This is an ongoing list explaining the reasons behind excessive oil consumption. Some of
it is personal knowledge and some is information I have collected from other websites.
If you have anything to add, please let me know.
Excessive Oil Use Definition
Smart state that more than 1 litre of oil loss over 1000 miles is excessive.
I'd have to agree, it's very excessive. If you experience half of that oil loss I'd recommend
getting the car looked at and possibly having the engine reconditioned. It's not going to fix itself.
Pistons And Cylinders
This is probably one of the main reasons for excessive oil consumption and can be the most
costly to sort out. Generally it happens through normal wear and tear but can be caused by
broken bits of sparkplug, bits of valve or a damaged piston ring rubbing the cylinder wall.
On the outside circumference of the pistons are a set of rings. Some are designed to seal the piston against the cylinder so compression is not lost and one is designed to oil the clinder wall.
If the rings are worn then oil can pass into the combustion area and be burnt off.
The best way to check for a damaged cylinder or piston ring without dismantling the
engine is by performing a standard compression test. That information can be found here.
A compression test may give normal figures at the beginning of the problem as the oil on the cylider wall can hold back the pressure of a cranked engine. You won't get a cloud of smoke with this fault, the best way to check is to remove a sparkplug and view the top of the piston.
A normal piston with have an even brown or black coating, if oil is entering
the cylinder, the coating on the edges of the piston will be washed away.
Valve Guides And Stem Seals
Valve guides can also wear causing oil to be lost in the combustion cycle but this is usually only noticed when the car is first started or if it has been sitting unused for a while. This allows the oil
to pool on top of the valves and starting the car allows the build up straight into the engine.
Smoke will be noticed from start up after the car has been resting a while.
This smoke will be a blue/grey smoke depending on the state of the oil.
The obvious thing to check is the visible parts of the engine. If you can see a point where oil is emerging then you have found a leak. If nothing is obvious, clean the engine up and have a look every day after driving. It has been known for oil to leak from the base of the dip stick tube.
Oil forming around the transmission seal or over the inside ends of the drive shafts is not
engine oil. This will be transmission fluid. You need to change the seals and top the fluid up.
Faulty Breather Pipe
The smart crankcase on the 450 and 452 has two breather pipes. The lower
pipe that connects to the TIK pipe usually draws air in to replace the air
going out of the top breather pipe.Because the top breather pipe is directed
straight into the intake manifold there can be boost or vaccum in this pipe.
During vacuum, the intake manifold it draws air from the crank case and through the top
breather, burnt oil vapour is extracted from the crank case and is burnt in the combustion cycle.
During boost, a check valve on the top breather pipe closes.
If this check valve becomes faulty it can allow the boost to flow into the crank case, when this happens the only way the boost can go is out of the lower breather pipe. The problem occurs because the movement of air causes oil to be blown do the lower breather and into the TIK pipe.
This oil is then sucked into the turbo and blown into the engine. The amount of oil burnt is usually excessive and black smoke will appear from the exhaust. Replace the top breather pipe.
Warped Head Or Damaged Head Gasket
With this fault you will usually see one of two things. Either oil gets into the coolant or coolant gets into the oil. If coolant gets into the oil you will notice a build up of what looks like mayonaise when you look into the oil filler cap. This will clog the oil galleries and cause more oil usage.
If the oil is getting into the coolant you will notice the oil sitting on top of the water in the
coolant expansion tank. This can increase the pressure in the coolant system and eventually coolant will be force into the engine causing the previous problem with the mayonaise.
Head gaskets can fail through age but can also become damaged through increased
compression.The head can become warped if the coolant system is not doing its job properly
and areas of the head overheat. This buckles the head causing internal and external leaks.
Using too thin an oil can allow a leak through a smaller gap. Using a thicker oil can reduce or stop oil loss in some cases but always use an oil weight within the recommendations of the manual.
Also some fully synthetic oils contain a detergent to help clean the engine as it circulates.
With old engines it isn't a good idea to use these types of oils as in some cases, it is the crap in
the engine that is sealing some of the cracks. Cleaning the crap away with detergents allows
the cracks to clear out and the leaks start. It is the same with engine oil flush. Don't use them.
Dirty oil is consumed at a much higher rate than clean oil because the contaminates in the oil prevent the oil control rings from seating properly. Fully synthetic is very robust and doesn't wear out like older types of oil. This does not mean that you should extend the servicing periods.
Your car should be serviced according to the handbook without fail.
Worn Main Bearings
Worn or damaged main bearings throw off an excessive amount of oil which flows along the rotating crankshaft and is thrown up into the cylinders. The amount of oil thrown off increases rapidly when bearing wear increases. Eventually, the amount of oil is greater than the amount
that the oil control rings can cope with. Oil then enters the combustion chamber and is burnt.
Leaking Turbo Seal
The turbo prop shaft connects the compressor to the turbine blades, this prop spins at
tremendous speeds so needs constant lubrication. The turbo prop shaft is sealed at each
end to keep the oil inside the turbo housing. If the seal on either side should become
damaged you will lose oil into either the air intake system or the exhaust system.
Oil entering the turbo air system is usually denoted by blue smoke on start up.
By printing this document I state I have read and understood this disclaimer