What Should My Compression Be At 30k Miles?

[larry chester]

I have a 2006 IS250 MT6. It has 30,000 miles on it. Over the past 6 months, I have noticed a "rattling" when I start out from a stop. At first I thought that it was knocking in the engine, but wasn't sure. Over the past 5 - 7K miles, I have received a number of warning "check engine" lights, and the error codes showed carbon buildup in the cylinders, resulting in misfiring on two or more of the cylinders.

My dealer told me that I wasn't driving the car hard enough, and this was causing the carbon buildup. They also suggested that I was buying cheap gasoline - but I only use Shell Premium - so that's not the problem. And, this is my second 2006 IS250 MT6, and in 50K miles on my first car, I never had any of these symptoms.

After digging in the service bulletins, the dealer noted that there were two service bulletins that talk about:

1. replacing the camshaft gear system, because it causes rattling when the engine is cold.

2. replace the valve lashing assembly because it was causing the valves to not be "self adjusted" properly.

With those problems, I was concerned about premature wear on my valves. The car has only 30K miles on it, and I expect to drive it till at least 200K. So, while they were doing this work on the car (over 16 hours of labor, and they had to pull the engine to perform those repairs.) I asked them to do a compression test on all of the cylinders, and report to me.

The "new" compression measurement on the engine should be 200 PSI. The mechanic's measurement of my engine came back with each cylinder measuring between 190 and 195 PSI. Now, I am no mechanic, so that is why I am writing this. With a Lexus engine with only 30K miles, shouldn't the compression be more than 190?? If it lost 10 PSI in the first 30K miles, and loses 10 PSI on each 30K miles, when I hit 200K, the engine compression would be about 140 PSI. That is NOT a good number.

So, am I worrying prematurely? Am I making a mountain out of a molehill? Is the compression number fine, and I should just be glad that they put in that service bulletin and move on?

I appreciate any skilled answer.

larry

[bartkat]

I woulnd't worry about it yet. The test could be off that much.

[1990LS400]

So, am I worrying prematurely? Am I making a mountain out of a molehill? Is the compression number fine, and I should just be glad that they put in that service bulletin and move on?

Yes, Yes, and Yes.

The reason that your engine is OK is that there is consistent compression in all six cylinders -- between 190 and 195.

An engine with compression problems most likely is not going to lose compression in all cylinders at the same rate.

I have actually had an engine replaced under warranty due to inconsistent compression -- on a Mercedes, no less. There was substantially more than the 10% acceptable variation in compression among the cylinders so I was surprised that the Mercedes dealer and even Mercedes corporate balked when their own documentation said the compression variation among the cylinders in my engine was unacceptable. I had to show them their own documentation to get the problem fixed.

The dealer representative that told you that you aren't driving your car hard enough is "full of BS". Your IS250 isn't an old racing car with carburators.

You're fine.

[CrunchySkippy]

An engine with compression problems most likely is not going to lose compression in all cylinders at the same rate.

I agree. What would concern me is if one cylinder wasn't consistent with the others.

The difference with your engine showing lower than spec compression might be as easy as the tech not being able to find the exact TDC in each cylinder. Its not an exact science without pulling the heads, inserting a dial indicator, placing a degree wheel on the balancer, replacing the heads and measuring compression. A piston stop is what I would use in my garage, but its not 100% accurate.

[smooth1]

I have a 2006 IS250 MT6. It has 30,000 miles on it. Over the past 6 months, I have noticed a "rattling" when I start out from a stop. At first I thought that it was knocking in the engine, but wasn't sure. Over the past 5 - 7K miles, I have received a number of warning "check engine" lights, and the error codes showed carbon buildup in the cylinders, resulting in misfiring on two or more of the cylinders.

My dealer told me that I wasn't driving the car hard enough, and this was causing the carbon buildup. They also suggested that I was buying cheap gasoline - but I only use Shell Premium - so that's not the problem. And, this is my second 2006 IS250 MT6, and in 50K miles on my first car, I never had any of these symptoms.

After digging in the service bulletins, the dealer noted that there were two service bulletins that talk about:

1. replacing the camshaft gear system, because it causes rattling when the engine is cold.

2. replace the valve lashing assembly because it was causing the valves to not be "self adjusted" properly.

With those problems, I was concerned about premature wear on my valves. The car has only 30K miles on it, and I expect to drive it till at least 200K. So, while they were doing this work on the car (over 16 hours of labor, and they had to pull the engine to perform those repairs.) I asked them to do a compression test on all of the cylinders, and report to me.

The "new" compression measurement on the engine should be 200 PSI. The mechanic's measurement of my engine came back with each cylinder measuring between 190 and 195 PSI. Now, I am no mechanic, so that is why I am writing this. With a Lexus engine with only 30K miles, shouldn't the compression be more than 190?? If it lost 10 PSI in the first 30K miles, and loses 10 PSI on each 30K miles, when I hit 200K, the engine compression would be about 140 PSI. That is NOT a good number.

So, am I worrying prematurely? Am I making a mountain out of a molehill? Is the compression number fine, and I should just be glad that they put in that service bulletin and move on?

I appreciate any skilled answer.

larry

Ok, where to begin.....

First, this 06 IS250 you have now, you must have purchased used correct? I see this is your second 06 IS250? So the carbon build up could be a remnant of the previuos owner yes? And they very well could have used cheap gas. In fact, what the tech is talking about regarding carbon build up so far sounds like an issue that can arise from using 87 octane fuels in a 92 octane system. I don't believe this has anything to do your issue, but it is possible when you also take into consideration your location. Engines in colder regions take longer to heat up in the winter, and can have a bit more carbon build up as a result.

Is carbon build up the problem here? I don't really think so. It sounds to me like the tech was just giving you some good advice regarding that issue for your future information.

So they did a compression test huh? You must be a PIA customer. LOL!! Are you taking this to a dealer?

The weakness of a compression test however is that throttle position, engine temperature, ambient air temperature, and a host of other factors can make the results vary considerably. What's worse, a compression test checks too many engine components at the same time. A poor reading can indicate so many things, it's hard to tell which engine part is at fault without doing a lot of other tests. A leakdown test avoids this difficulty. Air is pumped into the cylinder from an outside source, and the gauge reads the percentage that escapes, which not only eliminates all of the afore-mentioned variables, but as a bonus, makes it a simple matter to pinpoint the source of the leakage by wiggling and rotating engine parts while the test is underway.

For example: Let's say your engine begins to have smoke coming out the tail pipe. You have a shop look at it. Good results from a compression test combined with the smoking leads them to a diagnosis of trashed valve guides. Seems reasonable and you approve the work. But, the engine still smokes. Now you really have a problem, not to mention the shop you took it to. Enter Mr. Supertech, who produces a leakdown tester, and performs the following test. On each cylinder in turn, he finds TDCC, sets up the tester, and reads the percentage of leakage. They're all good and low. Hmm. Undaunted, our hero retests each cylinder, but this time he lowers the pressure setting on the instrument, and, rotating the crankshaft a smidge each time to slide the piston down the bore a little, picks up the problem, plain as day. On the #4 cylinder, the gauge now reads 60% leakdown when the piston is partway down the bore, indicating cylinder damage, which the teardown verifies. Seems one of those pesky wristpin circlips wasn't all the way into its groove. It subsequently popped out, and the wristpin tore a handsome trench into the cylinder wall. Why didn't the shop find it when the head was pulled for the valve job? Because two of the four pistons were at TDC. Why didn't the compression test pick it up? Because despite the trench, there was still plenty of cylinder area (the pin is more than an inch below the deck) in which to build adequate pressure during a compression test. This actually happened, and it illustrates both the weakness of a compression test and the comparitive strength of a leakdown test.

Ok, on to the your problem at hand. You said the issue was a rattle from a stop to when you begin moving? The rattle sound isn't when your starting the car is it? I want to be clear here. The car is already started, and running. You have engaged first gear and your about to engage the cltuch when you hear this rattling sound as the car begins to move. And it only does it at this point. Coorect or no? If not, then tell me exactly when it happens.

[larry chester]

First, this 06 IS250 you have now, you must have purchased used correct? I see this is your second 06 IS250? So the carbon build up could be a remnant of the previuos owner yes? And they very well could have used cheap gas. In fact, what the tech is talking about regarding carbon build up so far sounds like an issue that can arise from using 87 octane fuels in a 92 octane system.

So they did a compression test huh? You must be a PIA customer. LOL!! Are you taking this to a dealer?

Ok, on to the your problem at hand. You said the issue was a rattle from a stop to when you begin moving? The rattle sound isn't when your starting the car is it? I want to be clear here. The car is already started, and running. You have engaged first gear and your about to engage the cltuch when you hear this rattling sound as the car begins to move. And it only does it at this point. Coorect or no? If not, then tell me exactly when it happens.

Thanks, everyone for your comments. Yes, I bought this IS250 used. It had 11,000 miles on it, and ran flawlessly till about 3K miles ago, when I started getting the error codes and warning lights on the dash. So, I don't think that this was a problem with the original owner of the car.

Yes, oh yes, I am a PIA customer. But for what I pay to the dealer every 5K miles, asking them to do a compression test when they are tearing down the top side of the engine for a warranty issue . . . . . shouldn't be a problem.

Yes, the techs working on the car are at a Lexus dealer. This was $2,600 worth of work. Totally absorbed by Lexus.

Lastly, Yes, the rattle occurs after the car is started. Doesn't make any noise when starting or while idling, happens when the engine is cold, warm, hot. It is when I engage the clutch, and begin accelerating that I hear the rattle. It doesn't matter how much gas I give it, but it rattles just the same. It is just easier to hear the rattle when I just give it a little gas.

In the final analysis, I picked up the car yesterday evening. It certainly runs differently. There is much smoother engine response starting from a dead stop. No rattling, I think that it accelerates faster than before, but I suffer from the new tennis shoes syndrome. .

Still love my car, and now, it seems that it will run better from here on out.

larry

[sktn77a]

There's a TSB for the rattle and there's a new TSB for carbon buildup in the IS (this causes rough idling and error codes when you come to a stop and take off again). The carbon buildup has nothing to do with "not driving the car hard" - ask any BMW M5 owner - it's a design flaw (I can't believe the bull$hit some dealers try to feed us)! They probably did both fixes to your car.