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  #1  
Old 10-05-2008, 10:00 AM
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heater efficiency

I was told that diesels are not the fastest for interior heat and after 3 Vermont winters driving my TDI and Cummins, I have gotten used to very slow cabin heat until the vehicle is fully warmed up especially the Cummins.
Now with the MB's I am getting noticeable heat within 5 minutes of startup when it is 30's outside. What a pleasure.
My question is , how does Mercedes do it. Do they have a different more efficient method of heat transfer or what?
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  #2  
Old 10-05-2008, 10:43 AM
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I have run an `85 190d for 2 winters here in Wisconsin. It blows heat quicker than any car I`ve owned previous. Think the coolant circulation pump is the reason. All is good with mine `till 10deg.F and below. Then there is not much heat.
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  #3  
Old 10-05-2008, 11:01 AM
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The TDI is slower at warming up because its a more efficient engine and doesn't burn as much fuel...so it doesn't create heat as quickly. I would have thought the cummins would be like a furnace in just a few minutes
That's not the only factor though...the differences in the cooling systems in the different engines probably have more to do with it than just engine efficiency.
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  #4  
Old 10-05-2008, 01:13 PM
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It's probably also a function of the amount of coolant in the circuit with the thermostat completely closed (cold engine) compared to when the thermostat is completely open. Although I believe that there's a small amount of "leakage" around the t-stat that is designed into the cooling system, most of the coolant in a cold engine circulates only through the block and head, the pump and thermostat area, and the heater core and its plumbing. That small amount of coolant warms up quickly, thus giving you cabin heat in only a few minutes. I would guess that, in a Mercedes, more than half of the coolant is in the radiator and the expansion tank. Perhaps other engines have more of the coolant in the engine, or perhaps their thermostats allow more to circulate through the radiator, even with a cold engine.
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  #5  
Old 10-05-2008, 10:00 PM
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Its a simple answer....its because a Mercedes is: "Unlike any other."
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Old 10-05-2008, 10:11 PM
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The only time I've ever had trouble was one commute to and from work at about 10F when the blower fan on my 240D quit...
Well there was one time with my 190D and a bad thermostat.
I'll agree with the other poster on the design of the MB thermostat probably making a big difference. I've always had great heat in my cars even down well below zero.
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  #7  
Old 10-05-2008, 10:17 PM
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Quote:
Originally Posted by pizzachef View Post
The TDI is slower at warming up because its a more efficient engine and doesn't burn as much fuel...so it doesn't create heat as quickly.
The TDI is so efficient that recent VW TDI's actually have glowplugs in the engine block to heat up faster!
MB adds an electric heater to the HVAC system of its CDI models.

These cars heat up so quick because the precombustion chamber sits in the head surrounded by coolant. The coolant absorbs a lot of heat from the PC chamber, another reason direct injection engines are 15% more efficient.
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Old 10-05-2008, 11:10 PM
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Its also not as big as a cummins, therefore has less thermal mass. but then again, you'd think it would take forever to heat up because the block and head are solid iron
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Old 10-05-2008, 11:20 PM
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Could it have anything to do with MB's having bypass thermostats?
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  #10  
Old 10-06-2008, 11:25 AM
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Most likely a combination of an aluminum head, the coolant pump, and the indirect injection. My 124 doesn't start blowing air at me until the coolant in the head is hot enough to prevent cold air at the vents. I've got a pretty steep hill coming out of where I park the car every night. By the time I'm up that the blower starts blowing warm air and it's hot by the time I reach the stop sign 1/4 mile later.
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  #11  
Old 10-06-2008, 09:19 PM
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I think my Cummins has a bad t-stat. Temp guage never over 170*, I will be switching it out before too long since winter is a coming.
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1981 240D 132k 4 spd manual
Finally got the clutch bled!
2003 VW Jetta TDI 5 speed 216k
2002 VW Jetta TDI auto, 210k, Koni SRT, Frostheater, DG Alum Skidplate, ventectomy, Fuel pickup mod. Wife's car
1995 Dodge 2500 4x4 Cummins diesel, 5 speed 182k, 3rd gen trackbar, PSD steering shaft. Everything else that needs transport
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  #12  
Old 10-06-2008, 09:37 PM
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Volkswagon proved a diesel engine can have a heating system far more efficient than a gas car. Some examples of the jetta from 85 to about 90 will actually burn your skin off if you put you hand over one of the heat ducts before you have driven far.

My understanding was the head coolant is the only coolant circulated through the heater core on the early ones. . Quite a few people asked me if the car had an auxillery gas heater when they were in them from a cold start

. Volkswagon dealers explained the tdi engine was too efficient to generate much heat. That if true was an understatement. I suspect they got the design of their heater system wrong. The old jeta got about 50 mpg up here and the tdi about 60 mpg in Canada. Thats only a 20 percent spread in energy consumption. It alone could not count for at least an 80 percent reduction in heater performance in my opinion.
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Old 10-06-2008, 09:37 PM
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