1981 PONTIAC GRAND PRIX

Typical onset: 60,000-90,000 mi

Symptoms: Slipping between 1st and 2nd gear under moderate throttle, No 3rd gear or delayed engagement into overdrive, Burnt transmission fluid smell and dark brown fluid color, Complete loss of forward gears, reverse still works initially

Fix: THM200 (metric 200) was GM's weakest slushbox, especially behind V8s. Sunshell and direct clutch pack failures are endemic. Rebuild requires 8-12 hours labor, but most shops recommend swapping in a THM350 or 200-4R with custom crossmember mounts for longevity. Factory THM350-equipped cars are significantly more durable.

Estimated cost: $1,800-3,200

Symptoms: Hard starting when hot, floods and stalls at idle, Black smoke from exhaust, strong fuel smell in cabin, Fuel dripping from air cleaner base after shutdown, Surging at highway speeds, poor fuel economy below 10 mpg

Fix: Q-jet carbs on 1981 models suffer from deteriorated float needles, warped float bowls, and vacuum leak points. Ethanol fuel accelerates gasket/seal failure. Quality rebuild kits (Cliff Ruggles or similar) plus bowl resurfacing takes 4-6 hours. Many owners swap to Edelbrock 1406 for simplicity, but loses low-end efficiency.

Estimated cost: $450-850

Typical onset: 80,000-120,000 mi

Symptoms: Oil puddle under bellhousing area after overnight parking, Transmission covered in engine oil, clutch contamination smell, Rapid oil consumption, 1 quart per 500-800 miles, Blue smoke on startup if oil drips onto exhaust crossover

Fix: Two-piece rear main seals on these small-blocks weep as rope packing hardens. Proper fix requires transmission removal, 6-8 hours labor. Oil pan gaskets fail from heat cycling and often leak simultaneously. Both jobs done together make economic sense. Teflon seal upgrades available but require machining on older blocks.

Estimated cost: $850-1,400

Typical onset: 70,000-110,000 mi

Symptoms: Coolant weeping from intake valley, visible at manifold edges, Overheating under load, coolant loss with no external leaks, White exhaust smoke on cold start, sweet smell, Milky oil on dipstick if leak allows coolant into crankcase

Fix: Buick 231 V6 and Pontiac 301/Chevy 305 V8s use composite gaskets that deteriorate from heat and coolant. Job requires intake removal, valley cleanup, and gasket replacement—5-7 hours labor. Felpro or Victor Reinz gaskets mandatory; cheap parts guarantee comebacks. Check for warped manifold surfaces.

Estimated cost: $650-1,100

Symptoms: Doors misalign, won't close flush, or jam when opening, Visible rust perforation at rocker panels behind front wheels, Body flexes or creaks over bumps, steering column angle shifts, Floor pan rust-through near seat mounts, carpet always damp

Fix: G-body frames rust at body mount points and rear trailing arm brackets, especially where salt exposure occurred. Body mounts ($20 each) are easy, 3-4 hours for all eight. Frame rust requires welding or replacement sections—12-20 hours labor if extensive. Inspect carefully before purchase; cosmetic repairs hide structural rot.

Estimated cost: $400-2,500

Typical onset: 90,000-130,000 mi

Symptoms: Engine stumbles or stalls under acceleration, won't restart hot, Fuel gauge reads empty when tank is full, or stuck at half, Fuel starvation above half throttle, surging at speed, Whining noise from rear on startup that fades

Fix: Mechanical fuel pumps (pushrod-driven) fail from diaphragm wear; 1.5-2 hours to replace. Sending units corrode in tank, requiring tank drop—4-5 hours labor. In-tank sock filters clog from sediment in older fuel systems. Many swap to electric pump with return line for reliability.

Estimated cost: $350-700