knocking under load. Ask whether the car has been remapped and by whom, what fuel it runs on, and whether a compression test can be done before you buy.
Why it matters: The 2.5 uses cast pistons (the old 2.0 had forged ones), and a piston can crack between the rings, usually from detonation, which low-octane fuel, hard full-throttle use at low revs or poor tuning make more likely. Cylinder 4 is the worst affected. Low compression confirms it, and the fix is new pistons or a replacement engine. Specialists suggest the problem has been overstated, and a standard or properly tuned car with good history is the one to look for.
Rod bearing knock
What to look for: With the engine warm, listen for a deep, regular knock from the bottom of the engine that rises with revs. Check the oil level and look at the oil on the dipstick for metal flakes. Look in the history for oil and filter changes about every 5,000 miles with genuine filters.
Why it matters: The connecting rod bearings can fail if their oil supply is restricted, and failure is usually terminal for the engine. Frequent oil changes are the main protection, so a short, regular oil change history is a good sign.
Head gasket
What to look for: With the engine cold, check the coolant level and look in the expansion tank for an oily film. On the drive, watch the temperature gauge and look for white smoke from the exhaust. Ask whether the head gaskets have ever been replaced.
Why it matters: The head gasket on the 2.5 is prone to failure, which lets coolant and combustion gases mix. A car with a recent gasket replacement from a known Subaru specialist is in a good position.
More known issues, covered in the full guide for each car
- Oil leaks and a burning smell
- Turbo warm-up, cool-down and smoke
Cars with the EJ25
- Subaru Impreza WRX / STI GD: Hawkeye WRX and STI 2.5, late 2005 to 2007
- Subaru Impreza WRX / STI GR/GV: WRX (EJ255), WRX S and STI (EJ257), 2008 to 2014
- Subaru WRX STI VA: WRX STI (EJ257), 2014 to 2018
A pre-purchase inspection guide for your car
The CrankSight guide is a pre-purchase inspection (PPI) you do yourself, written for the exact model and generation you're viewing. It walks you round the car on your phone, with every check for that version, engine included: what to look for, where to find it, and what anything you find is likely to cost. As you go it builds an assessment of that car, and if you view more than one, it lines them up side by side.
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General points for the engine, last checked October 2026. Every car is different, so treat this as a guide to what to look at, not a verdict on any car. CrankSight is independent and has no connection with any manufacturer.