Greetings fellow Bonneville fans and Owners! My name is Jim, and I just recently purchased a beautifully maintained 2001 Bonneville SSEI from a friend of mine; a mechanic. This car was his baby. It has 65,000 miles. It'* in pristine condition, from body to interior. It has a deep throaty exhaust sound (Full Borla exhaust system). Well. He told me about the bad thermostat that was on the car, and said he'd replace it for me if I took it to GMC (He'* a certified mechanic). I told him it was okay, and would replace it myself. I went ahead and purchased the new thermostat/seal, as well as a manual so I can get a better idea on how to work on the car if need be.

Well, the check engine light has come on (stayed on) ocassionaly, as I haven't gotten around to putting the new Thermostat in. Everytime it'* been "Engine running cooler..." blah blah. I've had the code reset a few times. Well just the other day the light came on (stayed on) then eventually went off. It'* been extremely cold, so I know that'* the reason. It'* warmed up a lot, and I believe that'* the reason it went off. Well I've noticed a stall it seems in the Supercharger maybe? In mid-rpm range when letting off, then accelerating again, it almost seems to be a "knock". Now, normally I put Shell 23 octane gas in the car. My friend who sold me the car said that he doesn't recommend Citgo gas, because it'll cause knock. I put it in there once, just because it was closests, and it'* started.

So my question. It hasn't caused any flashing Check Engine lights, so i do not think it'* the spark plugs. Is it possible that this is because of the Citgo gas (which was 93 octane)? I'm gonna let this gas run through, then use what I've always used, in Shell. Hopefully that'll correct it. Just has me concerned. Every check engine light code has been for the thermostat. So hopefully I don't have a lower or upper intake manifold problem, as I know the Series II are susceptible to it. I love the car though, and I'm glad to be apart of the Bonneville Club!

Welcome to the club.
Some cars don't like particular brands of gasoline, and if your mechanic friend said the car didn't like the Citgo gas, I'd say follow his lead and stay away from it.

While the thermostat code may not seem like much, without the engine reaching proper temperature, it will not run properly. Get the thermostat replaced, codes read, and report back after those things are done. Also, if you can find out what regular maintenance (plugs, wires, O2 sensor, etc.) he had done, that would be helpful.

When I had the code pop up for the engine warming too slowly a new thermostat solved the problem. chances are it has failed in the open position.

Thank you for the quick reply, it'* greatly appreciated. Well, I went ahead and filled the gas up from a half tank with Shell gas. It was kind've acting the same. I did do a test tonight though. I took my baby out on the highway after filling it up; resetting the average mpg guage, etc. I wanted to see what my mpg were, because I know that with manifold leaks/issues, etc, that your MPG can greatly suffer. I was able to get it consistent at 26.2 mpg. This I felt was pretty good, as I didn't drive for *that* long. It was roughly twenty miles. I don't get a chance to take her on the highway a whole lot, so I found that pretty reasonable, considering it'* "factory" rated (at optimal driving conditions) at 28. This is also with a pretty dirty K&N cold-air: filter that needs to be recharged (got the stuff to do it). I noticed it'* like a clicking noise when the Superchargers guage reads just about 0. So I was thinking maybe it'* it sucking in air. Just feels like retard though.

I most definently will get the code, and report back to you guys. I intend on replacing the thermostat this weekend, as it'* just been way too miserable these past few weeks. Finally warmin' up! Also, I will check up with him on what he'* done maintence wise. Perhaps I do need to change the spark plugs and sensors.

One more thing? I read in the manual that the Supercharger guage is supposed to be centered on zero on start. When I turn the ignition it goes to zero, then all the way to +10, but then settles just above -10. When I asked him, he said it'* always been like that, from when he purchased it as a Certified Used car from his work at 21,000 miles. So do you think that perhaps I need to change the Vaccuum hose? I apologize if these questions have been beatin like a dead horse. Just, I am new here. So bare with me, lol.

Anyways. I thank you for the replies guys! It'* greatly appreciated. I love my Bonneville. It'* ride is so nice. Just with the upgrades it'* had done to it (Borla exhaust system, cold-air, and shorter pulley), I absolutely love it. I wouldn't trade it away for anything at this point. It'* a car geared towards the kid who grew up loving the Trans-Am, but has to settle for a family car . Not to mention the ride!

Semper Fidelis!
Jim

The clicking in the supercharger sounds like the coupler to me, Any SC guru'* got a better idea?

Your boost gauge is working properly. It will do the sweep when the key is turned on, and then settle just above the -10 to show that it is working

Thanks Archon, and the rest that replied. I'm gonna get the codes read tomorrow after work, analyze them; see what, if anything comes up. I'm kinda hoping that the noise is just *bad* gas. It was in no way doing that when I bought it a month back. This is the first time putting gas I normally steered away from. I know that certain gasses can have adverse effect on performance. For now I'm gonna let this tank go. Maybe buy some cleaner to run through the lines. Then STICK with one brand I know the motor likes! XD

One last thing, then I'll leave you fellows alone! I've been considering dropping some octane booster into my next tank. Maybe do that once every few months or so. I've read positive things about it, as well as negative. I'm sure that what the companies say it does in terms of "benefit" aren't necessarily 100 percent true. NOS brand has been given the best ratings anyway. So i figured maybe run that through once along with my standard gas, and get a few octanes higher. Hopefully. Or, would finding a gas station that sells higher than 93 be worth it you think? I dunno if the Bonnevilles sensors would be sensitive enough to tell the difference or not.

Anyway. Thank you once more. It'* greatly appreciated. I look forward to a longtime with this car. As well as future posts and discussions with you guys. It'* nice to know that there are so many of us out there, who can help and guide us through such situations. They most definetly can be stressful, and you've all made it a bit easier!

where are you located?

when the SC couplers fail they make a rattling noise at idle.

Octane booster is a JOKE, it raises your overall octane level by 0.1 to 0.2. If you need to run higher octane than 93 you generally want to use unleaded race fuel.

what size supercharger pulley do you have installed right now, you mentioned it was smaller than stock?

We're here to help people out, so you're not a bother. Don't waste your money on the octane boosters, they do virtually nothing but take your money. Stick with the 93 octane, and get the thermostat changed. We'll go from there to see what the noise may be. It could be something as simple as the front mount. Do you know what size pulley is on the supercharger?

Yes, it'* a 3.40 Pulley by Intense-Racing. Um, the noise doesn't (atleast I can't hear it) happen at idle. It'* past the 2000 rpm range, when the superchargers gauge begins to go above the 0 point. More specifically, around probally the 2200, then once It gets up to 3000 it stops. It'* still getting boost. But just doesn't feel as much as it had been just a week ago, before this new gas was put in. I know that my friend had just had many of the Superchargers parts replaced (he showed me all the reciepts), basically had it rebuilt.

Also, I am from Missouri