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Old 07-10-2001, 06:24 PM
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RunningTooHot RunningTooHot is offline
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Larry: I just now (days later) saw your response in the thread about diesel longevity – Thank you for sharing your knowledge with us here. I am still on the learning curve about the idiosyncrasies of the MBZ diesels, having previously owned only gasoline engined MBZ’s. I am trying to understand more about the theoretical aspects of diesel combustion as well.

You stated that <<“ Most everything in a diesel is backwards from a gas engine. More fuel versus air causes increased combustion chamber heat in a diesel. In a gas engine increasing air vs. fuel increases combustion chamber heat, and it certainly can increase it to a point where it does much more damage than merely causing a misfire. A lean condition in a gas engine can completely destroy it quickly with holes in pistons and burnt valves.”>>

I’ve ‘been there, done that’ with gas engines at track events. Amazing how quickly you can melt aluminum or toast valves when running a turbo’d engine under severe duty & then get a little transient fuel starvation!

However, its hard for me to comprehend the aspect of diesel operation regarding more fuel = more heat; I mean I can understand this up to a point - but then the lack of enough oxygen from an overly rich mixture should not burn any hotter. That is unless I am not aware of a fundamental difference that can be answered by this question: Do diesels run “lean” even when under *full* load? In other words, does a diesel NOT run out of oxygen before combustion temps get too high? (Thus injected fuel amount is the limiting factor?) Please don’t confuse this question with the obvious – I am aware that diesels inherently run in a lean condition due to no throttling, and that power output at anything less than full load is strictly a function of fuel quantity being injected.

The only other thing that I can think of is the relatively slow burn rate combined with enough oxygen to support it – does an overly rich mixture cause *combusting* (versus *combusted*) gasses to flow over the opening exhaust valve, thus causing the heat induced damage? If this is the case, I can see an opportunity for diesel hot rodders: how about sodium filled Iconel exhaust valves & ceramic exhaust port coatings? .

BTW: I am using a universal grade oil (Rotella T), having learned about it here. I don’t know if the PO did, but most likely not based upon the “quickie lube” type stickers on the car. And you are absolutely right about the staining power of this combo!

Thanks Again!
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