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Automania/Repair & Maintenance

AUTO QUESTIONS AND ANSWERS FOR WEEK 51 YEAR 2000

by Bob Hagin

Q. Why does the General Motors 3800 V6 engine, which is found in almost all G.M. cars, use so much oil? I have a 1997 Buick Le Sabre and it uses about 1.5-quarts of oil every 3000 miles. It has 28,000 miles on it now. I was told that oil consumption like this is normal in the 3800 V6 engine. Years ago, oil consumption meant bad rings or leaky valve guides.
N.M. Sacramento, CA

A. Oil consumption is an almost mystical thing and it rarely affects two cars the same way, even if they are the same brand, same year and have the same type of engine. No auto maker will tell a buyer or a mechanic what is "normal" oil consumption. The closest I've come across is that a factory will usually say that a vehicle's oil consumption in miles-per quarts Is "...within acceptable limits.." whether the consumption is 500 miles per quart or 10,000. Factory representatives say that "modern" engines run hotter and so are built to consume a certain amount of oil, but they don't say how much or how frequently. Oil rings, cylinder bore sealing and the condition of valve guides and seals can cause oil usage if they're not seated or sealing correctly. I recently pulled down a Toyota that uses oil and the only overt problem I could find was that the oil seal "fit" on the valve stems seemed loose. I've also come across piston compression rings that were installed upside-down and rings whose end-gaps were aligned which made an oil "path" to the combustion chamber for the oil to be pulled up. I've also seen imperfections in cylinder heads and faulty positive crankcase ventilation (PCV) valves cause it. In retrospect, maybe your Buick's oil mileage isn't so bad but don't try extending you oil change schedule.

Q. I have a 1990 Jeep Cherokee with a 4.0-liter six cylinder engine and it has to crank on the starter for quite a while before it will start. I have replaced the rotor, distributor cap, spark plugs and one internal part inside the distributor. The computer code told my mechanic what to replace but it did not help.
K.B. Sweet Home, OR

A. Sometimes a mechanic has to go beyond checking computer codes and do some old-fashioned troubleshooting. To start right, four-cycle gasoline engines need three things: compression, fuel and ignition. The major parameter is that they all have to be in sufficient quantity and be at the right place at the right time. Have a compression check done in the classic manner. Put a little squirt of oil in the combustion chambers, have the ignition disabled and the throttle braced open. The highest value should be within 10 percent of the lowest. An oscilloscope can pick up the initial firing voltage to see if it can support firing and the fuel delivery can also be tested with an injector or cold-start valve tester. They all have to be there at the right time so camshaft and ignition timing have to be checked. Hard-start causes could be "wet" spark plugs, a slight head gasket leak or half a dozen other things.

Q. I have a '94 Ford Ranger with a four-cylinder engine and automatic transmission. It has about 90,000 miles. It seems to be using transmission fluid at about a half-quart per month and more on long trips. There doesn't appear to be leakage but my coolant looks contaminated. Could the transmission cooler be leaking inside the radiator? Could the contamination damage my engine? Should I replace the radiator and flush the engine and transmission? I can't fix it for about a month or so. Any danger in that?
A.S. Chesapeake, VA

A. Better fix the problem right away. ATF in the cooling system is bad but if coolant gets pulled into your transmission, it will be an expensive fix.

 

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