northern33

Hi All,

I'm new to the forum but wanted to ask if anyone knew the ideal cylinder compression PSI in a 3UZ-fe in my LS430 from 2001. The car has done 186884kms and is in immaculate condition. I got a comp test done on it today and my results were...

#1 115PSi
#2 125PSi
#3 125 PSi
#4 120PSi
#5 120PSi
#6 125PSi
#7 120PSI
#8 130PSi

There are no noticeable outliers in terms of one cylinder being drastically different to the others but I just wanted to get a second opinion on what this means? Is the motor no good and how much longer can I expect it to last given these results (ballpark figure).

Apologies in advance if this question is a bit basic or I have missed an existing forum with what I'm looking for. As I said, I'm new and any pointers in the right direction or useful info is much appreciated.

Thanks

911LE

Those numbers look fine. They are close to each other. There are many things that can affect overall numbers such as:
Were all of the spark plugs removed or did you do one at a time?
Was the engine cold or at operating temp?
Was the battery fully charged?
Is the starter operating properly?
Were the fuel injectors disabled for the test?
The engines on these cars are very robust and reliable.

rkw77080

Here's a page taken from the 2003 (should be the same as 2001) LS430 repair manual on compression testing.

northern33

Thanks for the manual. But does that mean that the whole engine isn't compressing enough? Or is this something that just happens over time and the engine should be good for a while longer?

Thanks

911LE

Did you follow all the steps in the manual? The most important being that all the spark plugs must be removed. The goal of all of those steps is to get the starter spinning the engine as fast as possible. Lower cranking rpms will give lower readings. The real indication of wear is if the reading increases significantly with the addition of a little oil in the cylinder. This indicates worn rings.

rkw77080

As 911LE pointed out, the compression test must be performed properly for your measurements to be meaningful. The repair manual specified a number of steps such as warm up engine, disconnect injectors, crank engine to at least 250rpm, etc. Assuming that all these steps were followed, then your engine is in poor repair. Namely, none of the cylinders met the minimum 142 PSI requirement, and some cylinders exceeded the 14 PSI difference (which can create an uneven twist to the crank shaft).

The repair manual suggests to pour a small amount of motor oil into the cylinder before repeating the test. If compression improves, then you piston rings or the cylinder bore are worn/damage. This condition can deteriorate rapidly since gasoline will leak into the motor oil diminishing its ability to lubricate, and further wears down the piston rings and cylinder bore.

On the other hand if compression remains low, then, some or all of your valves are either sticking, or leaking, or possibly a sign of a bad head gasket. In this case, you will likely to have incomplete combustion in the cylinder and experience power loss. Un-burned gasoline flows out to the exhaust and can potentially cause damage to your catalytic converter, not to mention the poor MPG performance.

911LE

Is there a reason you did a compression test in the first place? Is the engine low on power, making off noises, burning oil, etc? If everything is normal I'm guessing you have nothing wrong and those lower numbers are just messing with you. If you go looking for problems you will always find them.

northern33

Well yeah, I only did the comp test because I bought the car second hand about a week ago and as it needs some other parts replaced (bushings etc...) I wanted to check the engine was all good before I spent any money on the car. The engine runs smoothly, starts first time every time, plenty of power, no burning oil etc.

I'm not so mechanically inclined so I actually got my local auto shop to do the compression test so I would assume that they probably didn't follow the exact procedure as outlined in the Lexus manual uploaded by rkw77080 which I guess may be the reason pressure was a little lower than specified in the manual?

911LE

Based on what you said I would say there is nothing wrong with your engine. I'm guessing the shop cut a few corners and that accounted for the lower readings. Change the oil every 5k, check the coolant level when you fill it up with gas, and do a timing belt every 90k and the engine should be the last part of the car to worry about. Just don't overheat it (ask me how I know)!

northern33

Thanks for the advice!

I feel like there's a story there?

911LE

https://www.clublexus.com/forums/ls-3rd-gen-2001-2006/812606-blown-head-gasket.html
Bought the car this way.