Leak-Down Test

[Michelle]

What's "ideal" or "normal" for a leak-down test on a V6 SHO?

And while we're at it, compression test?

Obviously comparing to each other is necessary, but just trying to find some numbers for these 3.0L. I'm not running stock pistons (have forged ones in there).

Much appreciated!

 

[St Louis SHO]

What do you have number wise?

anything over 30% leakdown is an issue for sure, and compression should be at least 150.

 

[Michelle]

I did the front three tonight and they were between 10-12%. Back three and compression test will be tomorrow after work.

 

[St Louis SHO]

Thats fine, so far... I'd run with it.

 

[Michelle]

I'd run it too if it weren't for the oil spraying out. Still getting some type of crankcase pressure. I still think it's coming from the base of the dipstick tube, but didn't take it off yet and replace the gasket. I'm still getting some type of pressure though to cause it to "spray" so much and drip.

Checking leak-down and compression for worst-case-scenario. ):

 

[SHOtime2511]

I've done copression tests on 2 SHO engines,both were strong runners and had 180/185+ across the board.

 

[RonPorter]

As with any compression test, you are looking for a low variance among all the cylinders. Any one cylinder way off the others can be a problem.

Blower/turbos will put more pressure into the crankcase, pistoin rings are not perfect sealing devices. Even if you seal up the dipstick tube, the issue is still there.

 

[Michelle]

Leak-down Test:

12% 10% 14%
12% 10% 12%

Compression Test 1:

190 190 190
180 180 178

Compression Test 2:

190 188 190
175 180 175


Thoughts?

 

[St Louis SHO]

Do what I said...

 

[Michelle]

Working on it! The bolts are off the dipstick tube and the bolts on manifold are soaked with penetrating oil so they don't break on me overnight.

 

[91PDXmocha]

Those #'s sound healthy for a 3.0 . Sounds like you on the right path . Double check all your pcv system and seal the dipstick.

 

[zak]

128 K mile 3.0, I am the original owner, oil changes every 3-4 K miles using semi-synthetic (Valvoline) or fully synthetic (SL rated Mobil 1 Hi Mileage) oil typically with the oversized Mobil 1 filter.

All readings taken hot and with the crossover tube removed from the intake. Compression done first, 80 feet above sea level. Input pressure on OTC leakdown tester (off Amazon) using input pressures between 95 and 100 psi. This tester is believed to have the FAA certified 0.04 inch orifice.

Cylinders
1-2-4
4-5-6

Compression
220-220-NA
205-217-210
max variance 7%

Leakdown in percent.

2-1-NA
6-2-3