What kind of leakdown percentage can be expected from a healthy 951 engine? While I am asking, what is a good compression figure to go by as well?

 

Do you have your own leakdown tester, or would you have the test done at a shop? Any idea of the make/model of the tester?

Any leakdown tester will have an orifice or restriction between the supply side pressure gage and the cylinder pressure gage, to create the pressure drop. The problem is that there is no SAE standard for the size of that restriction, so different gages will/may have different orifice sizes. Which allows for different air flow rates and different pressure drops. Point is, results from one gage will not match results from a different gage on the same engine.

Also, using the same gage on different displacement engines will not yield comparable results. 10% leak on a 2 valve, 75mm piston arrangement is worse than a 10% leak on a 4 valve, 100mm piston arrangement.

I had two separate shops perform leakdown tests on the same motor, and got results that varied by 35% - the results were worthless. So, bought my own gage some years ago to do my own testing. I typically see results less than 5% leak on ok condition 951 motors, using that gage (brand is Longacre). But as I mention above, that is specific to that gage and the 2.5, 8v engine.

With compression numbers, you mostly want to look for variation between cylinders. I have seen results range from the 120s to about 150 psi on a 951 engine, depending on the day and test conditions, temp, battery power, etc. If you get something like 131, 134, 130, 133 - that would be good. Something like 148, 145, 129, 147 would show that #3 has a problem.

 

just had all this done to my car. Leakdown was between 8-10% but compression on number three was 115psi and 140 on the other three. Found the head gasket was starting to go on number 3 but no smoke or oil/water mixture.

 

My "new" engine is 10% 10% 8% 7%

It's been so long since driving it I'm not sure if I should pull the head and play around or not..

 

My only suggestion is make sure your engine is up to temp before you do any testing.

 

Compression was 131 134 130 and 135. Leakdown was between 3 and 5 percent. So I guess that means the head gasket valves and rings are ok.

 

Yup, also remember the comression tester is an absolute gauge, so the comp numbers will vary with the weather (barometer)... 130 at sea level and 130 in Denver, CO are 2 totally different results... but neither really mean much by themselves...

leakdown of less than 10%, with less than 10% variation between cylinders is fine.. IIRC 5% leakdown is the spec limit for a new motor, but I could be wrong..

When my 951 engine came apart I was seeing 9% variation between cylinders, with 15% leakdown, all 4 oil rings were fubar, and the #3 and #4 compression rings were showing signs of impending death... bores looked pristene, but #3 and 4 were out of round (not tapered, just out of round).. engine has since been torn down, bores replated, rebored and are pristene and round again... hope to be putting engine together and into car in the not too distant future!

Your numbers look fine, shut up and drive!

 

Other thing to keep in mind when doing a compression test is to hold the throttle open when cranking.

 

So, my headgasket appears to be ok, and the oil cooler seals were replaced just a few hundred miles ago, so why am I getting oil in my coolant?

 

Oil in the coolant is most commonly from failing seals in the oil filter housing.

A good leakdown does not mean you do not have a small HG leak. 100psi for the test is 10x less than combustion pressures. An HG leak would have to be large for it to show during a leakdown, and there would be other obvious symptoms of that.

 

all my plugs are the same color. I am not loosing coolant. My overflow tank does not show pressure, even when it is hot I can take the cap off and there is no pressure, no foam, no bubbles, just oil.

 

Sidebar:

My HG failed, at 15PSI on the coolant, it was leaking coolant into 3 combustion chambers... but wasn't pressurizing the coolant while running, and was running very well, only pressure tested the coolant system due to the occasional "smell" of coolant in the exhaust... not every HG failure displays itself the same way..

 

My only point was that you can not rely on leakdown test results to discount the possibility of a small HG cylinder leak - it is an inconclusive test for that. And especially if you are looking for a water jacket to oil passage leak - that will absolutely not show up in a leakdown test.

If the oil seals are good/new, then oil in the coolant would most likely be coming from a HG jacket leak. There could be a crack in the block or or head (uncommon w/ the 8v heads) or maybe something failing in the turbo center housing to mix oil in with the coolant - but all of those would be very unusual.

How old is the HG?

 

hg is a few thousand miles old. No older than 10K I think. I have ALOT of oil leakage in my intake pipes from the turbo.

 

has anyone ever actually seen a turbo housing crack and mix oil and coolant or is this all theory?