Caller's question about blocking the radiator with a sheet of plywood

in order to improve the passenger compartment heat in cold weather. I listened to this on a recent Car Talk podcast. Ray and Tom both said it would work, and is commonly done in cold climates. The caller’s shop said it wasn’t necessary, b/c the thermostat provides that function. I got to wondering why blocking off the radiator has any effect on the heater? If the coolant is too cold to produce any heat for the heater, then the thermostat will be completely closed, and no coolant will flow through the radiator, right? So blocking off the radiator should have no effect on the heater. What am I missing? Is the mysterious “bypass” function involved?

It also blocks the (very) cold air from getting to the engine compartment. When it’s that cold the airflow would cool off the engine some. But I wouldn’t do it.


Ok, that makes sense. Thanks.

Good luck getting a piece of plywood in there. I used to use cardboard that could be bent or closed and then opened to fit into the space. Often you would cut a hole in the center to allow more air flow depending on temperatures. If you ever venture the midwest in the winter you will see lots of semis with the tarp covering the radiator and with the center open for air flow. If you didn’t do that, there was not enough engine heating in sub zero temps to ever get the car up to operating temperature.

1 Like

On a modern car I would not do it. I remember, when I was a pump jockey in the 60s, checking the oil on a Volvo it had, what appeared to be factory installed, a cover for the radiator that worked like a window shade that was operated from inside the car.

Yeah, I remember owning a car many decades ago that had a louver of some sort that you closed in the winter and opened in the summer. But you had to open the hood to do that. Looking back on my older cars, it may have been a Volvo 142.