Why is there gas in the oil on your 1997 Buick Riviera?

Answer 1

A Cold winter starts are the likely culprit. Engines require a significantly richer fuel/air mixture to start in cold weather. A high percentage of the fuel that's delivered from the injectors and vaporized into the air drawn into the engine condenses back into liquid on the cold internal engine components, including the valves, pistons, combustion chambers and cylinder walls.

The extra fuel supplied for startup ensures that enough fuel remains vaporized to mix with the air and ignite from the spark. Remember, the engine can burn only fuel vapor, not liquid fuel.

If everything goes according to plan, the engine fires up quickly on the richer fuel/air mixture, begins heating the internal engine parts and ultimately re-vaporizing the condensed fuel and burning it during the warm-up cycle. This is why an engine will flood so quickly in extremely cold weather if it doesn't start in the first few seconds of cranking.

In that scenario, the injectors continue to deliver fuel and more and more of it condenses in the combustion chamber, wetting and ultimately "drowning" the spark plug, making it incapable of firing. The result is a flooded engine.

In some cases, holding full throttle to "unflood" the engine by maximizing air flow and reducing fuel flow will allow the engine to start. When the engine management computer recognizes a wide-open throttle at cranking rpm, it cuts the injector pulse width in half to reduce fuel flow to help clear a flooded condition.

In your Buick, it would seem that at least some liquid fuel generated on cold starts is ending up in the crankcase mixed with the oil. A small amount isn't harmful, and in most cases will evaporate during a fully warmed-up drive -- perhaps 20 minutes. The danger, of course, is that gasoline is an effective solvent, diluting the oil and reducing lubrication to sensitive engine parts.

You should carefully check the components and function of the positive crankcase ventilation (PCV) system to determine if it's functioning properly.

It should draw combustion gases and pressure out of the crankcase and through the induction system.

If the PCV valve or system is not working correctly, excess combustion blow-by, including raw fuel from a cold start, can end up in the crankcase. An iced-up PCV valve, leaking or plugged hose or filter can effectively disable the PCV system, resulting in excess crankcase pressure.

A fuel pressure leak-down test also might help identify any internal fuel leakage from an injector or fuel-pressure regulator that might be allowing raw fuel to leak into the engine after shutdown.

The short-term answer is frequently changing oil to remove any soluble contaminants, including raw gasoline. That's why more-frequent oil changes are important in winter, particularly for vehicles operated in frequent warm-up/cool-down cycles and short-trip driving.

At this point I'd suggest that you continue to monitor the oil, change it frequently and check for a problem with the injectors or fuel management systems.

....my 1995 was running extremely rich due to 2 things: a bad coil..and 2 breaks in the supercharger plastic gasket under the nose of the SC. Does the SC sing when you hit the gas hard in neutral? if not look into that. Change the gasket and remove the nose and clean with brake cleaner and change the plastic controller and oil in the SC while it is off - make sure the bearings are tight, if not buy a reconditioned nose. ...also check the contacts on the coils and if the spark is getting to the plugs before buying a $23 coil. Problem solved.