Quote:
Originally posted by Brian Carlton
BTW, the 300D has the same engine and the same issues as the 300SD
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Actually, the year 300D in question (91) has a different engine. However, the general principles do remain the same. Please note everyone, that diesels do generate more heat when under load. Its perfectly normal for our temperatures to increase when running flat out, or up long hill, or when towing a trailer . Boost is not really the limiting issue so much, because after about 2000 rpm the wastegate dumps excess boost so that no further power is made. Once the load goes away, the coolant temperature should drop right back down. Using the A/C should cause the temperature to be higher, because there's a higher load, and of course because heat is being pumped out of the cabin.
Cooler is not always better - Mercedes doesn't want our engines running under 82 - that's why the thermostats restrict cooling at temperatures below that. (I think its 82, maybe its 85, you get the idea). Once the thermostat is fully open (94) the cooling system's capacity comes into play. Anything under 105 during the summer w/ A/C on really doesn't worry me. And as has been pointed out, we aren't hurting the engine unless you get to the point of overheating. Having said that, I do understand the concern people have, especially those who own the crack prone 300 SDL heads.
Finally, Brian's point is soooo important. There's 20 years of grime in most of our radiators. Obviously, their ability to transfer heat is somewhat compromised by the grit on the cooling surfaces.