Leakdown testing....

Yellowb1rd · 11:32 AM

Fellas,

I finally have a good reason to use my US General Leakdown tester that I purchased a couple of years ago. I've been attempting to perform a leakdown test on a spare S4 motor that I acquired to replace the one currently in my 89. I know that I'm at TDC on every cylinder I've checked (so far 1-4), and every single one of them reads 40 to 60 percent leakdown.

I even checked cylinders 5-8 on the one in the car (which I know are good), and I'm getting very similar leakdown measurements. This just cant be right, and I'm questioning the accuracy of the tester, but I don't see any widespread issues with this specific unit when doing an internet search.

I zero out the leakdown gauge (on the right), and the pressure reads about 15 PSI on the pressure gauge (on the left), and THEN I connect it to the hose that is screwed into the cylinder. That's the correct procedure as far as I know.

The replacement motor is still on the pallet, so it's painfully simple to get access to just about anything on the motor quickly. I have the valve covers off, so it's pretty easy to locate TDC based on intake exhaust valves position (both closed) in relation to the piston (just a tick past the topmost position of piston travel, when it starts to drop again). I am using a breaker bar to manually turn the crank to get the pistons to TDC.

Has anyone ever used the US General tester and experienced similar results? I want to get accurate leakdown numbers before throwing this motor into the car, but again, I question the accuracy of this tester.

US General Model number 94190

Fixer · 12:06 PM

Hey Yellowbird, I would start by saying; been there, and once it was my tester that was bad. Different brand.

Ideally you should do this test with a warm motor, all plugs in but the cylinder at TDC as you test.

I know this isn't an option for you and those numbers sound bad.

But if they all are consistently bad as you said (re cyl 5-8)

that would point to the tester being inaccurate.

Yellowb1rd · 02-09-2014, 12:56 PM

Agreed, fixer. It would be much better to do this on a warm motor, but that is definitely not an option. Any recommendations on a LD tester that has a reputation for being accurate? This is definitely holding up the progress.....

Fixer · 02-09-2014, 01:03 PM

Yellowbird,
i have a Matco brand and have had no issues with it.
hope you can return the one you have. -Matt

Danglerb · 02-10-2014, 04:02 PM

Start with a google for Harbor Freight "leak down" and see what you find. I recall some issues, but not what or how resolved.

Pete R · Pete R's Garage

Maybe the Chinese child that assembled the leak down unit had nap time in the middle of the assembly and forget something.

Crumpler · Crumpler's Garage

:d

dtw · 02-12-2014, 06:07 PM

I've never gotten good, repeatable leakdown results on a cold motor. Compression test, yes; leakdown test; no.

Yellowb1rd · 03-16-2014, 11:47 AM

Hey guys,

I ran the tests a few weeks ago after getting my new and MUCH more accurate LongAcre leakdown tester, which actually uses much higher inlet pressure than the US General tester. Perhaps others have had better results with the US General, but I would not recommend purchasing one. Spend the extra forty or fifty bucks and get a more reliable unit.

These numbers are about as accurate as I'm going to get with a cold engine that hasn't run in a car for an undetermined amount of time.
#1 - 7%
#2 - 11%
#3 - 9%
#4 - 9%

#5 - 11%
#6 - 15%
#7 - 14%
#8 - 5-6% ( test that one three times)

I will run the tests after the motor is placed in the car, and warm.