By Jim Kerr
The other day, a friend asked me about checking the engine oil level on a vehicle. This is a simple task, but it was then that I realized there is a whole generation of drivers out there who have grown up with vehicles that were fuel injected and didn’t need as much service work as their predecessors. Lift the hood of many vehicles and all you see are plastic covers. Even under the covers, there is still a maze of wiring and hoses covering the engine compartment.
Looking under the hood has been left to professional automotive technicians at repair shops, but there are many simple inspections and tasks that drivers should do on a regular basis between visits to the repair shop, and checking engine oil level is one of them.
A typical passenger car or light truck engine will contain between four and six litres of oil. Many of them hold about four and a half litres. When the engine is turned off, the oil drains down into the oil pan: wait a couple minutes, (longer if the engine is cold) and the level can be checked with the dipstick. The dipstick on many vehicles is identified with a yellow handle and the shaft will have at least two marks on it – Full and Add. Too much oil in the engine can cause problems. The crankshaft spins above the oil sitting in the oil pan. If the crankshaft hits the oil because the level is too high, it whips the oil just like you can whip eggs with an eggbeater. Air is trapped in the oil and it can’t be pumped properly throughout the engine. Parts can’t be lubricated properly and this can cause engine failure.
When the oil level is at the “Add” mark on the dipstick, the engine is usually down about one litre of oil. It is still OK to drive with this level, but quick turns, hard acceleration or braking can cause the oil to move to one side and uncover the oil pump pickup. Air is sucked into the lubrication system and the engine bearings lose lubrication for a few seconds. Do this enough times and you will damage the engine, so it is better to keep the oil level closer to the full mark.
With self-serve filling stations everywhere, there are many vehicles on the road that never get their oil checked on a regular basis. I have pulled the dipstick on many vehicles only to find oil on the very tip of the dipstick or not any at all. If there is no oil on the dipstick, the engine is more than two litres low and you may have already done damage to the engine bearings. Drivers have told me their oil level must be good because the oil light has not come on – but the oil light monitors oil pressure, not level. Most oil lights will come on if the oil pressure drops below about 7 PSI. If the oil light comes on because of a sudden loss of oil, and you can shut the engine off immediately, you have probably saved the engine. However, if the oil pressure drops because the oil level in the pan has been gradually getting lower, the engine will likely be damaged by the time the light comes on.
Checking engine oil level frequently is important during cold weather, especially if you take short drives. Condensation inside the engine will drain into the oil pan and sit in the bottom of the pan. The oil floats on top, so the oil level looks normal, even through the engine may be using some. Drive the vehicle on the highway and the engine gets hot and the condensed water in the bottom of the pan evaporates. Now the engine is operating with a low oil level.
Checking oil level with every fuel fill up is a great idea, and important if you are travelling. It can save you an engine.