96 740il overheated, runs, headgaskets??
 

Hi, I'm new here, just bought a friend's 96 740il with barely 98k, beautiful shape. They drove the car a year ago and overheated it, and I'm guessing that they did so all the way home. They did a owner installed new water pump at home. The car starts, runs smoothly with a slight skip after a year of sitting. After running for 4-5 minutes, the temp gauge is normal, but the car is boiling over agressively. I towed the car home, did a compression test (actually twice to compare results) and I've got the following results: the corner cylinders are higest ranging from 175-200lbs, the center two cylinders on each head are 122-155. Is is possible that a car with failed head gaskets or other damage could still have compression as high as 122-155? Any chance this might be something other than fatal? Any help is appreciated!!
Chris

Rule of thumb, when doing a compression test all the cylinders should be within 20% of each other. When you do this test you are cranking each cylinder the same number of times and writing down exactly as possible what each one is? 155 and 175 no real problem 122 and 200, problems. Need to know all the numbers in sequence, then I can tell you whether or not to do a CLT test which will tell you where its leaking from. Then we can decide if its fatal.

This car sat idle for about one year. After charging the battery, the car started and ran smoothly with the exception of a slight miss somewhere. The gas was (is) old. All I've done is run the car for about 5min and as it began to overheat, I shut it down. All plugs have a nice light grey/brown color and are all in similar condition. My compression readings are from the pass front corner to the pass rear, then continuing to the driver's front corner then to the driver's rear. I attached my compression fitting and cranked the car for a bit, I'd guess at least 5-7sec, until I saw the gauge stop "pulsing". The readings in order from the first test are: 179, 135, 160, 215, 170, 125, 135, 200. The second test I did in exactly the same fashion, just 5min later. The results were: 179, 140, 155, 210, 170, 122, 135, 185. This is the 4.4 engine, 98k. Any other info I can provide?? THANKS!

OK, good info here's what needs to be done, those numbers COULD be OK. Do the same test with all the plugs out of the engine. You need to watch the needle jumps and do exactly the same number for all cylinders. I generally look at five total jumps in each cylinder, stop, and then take the reading. I see a 215 and a 210 and a few other numbers that aren't necessarily bad but at the same time are borderline comparatively speaking (which is what a compression test is all about). 98k miles it should still have plenty of life in it as it IS building compression.

Those figures were with all plugs removed... Sorry for not mentioning that.

That's good, do the five pumper and lets see if those numbers fall in line. My gut right now is you're most likely OK, but its better to be sure.

if its boiling over at normal operating temps, its the head gaskets. if its overheating and boiling over , its the thermo-stat . pretty simple a bad head gasket will steam clean a spark plug. so see if #2 and #6 are really clean