Quote:
Originally Posted by kelvo
My understanding has been that diesel engines inherently run cold because they are more efficient and hence generate less 'waste' heat which is why they always take that much longer to warm up, particularly in cold weather.
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That's perfectly true. The high compression ratio of diesel engines makes for greater thermal efficiency. But, the 'waste' you mention is useful heat absorbed by the block because it's at a low temperature. A hotter engine runs more efficiently because a greater proportion of the total energy produced by combustion is used to do work. If you could get the block to a higher temperature in a short time, the fuel efficiency would increase. That's been reported by members after fitting the in-line stat system. But it's about as far as you can go without lagging the engine and such. MGR fitted the FBH to help provide provide a hotter block at startup. Of course, the FBH doesn't improve overall mpg because you're burning diesel to warm the engine without driving the car.
See:
https://en.wikipedia.org/wiki/Heat_engine
TC