I read somewhere that I can use RTV silicone instead of a regular rubber gasket as an engine seal.
Is this feasible?
The short answer is no. RTV silicon is a great modern sealant, but must be used in the knowledge that the sealant can block oil ways. It can destroy catalytic convertors, if it becomes diluted by engine oil contact, to the point that it gets left on the cylinder wall during combustion and ends up in the exhaust stream. Oxygen sensors can also be destroyed by being coated in silicon residue. Use only as directed, and replace a gasket with a gasket.
It is feasible, but not advisable. It mainly depends on where the gasket is you are replacing. Many engines today utilize formed rubber gaskets which are reusable and specific. There would be no good way to put the forming gasket material in place of this preformed gasket.
There are many places the RTV can be used on the vehicle. Usually it is used to help seal a solid gasket, or to keep the gasket in place during assembly. It should not be used as a replacement for the gasket, though.
It is fine to use the correct RTV sealant instead of a gasket if used in the right application (oil, high temp, fuel). Not, however, if the gasket thickness is required to produce a specific amount of clearance. RTV sealant is better than primitive gaskets in most applications ie. Water pumps, thermostat housings, intake manifolds, sump pans.
It depends on what gasket you are choosing to replace, and on what engine, but for some small number of gaskets on some engines, it is possible, yes.
However, you should almost never do that, and should always use the gasket. Some gaskets also require using RTV or other sealant compounds in small amounts at certain spots on the gasket, such as at contact points where the two mating surfaces are not exactly flat (humps in oil pan for front/rear main seals for example).
Here is what Permatex, a leading manufacturer of RTV silicone, says about their high-temp. version of the sealant:
"Suggested Applications: Valve covers, oil pans, timing covers, water pumps, thermostat housings, transmission pans
Permatex High-Temp Red RTV Silicone Gasket Maker is formulated for high temperature applications or heavy-duty use such as towing. It replaces almost any cut gasket by making reliable 'formed-in-place' gaskets that resist cracking, shrinking and migrating caused by thermal cycling. Coats pre-cut gaskets to increase reliability. Resists auto and shop fluids, with a temperature range of -65 degrees fahrenheit to 650 degrees fahrenheit intermittent. A first generation 1970-1980 gasket maker, it is OEM specified. Permatex offers significant performance advantages which include outstanding oil resistance, excellent torque retention and hi-temp, sensor-safe properties. Extended warranties, engine sensors and new component materials such as aluminum, bi-metal alloys and high-tech plastics, have created the need for superior RTV silicone gasket makers in both OEM production and service applications."