![]() Intake valves with poor valve guide seals can easily pull oil through the valve guide and into the combustion chamber. If so, then this is a good indicator of an oil consumption problem. These seals can become brittle with time and heat cycles and easily fail. There are some really good valve guide seals that will probably require machine work to install on your heads that might be one way to reduce the amount of oil the engine uses.ĭo you know what kind of valve guide seals are on the heads now? I’m not really conversant on big block Mopars but I believe these engines use an umbrella seal on the intake valves. If the engine smokes slightly on deceleration then it might just be valve guide seals. If the cranking pressure test comes in even at 175 to 185 psi for example, this test would not point to a problem. But frankly I’m not sure that 1,000 miles for a quart of oil is really all that bad and you might just be chasing a problem that isn’t necessarily excessive. That would be a clear indicator of a problem. Let’s say that you find a weak cylinder and there’s more oil on that spark plug than on the other plugs. If you discover one cylinder at 185 psi for example but another at only 155 psi, then that cylinder clearly is under-performing but may not necessarily indicate oil usage. It’s best to test each cylinder the exact same way. A higher number means more cylinder pressure which is a good thing. That’s why I think a compression test is a better overall indicator.įor the compression test, look for all eight cylinders to be within 10 percent of each other but also you will be looking at the actual pressure reading. ![]() A leakdown test unfortunately will not necessarily indicate a problem involving high oil usage. However, it does not sound like that is your problem. Of course, if you find one or two cylinders with exceptionally high leakdown rates, that would indicate a problem in those cylinders. Race engines generally shoot for much lower numbers of less than five percent, but street engines rarely achieve this rather low percentage. Most mild street engines will probably test at 10 to perhaps 20 percent leakage. For those who may not know what a leakdown test is, this involves a tool that pumps air pressure into a cylinder with both valves closed and displays on a gauge the amount of leakage that is expressed as a percentage. The short answer is I think a compression test will tell you more than a leakdown test. Will the compression and leak down tests determine which way to proceed? Thanks so much for your advice. Will those tests tell me if it needs valve work or new pistons/rings? I’ve heard that many times it’s more economical to get new aluminum heads than to rebuild my existing “906” heads? But if it needs new rings/pistons/bearings, I will plan a full rebuild. I have a good compression tester, and have heard about leakdown testers. The engine does have some “blow by” coming out the valve cover breather when it’s warm. ![]() The engine runs good but it uses about a quart of oil in 900 to 1,000 miles. I’ve had it since 1998 and I’ve put about 28,000 miles on the car. The 383 in my ‘68 Road Runner is lightly modified with a 750cfm Holley carburetor, headers, Edelbrock RPM dual plane intake, Mopar electronic ignition, and a mild hydraulic cam.
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