Leak down %?

I have searched and looked at the archives (when they were up ) regarding leakdown numbers, and am still confused. Just saw another thread where someone turned down a 355 due to leak down % up to 12 or so...

I brought this issue up at lenght with LFSC when I got my testarossa. I asked what a normal leakdown % was. On a ferrari like a 308/or testarossa up to 12/13% is normal, 18-20% likely means an abnormality. I pointed out that most folks on this board quote 5% or less. The folks at LFSC seemed genuinely shocked - said these cars didn't post numbers that good when they were NEW. Now this may not apply to the 355's and later, maybe the machining was improved since then.

I talked to my mechanic who works on american cars/japanese cars and the like. He told me that 20-30% and you have issue's. 15% and less is likely not an issue. Also said this isn't an exact science - three different mechanics will get 3 different readings. Is it a garage queen, with valve buildup? How warm was the motor? When were the valves last adjusted? Etc.

I asked LFSC what MOST older cars have as a leakdown %, and they said up to 12/13% is ok, usually gets better with prolonged driving. Very low mileage cars tend to have leakdowns that improve as you hit 20-30k miles. 18-20%, look for problems. How are folks getting 2-3% leakdowns??? New motors aren't even that tight! LFSC also said that very few if any buyers even do a leakdown, especially on the older cars. They do recommend it on the 355's, but most of the cars preceding these are known to have durable valves/seals and it is a non issue...

Any ferrari mechanics want to definitively chime in. LFSC has a great reputation, so I would think they would know.

 

Another quick note: do you guys do it cold, or hot? My understanding is it should be done at normal operating temp - but hardly anyone does it this way. The ferrari mechanics specifically wanted the car cool to do it. I was going to ask the mechanics to testdrive the cars first, and then do it. But 2 seperate mechanics told me that if we testdrive it, we can't do the leakdown the same day...

Seems to me this is more of an issue of getting burned on a hot motor...

There are so many questions on leakdowns that a FAQ would be a good idea on it...

 

Thanks for the reply, rifledriver!

What is a reasonable leakdown on a 308? 348? testarossa?

355's are 5% or less from what you are saying.

How big of a difference is it cold, to hot?

Thankfully, my cars #'s were ok. But everyones definition of a good number seems to vary, and I wonder if this is model dependent...

Did the 308/testarossa's have nikasil?

When I bought my car, the leakdown was done cold, and the numbers were 3%-10%. LFSC said these were "excellent" numbers for a testarossa. "Much better than average." I got this in WRITING from both the salesman AND the head of the shop. I had an independent mechanic look at the numbers, and he concurred with the opinion above...All said it would be slighter better if hot, and with some use (car has 10k miles)...

I really wonder how we have so many opinions on this.

 

Just an interesting update. I was looking at the BMW boards (my other toy), and they also of course do leakdowns. Of interest, BMW spec their motors to have a 5-8% leakdown NEW. Recommend replacement at 16% leakdown. Here are some pointers they compiled on their board:

(http://www.e38.org/nikosil.html#matter)

"The leakdown test is a manual test, and the tech who completes it must write the score for each cylinder on the test print-out by hand. Results can vary based on several factors - here is a detailed discussion from the E34 530i/540i mailing list about important leakdown testing variables - ones you might want to discuss w/the tech who is testing your car. If you have the test completed, be sure you retain a copy of all the test documents for your records, and verify that they have the leakdown numbers written in as well. Since the leakdown test is a manual test, it is susceptible to human error. If your results are too good to be true (less than 5% on any cylinder) you should pursue another test, or maybe go to another dealer. Cylinders in a new engine will generally have scores in the 5% to 8% range."

Temperature of the engine, this is very important, if BMW specs it to be at Normal temp, it needs to be at normal temp. If BMW specs cold, it needs to be cold. This will make a HUGE difference, for example, if they spec it to be cold and they test it hot, this will produce much better,(probably passing),results.
Oil viscosity, In my opinion, not very important, most all of the oil will have drained out of the cylinders by the time the test is performed. Unless done HOT, then thick oil may make a marginal difference.
Cylinder at top dead center, This will bring ENORMOUS differences in the results. In aircraft, they turn the engine back and forth to get the best results, while the test is being performed. I have seen a failing cylinder suddenly "pop" into a passing cylinder, just by rotating the engine back and forth to seat the rings and/or valves. I think this is a good & acceptable thing to do, otherwise you are just looking at one spot, that may not even be perfectly TDC.
Calibration of the leakdown tester, This is also very important. BMW should have a "Master orifice tool" that the mechanics should use to verify that their pressure regulator and gauges are reading correctly, prior to the test.
Seal of leakdown tester hose to the cylinder, Although this is important, I can't imagine a mechanic allowing that connection to be anything but perfectly air-tight.
Cylinder ring alignment at the time of the test, This is the #1 biggest reason that you could pass one day with flying colors, and fail miserably two weeks later, or vice versa. For that reason alone, I can't believe that BMW didn't require at least two tests. I suppose that is why they created the idle quality screening first. I have my aircraft tested at every oil change, because once a year during the annual inspection does not tell you very much.


Food for thought. Rennlist quotes 1-2% as normal...

 

Subura forums, wrx faq:

2% or less-race engine quality ring seal
5-10%-good engine
under 20% Reasonable. You shouldn't see any problems
over 20%- there is some wear, or leakage



Gets interesting, doesn't it???

If bmw quotes 5-8% as NEW engine leakdown, how is the ferrari assumed to achieve lower numbers? Seems that the germans and japanese maufacturers would build to at least the same tolerances. This is somewhat anecdotal, but interesting none the less...

 

From a volvo board:

"Your engine's cylinders appear to be within specification. This would suggest that the rings, bores and valve seats are in good condition. To be really sure, you may wish to have a leak-down test performed. This involves filling each cylinder with compressed air of a known pressure and noting the leakage that occurs. 5% leakage is excellent, 10% is good and 15% or more indicates wear of some kind. The leakdown test will pin-point exactly where."

 

Alright, can you tell I'm extremely bored and tired at work...on call...can't go home...sigh...

I'm sure if I looked hard enough I could find some site somewhere that said a 50% leakdown was normal ( ).

But I did find it interesting that multiple sites stated that agressive driving/techron/ frequently improve leakdown %. And testing a motor cold may yeild a 2-3% worse leakdown number...

Maybe the difference between numbers quoted on this site have more to do with the operating temp of the motor when checked...

I would assume that on a 12 cylinder motor this test takes some time (anyone want to chime in on the time it takes???). Wouldn't the temp of the motor be very different from cylinder #1 to #12 (LFSC billed 2-3 hours)?

Oh well, micellaneous ramblings from a sleep deprived fool...