The 2021 Forester with the FB25D engine represents Subaru's latest iteration of the naturally-aspirated 2.5L boxer. While this generation largely solved the head gasket issues of older models, it introduced new vulnerabilities in the CVT cooling system and shows concerning patterns of premature internal engine wear in a subset of units.
CVT Transmission Oil Cooler Failure
Occasional · high severityTypical onset: 40,000-80,000 mi
Symptoms: CVT fluid mixing with coolant (strawberry milkshake in overflow tank), Transmission slipping or shuddering, Overheating CVT with check engine light, Coolant level dropping with no visible external leaks
Fix: Replace external oil cooler, flush both CVT and cooling system completely, inspect CVT for coolant contamination damage. If caught early (no slipping), cooler replacement alone is 3-4 hours labor. If CVT internals are damaged, add CVT replacement at 8-10 hours total.
Estimated cost: $800-1,200 (cooler only) or $5,500-7,500 (with CVT replacement)
Premature Piston Ring Wear / Oil Consumption
Rare · high severityTypical onset: 60,000-100,000 mi
Symptoms: Excessive oil consumption (1 qt per 1,000-2,000 miles), Blue smoke on startup or acceleration, Fouled spark plugs, P0300 series misfire codes
Fix: This is the FB25D's Achilles heel when it happens. Requires complete engine disassembly, piston ring replacement or full shortblock if cylinder wear is excessive. Factory-spec piston ring job is 18-22 hours, shortblock replacement is 20-24 hours including fluids and timing components.
Estimated cost: $4,500-6,000 (rings) or $6,500-8,500 (shortblock)
Engine Mount Failure (Transmission/Rear Mount)
Common · low severityTypical onset: 70,000-110,000 mi
Symptoms: Clunking when shifting from Park to Drive/Reverse, Excessive vibration at idle, Visible engine movement during acceleration, Thud felt through floor when accelerating from stop
Fix: The rear transmission mount deteriorates from heat and CVT vibration. Straightforward replacement, 1.5-2 hours labor. Usually replace transmission mount and rear engine mount together as preventive measure.
Estimated cost: $350-600
Fuel System Contamination from Fuel Filter Housing
Occasional · medium severitySymptoms: Rough idle or hesitation, P0087 (fuel rail pressure too low), Hard starting after sitting, Check engine light with fuel trim codes
Fix: The in-tank fuel filter housing can crack or allow debris past, contaminating injectors. Requires dropping fuel tank, replacing filter assembly, and often cleaning or replacing fuel injectors. Tank drop and filter is 3-4 hours, add 2-3 hours if injectors need service.
Estimated cost: $600-900 (filter only) or $1,200-1,800 (with injector service)
Head Gasket Seepage (Not Failure)
Occasional · low severityTypical onset: 80,000-120,000 mi
Symptoms: Minor external oil seepage at head gasket mating surface, Slight coolant smell but no overheating, Visible wetness on block below cylinder heads, Not the catastrophic internal failure of older models
Fix: The FB25D rarely suffers internal head gasket failure like EJ engines, but external seepage still occurs. If caught before major coolant loss, it's a monitoring situation. Full replacement is 12-14 hours labor, but many owners defer this unless actively losing fluids.
Estimated cost: $2,800-3,800 (if you do it preventively)
Solid choice if you verify no oil consumption history and CVT has been maintained, but budget $1,500 for potential CVT cooler work — avoid any high-mileage examples burning oil.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.