Update at bottom of page.

Here's the results (9.0:1 pistons)

Cyl #....Compression.....Leak down
1............200...................27%
2............200...................23% 2nd reading: 20%
3............205...................25%
4............202...................27%

State the motor was in during leak down test: normal operating temp, oil fill cap removed, rad cap removed, pcv valve removed, dipstick removed, all spark plugs removed.

During the leak down test I could hear a very slight leak from the dipstick tube. I couldn't FEEL the air escaping from the tube but could hear the difference in sound when I placed and removed my finger from the tube. There were no audible leaks nor feeling of leaks from the rad, or adjacent cylinders.

I conducted the tests because I thought I had a bad head gasket because my oil looks milky. There's some milky residue inside the oil filler cap and in the catch can.

So whats up with my motor? Is it possible to have such high leak down numbers with good looking compression numbers?

This is the leak down tester I have. All my results were in the green zone. ???
http://store.summitracing.com/...w=sku


Modified by Mikey3000 at 8:35 PM 12/11/2007

 

did you 0 out the laek tester for the air pressure supplied to it? the leak is high but compression is good for the compression level, you sure you don't have higher compression than 9-1? if it looks milky it may be a slight crack in the block or slightly blown head gasket only leaking through under boost. my head gasket was leaking combustion gas into my coolent only under boost. normal driving couldn't tell. i replaced with an oem good so far, was running a cometic w/arp's. see if adding a little oil through the spark plug hole helps.

 

I had a similar problem however i had 70%+ leakdown but decent compression. My rings were gapped crazy big and top rings seized to the piston as well as a few bent valves but the car ran perfect and didnt smoke. Re-rung it and new valves and 0% leakdown so go figure.

 

Also make sure when you are doing the leakdown test that the valves are in fact closed.

 

compression test numbers dont mean squat half the time. I've seen a number of cars with bad ringlands or something that tested perfect.

 

but isn't it also strange that my leak down figures are very close to one another?

 

thats why i asked if you calibrated the testor for the air pressure.

 

Not really, those aren't all that bad, just make sure your crankcase is well ventilated, but milky oil and oily residue on the radiator cap would make me pull the head anyway, you've got water mixing with your oil somewhere and it's usually from the head gasket. Then when it's apart you can check how the valves are seating, the head and deck for warpage, and check the cylinder walls for scoring, and get a fresh head gasket and a new set of studs on it. Pulling the head is easy enough that I'd definitely do it if I suspected something was wrong.

 

i'm pulling the head soon to get head work done so it will be getting freshened up. i don't have oil on the rad cap but the milky stuff is bothering me. i think i have it well ventilated, the catch can blows oil everywhere when under load.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosstboy &raquo;</TD></TR><TR><TD CLASS="quote">thats why i asked if you calibrated the testor for the air pressure.</TD></TR></TABLE>

how would i do this? when i hooked up my air source to the regulator on the tester, i turned the **** so the gauge on the right read in the center of "SET" like the directions said. with the right gauge at that setting the left gauge read about 100 psi.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosstboy &raquo;</TD></TR><TR><TD CLASS="quote">thats why i asked if you calibrated the testor for the air pressure.</TD></TR></TABLE>

And what he said, if you just put 100 PSI on it and cap the end, do both gauges read the same PSI? My Summit tester is 2 PSI off, so I have to take that into account. Mine also came -w- a leaky POS line that threads into the spark plug hole, and it wouldn't read right until I replaced it.

 

Never mind, your tester doesn't have two guages that read in PSI.

Did you try pouring some oil in the cylinders to see if your leakdown % goes down?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rmcdaniels &raquo;</TD></TR><TR><TD CLASS="quote">Never mind, your tester doesn't have two guages that read in PSI.

Did you try pouring some oil in the cylinders to see if your leakdown % goes down?</TD></TR></TABLE>

No I didn't. You think I should give that a try?

 

That will tell you if it's leaking past the rings. Leakdown should go to 0% for a brief time until it pushes the oil past the rings.

Leakdown numbers will vary with the tester and the build. Motors that are built for lots of boost with large ring gaps may tend to have higher leakdown numbers, but they still run fine. I'd be more worried about the water in the oil than the leakdown numbers.

 

it could possibly help the rings seal better so if you still leakdown higher its in the head/ hg.

do you have aftermarket cams/gears.

im in the same position you are:
my compression is 190-195 on a 9:1 motor
leakdown is #1- 20%
#2 - 18%
#3 - 15%
#4 - 20%

my car is mixing coolant/oil like ive never seen. the whole bottom of my valvecover is chunky white ****. im 99% sure that my head surface warped a little and my car is mixing along the headgasket surface. you might have the same problem

 

i have stock cams and aem adjustable cam gears. i'm thinking maybe intake valves were open because i didn't take too much time to make sure each piston was at TDC using the crank pulley dot, i just estimated using the cam gear marks.

the question is, how many degrees after TDC do my valves begin to open? how much error do i have before and after TDC where my valves are fully closed? I would think the exhaust valves are closed at least 15 degrees BTDC and the intake at least 10 ATDC. i guess i'll check out my helms and maybe retry it tonight.

 

Or you can just pull the valvecover off real quick to visually confirm the valves are closed.

 

I just put something long and thin (I use a long bamboo skewer) in my spark plug hole, resting on top of the piston. Then I can see exactly where TDC is.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Boner_Ben &raquo;</TD></TR><TR><TD CLASS="quote">Or you can just pull the valvecover off real quick to visually confirm the valves are closed. </TD></TR></TABLE>

too much work

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rmcdaniels &raquo;</TD></TR><TR><TD CLASS="quote">I just put something long and thin (I use a long bamboo skewer) in my spark plug hole, resting on top of the piston. Then I can see exactly where TDC is.</TD></TR></TABLE>

i like this idea!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rmcdaniels &raquo;</TD></TR><TR><TD CLASS="quote">And what he said, if you just put 100 PSI on it and cap the end, do both gauges read the same PSI? My Summit tester is 2 PSI off, so I have to take that into account. Mine also came -w- a leaky POS line that threads into the spark plug hole, and it wouldn't read right until I replaced it.</TD></TR></TABLE>
I've had seriously bad luck with miscalibrated leakdown testers. 3 that i've used would read only about 30psi on the input gauge while the output read would be at 0% leakdown. If i turned the input any higher the output needle would peg all the way around onto the stopper pin past the set area . Two of them were cheapy harbor freight testers(brand new out of box), and one was a mac tools. Finally i used a 4th one that was snap on and it worked flawlessly.

 

I retested this evening and here is what I got...

Again the engine was at normal operating temperature.

Cyl.....Leak down.......Leak down with oil
1.........21%..................21%
2.........23%..................20%
3.........21%..................20%
4.........19%..................20%

I think the reason all the readings are lower is because the engine was warmer than it was yesterday. Yesterday I did the comp. test 1st so it had all that time to cool down.

Something I also notice was smoke or steam coming from the catch can breather when I was pumping air in the cylinders. I guess that makes sense though with the readings I'm getting. It looks like I have a pretty big gap on my rings.

 

thats weird that its so even across, yet still high leakdown.

 

20% is nothing to worry about, turn the boost up

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SOHC_MShue &raquo;</TD></TR><TR><TD CLASS="quote">thats weird that its so even across, yet still high leakdown.</TD></TR></TABLE>

i know!

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by T4eg &raquo;</TD></TR><TR><TD CLASS="quote">20% is nothing to worry about, turn the boost up </TD></TR></TABLE>

thats what i'm talkin bout!