Steve Weiner-Rennsport Systems

Recently, I’ve received an increasing number of questions regarding leakdown test results and how to interpret them. In almost all cases, the technician failed to take a moment to note WHERE any observed leakage came from, rendering the test results almost useless. Simply noting the numbers on the gauge lacks the necessary context to make the procedure valuable.

The real value of leakdown testing is to give the owner a “snapshot” about general engine health so without noting the source of any observed leakage, one really doesn’t know anything useful about the health of the engine.

My advice would be to ask the technician to not only record the values from the leakdown gauge, but listen to the air cleaner entrance, exhausts, and oil tank filler to note whether any leakage may be coming from the intake valves, exhaust valves, or past the rings, respectively.

Remember, you are the one paying the bill and you are both entitled to and deserve the full value of such engine diagnostics.

Goughary

Thank you Steve.

Flat6 Innovations

Too many techs simply do not understand the principles of the test... They often times perform the tests at crank positions where valves may be cracked open, too... Thats a total waste of effort!

ras62

Many of these leakdown gauges are marked green/yellow/red with the green section running from 10%-40% yet a reading of 30-40% would normally indicate problems. Why the apparent discrepancy?

Steve Weiner-Rennsport Systems

That's a good question since anything over 20% is major cause for concern.

I use a Snap-On MT324 and it has no such markings on the face (thank God).

ras62

I think the answer lies in the fact that these leak down testers can be used across a wide variety of engine sizes. A small leak on a large capacity engine would look the same as a big leak on a small capacity engine i.e. the leakdown figures would be the same for both engines because of the way the tester works as its simply an in line flow restrictor.
The readings are measured as % and as such have no absolute value e.g cc/min, the important thing is repeatability and knowing what results mean on a particular engine type....hence the rather misleading coloured sections and why different types of testers will record different results on the same engine.
Interpretation of the results lies very much down to the engineers own experiences in doing similar tests with that particular tester.

Flat6 Innovations

A leak, is a leak, no matter the displacement of the engine. The tester is just there to indicate the leak, no matter how large, or small it may be.

It's up to the person doing the test to interpret the data, and pay attention to where the source of the leak is. Then, look deeper.

What impacts the percentages of leakage more than anything, is test pressure from the compressed air source. The tests are 1:1 when test pressure is at 100 PSI, any other test pressure, above, or below this requires some correction.

I always perform both leak down and compression tests when evaluating an engine. Often times the leak down tells me more about where the issue exists, but the compression test tells me more about the severity of the issue.

Mark Brook

Steve,

My leakdown measured the following;-
1=0%
2=20%
3=20%
4=10%
5=20%
6=20%

All rings........... My Indy tells me that 20% is still 'in tolerance'. Both the top and bottom were refreshed about 45k miles ago with new rings etc, but he puts the leakage down to the engine builder not replacing the misshapen barrels.

What do you think?

Mark 90 C2?

Flat6 Innovations

Was the engine warm or cold? Makes a big difference.

20% is well outside of my allowable, if I found 20% I'd verify the valve adjustment and re- test, hoping for a better outcome.

Not replacing/ re- plating cylinders could easily lead to this. Why people do not do things completely, never ceases to amaze me.

Mark Brook

Engine was hot and the valves were freshly set

Flat6 Innovations

If all the leakage was past the rings, then I'd say that cylinder ovality and taper are playing the role of the culprit.

Mark Brook

I should add though, that the Indy in question showed me on his gauge, and 20% is still in the 'green' section on the dial, meaning 'within factory acceptable tolerance'.

Mark Brook

Yeah, that was his diagnosis. It pulls like a train, so if there are some bhp that are escaping, I certainly don't notice them........

mickfluff

I keep hearing compression most important that one can get 20% leak down numbers but if compression strong then less a concern. This just what I have read... heard many do compression only on a PPI (I always do both) .....

Mark above, that gauge (i have seen it) states 30% still acceptable and think up to even 40% still in "the green".... so caution on the gauge.

Flat6 Innovations

Anything is in tolerance if you're level of acceptance is open enough.