[2007tacoma]

I did a compression test over the weekend to track down an idle issue and notice one of the cylinder was 5psi lower than the rest. The other three cylinder has 195psi each. The 4th cylinder has 190psi. What should the compression be at?



The car has 132k miles now....is it time for me to rebuild the head?



thanks

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[flash]

the numbers are fine for that mileage (quite good actually) - the variance would not be the idle issue - further, these engines hunt a little bit anyway (+/- 50rpm) - if it's more than that, it could be a number of things (dirty MAF, old plugs, worn cap or rotor, yada yada)

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[ds968]

Bob, looks like you answered for each of the six cylinders, not to mention that we only have four.. <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />

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[tamathumper]

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[flash]

tried fixing that yesterday - weird access problems with the satellite - fixed now

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[986boxster1998]

My engine has 162,000 miles and I decided to do a compression test after work today getting:



Cylinder # / Dry / Wet

1 / 180 / 225

2 / 177.5 / 222.5

3 / 175 / 217.5

4 / 167.5 / 220



Do these numbers seem like an engine in good health, or would I need a leak down test?

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[Cloud9...68]

My gut reaction is that you're seeing a little too much variance among the cylinders for comfort, but given the huge range of numbers that have been reported in these tests by forum members lately, I'm beginning to suspect the accuracy of this test. I completely rebuilt my engine at 115K miles (not because it desperately needed it - just something that snowballed down a VERY slippery slope), and had the cylinder bore diameters measured by a reputable machine shop. The shop owner concluded that my cylinder bores show close to zero wear, and that my block should be good for about a million miles, and that this isn't uncommon for these engines. Similarly, the guy who rebuilt my head (a specialist who does nothing but head work for a living) said the valve seats were about the hardest he's ever run across, and that similarly, they showed virtually zero wear (the guides, on the other hand, were somewhat worn). My compression numbers were all in the 170s, which is indicative of a "tired" engine, but unless the rings were significantly worn, the physical evidence from my engine's major wear areas was significantly out of sync with my compression readings. So yes, I would have a leakdown test done for confirmation. Please report back what the test shows.

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[986boxster1998]

Did a compression test on the other car (118,000 miles, with about 20,000 since the top of the motor was refreshed) getting:



Cylinder 1: 192.5 PSI (5 Cranks) and 200.0 PSI (6 Cranks)

Cylinder 2: 190.0 PSI (5 Cranks) and 197.5 PSI (6 Cranks)

Cylinder 3: 190.0 PSI (5 Cranks) and 197.5 PSI (6 Cranks)

Cylinder 4: 187.5 PSI (5 Cranks) and 195.0 PSI (6 Cranks)



This thread now has three recorded compression tests all showing lower compression in cylinder #4 is there any reason to expect this trend?



I thought that having almost extactly an extra 7.5 psi on each cylinder after letting the starter turn over an additional time was interesting as well.



Any thoughts are welcome. Thanks, Dan

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[bombfactory]

I just got about 208 psi across all 4 cylinders with the engine warm. Flash said this a little too high - might have crud on my pistons. 131k miles on the engine.

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[flash]

200ish is a good number for a tight motor, or normal number for one with a shaved head, a high number for a motor with miles, but "crud" on the pistons, or one with a weeping gasket. gauge accuracy is a variable too.

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[Cloud9...68]

So with all these variables, is a compression test of any real value?

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[flash]

sure - you just need to know what else might affect things (mileage, gunk, head rework, etc.)

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[Cloud9...68]

Yes, but how "knowable" are these factors? Seems like a leakdown test is a much better test, although even it has its limitations.

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[flash]

sure, but it depends on what you are trying to determine. if all you want to know is the relative condition of the engine, a compression test will generally do it, as long as the numbers are decent. if the numbers are low, then a leakdown is in order.

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