Does the ambient temperature affect the numbers you get with a compression tester? I have a Craftsman compression test kit, and I've noticed that over the past 3 times that I've done the compression test my numbers have dropped. I'm not sure if I should be concerned or not. The thing is, even though the numbers have always dropped, they drop consistently. Cylinders 1, 3, and 4 always read about the same and cylinder 2 is always about 2-3% higher than the other 3.

The thing is, the first time I did the comp. test, ambient temps were probably in the 40s. I blew 240-250psi. The second time I did the test, ambient temps were in the mid- to upper-60s and I blew 230-235psi. This last time, ambient temps were in the low 90s and I blew 210-220psi.

Should I be worried? Or is there some physics at work here that I'm not aware of?

 

just did mine recently

- Warmed up to 3 bars @ WOT
- odo: 32,000mi

cylnder 1 - 240 psi
clynder 2 - 240 psi
cylnder 3 - 230 psi
cylnder 4 - 240 psi

 

Make sure you are consistent when you run it:

1. Hook the car up to a charger for consistent cranks
2. WOT
3. And make sure the engine is at normal operating temperature

I guess maybe with colder ambient temperatures, the air is denser and you may pack a little more cylinder pressure, i've done mine in cold and warm weather and i've gotten almost the same results.