500SL Mystery Thermostat Housing

[Don K]

Replacing the thermostat on my 1985 500SL/Euro. The thermostat housing has a vent hose fitting which goes to the radiator and to the fill tank (through a tee fitting). While cleaning the housing I noticed that the vent fitting was blocked. Should be a simple small hole that goes into the sidewall of the large hose fitting on the housing. Thought at first it was blocked with corrosion but it would not open even when drilled. I have now concluded that the small hose fitting was either blocked on purpose at the factory or it was a defective part. If it was blocked on pupose then why run a vent hose to it ?

Has anyone noticed this before ? The real question is should I persist in drilling out the fitting ??

Any help appreciated.

Don K
Houston, TX