I hope you regularly check your smart car's oil. If you don't, you should at least once per week, and if it uses more than 1 litre every 1000km (600 miles), you may have a problem, infact, you have definately got a problem! Read on for more information on what to check and try if your smart car is using excessive oil. (Picture courtesy of Flikr some rights reserved )

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How do I know if it's using oil?

It should be obvious if you're checking your oil regularly, but some signs are smoke from the engine under acceleration, and more obviously, oil spatters over the back of the car. There's only two ways that oil can disappear, it's either burned or leaked.

Note: this applies usually to the Fortwo 600cc and 700cc, and the Roadster models. The diesels and mitsubishi based engines are not usually affected by oil consumption problems. 

Causes of Oil Consumption

1) Top Breather Pipe.

The top breather pipe allows excess pressure to exit the crankcase, but with this top breather either blocked, or the one way valve broken, pressure builds in the crankcase and causes oil consumption to rise.

2) Leaks

If it's leaking, you'll soon spot it, there are some common oil leak points in smarts, the crank bearing oil seals are common place leaks, as are the dipstick oil seals. You may also get an oil leak around the sump, though it's less common. It should be fairly easy to see an oil leak, place some cardboard under the back of the car and leave it there overnight, you'll soon spot where it's leaking from.

3) Oil Control Rings

The piston has an oil control ring, over time this gets clogged and stuck in it's grove within the piston, this allows excess oil to stay in the cylinder and be burnt as part of the combustion cycle, which leads to other problems eventually like burnt valves.

4) Valve Stem Seals

The valve stem seals stop excess oil entering the cylinder via the valve stems, these do wear over time, and can become a cause of oil consumption. This is most noticable as a plume of blue smoke at startup as it allows oil to pool and enter the cylinders on startup.

5) Turbo

The turbo bearings can leak and cause excessive oil usage, it's not very common, but it can be a cause. It can either manifest itself as black smoke if it's being burnt in the exhaust side, or blue smoke if it's being burnt in the cylinders. Changing the turbo is the only cure.

Prevention

There's virtually nothing that can be done to stop this, some smarts are better than others, so it's pretty much luck of the draw which one you get. Though I personally believe that changing your oil more regularly than the service intervals will make your engine last a lot longer. I believe you should be changing your oil at 5,000 miles. If you have a Brabus, or highly tunes smart, you should be changing your oil at 3,000 miles. It may seem expensive, but in the long run it should go a long way to protecting your engine.

Cures

There's only one long term cure for excessive oil consumption, and I'll come to that in a minute, but there are some things you can try that will prolong the inevitable.

1) Change your oil grade.

Usually your car will be running on 0w40 or 5w40 oil, should it start using more, it's recommended to change to a 10w40 oil.

2) Change the top breather hose

If it's blocked, it can cause excess oil consumption

3) Try an engine additive.

There are some engine additives for high milage engine that say they'll stop oil consumption, I've tried Wynns, and it did work, for about 2 months...

4) Change the valve stem seals

This isn't that common, but if you're still seeing plumes of smoke on acceleration it may be worth getting these done.

5) Engine rebuild

This is very common, according to a poll currently running on my site, near enough 50% of the respondents have had an engine rebuild. Usually it involves changing piston rings and getting the cylinder head refurbished, expect to pay £600 to £1200 for an engine refurb.

6) Turbo change

While your engine is getting rebuilt, get them to test the turbo for cracks and play in the bearing shaft. Better to get it done while your engine is being rebuilt.

Conclusion

The smart engine is a small engine with a lot of power for it's size, you need to change the oil more often than service intervals recommend, and you need to factor into the running costs of your car that at some point, usually between 40,000 and 80,000 miles your car's engine will need rebuilding.

  I  recommend www.smartdoctor.co.uk for rebuilds as he fits a new cam chain kit which some rebuilders don't do.

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