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Many manufacturers won’t perform any warranty engine repairs until the vehicle is consuming about 1.2-1.5 litres per 1,000 kilometres.Maciej Korzekwa/Getty Images/iStockphoto

Decades ago, it was rare to add oil to a vehicle in between oil changes, now it is considered normal. But when is it too much oil? When testing for oil consumption, you are trying to figure out how many litres are being used over 1,000 kilometres. Most manufacturers use the same method.

Your vehicle is topped up as accurately as possible so that the oil level resides at the dip sticks upper-level mark. For those cars without a physical dipstick, it is done using the built-in electronic dipstick. From there, the mileage is recorded and you are sent on your merry way. During the next 1,000 kilometres you are asked to not add any oil. After driving 1,000 kilometres, you return to the dealership for another inspection. The technician will add oil again to return the level to the upper most mark and record how much oil was required on an oil consumption form/worksheet. This procedure will typically happen three times. While this eyeball procedure may not seem like a sophisticated method, it gets the job done and average oil consumption can be calculated. After the test is complete, the dealer service staff will check with manufacturer guidelines to see where your vehicle falls.

Consuming one litre per 5,000 kilometres 20 years ago was considered a problem. Now it is normal. Many manufacturers won’t perform any warranty engine repairs until the vehicle is consuming about 1.2-1.5 litres per 1,000 kilometres. When your vehicle oil results are midway, you will usually be told to live with it if the dealer can’t find any other possible causes for the oil consumption. Two areas that will be checked as they could also cause oil consumption are issues with the crankcase ventilation system and faulty turbochargers. Many manufacturers now use low-friction engine piston rings to assist with fuel consumption. Unfortunately, the use of these piston rings can sometimes lead to elevated oil consumption. If you think your vehicle is in what I call the midway region, it is worth your time to have the test done and results recorded for warrantied vehicles. While it may not lead to any warranty repairs at that time, the problem will usually worsen. Hopefully any subsequent repair can be done before the manufacturer warranty expires.

I have never personally owned a vehicle that used that much oil, but I have talked to many of you. What a pain it must be to have to add oil that often. Add to that, for vehicle’s that take specialty synthetic oils at $12-14 per litre, this can add up very quickly, especially when driving 20,000-plus kilometres per year.

Your automotive questions answered

Hello Lou,

I have a 2013 Kia Forte, which has been a remarkably dependable car. I recently brought it in for an oil change and was asked if I wanted the fuel line flushed … for $99. I was told it should be done every 40,000 kilometres. Is the attendant right, or is there an additive of some sort that can do the trick?

With thanks, Rob R.

I’ve never been a supporter of flushes, especially a fuel-system flush. They are commonly referred to as wallet flushes. All one must do is walk down the aisle at any auto parts retailer and you will quickly realize that chemicals are big business. Do flushes and chemicals added to the crankcase and fuel tank work? I’m sure on some micro scale they do, as people keep making chemical purchases and swear by their favourite fix-in-a-can product. But I have never found anything that I can reliably recommend as something you need to rush out and buy.

However, I am a believer in engine decarbonization for direct injected vehicles only. I mention this because many people confuse the procedure with fuel flushes. There are several manufacturers that have plenty of problems with intake valve carbon build up that unfortunately needs to be regularly dealt with. Rob, do an online search for your model and carbon build up and you will see your model is one of those that is well known for this issue.

I came across your past article about whether someone should get an “expensive” engine/oil system flush. I needed two spaced a few months apart. But it took about $1,300 in service charges for trial-and-error diagnostics for my 5.7-litre Toyota Tundra’s poor gas mileage to finally arrive at that conclusion and address the root cause.

It all began when I broke habit and bought some cheap oil on sale. After doing the oil change and driving a hard 15,000 kilometres on it, I noticed my mileage had gradually decreases to nine miles per gallon (MPG) from 14.

I looked up “sludge in my oil” on the internet and learned this is caused by the condensation of a water-based liquid mixed with the oil. If the liquid is coolant, most likely a torn/damaged head gasket is allowing coolant to enter the engine’s oil passages. But the sludge from coolant is supposed to be cream colour, not black. Another potential source of sludge is your oil completely breaking down and then burning when the engine exceeds the oil’s thermal limit. That kind of sludge is black.

After many repairs at the dealer, I stopped at the Speedy and spent $60 on a flush. Most of their final $170 bill was seven quarts of pricey oil and a filter. But afterward my MPG shot up like a rocket. It drifted down again over the next six weeks of driving to about half its all-time low, so I checked the oil cap, and it was caked with sludge, but this time cream-coloured. My new theory was that the cheap oil couldn’t handle 5,000 kilometres, much less 15,000, generated more sludge than one flush could remove, and the remaining got dunked and cleaned in my brand-new synthetic oil. But it relodged in all those special places and ways that hurt my fuel efficiency.

Back at Speedy four weeks later, I had them check the filter. About half as much sludge this time, and cream coloured, like in the cap. I did the flush and MPG came back as expected and has held for three months. The end, I hope.

So yes, most people never need an oil system flush, as long as they never lapse on scheduled changes.

Regards, Scott

Thanks for the email, Scott.

My first question is, 15,000 kilometres on an oil change, I hope that was a one-off accident and not a regular occurrence. My next thought is, I can’t believe that an oil flush would change fuel economy to that extent. I trust your fuel economy findings; I just think something else has to be responsible for the drastic change.

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail, placing “Lou’s Garage” in the subject line.

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