Covering the upper and lower grilles (and leaving the lower outer grilles uncovered) does indeed make for warmer coolant temps and better interior heat. When this airflow is not blocked off, I figure that, either the thermostat does not stop coolant flow from the radiator completely, and/or colder air in the engine compartment simply cools the engine off by passing over its metal surfaces. It seems that, even without blocking off the radiator, the coolant temp stays up when cruising on the open highway, but slow down to drive thru a town, and down the temp goes. If you leave it idling to run in to a convenience store, the temps are below the three hash marks when you come out, unless you turn the blower way down. All of these situations are improved when you block off the radiator.
Hey Bruceps: Wow! Elegant solution using 1/2" foam insulation! I'll give it a try. I can see that for "warmer" winter temps, it will be easy to pull one ,or even two, of the strips out for extra cooling, although, even with the upper and lower grilles completely covered, I have not experienced overheating up through 45 deg F.
I, too, have installed a tdiheater.com circulating pre-heater, and it is truly wonderful.
Although I have been cautioned not to do this by other list members, I continue to leave it plugged in while warming up at idle, for faster warmups. I turn the heater control full on, and the blower to the first position. After 10 minutes of idle, the coolant temp gauge reads between the three hash marks and the normal straight up 190 deg F mark. So, doing this, with heated seats and the interior semi-warm, things are tolerable right from the start of the trip.
Diesel efficiency and gasser heat ... yeah!
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