Compression test number - Good or not?

[turboman38]

Sounds like a quart for every 1000 to 1500 is a normal occurrence. That makes me feel a little better. My car was burning a quart every 2000 to 2500 miles but it recently increased in the last two months to a quart about every 1000 miles. I am just trying to figure out why it changed.

[ehsnils]

A valve seal that has gone bad or the pcv. Can of course be the turbo that's getting tired too.

 

But the best indicator can be the color of the spark plugs. that can tell you if it's a general problem or if it's located at a single cylinder. A single plug that's somewhat darker is an indication of a single cylinder issue.

 

Otherwise you can check the intake before and after turbo for oil residue. It's not conclusive, but can give a lead. You may need to clean the intake before to make sure that you see "feesh" oil there.

 

If you have oil residue already before the turbo it's something with the pcv, but if it's after turbo it's probably the turbo.

 

Also check for external leaks.

 

A different brand or viscosity of oil can also be the cause

[turboman38]

spark plugs were all the same color and in excellent shape.

[ehsnils]

That means that either the leak is not related to a specific cylinder or it's so small that the coloring of the spark plug is not noticeable. So look for leaks that are common for all cylinders. Like the PCV. Just check all steps of the intake and see where oil starts to appear. You may have to clean out the intake parts first at key positions to avoid confusion by old oil traces.

 

Of course - the problem may also be the exhaust side of the turbo in which case no oil enters the engine.

[elaforest]

I've rad somewhere(don't remember) but the compression may be different depending where you are situated(sea level) is this true?

[Max Capacity]

I've rad somewhere(don't remember) but the compression may be different depending where you are situated(sea level) is this true?

 

 

That may be true, but the difference is so minor. I doubt your $15.00 gauge would show the difference. You'd have to be at 20,000 ft to make a big difference. I do testing at work where we use PSIG and PSIA gauges for different leak tests. It's not a factor on a car engine.

[elaforest]

So what would be considered a "normal" compression for a 3-5yr old car. I know about the 7psi difference and that under 7 its good.

Did mine and had 145-140-145-140. Engine warm, did oil change at the same time.

Cobb says a healthy engine: 150-170 psi per cylinder, but from what I see most people are below 150psi

[ehsnils]

And almost everyone uses crap meters - don't consider the values to be PSI, count it as number of chickens on a string or something.

 

The cheap meters are usually good enough to allow you to compare the cylinders with each other so as long as you have numbers that are close to each other you are fine.

[sqc151]

Don't know which ones are 1,2,3 and 4 so here are my numbers by location.

 

Driver rear - 126 - 127 - 4

Driver front - 130 - 2

Passenger rear - 137 - 3

Passenger front - 130 - 1

[IanB]

And almost everyone uses crap meters - don't consider the values to be PSI, count it as number of chickens on a string or something.

 

The cheap meters are usually good enough to allow you to compare the cylinders with each other so as long as you have numbers that are close to each other you are fine.

 

Fully agreed, worry less about the actual numbers, and more on what the numbers mean. The gauges most people use are not accurate, but they are consistent, and work just fine if you know how to interpret the results.

[Morals]

Impressive, I feel like I just got a quick weekender college course on shit to look for. Digging it.

[BOB007]

About to purchase and got readings of 100, 110, 115, 120

This ok to buy?

[AZZMAN]

Nope. They should be around 135-140. AND they should not vary much more than 5-8.

[BarManBean]

Yup, azzman is correct, don't buy that car. They can even be a bit lower than 135, but they should be consistent.

[Soarer]

FSM says:

 

Compression

A: INSPECTION

CAUTION:

After warming-up, engine becomes very hot. Be careful not to burn yourself during measure- ment.

1) After warming-up the engine, turn the ignition switch to OFF.

2) Make sure that the battery is fully charged.

3) Release the fuel pressure.

<Ref. to FU(H4SO)-39, RELEASING OF FUEL PRESSURE, PROCEDURE, Fuel.>

4) Remove all the spark plugs. <Ref. to IG(H4SO)- 5, REMOVAL, Spark Plug.>

5) Fully open the throttle valve.

6) Check the starter motor for satisfactory perfor- mance and operation.

7) Hold the compression gauge tight against the spark plug hole.

NOTE:

When using a screw-in type compression gauge, the screw (put into cylinder head spark plug hole) should be less than 18 mm (0.71 in) long.

8) Crank the engine by means of the starter motor, and read the maximum value on the gauge when the pointer is steady.

ME-00192

9) Perform at least two measurements per cylinder, and make sure that the values are correct.

Compression (350 rpm and fully open throttle): Standard:

1,020 — 1,275 kPa (10.4 — 13.0 kgf/cm2 ,

148 — 185 psi)

Difference between cylinders:

49 kPa (0.5 kgf/cm2, 7 psi) or less

[BarManBean]

7 months later...on a 6 year old thread...