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Normally the compression test needs to show above a minimum 135 or 140 psi (you might see 190 psi) and for all numbers to be relatively close together (within 5 or 10%). Cylinders that are significantly different/lower than the others is one warning sign.

But you can have good or decent compression test results with a blown headgasket ... which is why a leak down test is more definitive for HG issues.

If you get the car running, one easy check (if there is leakage into the cooling system) is if the upper rad hose becomes quickly pressurized on a cold start before the coolant has had a chance to warm up. Open then close the expansion tank cap on the cold engine to equalize pressure with atmosphere. Hose should be soft & pliable. Start engine then check hose in about one minute. If pressurized before coolant has warmed up & thermally expanded, then HG or cracked head is leaking into coolant system.
 

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Discussion Starter #23
I would still assume the worse and bargain accordingly. Who else id going to buy it?
Yeah I definitely let me friend know that there's a chance we'd need to put a new engine in it. And who else? Just him
 

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Discussion Starter #24
Normally the compression test needs to show above a minimum 135 or 140 psi (you might see 190 psi) and for all numbers to be relatively close together (within 5 or 10%). Cylinders that are significantly different/lower than the others is one warning sign.

But you can have good or decent compression test results with a blown headgasket ... which is why a leak down test is more definitive for HG issues.

If you get the car running, one easy check (if there is leakage into the cooling system) is if the upper rad hose becomes quickly pressurized on a cold start before the coolant has had a chance to warm up. Open then close the expansion tank cap on the cold engine to equalize pressure with atmosphere. Hose should be soft & pliable. Start engine then check hose in about one minute. If pressurized before coolant has warmed up & thermally expanded, then HG or cracked head is leaking into coolant system.
How pressurized should it feel if the head gasket is gone? Would it be noticeably different than my own warm car's BMW upper rad hose? I could compare my warm rad hose with my BMW (With a good head gasket) and then compare the car with the possible blown head gasket.
 

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Different compression gauges will give different results. Consistency is key. People like to see no more than a drop of 10% across all cylinders.

For instance the last time I tested a car with a head gasket, I had 5 cylinders at 150-160 psi, and one at 90psi
 

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Different compression gauges will give different results. Consistency is key. People like to see no more than a drop of 10% across all cylinders.

For instance the last time I tested a car with a head gasket, I had 5 cylinders at 150-160 psi, and one at 90psi
Good point, I didn't mean to imply that a compression tester would never reveal a headgasket issue, just that it can miss some headgasket issues if they are not too extreme.

Last year I checked a friend's 325i that showed nothing obvious with a compression test, and even the leakdown percentages were not very much, but there was air bubbling out through the coolant in ET on multiple cylinders. That engine had cold start misfires, though not everytime, and unexplained coolant loss, but otherwise it ran great once warmed up.
 

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How pressurized should it feel if the head gasket is gone? Would it be noticeably different than my own warm car's BMW upper rad hose? I could compare my warm rad hose with my BMW (With a good head gasket) and then compare the car with the possible blown head gasket.
Yup, compare to the known good engine. The hose should be soft with the cold engine and within a minute before anything has warmed up, it will become inflated and firm if there is a HG issue, maybe like a bike tire. Normally even when hot you can still squeeze that hose inward.
 

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How pressurized should it feel if the head gasket is gone? Would it be noticeably different than my own warm car's BMW upper rad hose? I could compare my warm rad hose with my BMW (With a good head gasket) and then compare the car with the possible blown head gasket.
Take the cap off with the engine cold to release any residual pressure then reinstall it. Start it up and monitor the firmness of the upper hose. Should not have any significant pressure for at least 5 minutes or when it's getting near operating temp.

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Good point, I didn't mean to imply that a compression tester would never reveal a headgasket issue, just that it can miss some headgasket issues if they are not too extreme.

Last year I checked a friend's 325i that showed nothing obvious with a compression test, and even the leakdown percentages were not very much, but there was air bubbling out through the coolant in ET on multiple cylinders. That engine had cold start misfires, though not everytime, and unexplained coolant loss, but otherwise it ran great once warmed up.
I recently had a similar issue on an ecoboost mustang that was purchased from the dealership I work for. The only symptom that car had was check engine light with some misfire code and it only misfired for 5 to 10 seconds after starting. No overheating, no milkshake, nothing else. The 2.3 ecoboost is know for head gasket problems (usually on the middle two cylinders) so I did a leak down test with the coolant reservoir cap off. I like to leave the cylinders pressured for a few minutes while monitoring coolant level. When I got to cylinder 3, the coolant level started rising in the reservoir (which was low) and then bubbling. A head gasket and bolts fixed it. A compression test simply can't test for this type of thing. A leak down test can be done on a car that doesn't run or even crank, you just need to turn the engine by hand.

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A head gasket and bolts fixed it. A compression test simply can't test for this type of thing. A leak down test can be done on a car that doesn't run or even crank, you just need to turn the engine by hand.
I never tried testing it by turning it over by hand, might try that if I get another chance. You could also use the starter to turn the engine over (pull fuel pump fuse, and disable the ignition system as you do for a compression test) and add distilled water to expansion tank and look for bubbles / rising level. You could ID the specific cylinders with issues by pulling all the spark plugs except one and crank, then move the spark plug to the next cylinder.

 

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I never tried testing it by turning it over by hand, might try that if I get another chance. You could also use the starter to turn the engine over (pull fuel pump fuse, and disable the ignition system as you do for a compression test) and add distilled water to expansion tank and look for bubbles / rising level. You could ID the specific cylinders with issues by pulling all the spark plugs except one and crank, then move the spark plug to the next cylinder.

I meant leak down test can be done without a battery or starter or even a key. A compression test requires the engine to crank with a strong battery. For a leak down test you need to set each cylinder to TDC compression stroke (all valves closed) by hand precisely at TDC or the air pressure will push the piston down until valves open.

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I never tried testing it by turning it over by hand, might try that if I get another chance. You could also use the starter to turn the engine over (pull fuel pump fuse, and disable the ignition system as you do for a compression test) and add distilled water to expansion tank and look for bubbles / rising level. You could ID the specific cylinders with issues by pulling all the spark plugs except one and crank, then move the spark plug to the next cylinder.

That method could work if it's a bigger leak. It would give the starter and battery a hell of a workout. You can get a rental leak down tester from the part store if you don't have access to one. Cheaper than cooking a starter and more conclusive.

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A leak down test would be better than a compression test. I would also fill the expansion tank to the top (yes, overfill it) when doing the leak down test. If there is any leakage from the combustion chamber into the cooling system you will see it overflow and or bubble.

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True, albeit in a cold and not a heat soaked state.
Good trick.
 

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I meant leak down test can be done without a battery or starter or even a key. A compression test requires the engine to crank with a strong battery. For a leak down test you need to set each cylinder to TDC compression stroke (all valves closed) by hand precisely at TDC or the air pressure will push the piston down until valves open.

Sent from my S61 using Tapatalk
Right, but that would require OP to bring a compressor ... I thought you were describing an alternate way of "leakdown" testing that could be done in the field without compressed air.

The guy in the video had a charger hooked up to keep the battery going, and with only one spark plug installed at any one time it won't stress the battery or starter any more than a regular compression test would, especially if plenty of cool down time is allowed between cylinders. OP could potentially use jumper cables and his running car as a battery charger if needed.

And I agree that this might not work with a very small HG issue ... compressed air would be the ideal way to check for HG issues.
 

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Discussion Starter #35
Thanks for all the help. Me and my friend were ready to drive down there this Sunday and pick her up. But the seller wouldn't budge on price at all. So we decided it wasn't worth the buy since the asking price was over a grand.
 

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1)Did you actually see the gauge showing lower temperature, or just your wife's story? When the head is overheated, the sensor is hot and so the gauge should show high temp regardless with coolant or empty in the head. This same scenario happened to my wife, but the gauge needle moved pass and locked at the right side, until I turned on the key the next morning to get the needle back to normal position.

2) Why you couldn't bleed properly on the 2nd car?
1) Yes and yes, sort of. It overheated and she pulled over and called me. I told her to wait and I left work to go meet her, and by the time I got there, 10 to 15 minutes, she was gone. I went straight home and the engine was just super hot. You could tell by the sound. I said why didn't you wait and she said "I tried it again and the temp gauge wasn't high". I checked and sure enough it wasn't. The engine was crackling and sizzling so bad I thought it was toast. No coolant at all. But rebuilt the cooling system and it want another 3 years and 50k miles and sold it running great. Perhaps the sensor was damaged?...
2) I got that one cheap because the previous owner or their mechanic buddy couldn't bleed it properly. I rebuilt the entire cooling system and bled it and it was fine and drove well past 265k when my brother-in-law sold it. It might still be going.. Who knows why the previous mechanic couldn't figure it out, but they had damaged the bleeder screw and drilled a hole in the top of the new expansion tank - out of frustration I guess.
 

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Thanks for all the help. Me and my friend were ready to drive down there this Sunday and pick her up. But the seller wouldn't budge on price at all. So we decided it wasn't worth the buy since the asking price was over a grand.
Bummer, but don't worry, the seller might change tune after they can't unload it. Politely remind them that these cars aren't worth too much even if they are running, it is a big risk for a buyer and that you are interested at $ and to contact you if they reconsider. Also, I am not sure by you, but near me I see cheap E46s with fixable mechanical issues listed cheap all the time.
Good luck.
 

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1) Yes and yes, sort of. It overheated and she pulled over and called me. I told her to wait and I left work to go meet her, and by the time I got there, 10 to 15 minutes, she was gone. I went straight home and the engine was just super hot. You could tell by the sound. I said why didn't you wait and she said "I tried it again and the temp gauge wasn't high". I checked and sure enough it wasn't. The engine was crackling and sizzling so bad I thought it was toast. No coolant at all. But rebuilt the cooling system and it want another 3 years and 50k miles and sold it running great. Perhaps the sensor was damaged?...
2) I got that one cheap because the previous owner or their mechanic buddy couldn't bleed it properly. I rebuilt the entire cooling system and bled it and it was fine and drove well past 265k when my brother-in-law sold it. It might still be going.. Who knows why the previous mechanic couldn't figure it out, but they had damaged the bleeder screw and drilled a hole in the top of the new expansion tank - out of frustration I guess.
I am laughing reading your story, as my wife did the same after the tank ruptured and dump all coolant on our driveway, then she drove it to shop with zero coolant; the head was so hot that it expanded and pull 6 head bolts out of 14 off the block. However the temperature gauge moved pass the right most position and locked there. Her reasoning was that only the low coolant light was on, and the book said top it off soon, whenever I was home from work. No call or msg, just drive. I went home that evening with flowers for her Valentine day, and saw the big coolant mess on the driveway and almost had a heart attack. Took me the next 2 weeks to fix all of this in the cold February.
 

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I had the exact same experience with my wife driving my first E46 (325Ci). ET blowout, total coolant loss, massive overheat, new engine time. The only upshot was I ended up doing a B30 swap, learning how to update DME software, and the rest is history.
 
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