I've had an interesting time getting new plugs for my '86 300E with the 103.983 engine. I was ordering some items from an internet suppler and I included an order for the Bosch H9DC Supers. What I got was HR9DC resistive plugs.
I knew from my reading here on this forum that the resistor plugs are a no-no for the 103 engine. I went out locally and found a parts house with the H9DC0 plugs which was what were in the engine when I bought the car.
The supplier gave me a refund on the wrong plugs without having to return the plugs (very courteous). It was what they told me that I want to share with the forum. The supplier said that their information was that Bosch recommended the HR9DC plugs for the 103 engine and that Bosch's Atlanta warehouse only had 2 H9DC plugs in stock, implying that these were not going to be available.
I went to the Bosch web site to look up what they actually recommended for the 103 engine. Here are the plugs they listed:
4304 Platinum2
H9DC Supers
H9DC0 Supers
7574 Supers
4459 Platinum
4211 Platinum
HR9DPX Platinum
The last plug listed is clearly a resistor type. I don't know if the platinum plugs with just numerical designations are resistor type or not.
This just points out how we need to be careful in buying plugs and not to take even what the manufacturer of the OEM plugs has to recommend.
