First of all, not changing the oil is really really stupid, and I should know. More on that later.
When it comes to advice on oil brands and oil changes, people are going to go by what they have experienced in the past, and those experiences are going to be as varied as the people who had them and the vehicles they involved. I can offer some generalizations that you can use when you hear these stories.
All oils contain a lot of additives that wear out over time, typically in about 3,000 miles. The oil is still oil after that time, and it still has the same lubricating properties, ... However, some of those additives that wear out improve on those lubricating properties. You may have lost the additional protection but you haven't lost all of the protection. Oil lubricates by isolating moving parts from each other when it's under pressure. It doesn't lose that ability from age.
Another function of oil is to remove heat, mainly from the pistons and cylinder walls. It can still do that as long as the level isn't too low and it can be pumped around freely. It also carries dirt away to be trapped in the filter. Here is where you can run into problems. All engines have some blowby past the piston rings, and that exhaust gas and unburned raw gas condenses in the oil to form sludge. In its worst form, that sludge sits in the bottom of the oil pan and doesn't do much, but when it is dissolved into the oil, it passes right through the filter just like the rest of the oil. Sometimes, when the engine is stopped, that sludge coagulates in the filter and plugs it. All engines have a bypass valve to allow unfiltered oil to reach the engine when the filter becomes plugged. That valve can be built into the filter or into the filter housing on the engine. Dirty, unfiltered oil is bad, but it's better than no oil at all. The problem is you can have soot and other particles circulating in the oil and never know it. That is a big cause of worn crankshaft and connecting rod bearings, but we just attribute that to normal wear when we tear the engine down to rebuild it.
You will often hear people say switching to a certain brand of oil caused a leak or blue smoke from the tail pipe. I had a former student with an early '70s Ford pickup truck, (which is rarely seen here due to road salt and rust), that had no oil leaks. He started using a popular synthetic oil and immediately had a puddle wherever he parked. When he switched back to his original brand, the leak cleared up. At issue here, as I've been told by the experts, is the mixing of the different additives in different brands of oils. Those include seal conditioners, rust inhibitors, detergents, and viscosity index improvers. I've heard similar stories years ago, but people who stick with one brand of oil seem to have fewer leaks.
Now for the other side of the story I eluded to. I have well over 400,000 miles on the engine in my '88 Grand Caravan, (another vehicle you never see around here due to rust), and under the assumption the engine was on its last legs 12 years ago, I stopped changing the oil. At the time I had students chasing leaks so I was always adding oil anyway. Each time they found and fixed a leak, the next leak was worse. Turned out fixing those leaks cause more pressure to build up and push the oil out of the last leak, a pin hole rusted in the top of the oil pan. With that fixed, I still never changed the oil to continue the "experiment" to show my students what engines are capable of. What's happening though is the engine still uses about a quart of oil every 800 to 1,000 miles, so I'm always adding oil with that quart of new additives. One quart of oil has enough additives for the engine. Five quarts of new oil has five times the new additives but those don't last five times longer. All the additives wear out at the same rate. The goal is to get them to last 3,000 miles. I have new additives every 1,000 miles.
That's the good part of the story. There's still the sludge and blowby to deal with, ... And I haven't. In this respect, that is not neglect; it's abuse, and I am definitely not suggesting you or anyone else do this. My engine has run for so long like this and for over 100,000 miles that it's pointless to grow a conscience now. I add the cheapest hardware store oil I can find but I've stuck with that brand all these years.
I also have a '93 Dynasty that has had only one oil change in its life, but that car has just over 4,200 miles. I plan on changing the oil soon, and much more often than the recommended 3,000 miles, because the additives do wear out too with age, even when the engine doesn't get run much. That one only gets Mopar oil because I have a lot of it and that's what I started it on when I worked at the dealership. It is no better or worse than any other brands. They just buy it from a supplier and put their own name on it.
I have an '80 Volare that gets a name brand oil at each oil change, but that one too doesn't get changed too often. The car only has 45,000 miles on it.
You won't find anyone who knows about engines to tell you to not change the oil. The oils today are continually getting better and they're developing better additives. Your engine won't need or benefit from most of those improvements, but it's still very cheap insurance to help your engine experience the least amount of wear. Don't waste time planning on replacing your engine. I did that based solely on high mileage, and as it turns out, the engine is going to outlast the body. I still use that van to drag around a tandem axle enclosed trailer that's bigger than the van. Most engines wouldn't tolerate that either.
Sunday, January 12th, 2014 AT 5:50 PM