S15 SR20DET possessed Compression #'s & cause

[ask52]

figured the issue to be either fuel in the cyl or compression tester issue. engine was mint inside.

[Ka-t in progress]

Do a leak down test,at least find out which cylinder it is. Does your oil look milky in any way? Only guess I have is possibly the headgasket expanding and causing a lower compression number.

[ask52]

edit, has been figured out.

[Kingtal0n]

Picked up a wrecked car the other day, 99 s15 sr20det engine. Looked to be pretty much stock, had an oil cooler fitted to it. Intercooler pipes were all clean, no signs of oil passing through...

The rad and oil cooler were toast from the wreck so I did a cold compression test, had 140psi across pretty much dead on each hole. the next day picked up some block off fittings for oil lines and fit a rad to the motor. Engine seemed to run fine no blue smoke or knocks. warmed it up/pulled plugs to compression test it, fully expecting it to be 155 ish, the fucker only had 120-125 across!!!!

Put the plugs back in fired it up, pulled the oil cap and its pushing air out the oil filler.... wtf. has anyone had compression drop when hot?? Ive never had this happen before... ps after it sat for 1hr cooling down a bit I compression tested it again and the numbers were up around 10psi per hole!! put some oil down #1 and its 165psi.. Guess is rings are fucked :facepalm:


All of this is normal. The compression probably dropped when the starter got hot and turns the engine more slowly. The air you feel coming out of the crank case at idle is from the PCV system.

Get the engine hot, take out all the plugs, hold the throttle open, and hook a jump box or second battery to it and spin it, your compression will come back up.

If you dont see blue smoke or smell oil at the exhaust everything is fine. Bet it runs damn good too.

[iRONDONkey]

i do believe that you have a healthy engine, as long as all your compression numbers are the same.

[fullthrottle]

Did you cut fuel to the cylinders when you check it while warm? Fuel will make ur compression read low.