Dear Ole Mechanic;
All of a sudden my old ranch truck started burning oil. It is a '88 Chevy ¾ ton pickup with a 350 V8 engine, a manual transmission, and it has about 190,000 miles on it. I know that there are a few leaks, as it will mark its spot if I park it over a clean part of my driveway; however, the spots are only three or four inches across. It also blows some blue smoke out of the exhaust when I start it and when I shift gears, but not when I am running at a steady speed. I checked a couple of spark plugs and they were dark colored, but not oil-fouled. The problem is that after three or four days of use, it usually needs one and sometimes two quarts of oil. Six months ago, I could go three or four weeks before it would need a quart of oil.
Would a new set of rings cure the oil use?
in the Oil Business
Dear Oil Business;
From your letter, I don't think that a set of new piston rings will help all that much. Rings usually do not cause an increase in oil loss ‘all of a sudden,’ unless the engine has some other problem-- like overheating. Also, installing new piston rings is not as easy as it use to be. To begin with, all of the fuel-injection and related sensors are a real headache to remove and get hooked back up correctly. With 190,000 miles, there will be a ring-ridge at the very top of the cylinders that must be removed so that the pistons will not have broken ring-lands when they are removed. Speaking of removing the pistons, there is not enough room under the engine to get the oil pan off. The frame cross-member is in the way. If you can not get the oil pan off, then you can not unbolt the piston’s connecting-rods from the crankshaft to get the pistons out. Really, you should pull the engine out of the truck. Do you really want to put in new rings in the engine without putting in new connecting-rod bearings? You would be restoring the pistons ability to produce power and then putting that power through old rod bearings. Even if you put new rings and bearings, that would not address the oil that is lost through the worn valve-guides in the cylinder head. By the way, that is probably where the oil is coming from that produces the blue smoke on start-up and when shifting gears. To address all of the worn components that could possibly be causing the oil loss is going to run you anywhere from about $1,500 to $2,000. Are you aware that you can get a rebuilt engine from most of the auto parts houses for about $1,800? It would come with a one year warranty, too.
Something tells me that the ‘sudden’ oil loss may not be related to the engine’s internal condition. What I would suggest is to park the truck over a clean area in the driveway and let the engine run for 10 or 15 minutes. If there were one or two quarts of oil going through the engine, there would most likely be oil-fouled spark-plugs, so I bet that a recent bad oil leak is causing the loss of oil. I suspect that one or more of the spots will be much bigger than three or four inches in diameter. Then you can follow the trail of oil up to the real bad leak that is at its worst only when the engine is running.
Herr Professor Nuzanbolts
Followup:Not in the Oil Business took my advice. He found that the oil-pressure sensor was leaking rather badly. The repair cost him $5.88 for a new oil pressure sensor--which he installed himself.