I was driving today, and was doing an acceleration from 70mph, trying to reach top speed, but I experienced a knock in 4th gear at around 5500rpms. When it knocked, it sounded like a hose blew loose, because the boost dropped too (I could see it out of the corner of my eye), and power stuttered for a brief moment and then all resumed as normal. We're talking not even a second. I am running 15lbs of boost, and using the Intense Stage 3 kit.


I still continued to push it. And stopped just a little over 140mph, and took a picture. I was hoping to hit 145-150mph, and I know it's possible, but it is just too hot here in Phoenix. After my run I pulled over to look under the hood, and my intercooler fluid was BOILING! That is probably why I had knock, I doubt the intercooler works at all with boiling liquid running through it.

Should I change the fluid out to Red Line Water Wetter? That should be able to withstand more heat right?

I was running it hard tonight, so I know the supercharger and all the coolant was pretty hot to begin. Not to mention it's still 103* outside at 11pm.

Here's the pic I took. Sorry for the blur. I was using my camera-phone, and driving 140+mph so I needed to look at the road.

 

103 outside... Damn. It has been 90 here and that is considered very warm for us. Looks like that was at night too, glad I don't live there, lol.

I had my car to 160, or so the needle said and experienced no knock. On the cooland thing, lately mine has been just burning it up like nothing. Mine boils like that often, but I just thought that was normal. At those speeds I'd imagine things get hot.

 

My Thermometer reads 121* during the day, this 103* was just a few minutes ago at 11pm tonight. I hope it was just the heat causing knock, and not something serious.

 

first of all your intercooler water cant boil cuz it uses your engine radiator water to cool =the intake charge.. water and antifreeze cant boil or freeze.. make sure your useing 93 octane or higher on your car, knocking usally means low octane, heat and presssure.

 

First off, 93 octane is not available in Arizona. We have 91 octane as our Premium fuel. And the Intercooler does not use the radiator coolant, it is a different loop, and has it's own tiny resivoir. And yes Antifreeze can boil AND freeze, it just takes higher temps to boil, and lower temps to freeze than regular water.

 

Of couse a glycol-water mixture can boil or freeze, the added glycol just lowers the freezing point of the mixture. Hence the temperature rating your will find on the glycol you buy.

Edit: Looks like you beat me to it

 

To clarify my statement above. The intercooler uses the same TYPE of coolant (DEXCOOL), but is not in the same loop with the radiator, they flow and over flow on their own.

 

Anti freeze can boil for sure. It boiled right out of my jetta onto the street when it overheated due to katrina!!!!

 

Back to my point, how do I correct it. I understand I need more octane, but racing fuel is too expensive to drive around on. Can I be running too lean? Is there any other problems that could cause this? I've never felt it before, even in my grand prix, which I know had lots of it.

 

You can always get a scan gauge to monitor the knock. Also a wideband would let you see if you are running lean. If you were running lean, you would have threw a code most likely.

 

you might wanna make sure you don't have a leak in the system. The only time you coolant should boil is when air can get to it. boil releases gas into the sytem but if its a closed system like ours it can't boil cause there is no where for the gas to go. That's what happens when you take the radiator cap of when the coolant is to hot.

 

There is an overflow tube, so it can boil over, as the gas would vent out of that tube.

 

The only times I threw lean codes were when I put midgrade gas in to try to save money, and it was a bad idea, since our midgrade is 89 and our premium is 91, it was like putting most peoples low grade in. I wish we had 93 octane. There are a few stations around here that have 100 octane, but thats $5.99/gallon.

 

the reason your boost dropped was the engine retard due to knock, it retarded it so much so you didnt go boom and stopped the knock....if your not usin 91 octane since thats the highest you have use it if you are dont ever do that again lol thats pretty much all i can say orrrr order huge drums of 93 but idn wat to tell ya your SOL if its doin that with 91

 

91 octane would probably normally be ok, but if its been 120 there you shouldn't be running your car so hard. You are gonna get knock with those tempuratures at those speeds especially with only 91 octane due to the extreme tempuratures. It has been 100 here and I have been taking it real easy on my car.

 

why were u going 140mph

 

The real question is.. Why wasnt he going 140mph

 

Why are you going 140 mph? If you're trying to kill yourself, there's easier ways.

Especially at temperatures like that.

What do you think would happen if you had a blow out at 140 mph?

 

Because I can

 

I understand the risks. It's my decision. Some people sky dive, I like driving fast.

 

Yeah I figured it was being retarded because of the knock, but I have never felt it before to that degree.

I just montiored my knock, and I am getting 3-7* at around 4500 rpms, then it goes away, and that's only under WOT. I do have spikes of 43degrees (yes, fortythree) when I shift gears, so I don't know if that's just the timing getting dropped while the clutch is engaged. I'm sure it is, but I don't have much experience with this.

 

Funny reading a post like this on a sport compact forum. 98% of cobalt ss/sc owners have gone this fast. The other 2% lie about it.

 

I've done it too, and now that I look back on it, I can't believe I was that stupid.

Unfortunately, when you do this on a public road, you're endangering not only yourself but those around you.

I don't see why it's so hard to go to a sanctioned race track and do it...

 

A second IC heat exchanger would help as well as a larger resevoir tank. Then again pushing your car that hard this time of year is not advisable in my book.

 

Its definitely a bad idea to run your boosted engine that hard at those ambient temps.
Sounds like your intercooler saturated with heat and could no longer cool the charge. Maybe try some sort of cooling system additive to help make the intercooler more efficient.