9/1/2003
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Around the Block
By Don Fedak
At a recent technical presentation by a respected representative of a piston ring supplier, things got a little out of hand when it was suggested that half of all independent aftermarket machine shops may be either out of date and ill-equipped or misinformed as far as cylinder finish is concerned. The reason? Because the OEMs are looking for oil consumption rates of less than one quart per 15,500 miles.
Clearly, the people in the audience must have either been asleep or born yesterday because they just nodded when this totally ludicrous statement was made!
Someone needs to do the math for heaven’s sake...one quart in 15,000 miles is still only one part per gazillion even if none of this oil is burned in the engine or the catalytic converter before it reaches the tailpipe. And of course, most of the oil which isn’t lost due to leaks will be burned during combustion.
Today, vehicle manufacturers are focused on lowering emissions and, at the same time, they’re asking for low-tension oil rings to reduce friction and increase efficiency. Low emissions and low ring tension are not compatible; something has to give.
This low-emissions/low-friction dilemma is nothing more than a head game played by engine designers, parts suppliers and OEM bean counters. The designers set an unrealistic goal for ring suppliers which they know is impossible to achieve. Eventually, the suppliers admit defeat and the contract administrators then demand that the "inferior" rings be supplied at a lower price.
Excessive oil consumption and high emissions are commonly heard complaints in the engine service business. And most of the time, the fault is not with the rings – whether they’re cast iron, high-strength steel, chrome- or molybdenum-coated, or high- or low-tension – so long as second rings are not installed upside down or oil ring expanders are not overlapped.
Most ring manufacturers that supply their OEM customers with low-tension oil rings pack higher tension rings in their aftermarket sets. All other things being equal, rebuilt engines consume less oil than new engines. But every so often, a new or rebuilt engine is returned with the complaint that "it uses oil." The first thing to do is verify the complaint!
We were once asked to examine a fairly new car because the owner said it had suddenly started to use oil; apparently, this low-mileage unit had used two quarts of oil during a 200-mile trip. We checked it over, found nothing amiss and checked with the dealer. He claimed that no previous complaints had been recorded against this vehicle by the manufacturer.
We speculated that the owner may have been short-dipsticked by an over-exuberant gas station attendant. So, we installed fresh oil and a filter, gave him a big jug of oil and showed him how to check the oil himself. Not mysteriously, his engine stopped burning oil as fast as it had started!
The brand or type of oil can also cause oil consumption. Some cheap oils contain large amounts of volatile hydrocarbons which quickly evaporate and lower crankcase volume as soon as the engine oil reaches normal operating temperature. At the other extreme, synthetics may increase oil consumption in worn engines.
Missing, worn or loose valve stem seals or worn intake or exhaust valve guides can also allow engine oil to enter the combustion chamber. Any of this oil that doesn’t burn completely during combustion will show up in the exhaust as smoke. If an engine that uses oil doesn’t smoke, the oil is either leaking or the oil is being burned during combustion or in the catalytic converter.
In the latter case, smoke will appear on cold start and disappear as soon as the catalytic converter warms up.
And driving habits can also be important. The owner of a diesel-powered pickup truck was puzzled because the oil level in the crankcase changed only when his son or his father drove the vehicle. When his teenage son drove the truck it "burned" a lot of oil. But when his father borrowed the truck, the engine "made" oil; i.e., the oil level in the crankcase actually increased.
When the owner drove the vehicle, excess fuel from leaky injectors leaking past the rings in this worn engine just matched the amount of crankcase oil going the other way. His son had a heavy foot, so when he was driving, the amount of engine oil getting past the rings was not matched by fuel wash and the oil level in the pan decreased. The grandfather’s light foot reduced the amount of engine oil getting past the rings, so the crankcase level rose as the engine oil became diluted with diesel fuel.
So, if an engine uses oil, what is considered reasonable and what is not? At one extreme, we have a drag racer customer who prefers to give up a little power and use standard tension oil rings because he has found that low-tension rings allow enough oil into the combustion chamber to foul spark plugs in one quarter-mile pass!
The other extreme, 15,000 miles per quart, strikes this engine rebuilder as bordering on the ridiculous. And these same designers who target these low oil consumption rates for new engine designs intentionally over-fuel their down-sized engines to boost power. Down the road, with rings washed by fuel, engines such as the ubiquitous "Four point Three" inevitably become oil burners and an effective job creation program for all engine rebuilders.
And, in case you ever wondered why engines need oil at all, be advised, as we were recently by a yuppie BMW owner, that oil’s only needed to "put the ‘oil’ light out."
Don Fedak is the owner of RPMS a machine shop located in Brantford, Ontario.
dfedak@engine-builder.com