I always get into arguments with my boyfriend about cars we both think we are right. (Pretty typical) so I thought I'd get some answers to a few questions, and opinions from some unbiased outsiders. And if I've been wrong at least I will know so I can do right by my car. (And my boyfriend , I guess lol)

  • Should you always start your vehicle and let the engine warm up? Especially in the winter? And for how long roughly? ( I say yes, he says for like 2 minutes but that doesn't seem right to me. It seems a tad pointless actually. But I could be wrong. I let mine warm up in the winter till my car is warm or go at least 5 minutes.)
  • Is it bad for your vehicle to start it with the heat/air on? ( he says it's bad go it but I've never heard that before.)

2 Answers 2


Both of you are partially right.

The engine oil should be warmed properly before hauling ass. Most cars don't have an oil temperature sensor and display for it, so as a rule of thumb it can be said that engine oil takes about twice as long to reach operating temperature than the coolant. So, if you require 4 minutes to get the coolant to operating temperature, wait 8 minutes before hauling ass.

However, the proper way of warming your engine is not by idling; it is by driving gently. Idling just wastes fuel and also is an extremely inefficient way of heating the engine due to the small amount of fuel injected. If you let the engine idle, it stays at low temperature longer than it would stay by driving gently.

Some hybrid cars have a battery that can be charged by the mechanical energy produced by the engine instead of idling pointlessly. If the battery is not full, you can expect pretty good warmup performance on these hybrid cars even when being at standstill. Remember, it's not idling then, it's charging the battery. Also, it is easier to avoid high engine loads on these hybrid cars when cold; the control computer probably already has the code to avoid high engine loads on a cold engine, instead providing power from the battery as needed.

Modern engine oils, however, are pretty good even when cold. So it's not like you will destroy your car in few years if you fail to use the best warmup procedure. You will just get somewhat reduced number of miles from your engine before it dies due to old age.

As a hint, if you are in a cold climate, consider installing an electric block heater. This reduces the warmup time considerably when cold.


It depends primarily on the oil. If multi-viscosity,i.e. 5W30, the oil will effectively be of lower viscosity when cold and a greater viscosity when hot. So once you have oil pressure the system is lubricated. However, it’s best to take it easy since the cold bearings and journals of differing materials will have less than ideal clearances until hot.