Nope, you are fine on both counts - my 300 Tdi 90 is exactly the same, except that I've lost the rubber bit off what is the air-intake to the heater, all it means is I probably suck in a bit more air from the engine bay to the heater than you do. As for the engine temp, thats exactly where mine sits unless I'm towing something really heavy. Again, all fine ecxept it probably means the engine never really gets up to temperature and the heater is a bit less effective than it could be. I've an electric fan sitting in the shed waiting to be fitted so that rather than be cooled all the time the engine will only be cooled when a thermostat says it hot.