Over the winter months a daily-driven vehicle (especially one that is parked outside each night) can have extra moisture built up in the oil system due to condensation. Moisture reduces the lubricious properties of the oil until it’s burned off during normal driving. However, if your drives are constantly short, the chances of having more moisture in the oil is likely, and an oil change can be a good idea. One way to check the oil for excessive moisture is to remove the oil cap or dipstick and make sure there is no mustard-like residue on them.
There are also those who specifically use a lighter-weight oil in the colder months for better lubrication during start up. If you’re one of these peeps, make sure to back to the necessary heavier weight oil (if applicable) as recommended by your owner’s manual or engine builder.
Several of the BMW M cars recommend up to 60 weight oils in normal driving conditions so make sure you're back to this for the hotter months at least.
If you’ve got the same air filter from the fall, and live in an area where there is actual fall weather (ie, the leaves fall!), then chances are that your engine filter is dirty. Most air boxes are very easy to open and check the air filter. Open your airbox if you can, check the air filter, and tap off any debris it may have captured.
One of the best bangs for the buck is a simple air filter swap, like with a K&N (or equivalent) drop-in filter. Depending on the car, these inexpensive filters improve fuel economy and horsepower by around 1-2%.
#9: RUBBER HOSES
In an area with hot summers and cold winters, this temperature change can take a serious toll on your engine’s rubber lines, especially if you park outside in cold weather. Think about the temperature difference between parking outside overnight in -10F and then having an engine bay that sees radiator temperatures of up to 210F that same day. Over time, rubber lines will start to crack, and these lines can include certain ones for fuel, oil, coolant, and vacuum. Makes sure to thoroughly check inside the engine bay and replace any lines that may show signs of drying up or cracking.
#10: CHANGE THE SPARKPLUGS
In the cold winter months, the sparkplugs can get a lot of moisture exposure, causing corrosion build-up and therefore premature fouling. If you have a high performance car that you want ready to carve up the canyon or mountain roads, a fresh set of plugs will ensure optimum performance. After all, the ignition system is only as good the plugs delivering the spark.
In a lot of our project cars, including Project E46 M3 and Project Supra, we like to use NKG Iridium plugs from Sparkplugs.com.
When checking spark plugs, you'll want to see a light grey or tan hue in the coloration like the one above. If it's wet or really black you could have a fuel-rich scenario. This can happen in extreme cold driving, where the car has issues getting up to operating temps. If that happens, many cars' ECUs will keep dumping excess fuel into the mixture, thinking the car is still in warm-up mode. This is also reason why the fuel economy usually tanks in the winter months vs spring or summer.