Vehicle
Pontiac Bonneville
The large front-drive saloon, and for most of its later life a 3.8 Series II V6 car — which makes it a useful reference point, because that engine appears across half of GM's front-drive range and carries the same fault everywhere. The upper intake manifold gasket degrades and leaks coolant internally, producing misfires, lean codes and a slowly disappearing coolant level with no visible leak; it is the first thing to check on any 3.8 rather than the last. The supercharged SSEi adds an Eaton blower whose coupling and bearings are a separate wear item, and the 4T65E transaxle behind both is where the remaining complaints live.
Generations
-
Sixth and seventh generation 1981–1991
The downsized G-body and then the first H-body car; the 3.8 V6 arrives here and brings its intake gasket story with it.
- Body styles
- Sedan · Coupé · Estate
- Platform
- GM G-body and H-body
- Engines
-
- 3.8 V6 — petrol · 111–126 kW (149–169 hp)
- 5.0 V8 — petrol
- 4.1 V6 — petrol
- Transmissions
- 3-speed THM200 automatic · 4-speed 200-4R automatic · 4-speed THM440T4 automatic
- Drivetrain
- Rear-wheel drive · Front-wheel drive
-
Eighth generation 1992–1999
3.8 Series I and II, supercharged on the SSEi; the upper intake manifold gasket leaking coolant internally is the defining fault.
- Body styles
- Sedan
- Platform
- GM H-body
- Engines
-
- 3.8 V6 — L36 · petrol · 153 kW (205 hp) · 312 Nm (230 lb-ft) · Series II 3800
- 3.8 supercharged V6 — petrol · L67, SSEi
- 3.8 V6 — L27 · petrol
- Transmissions
- 4-speed automatic
- Drivetrain
- Front-wheel drive
-
Ninth generation 2000–2005
Adds the 4.6 Northstar on the GXP, whose head-bolt threads pulling from the alloy block is a different fault entirely from the 3.8's gasket.
- Body styles
- Sedan
- Platform
- GM G-body
- Engines
-
- 3.8 V6 — L36 · petrol · 312 Nm (230 lb-ft) · Series II L36
- 3.8 supercharged V6 — L67 · petrol · 380 Nm (280 lb-ft) · L67, SSEi
- 4.6 V8 — LD8 · petrol · 205 kW (275 hp) · 407 Nm (300 lb-ft) · Northstar, GXP
- Transmissions
- 4-speed 4T65-E automatic · 4-speed 4T65E-HD automatic · 4-speed 4T80-E automatic
- Drivetrain
- Front-wheel drive
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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