Skip the auto shop - Our mechanics make house calls

Q: Why am I getting low compression?

asked by on

i did get the head surfaced and "only the head surfaced" I am getting 85psi in cylinder 1 125psi in cylinder 2 120psi in cylinder 3 125psi in cylinder 4. why would I get low compression all of a sudden? should I try the test with air tool oil? I have not changed the oil will that make a dif? thank you so much for your time.

My car has 207000 miles.
My car has an automatic transmission.

The low compression in cylinder 1 can be that your rings are not sealing or the head has a crack that did not get seen during the resurface. You can try the oil in the cylinder and see if the pressure increases to what the other cylinders have. This would be rings on the piston if it does. You can pressurize cylinder #1 with about 120 psi air pressure and see where the air leaks out of. If you hear air coming out of the crankcase through the oil fill cap hole then you have rings on the piston are not sealing. If the air comes out of the exhaust or intake then a valve is not sealing. If the air comes out of the radiator when cap is off then the leak is a cracked head. You should change the oil and filter to get any water that may have got in it out of the engine. If you would are still having a hard time diagnosing this issue by yourself, you can seek help by hiring a professional technician, such as one from YourMechanic. They will be able to accurately diagnose your rough running concern.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Water Pump

If the overheating problem was not resolved with the new radiator and thermostat then it is not safe to drive the car simply because overheating will damage the engine. If, however, the overheating problem was resolved with the installation of...

Q: Possible clutch issue?

Hi there. From the description you have provided, I do not believe the inoperative clutch is an electrical issue. The hard to shift into gear and clutch pedal staying down once depressed, leads me to believe, it's a failed clutch...

Q: How do I select a USB file to play?

Once a USB device is connected, it is very easy to select a file to play: 1. Press the selector knob to display the folder list. 2. Rotate the selector knob to choose the desired folder. 3. Press the selector...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.