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Oil Monitoring Systems

Mercedes calls their unit a “Flexible Service System”. The FSS on some Mercedes vehicles monitors actual oil quality as well as operating conditions (such as the number of cold starts, average engine temp, mileage driven, oil sump level, rpms, etc.). To measure oil quality, there is actually a sensor that measures the electrical conductivity of the oil. The higher the conductivity of the oil, the greater the need for an oil change, according to Mercedes. Of course, this isn’t likely a perfect model, and will not be nearly as accurate as an actual oil analysis in determining true oil quality, but it is better than no measurement at all.

At any rate, as electrical conductivity increases, this value is combined with all of the operating condition data and run through a special algorithm to determine if the oil is ready for a change. When a change is necessary, a light will flash on the instrument panel indicating such.

The other Mercedes FSS unit, which will be somewhat less accurate, does not actually measure the electrical conductivity of the oil, so it is not testing the quality of the oil in any way. It does, however, measure all of the operating conditions and uses the algorithm to predict when an oil change will be necessary.

This is actually how the GM oil monitoring system works. It does not measure oil quality via electrical conductivity or via any other means. It simply measures operating conditions and “calculates” when an oil change should be necessary based upon those conditions.

So, How Accurate Are These Units? Can They Be Trusted?

That’s a tough question to answer at this point. First off, these systems haven’t been in use long enough to really have much in the way of hard statistics comparing vehicle/engine life with or without these systems in place. Second, many drivers do not trust the longer drain intervals recommended by these units and change the oil sooner anyway, offering, again, little data to show whether the drain intervals recommended by these systems are conservative enough to maintain engine protection equal to that attained with shorter change intervals.

Since these units do not FULLY measure oil quality, in the same way that an actual oil analysis would, it is unlikely that they are completely accurate, but there is good reason to believe that they are fairly accurate.

The problem, from my perspective is, how were the limits set? Quite frankly, it’s in the best interests of vehicle manufacturers to have their engines begin to decline in performance somewhere shortly after the 100,000 mile marker. Many people these days don’t expect a vehicle to perform well much beyond 100K, so building a vehicle and recommending maintenance practices that will help the vehicle perform longer than that is not in the best interest of the OEMs.

So, I would be willing to bet that, if you are an individual that likes to keep your vehicle as long as possible, oil quality limits have been set to a lower standard than would be appropriate to getting the absolute most mileage from your vehicle. It really only stands to reason.

How many companies do you know of these days that build MORE quality into their products than their typical customer expects? Not many. In fact, unfortunately, I’d be willing to bet that most of us could count on one hand the number of products we’ve purchased over the past year that offered quality/durability that was BETTER than we expected. Although this is a sad commentary on the business world we currently live in, it is a pretty accurate reflection of the attitude of most companies these days. Why would today’s automobile manufacturers be any different?

Of course, that being said, I have no proof of the above statements. There do not appear to be any websites out there collecting oil analysis data from GM and Mercedes owners to compare the ACTUAL oil quality to that “measured” by the oil life monitors. I looked. In fact, if you happen to know of one, please let me know – I’d love to see the results. I’m guessing I know what they’d be, but I’m certainly open to the possibility that I’m wrong.

I think the main thing to remember is, nobody yet REALLY knows just how accurate these oil monitoring systems are nor how conservative their oil change interval recommendations are. So, be careful how much trust you put on their oil change interval recommendations.

Syn vs. Petro – Does INITIAL Oil Quality Affect Recommendations

Well, that’s an interesting question. As it turns out, these systems can’t tell whether you’ve got synthetic or petroleum oil in the crankcase, and, this DOES make a difference. In fact, we can see this in the light of a class action lawsuit that was filed against Mercedes Benz a few years back.

Apparently, the MB FSS assumes the use of synthetic oil in the engine. Most Europeans are using synthetic oil by default, since typical oil drain intervals in Europe are MUCH longer than those recommended here in the states (although that gap is closing). In contrast, most North American drivers are still using petroleum oil.

Well, there were no significant warnings given to these MB owners with regard to the FSS units and the use of petroleum vs. synthetic oils. So, many users were utilizing petroleum oils and using the FSS as a guide for when to change their oil. Unfortunately, since the FSS was designed to recommend SYNTHETIC oil drain intervals, severe sludging was occurring in these vehicles. The petroleum oil simply couldn’t hold up for the oil change intervals the FSS was recommending. Bad news for your engine.

In the end, the vehicle owners won their suit and there was a 32 million dollar settlement issued against Mercedes. It is my understanding that MB is now very careful to make it explicitly clear what type oils should be used in order to rely on the results of their FSS monitor.

So, clearly it makes a difference. And, since these systems can’t tell what type of oil you’re using, you’ll need to adjust accordingly. The way I understand it, the GM units assume petroleum oil usage (with the exception of vehicles which specifically require synthetic lubricants – such as the Corvette). So, if you’re using synthetic oil in a GM vehicle that does not specifically require it, the oil life monitor will likely “go off” much sooner than necessary.

I have heard that you can have the dealership adjust these units to account for the fact that you’re using synthetic oil, but, even then, there are significant differences in quality from one synthetic to another, so this may still not be completely accurate. If you’re using a premium synthetic oil which is designed for much longer oil drain intervals (such as AMSOIL’s 25,000 mile oils or Mobil 1 Extended Performance 15,000 mile oils), the unit will very likely “trigger” sooner than necessary. However, at least you’ll know that you have a considerable margin of error due to the enhanced quality that is built into those oils.