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Volvo heater

I’m having an issue with the heater in my '98 Volvo S70. The heater core was replaced recently because it was leaking coolant. Now whenever we turn on the defroster we get a very strong oily smell enough to make your eyes and throat burn and the windshield gets an oily film on it. At first I thought it might possibly be from a/c compressor oil but there’s no refrigerant in the system. The new heater core didn’t seem to have any type of protectant on it or anything. My mechanic who installed it has rechecked it out and is baffled as to what is causing this issue. The new core was also checked for any leaks and none was found. Doesn’t smell anything like anti freeze anyway. Any help and insight into this would be greatly appreciated.

You do not get this smell when you run the heater in non-defrost mode? If yes, then the AC compressor is involved, as the difference is that defrost turns on the AC.

Ask the mechanic to disconnect the compressor. I’m not an expert, but I understand that usually you can use a different belt to skip the compressor pulley. Or perhaps you can have him pull a fuze that causes the compressor clutch to be deactivated.

If there’s no refrigerant in the AC system, the low pressure switch in the system is going to prevent the compressor from operating.

So that’s not it.

What might be causing the smell is debris on the blower motor resistor.

These resistors are mounted on the heater box. The heat sinks (the silver colored fins) stick inside the heater box so that they can be cooled by the fan as they can get pretty hot.

So you might ask your mechanic to remove the resistor to see if there’s anything on the resistor creating the smell.


My wife tells me that the smell occurs with either the heater or the defroster on. My mechanic and myself have both smell this odor… Very strong oily smell that makes your eyes, nose, and throat burn and will give you a headache if breathed in enough. It is also leaving an oily residue on the windows in the vehicle. I will definitely check out the blower motor resister though. My wife drives the car most of the time and she is saying the smell has been going on for a couple of weeks, happened right after the new heater core was installed and has not lessened in intensity.
Thank you for the replies!!!

No matter what your mechanic is claiming, I believe that there is a coolant leak, either from the heater core itself, or–more likely–from a loose clamp linking the heater core to the cooling system.
You may need a different mechanic to verify poor workmanship on the part of the original mechanic, or a defective heater core.

Devil’s in the details.