Is the blow-by test still generally valid?
12-13-2004, 04:37 PM
#1
Instructor
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Location: Iowa
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Is the blow-by test still generally valid?
I'm referring to the quick test to see if a car has issues with compression due to rings or valves. Many years ago, I was told to remove the oil filler cap with the engine running and feel to see if there was air (and maybe oil) blowing out. The stronger the air flow, the worse the wear / damage to the engine. This test has worked fairly well for me on many 1970's and 1980's vehicles.
Recently, I was told that test wasn't always valid or useful any more. Specifically, I tested a 1998 Toyota Corolla with only 45,000 miles on it and regular 3000 mile dealer service. When I tried the blow-by test, it felt like a hair dryer on max and in a second my hand was covered with oil. That was the worst I've felt on any used car.
So, is the test still valid? Are there any vehicles or years where it might not work correctly?
thanks,
Bryan
Recently, I was told that test wasn't always valid or useful any more. Specifically, I tested a 1998 Toyota Corolla with only 45,000 miles on it and regular 3000 mile dealer service. When I tried the blow-by test, it felt like a hair dryer on max and in a second my hand was covered with oil. That was the worst I've felt on any used car.
So, is the test still valid? Are there any vehicles or years where it might not work correctly?
thanks,
Bryan
12-14-2004, 02:28 PM
#4
Race Director
That test CAN be used to check for ring-wear. But how do we know that the oil hitting your hand wasn't from the crank sloshing oil around? A leakdown test with measured numbers would be better.
