I am in the process of purchasing a 2006 Honda s2000 and decided to hire a mechanic to do a compression test on the motor. The test results where #1 180, #2 178 ,#3 179, #4 182. That seemed a little low to me so I asked the mechanic if he did the compression test with the engine cold and he said yes. He had already finished the test and left before I could ask him to redo it with the engine at operating temp.

Is there a big difference in compression between a cold or warm motor if so how much is the usual difference? Additionally, should I be worried about these numbers and do a compression test myself after I test drive the vehicle?

Thanks for your help.

 

How many miles on the car? Yes that is a low number by the book but I understand there can be variance between gauges and what is more important is the consistency across cylinders.

 

The car has 79000 miles and is stock for the most part. The only weird thing is that the previous owner had an upgraded clutch and the most recent owner changed the clutch to stock because he did not like the clutch.

Why would the previous owner upgrade the clutch on a stock car unless he removed the supercharger or turbo before he sold it.

 

My 2.4L stroker AP2 block's compression results are consistently 230 cold and 250 warm.

Compression testing a warm engine is important but so is a healthy battery. Check if the battery is old.

And yes, you have a valid point on the clutch.. it is also one of the "free" upgrades you do when you swap an engine (I did mine when I switched the shortblock from 2.0L to 2.4L). Check to see if the shortblock's number matches the rest of the car. Given the lower compression numbers, I'd wager it will match.. but that you're likely spot on that the previous owner drove it hard and/or had a FI setup.

 

From your numbers it seems like there is a 10% difference roughly from a cold to warm engine. I will ask in regards to the battery's age and ask regarding signs of mods (oil bung in oil pan, whole in front shroud for intercooler piping, etc).

Even though there is lower compression, should I still due my due diligence and find out more or move on?

 

I find it a bit odd that all the clyinders are that low. I have seen MANY faulty compression gauges not read high enough. A harbor freight gauge will only read to 180 while a snap-on will read to damn near 300.
For reference, my ap1 had 180 on cylinder #2, that equated to 45% leak past the rings on that cylinder....You'd never know though, as it seemed to run just fine.

If you want the whole story, tell your mechanic to do a leak-down test. That will tell you the true state of the engine.

 

I just looked up the compression tester the mechanic used and it's branded Pittsburgh automotive. When I look this brand up, it is sold from harbor freight.

It seems that I should do my own compression test with a better gauge to confirm the original results.

 

Cant vouch for said car, but I see people put heavy duty clutches in stock engine S2000's. Most of my jobs I do customer states "I want a heavier pedal feel" or "I will go turbo in the future"
Run a leak down test on the car and look at results. Kudos on most recent owner putting factory clutch kit in.

 

The HF compression gauge reads low. Very low. Or maybe it just becomes very inaccurate at higher pressure levels. In any case, I had similar low results from a brand new HF gauge. I rented a different one from AutoZone, and it gave much more realistic results. I was in the upper 220's low 230's range.

I returned the HF gauge.

Since your numbers are so consistent, I think you are good.

But I wouldn't be surprised if mechanic never even tested anything. I bet he just started it up, heard it all sounded good, and made up what he assumed would be solid, healthy numbers.

Those would be perfect numbers for most any other engine. But our cars have way higher compression than most.

If he did really do the test, what did he torque the plugs to when he was done? I would be concerned he looked up specs and got the old ones, which are too low. Honda revised them. Plugs can come loose which can actually destroy an engine.

I would buy the car, and retorque the plugs.

 

The mechanic sent me pictures of the psi in each piston so I am sure he tested it. So it could be the gauge, cold test, or the engine itself has low compression. Will try and figure it out.

should I be worried if the compression reading are correct?