Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site watmum.UUCP Path: utzoo!watmath!watnot!watmum!gvcormack From: gvcormack@watmum.UUCP (Gordon V. Cormack) Newsgroups: net.auto.tech Subject: causes of blue smoke: ring wear vs. valve seal wear Message-ID: <318@watmum.UUCP> Date: Thu, 7-Nov-85 10:24:17 EST Article-I.D.: watmum.318 Posted: Thu Nov 7 10:24:17 1985 Date-Received: Fri, 8-Nov-85 06:12:14 EST References: <1278@ihuxi.UUCP> Distribution: net Organization: U of Waterloo, Ontario Lines: 35 Many, many people have posted articles to the effect that blue smoke on closing the throttle is a symptom of valve-guide wear, not ring wear. I think these statements are misleading. In my experience, the symptoms are exactly consistent with ring wear. There are a number of reasons why the smoke appears on closing the throttle. First, there is less fuel being burned, so that for a constant amount of oil getting into the cylinder, the oil-to-gas ratio is much higher. Second, the combustion is not nearly as complete, so the oil that gets in is not burned well. Third, as has been pointed out, the vacuum tends to draw more oil into the cylinder. This happens whether the leakage is at the rings or at the valve guides. I have not conducted a statistically valid survey (I am sure the other posters have not, either), but in my experience high oil consumption is almost ALWAYS caused by ring wear and almost NEVER caused by valve wear (5-0 on cars I have actually repaired). A couple of tests have been suggested. These tests can positively indicate ring wear, but if they are negative they indicate nothing. One test is the wet/dry compression. If your compression improves by adding a teaspoon of oil to the cylinder, the rings are certainly shot. A simpler test is to remove the oil filler while the engine is running. If puffs of partially burnt gas and exhaust come out, the rings are shot (there should be a slight vacuum, assuming your PCV system is working). I won't argue too strongly against replacing both the rings and the valve guides, but I think it is holding out false hope to suggest that fixing the valves alone is likely to cure heavy oil consumption. ASIDE: It has also been suggested that it is impossible to remove the oil pan on FWD cars. In the vast majority of cases, it is indeed possible, and is often easier than with RWD cars.