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Old 06-06-2017, 02:23 PM   #1
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09 SS Overheated - What now?

I had a bit of an adventure this past Saturday. 09’ SS, 116k miles. No previous cooling system service since I've had it (Oct 2014 76k miles). Occasional small coolant additions (half a gallon of 50/50 Dexcool water premix over 2.5 years).

We were running some errands and the temperature was in the mid 80’s so I had the AC on. A few miles into the drive I noticed that the AC wasn’t blowing cold whenever we stopped. By the time we got on the freeway (2-3 mi. from home) the car was just heating up and most of the driving afterwards was highway/freeway speed where adequate cooling occurs at which point the AC worked fine and I didn’t think anything of it. We stopped for 1-2 hours on our first errand at which time the car cooled off. We then drove another few miles down the highway to a busy main road to run a few more errands and this is where things went downhill.

We were in stop and go traffic for about five minutes after getting off the freeway and while at a traffic light the dreaded over temp warning light goes off on the dash. I quickly scan the temperature gauge and its pegged straight up. I scroll through the DIC menu and sure enough 251’F. Oil temp according to the aeroforce gauge is 248’F. I then limped it into the next parking lot and immediately shut it off. Total time above 250’F was probably about 2-3 minutes, and maybe about 5 minutes above 230’F. All idling or less than 2k RPMs during this period. There was no steam or coolant smell and the reservoir still had 1-2” of coolant in it. While I was waiting for it to cool down I checked the fuse for the radiator fan which was fine (later confirmed with a multi-meter). After the temperature came down to about 210’F I started it back up and sure enough the radiator fan didn’t work with the AC turned on. I waited another half hour or so until the temp was down in the 170’F range and hightailed it back home on the freeway, temps were normal (190-200) as long as air movement was present. Once home, I let it to idle again until the temp reached 225’F and still no response from the radiator fan. At this point I assumed the fan was dead and ordered a new one ($175 for an AC Delco unit with temperature module on Amazon). Delco part no.
15-81765 15-81765


First off why doesn’t the moron light go off at 230’F or 240’F, you know, BEFORE the chance of major engine damage occurs. What the crap GM?

Second, how screwed am I since the engine hit 250’F? What should I be doing as preventative maintenance or diagnosis to check the extent of the damage?

Last edited by 87ninefiveone; 06-06-2017 at 07:48 PM.
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Old 06-06-2017, 04:06 PM   #2
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You're probably looking at a head gasket, maybe a warped head. How old is the Dexcool, well that doesn't matter after hearing to those temperatures it must be drained, as it gets weird after 230 degrees.
While cold I would do a compression and a leak down test on all four cylinders, if they're all within spec, drain and flush the coolant, swap out the thermostat, and the Dexcool.
Don't forget get the correct 180 degree AC Delco thermostat and only use Dexcool 50/50 mix with distilled water.
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Old 06-06-2017, 05:33 PM   #3
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X2, you should be OK.

Evidently you parked before it went into "save my life" mode. Where the cylinders take turns taking a cycle off.
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Old 06-06-2017, 05:38 PM   #4
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I'd still pull the head , change the timing chain, head gasket, but I'm an old racer who has experienced similar situations and gambled on the old boiled engine, that was way more expensive!!
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Old 06-06-2017, 07:45 PM   #5
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Thanks for the quick replies gentlemen. I'm afraid doing head work is above my skill level.

I can do the compression test this weekend which will also give me the opportunity to pull the plugs and check for coolant contamination. I don't have the means to do a leak down test, but as far as I understand it this shouldn't be necessary anyways as long as the compression test is okay (right?).

I can also see swapping the coolant as a good preventative measure, but will probably just have a quick lube place use a machine to do it since I don't have a good way to collect and dispose of the fluids.

This is my only car so I've been making the daily drive to work on the freeway and the thermostat is operating as it should and keeps the car between 189-196 range while driving at speed. Temps only start to creep up on me when I sit for extended periods. I can't wait for that fan to show up tomorrow so I don't have to keep freaking out every time I see a red light.

In regards to the temperature I reached and insta-death. I've read a lot of threads going back the last couple of years on overheating SS cars and I've seen it suggested that the head is toast after about 240F or so. Most of these suggestions come from the same few users. What I don't see a lot of is any posts confirming that the head was toast after an overheat or any data backing these claims up. I can't help but feel that GM wouldn't design a warning light that doesn't come on until ten degrees after your engine is toast. Some engineer somewhere had to test this and come up with a real number where damage occurs and then back down from there to provide some margin of safety to prevent problems. The manual also says that you don't even need to shut off the engine in the event of an over temp light as long as no steam is present (it also assumes your stupid electric fan hasn't given up the ghost though).

Wishful thinking maybe, but I suppose we'll see when I do a compression test.

EDIT: Just checked the radiator fluid (not the reservoir stuff) and engine oil filler cap, no signs of milkshake so that's a plus.
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Old 06-06-2017, 08:40 PM   #6
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"might" cause problems is not the same as "will" cause problems.

When my 2.2L overheated the light and warning did not come on until 250F, but I could tell something was wrong before that. Loss of power, bogging down etc.
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Old 06-06-2017, 09:43 PM   #7
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Did you end up having to do head work?
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Old 06-07-2017, 07:39 AM   #8
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I did at 250 degrees, in my 2.2, I replaced the head gasket. No coolant in oil , good compression, just a precaution.
Just ensure they use 50/50 Dexcool!
Thermostat should be 180 degrees
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Old 06-07-2017, 09:57 AM   #9
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Mine had other problems, new engine transplant.
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Old 06-07-2017, 06:56 PM   #10
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Checked my coolant and oil again today. Both are still clear with no signs of emulsion present.

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I also think I found my slow coolant leak. It was the radiator cap of all things. The o-ring had gone completely flat. New unit is on the left.

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I picked up new Delco plugs at the dealer ($12/ea ouch!) and once the air box grommets come in I'll do the compression test. The new radiator fan showed up today as well, so I'll get that in tomorrow.
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