1995 Oldsmobile Ciera Does This Sound Like A Heater Core Pr

Hi:
First, sorry about the delay. As far as the problem, chances are you have a very small pinhole in the heater core. What happens is when you build pressure in the system, it may come out and cause the odor.

As far as the replacement, it isn't a fun job.

Here are the directions I found for it:

Disconnect the negative battery cable and drain the cooling system.
Disconnect the heater hoses from the heater core inlet and outlet connections in the engine compartment.
Allowing residual coolant from the heater core to drain. Cap the openings.
Working inside the vehicle, remove the lower instrument panel sound insulator.
Remove the heater floor outlet duct screws or clips and remove the duct.

Remove the heater core cover by removing the attaching screws and clips.
Remove the heater core cover.
Remove the heater core retainers and remove the heater core.

To install:

Position the heater core in the housing and install the retaining straps.
Position the heater core cover on the housing and install the attaching screws and clips.
Install the floor outlet duct and attaching screws or clips.

Install the lower instrument panel sound insulator.
Working in the engine compartment, connect the heater core inlet and outlet hoses.
Fill the cooling system.
Start the engine and check for coolant leaks. Allow the engine to warm up sufficiently to confirm the proper operation of the heater.
Recheck for leaks. Check the cooling system level.

Air Conditioned Models
Drain the cooling system.

If equipped with a diesel engine, raise and support the car on jackstands.
Disconnect the hoses at the core.
On diesels, remove the instrument panel lower sound absorber.

Remove the heater duct and lower side covers.
Remove the lower heater outlet.
Remove the two housing cover-to-air valve housing clips.
Remove the housing cover.
Remove the core restraining straps.
Remove the core tubing retainers and lift out the core.

To install:

Install the core, then attach the core tubing retainers.
Attach the core restraining straps.
Install the housing cover, then install the two housing cover-to-air valve housing clips.
Install the lower heater outlet, then attach the heater duct and lower side covers.
On diesels, install the lower instrument panel sound absorber.
Connect the hoses at the core.
Lower the vehicle if raised and supported.
Fill the cooling system.
Start the engine and check for coolant leaks. Allow the engine to warm up sufficiently to confirm the proper operation of the heater.
Recheck for leaks. Check the cooling system level.

As far as parts and labor, I found it to run 2.3 hours and an aftermarket core to cost around 30 dollars.

Let me know if this helps or if you have other questions.

Joe