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Discussion Starter · #1 · (Edited)
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I just purchased this '98 540i with 138K miles on it. The previous owner said it may need to have the head gasket replaced and a valve job. I didn't ask him why he thought that, but I have sent him an ol' email to check.

I changed the oil and did not notice any water in the oil and there is no smoke coming from the tailpipes. I am pretty sure the cats are bad though as they are rattling. I do not notice any performance loss, but then again, I haven't driven another 540...

I decided to do a compression test on it...and as I still haven't purchased a bentley yet (coming...) I don't know which cylinders are which, but here is what I got.

Passenger side, from Front to rear:
220, 220, 220, 235

Drivers Side from Front to rear:
225, 225, 230, 235

How do those numbers look?? What should they be at? It seems a little wierd to me to have a variation as much as that.

Any insight would be greatly appreciated!

Thanks!

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ben99 said:
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I just purchased this '98 540i with 138K miles on it. The owner said it may need to have the head gasket replaced and a valve job. I didn't ask him why he thought that, but I have sent him an ol' email to check.

I changed the oil and did not notice any water in the oil and there is no smoke coming from the tailpipes. I am pretty sure the cats are bad though as they are rattling. I do not notice any performance loss, but then again, I haven't driven another 540...

I decided to do a compression test on it...and as I still haven't purchased a bentley yet (coming...) I don't know which cylinders are which, but here is what I got.

Passenger side, from Front to rear:
220, 220, 220, 235

Drivers Side from Front to rear:
225, 225, 230, 235

How do those numbers look?? What should they be at? It seems a little wierd to me to have a variation as much as that.

Any insight would be greatly appreciated!

Thanks!

Pics for views!

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Those numbers seem fine however, I recommend doing a cylinder leakdown test as well.
 

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No, that isn't the same. The compression gauge has a check valve that prevents the needle from dropping, even after you have removed it from the engine. (at least that is how my compression gauge works)

Garrick
 

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ben99 said:
What would be the difference? When I did the compression check, I let it sit for about 30 seconds and the needles didn't drop. Is that the same?
When you do a normal compression test, you are checking cylinder sealing. You do not leave the needle sitting for 30 seconds. That doesn't do anything except giving you the result of the engine compression test. You can remove the fitting from the spark plug hole and the needle will stay there till you press the release valve button.

Did you perform the compression test with the throttle body open? Engine temp also has an affect and should be done when warm or maybe a bit hotter.

After you do a compression test, you do a cylinder leak down. If you have low compression test numbers then you have to find out why is it low and where the leak is. A cylinder leak down applies about 100psi into the cylinder when the piston is at top dead center. The tool will have two gauges..the psi thats going into the cylinder and the other gauge will how much leak there is.

Respectable leakage numbers would be anywhere from 8 to 12 percent with a variation between cylinders of 4 to 5 percent, but it's possible the variation could be as high as 10 percent.

If you have high leakage you have to listen to where the air is escaping.

If you hear it coming from the exhaust its the exhaust valves.
If you hear it coming them the intake manifold or air filter then it's the intake valves
If you hear it coming on top of the valve cover or oil filler cap, then the rings are shot
If you see cooling rising from the expansion tank, then you have a blown headgasket
 

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A cool trick I've learned to determine if you've got a blown head gasket is run the car at idle with the coolant filler cap removed.

Use an emissions test sniffer (exhaust gas analyzer) to sniff the coolant at the radiator. If there's ANY exhaust gases in the coolant, the emissions sniffer will pick them up.
 

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Discussion Starter · #7 ·
Did you perform the compression test with the throttle body open? Engine temp also has an affect and should be done when warm or maybe a bit hotter.
Engine was at operating temperature, but throttle body was not open....

I am not sure if I have the equipment for a leak down test. Is this something I can do from home, or should I just take it to a shop (what would they charge)?
 

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Discussion Starter · #9 ·
BTW, did you replace the intake manifold gaskets when you replaced the rear oil separator plate behind the intake manifold? Sounds like you didn't remove the intake manifold.
I didn't replance any of that...just did the compression test. Basically, I am trying to determine if I need a new headgasket or valve job.

Thank you for all your help!
Ben
 

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ben99 said:
I didn't replance any of that...just did the compression test. Basically, I am trying to determine if I need a new headgasket or valve job.

Thank you for all your help!
Ben
Ben,

If you're not overheating, coolant is being pressurized, or oil is leaking from the side of the cylinder heads, then you do not need a headgasket.

I don't think you even need a valve job too.
 
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