Check this out - you'll be glad you did!!!

From : Annonymous

Q: treydog90spam@hotmail.com says... on the chevy group i follow there is a guy asking about covering the radiator on his diesel for the colder winter season. i am assuming he lives in a colder part of the world. most vehicles have a thermostat to control the flow of coolant through the engine but also have a bypass so that there is at least a little flow regardless. the bypass may be an orfice in the thermostat or its housing or a separate hose. if there is too much bypass flow to reach normal operating temperature the engine can benefit from a partial blockage of radiator air flow. bypass flow varies all over the map depending on what the strategy of the designer was at that moment so you have to make your own call based on the behavior of your own vehicle. an extreme case in point was my old 78 chevy van which would not produce any heat at all when the mercury dropped below freezing. i formed a piece of sheet metal whth a few holes in it to drop in front of the radiator and that helped somewhat but still was slow to warm up and didnt quite reach the normal range on the temp gauge. on closer inspection i discovered that the heater core was plumbed with 3/4 hoses that went from the engine directly back into an extra fitting on the radiator and the flow was huge! i guess the designer thought this was the way to make lots of heat for the cavernous van interior but it was having the opposite effect. i purchased a shut-off valve at the local autopro and installed it at an easy to reach location under the hood. with a little experimenting i found a setting where it stangled the flow down to maybe a fourth of original and thereafter had toasty feet. i left my restrictor valve in permanently and pulled the sheet metal out for warmer weather. point being; the makers dont always get it right and you do what you gotta to make it work. .