1991 VOLVO 740

Typical onset: 120,000-180,000 mi

Symptoms: Blue smoke on deceleration or startup, Loss of boost pressure, Rattling or whining from turbo area, Eventually catastrophic knock and oil consumption if ignored

Fix: Turbo seals fail from age and heat cycling, dumping oil into exhaust or starving the turbo bearing. If caught early, turbo rebuild or replacement runs 6-8 hours labor. If ignored, owners face full engine rebuilds (pistons, rings, bearings, head gasket) due to oil starvation damage—easily 25-35 hours labor for a proper job.

Estimated cost: $1,200-2,500 for turbo alone; $4,500-7,500 for full engine rebuild

Typical onset: 80,000-140,000 mi

Symptoms: Pink or milky transmission fluid, Transmission overheating, Coolant loss with no visible external leak, Erratic shifting or slipping

Fix: The transmission cooler inside the radiator fails, allowing coolant and ATF to mix—a death sentence for the AW71 automatic. Requires radiator replacement, full transmission fluid flush, and often filter/pan service. If contamination has progressed, transmission rebuild or replacement needed (15-20 hours). Preventive external cooler install adds 2-3 hours but saves transmissions.

Estimated cost: $800-1,500 if caught immediately; $2,500-4,000 with transmission damage

Typical onset: 100,000-150,000 mi

Symptoms: Clunk when shifting from park to drive or reverse, Vibration at idle in gear, Visible sag or separation of rubber mount

Fix: The rear transmission mount disintegrates from age and fluid contamination. Replacement is straightforward—1.5-2 hours including trans support—but delayed replacement accelerates wear on the tailshaft bushing and driveline components.

Estimated cost: $250-450

Typical onset: 60,000-120,000 mi

Symptoms: Rough idle or stalling, Oil leaks from valve cover or rear main seal area, Excessive crankcase pressure (oil cap pops off), Check engine light for lean condition

Fix: Volvo's flame trap (PCV oil separator) clogs with sludge, causing crankcase pressure to blow out gaskets and create vacuum leaks. Requires flame trap replacement, PCV hose inspection, and often valve cover gasket while you're in there. Total 2-3 hours labor. This is preventive maintenance that saves major oil leaks.

Estimated cost: $300-550

Typical onset: 150,000+ mi

Symptoms: Intermittent stalling or no-start, Rough running that comes and goes, Multiple sensor codes without obvious sensor failure, Engine dies when hitting bumps

Fix: LH-Jetronic wiring harness insulation becomes brittle from engine heat, causing shorts and opens. Diagnosis is tedious (3-5 hours), and proper fix involves harness replacement or extensive repair/re-sleeving (6-10 hours). Many techs do patch jobs that fail again within a year.

Estimated cost: $800-1,800 depending on extent

Symptoms: Overdrive won't engage or disengage, No click from relay under dash when pressing OD button, Intermittent OD function

Fix: If equipped with M46 manual with electric overdrive, the relay fails from contact wear. Replacement is 0.5 hours and cheap, but affects highway fuel economy. OD solenoid on transmission can also fail (2 hours labor).

Estimated cost: $100-200 for relay; $400-600 for solenoid