nine9six

LAUGHING OUT LOUD!!!

Point well made regarding any tech who performs a leakdown with no inclination to apprise the customer of where the leak is coming from.

Especially considering the time and expense for performing said leakdown...

race911

I'm testier than normal this week after hearing of a perfect ~40K mi. 4S that has had its engine mangled by a "reputable" shop for an smog-fail SAI top end +......a job which should be a slam dunk for even 50% of us here.

911CabSteve

back in 2006, the my 1996 993 C4S I had JUST purchased had about 15% leakage from one cylinder and Andial said they thought it was carbon build up (like Steve W alludes to in this thread). Andial did a solvent flush of the head/valves and I drove it for years with no issues. The engine just dyno'd last year at 224 HP.. For an engine with 85K on it, I was happy with that result.

Steve Weiner-Rennsport Systems

Precisely!

A properly done leakdown test performed by competent personnel shows exactly where any observed leakage is coming from. While some valve issues are serious (such as valves wobbling all over the seats caused by worn or poorly-fitted guides), many problems are due to heavy hard carbon buildups which can be fixed by a treatment or two of the proper chemicals.

We used to have a device called a Motorvac which did a pretty decent job of loosening such deposits, followed by an "Italian Tune-up" to get them out of the combustion chambers. This resulted in restoring the lost compression caused by leaky valves and enabling a car to pass smog and remain OBD-II compliant. It sure saved a lot of customers from having unnecessary (and expensive) repairs.

JMHO, but I would not want to make a purchasing decision based on faulty and/or incomplete information, given the potential consequences.

600RR

I am looking at a 993 with 25,000 miles. Leak-down is no more than 3% on any cylinder, BUT the compression numbers are 195-200-205-185-195-200. I understand that one wants no more than +/- 5%, and that the absolute numbers are less important than the variance.

Question. Does the +/- 5% imply a max of 10% from high to low? Or is it that the low should not be anymore than 5% from the high?

Should know this but I don't.

Appreciate any input. Thx.

vincer77

^^I think that the leakdown figures are a better representation of the engine condition than compression. Looks like a good one to me.

Mike J

That is a bit of a range - I would take the maximum variance spread over the average - so that would be 20 /197 ~ 10%. That is OK, but its right on the boundary. Given the really good leak down values, it sure sounds like a good engine that has a bit of piston/piston variance, or it was done with a not-to-accurate compression gauge, or there was some other variance involved (like the battery was run down). It's hard to tell sometimes unless you do the work yourself -

Did the mechanic also comment on other things, like plug condition, etc? This is often impossible to get from a seller, any idea of the oil consumption?

Sound like a good one though.

Cheers,

Mike

billqj

IMHO, Steve Weiner's answers are the right ones. Need to find out what is leaking, then go from there.

Bill

Mike J

Darn, the rest of us hate being wrong.

Not so easy with a good leak-down result since nothing for that test is "leaking", so you will not be able to distinguish between valve and rings for instance.

On a compression, there are no indicators on what is possibly at fault, just that the compression is either good or not. The leak down is usually the diagnostic tool used after a poor compression result used to isolate the possible trouble spot - but in this case it can't be used.

I would say the compression results are not bad, they are just not a good as should have been expected given the leakdown. However, we do not know the conditions of the compression, or the technique, or the specific tools used, or their accuracy, or the battery level in the car, or ... well you get my drift.

Cheers,

Mike