Need a little help...the current owner of my early 93 GTS wrote me asking
about high oil consumption...about 400 miles to a quart.
There were a series of posts on this a few weeks ago, and it seemed that up to a quart every 600 miles was "in the reasonable range". However, a quart every 400 miles seems very high. He had compression and leak down tests done with the following results:
Comp. test: 1) 182, 2) 190, 3) 177, 4) 185, 5) 200, 6) 189, 7) 189, 8) 185
Leakage test based on 100 psi: 1) 88, 2) 94, 3) 79, 4) 80, 5) 76, 6) 84, 7) 94, 8) 84.
Are these results "normal?" Would they be symptomatic of high oil consumption?
When I owned the car about 2 years ago, it averaged about a quart every 1000 miles. There was an owner (a neighbor of Wally's) between the current owner and myself and we are not sure of how he treated the car, although he only put about 2000 miles on the car in about 18 months.
It's hard to believe that oil consumption could increase so much in less than 3000 miles - from 1 QT every 1000 miles to one every 400 miles.
The current owner would appreciate the lists "collective wisdom"...and it's a tribute to the individuals here that two years after selling the car I am still subscribed. Great list, great bunch of guys.
The leak down indicates poor ring sealing to the cylinder ....very poor, the engine must be rebuilt.
Jim Bailey [email@example.com]
There was a useful thread on leakdown tests on the forum recently. I've attached the link and Andrew Olson's informative response below. I'm not an expert but his explanation sounds logical.
When I looked at the numbers you sent I was surprised that #5 had the worst leakdown AND the highest compression. Perhaps blowby and poor combustion have led to a higher level of deposits on the piston top and head.
There are other sources of oil consumption to be considered, such as bad valve guide seals and crankcase ventilation.
How does it run? How does he drive it? What does the tech who did the tests say?
P.S. Jim's very likely to be right and he's the bearer of bad tidings. But if he's right there's nothing to lose from trying some parts store elixir to "free sticky rings" or "stop blowby." The worst that could happen is that the rebuild is delayed for an "additive effect observation period."
OK I keep seeing ref to a leak down test can someone please tell me what it is and how its done and what it tells you?
A leak down or "cylinder leakage" test is similar to a compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss.
A leak down test requires the removal of all the spark plugs. The crankshaft is then turned so that each piston is at top dead center (both valves closed) when each cylinder is tested. Most people start with cylinder number one and follow the engine's firing order.
A threaded coupling attached to a leakage gauge is screwed into a spark plug hole. Compressed air (80 to 90 psi) is then fed into the cylinder.
An engine in great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble.
The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the tailpipe, it indicates a leaky exhaust valve. Air coming out of the throttle body or carburetor would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.
A leakage test can also be used in conjunction with a compression test to diagnose other kinds of problems.
A cylinder that has poor compression, but minimal leakage, usually has a valvetrain problem such as a worn cam lobe, broken valve spring, collapsed lifter, bent push rod, etc.
If all the cylinders have low compression, but show minimal leakage, the most likely cause is incorrect valve timing. The timing belt or chain may be off a notch or two.
If compression is good and leakage is minimal, but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery (bad injector) or ignition problem (fouled spark plug or bad plug wire).