I know how to do a compression test on my car and have a compression tester, but how do I do a leakdown test? Do I just not relieve pressure from the compression tester for X amount of minutes? If my compression was ranged between 162 and 168, what would be a good leakdown number?


TIA
Andy

 

A leakdown test is performed using an air supply regulated to 100psi with a pressure gauge near the fitting that goes into the spark plug hole.

Turn the crank such that the valves going to that cylinder are all closed. Turn on the 100psi air supply. Read the gauge.

100-97psi Excellent condition
96-93psi Good condition
92-89psi Okay, could use help
<88psi time for a rebuild...

If you hear air leak noise coming out of the exhaust pipe, you have leaky exhaust valves. If you hear noise coming out of the intake, you have leaky intake valves. Noise coming out of your dipstick hole is bad rings. Bubbles coming out of your radiator filler hole is bad head gasket.

Your compression numbers are nice and even, but they seem to be a bit low. Did you do the test with the engine fully warm? Is the battery nice and strong?

 

The engine was warm and it was cranking good. I know i have an oil burning problem. I go through a quart about every 800-1200 miles. the engine has 235,xxx miles on it and i am running mobil 1 15w50 cause it burns less and runs smoother. I just wanna know how much time i have left b4 i need to throw an ef si engine in my 89 rex dx. i have the air supply, how much do the testers cost or can i make my own...

Andy

 

If you suspect an oil burning problem, then why not detect and try to repair the problem before you decide to drop in a new motor..
The only thing you would have to lose is a few bucks for whatever is creating the problem if you have already considered the motor junk.. 235.xxx miles is a hella alot of miles! attempt to re-build it, you may be surprised how easily it can be done.. I did mine in 2 1/2 hours and had 170k and cost me about $150.. but again...i'm just damn good!

 

Why would that be Tek? teach me something before I create my own mistakes!

 

If you already have an air supply that can be regulated to 100psi, the only thing you need are pipe fittings to go into the sparkplug hole and fit the other pieces together, a pressure gauge that reads up to 100psi, and preferably some sort of venting valve to blowoff the air when you're done reading each cylinder. The parts you're missing will cost you <$30.

Your engine will continue running even if the compression is about 130psi, albeit very weakly. The only thing that would kill your engine is if you accidentally starved it for oil or overheated it. So basically, keep your eye on the fluids and it'll run forever.