alright to start off i have a stock ls block internally with a gsr head. i tested 150 compression on all cylinders. throttle was open and car was warmed up.i do lose some coolant every now and then . no oil/water mix. i dont lose any oil. my levels stay good. i can dog it for a week and you probably couldnt notice any change on the dipstick. im leaning towards headgasket but not sure.. any imput would be appreciated of the cause of the low compression. someone told me i could get a valve adj and it could raise it back up.

 

head could use a valve job, i had this problem on one of my gsr builds.

 

i hope thats it.. would be alot cheaper. if i have time friday imma try and do my first leakdown test.

 

If the compression is even across all cylinders then its unlikely valve or head related. I would say headgasket since you are losing coolant. It could also simply be worn cylinders/rings. After you do a dry test, drop a little oil in the cylinder and repeat the test. If your compression numbers go up, you know the bottom end needs repair. If it doesn't change significantly you have a headgasket/head problem. A leakdown test would further detail the source of the leak.

 

also cbaber. ive been using plain water as a coolant. would that matter? or do i need to flush it out and mix 50/50

 

Go to AutoZone and rent a radiator pressure tester. It basically tests the system for leaks. If you are using plain water and your radiator cap is bad, or their is a small leak somewhere letting pressure out, your water could actually be boiling away.

Using straight water in summer is not a big deal as long as it is properly pressurized. The increased pressure in the system raises the boiling point of the liquid, which is why the water won't boil at it's normal 100 C boiling point. Water is actually better at heat transfer than antifreeze mix. So that isn't your problem.

Do you notice your motor stumble a big right after you start it, and then it runs fine?

 

not really. it used to when i was running big injectors and a shitty tune when i first got it. but now i got stock gsr injectors back on it and a proper tune. i just got done driving over 160 miles. most around 3500 rpms on the highway. i lost maybe 4ozs of water. just guessing.

 

alright so i did the thing where you take the rad cap off and crank it uo when its cold. i did NOT get any bubbles. but after about 20 seconds it started overflowing.

 

I'd say ur comp is even across the board. Although u can have good compression an still have a blown head gasket on one of the water jackets. Plus if it were leaking into the cylinder u would see white smoke from the tailpipe and smell coolant burning. If u want to be sure, pressurize the system and take a boroscope into the cylinder.

 

mean b18, im a noob. taking a boroscope into a cylinder in a different language lol.this is my first motor id be digging into. lol. i know some basics though. i dont see any smoke at all coming from my exhaust. i do not have coolant as im running just water.

 

I'm honestly surprised nobody has suggested this yet.

Leakdown test.
Isolate the issue vs guessing.

 

ill try that leakdown next. but heres an idea maybe.. maybe the compression tester gauge was off? it was a rental tool after all. and im exactly even across the board. i think imma go try another tester first.

 

most likely can just be head gasket if your seeing a lose in coolant