09 SS Overheated - What now?
06-08-2017, 02:42 PM
#12
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Join Date: 10-11-2014
Location: nc
Posts: 51
Well, I replaced the radiator fan today. Took longer to haul the tools out to the driveway than it did to replace it, and bonus the fan spins once installed. One problem solved.
I also did the compression test. Pro tip, if you have an SS buy replacement rubber grommets for the air box ($5/ea, need 3 of them) before you remove it, they disintegrate upon removal.
Cylinder 1: 125 psi
Cylinder 2: 138 psi
Cylinder 3: 143 psi
Cylinder 4: 148 psi
I ran each cylinder three times and averaged the numbers to get the results above, all test results were within a few psi of each other. I then ran cylinder 1 again with a bit of oil in it and got 125-130psi, so the rings appear to be good at least. So I'm 15% low on cylinder 1 when compared to the average of the other three cylinders, which isn't optimal but doesn't seem to cause a performance loss or cause misfires.
Also, I was expecting numbers around 135psi based on 9.2:1 compression figures I've seen for the engine, anyone know what the nominal value is?
Plugs looked good and had consistent appearance across all four cylinders, no signs of coolant entering the combustion chamber and no oil fouling. Plug 1 did have some serious rust going on though but it was just the threads and nut which makes me think the hole got some water in it when someone tried to wash the engine or something. I have no idea how old these plugs are but Ive had the car for the last 40k miles and never replaced them.
Plugs pictured are cylinders 1-4 left to right.
Thoughts?
I also did the compression test. Pro tip, if you have an SS buy replacement rubber grommets for the air box ($5/ea, need 3 of them) before you remove it, they disintegrate upon removal.
Cylinder 1: 125 psi
Cylinder 2: 138 psi
Cylinder 3: 143 psi
Cylinder 4: 148 psi
I ran each cylinder three times and averaged the numbers to get the results above, all test results were within a few psi of each other. I then ran cylinder 1 again with a bit of oil in it and got 125-130psi, so the rings appear to be good at least. So I'm 15% low on cylinder 1 when compared to the average of the other three cylinders, which isn't optimal but doesn't seem to cause a performance loss or cause misfires.
Also, I was expecting numbers around 135psi based on 9.2:1 compression figures I've seen for the engine, anyone know what the nominal value is?
Plugs looked good and had consistent appearance across all four cylinders, no signs of coolant entering the combustion chamber and no oil fouling. Plug 1 did have some serious rust going on though but it was just the threads and nut which makes me think the hole got some water in it when someone tried to wash the engine or something. I have no idea how old these plugs are but Ive had the car for the last 40k miles and never replaced them.
Plugs pictured are cylinders 1-4 left to right.
Thoughts?
06-08-2017, 06:27 PM
#17
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Thread Starter
Join Date: 10-11-2014
Location: nc
Posts: 51
Donbrew, I thought what you said as well as soon as I saw the rust. But hold on a sec...
1. The color of dexcool has nothing to do with the rust. Sure, both orange, but so what?
2. If steam is escaping through all those threads then why aren't combustion gases? This looks more like failure of the protective coating on the plug followed by Aluminum/steel corrosion to me.
3. The plug didn't look steam cleaned.
4. No evidence of coolant combustion at cold start.
5. No coolant smell in the engine bay while idling or after running.
6 No bubbling is visible on the upper radiator hose fill point while running at temp.
I think the spark plug corrosion is just a coincidence. Easy enough to test though as I should see the same corrosion within 50-100 miles of driving since that's about what I've done since this happened Saturday. I'm not saying that I don't need some sort of work done, I'm just not convinced that it's a head gasket yet.
As for the coolant it was never low in the system. The overflow was down a bit, but checking the fill cap showed fluid right up to the level it should be (and still is). The root cause of the overheating was the fan not working, trying to run the AC, low speeds, and high ambient temps.
Anyone know the definite number for what I should be seeing from the compression test for the LNF?
1. The color of dexcool has nothing to do with the rust. Sure, both orange, but so what?
2. If steam is escaping through all those threads then why aren't combustion gases? This looks more like failure of the protective coating on the plug followed by Aluminum/steel corrosion to me.
3. The plug didn't look steam cleaned.
4. No evidence of coolant combustion at cold start.
5. No coolant smell in the engine bay while idling or after running.
6 No bubbling is visible on the upper radiator hose fill point while running at temp.
I think the spark plug corrosion is just a coincidence. Easy enough to test though as I should see the same corrosion within 50-100 miles of driving since that's about what I've done since this happened Saturday. I'm not saying that I don't need some sort of work done, I'm just not convinced that it's a head gasket yet.
As for the coolant it was never low in the system. The overflow was down a bit, but checking the fill cap showed fluid right up to the level it should be (and still is). The root cause of the overheating was the fan not working, trying to run the AC, low speeds, and high ambient temps.
Anyone know the definite number for what I should be seeing from the compression test for the LNF?
Last edited by 87ninefiveone; 06-08-2017 at 07:06 PM.
06-08-2017, 07:04 PM
#18
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Join Date: 10-11-2014
Location: nc
Posts: 51
Found a thread over on the cobalt forums about compression tests. Seems 140-155 psi is the normal range for the LNF. GMs official word in the service manual only says all cylinders >100 psi and no more than a 30% difference between min and max values. By that measure I'm fine, but 30% variance is huge.
Looks like the next step is a leak down test.
Looks like the next step is a leak down test.
06-08-2017, 07:41 PM
#19
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Join Date: 05-01-2014
Location: California
Posts: 7,785
I'm tending to agree with don also. Cylinder #1 is a little low compression, and also has the discolored plug. Just because your oil and coolant haven't mixed, you may still have a tiny head gasket leak. Coolant into the combustion chamber, but not into the crankcase. Good news for your rings.
Your slight loss of coolant in the recovery tank speaks to this also.
Hopefully the leakdown test will be conclusive. My compression problem was gunk buildup on the intake valves. cylinders 1-3 had 2-4% leakage, and cylinder 4 had 23% leakage(crankcase and intake, loudest from crankcase). After shell blasting, cylinders 1-3 have 2% leakage and cylinder 4 has 5-6% leakage (crankcase).
Your slight loss of coolant in the recovery tank speaks to this also.
Hopefully the leakdown test will be conclusive. My compression problem was gunk buildup on the intake valves. cylinders 1-3 had 2-4% leakage, and cylinder 4 had 23% leakage(crankcase and intake, loudest from crankcase). After shell blasting, cylinders 1-3 have 2% leakage and cylinder 4 has 5-6% leakage (crankcase).
06-08-2017, 08:19 PM
#20
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Join Date: 01-23-2009
Location: Fredericksburg, Virginia
Posts: 24,660
OK. Don't believe me. I tried.
After you take the head off you will find a fault between cyl #1 & cyl #2. You will identify it by the orange streak.
Now removing my Carnac the Magnificent turban.
After you take the head off you will find a fault between cyl #1 & cyl #2. You will identify it by the orange streak.
Now removing my Carnac the Magnificent turban.
