hrsteel

My car had been losing coolant at an accelerating rate for about the last 10k miles (after I changed the headgasket). I ended up overheating pretty good two or three times. I garaged it for 6 months, but have finally found the time to work on it. My suspicion is that the head was warped when I put on the new gasket and it just all went to hell from there.

I wanted to check compression to see if I was going to have to pull the whole motor or just the head. I pulled all the plugs and put the compression tester in #1 and started to turn the motor. I stopped when I saw water spraying out of the engine onto the wall. Pulled the tester and spun the motor until most only a mist came out of the plug holes. Ran compression test on all 4.

The numbers I got were 190 240 220 190. That seemed really high. I figured that either my tester was bad, or I had still had enough water in there that the readings were off. I left the motor open last night and today, and checked my tester against one at work. It was good. When I got home, I checked #1 again, still 190.

Do these numbers sound close to right to you guys? It's an 85/1 2.5NA, bone stock as far as I know.

inactiveuser92616

fluid in the combustion chamber could increase your #s

George Boss

Those numbers are too far apart. They should be within 10% of each other. I agree with patrat. Check your oil and your overflow reservoir. Does the oil look chocolate brown and frothy, almost like chocolate milk? How about the coolant in your reservoir? If it does, you have a common 944 problem called "mixing". This can be VERY expensive to repair, not to mention the havoc it will cause in lubricating your rods and bearings.
If not, check you oil level to make sure it's not over-full. Let me know how you make out.

Granite 944

Well........I guess theres no doubt! Headgasket problem.

I know, just for giggles.........your SURE it was coming outta those spark plug holes........right? sorry.

hrsteel

I know water is getting past the headgasket and into the chambers. When the car was running the oil looked fine. I know the head has to come off and most likely be decked. I was running the compression test to try to see if the cylinder walls were scored to hell and back. What I'm wanting to know is what are reasonable compression numbers?

Note: After I thought about my old physics classes, it occured to me that there is no way I should have pressures over 150lbs, so I must still have a bunch of water in there. No matter, the head is coming off. Now I'm just praying that the block is not warped.

hrsteel

Ok, so my roomate and I did some more math. We made the following assumptions (they are simplyfied, I know) CR 10:1, "ideal" cam, and perfect reing and valve seal. A compression number of 240 means that I have about an ounce of water in the cylinder. I can believe that.
Off with its head!

Granite 944

All I can tell ya is this. My early cars have compression readings of around 170 up to 192 lbs. I feel that the two cylinders that your saying are at 220 and 240 are either from the water intrusion, or carbon buildup.

I would'nt consider one of these earlier engines (2.5L na's) good at all, if it didn't show a compression reading of 160lbs or better when hot, and tested correctly, with a known good gauge.

Note: water/coolant, or oil in excess, introduced into a compression gauge durring testing, WILL ruin it. All gauges will read slightly differently, and at different levels. The key of course is the consistancy of readings between cylinders. 15 to 20 percent difference is the number I go by for "problem" considerations. Leakdown test would be done accordinly afterwards, depending.

Remove the head. Look for gouges on head, block surfaces (especially around the compression sealing rings), use a good straightedge accross both mating surfaces (after cleaned, of course in all directions) to see. I don't recall what spec says flatness should be right off hand. Less than .002" TIR. IIRC. Also look carefully at the condition of the head studs, and the proper cleanup and prep processes for installing these heads. Good luck! I'm no expert by ANY means. Just a kinda fairly experienced home mechanic.