Cadillac Owners Forum banner

1 - 13 of 13 Posts

·
Registered
2008 STS
Joined
·
11 Posts
Discussion Starter #1
Hi Guys. New to the forum because I just bought my first Caddy. It's an 08 STS 4.6 RWD beauty. She has 108,000 miles. 9718732994.jpg
A few days after I got it home I started hearing a knocking noise. Hasn't been getting worse but it wasn't noticeable at the dealership. I found a youtube video that is not my car but the engine in the video sounds exactly like mine does at idle. https://www.youtube.com/watch?v=PA5wMF785RI
The noise is fairly loud in the cabin during acceleration. Especially with the radio off it can be heard through the first three gear shifts until it levels out in speed.
I have the entire service history of the car. She was regularly looked after and ALL factory recommended maintenance was performed right on time. She had one owner before me and really looks to have been babied.

She runs perfectly and idles very smoothly. Plenty of power out on the highway and doesn't skip a beat.

My first guess was carbon knock but the sound does not change or go away when it warms up. Does this ring a bell with anyone on where I should begin to look? I have read mixed reviews of top end engine cleaners.

Thanks in advance for the advice. - Carl
 

·
Registered
05 STS4
Joined
·
4,241 Posts
The YouTube video describes it... It's VVT noise. Run premium fuel like you should and the noise is reduced however its NORMAL and ALWAYS PRESENT.
 

·
Registered
2006 STS 1SG & 2007 STS 1SE
Joined
·
7 Posts
Welcome! Congratulations on your purchase.

Don't worry! The longitudinal (as opposed to older transverse-mounted) Northstar is nearly bullet-proof. My wife's 2007 is a bit noisier than my 2006, but as 1BadCadSTS accurately notes, VVT is just noisy. Many blends of regular run just fine, but if you notice a difference with mid-grade or premium, go for it. I don't experience any improvement in mileage and only a modest boost in performance (if any). I usually run regular; my wife always does.

The forum must contain thousands of posts on the topic. I find the engineering POV the most interesting; higher octane fuel burns slower and does not contain more energy. It's not intuitive at all.

Do use Top Tier gas. It contains the additives high performance engines need to help keep throttle-bodies and fuel systems clean. The STS throttle is 'drive by wire', so if your throttle is at all sticky or jerky off the line, clean the throttle-body. That is worthwhile service.

Resist any temptation to over-tighten the intake manifold bolts. 10-11 inch-pounds isn't much and is about the only odd problem that comes up a lot. The 4.6 thrives on hard use. See the WOT references in the 'Sticky' thread at the top of the forum. My 2006 is over 100,000 miles and uses less than a pint of oil between changes (Mobil1 when the OLM reaches 0%) more than 15,000 miles.

Again, Welcome and enjoy!

Drive it like you stole it!
 
Joined
·
12,816 Posts
Hi Guys. New to the forum because I just bought my first Caddy. It's an 08 STS 4.6 RWD beauty. She has 108,000 miles. View attachment 279882
A few days after I got it home I started hearing a knocking noise. Hasn't been getting worse but it wasn't noticeable at the dealership. I found a youtube video that is not my car but the engine in the video sounds exactly like mine does at idle. https://www.youtube.com/watch?v=PA5wMF785RI
The noise is fairly loud in the cabin during acceleration. Especially with the radio off it can be heard through the first three gear shifts until it levels out in speed.
I have the entire service history of the car. She was regularly looked after and ALL factory recommended maintenance was performed right on time. She had one owner before me and really looks to have been babied.

She runs perfectly and idles very smoothly. Plenty of power out on the highway and doesn't skip a beat.

My first guess was carbon knock but the sound does not change or go away when it warms up. Does this ring a bell with anyone on where I should begin to look? I have read mixed reviews of top end engine cleaners.

Thanks in advance for the advice. - Carl
Hello Carl,

Congratulations on your STS. I realize that you are reaching out to other forum members regarding this situation, but I am here to assist by PM as well. Please send me the name of your involved dealership, full name, VIN, phone number, and mileage to be of further assistance.

Enjoy your evening,


Brandon M.
Cadillac Customer Care
 

·
Registered
2009 STS Northstar
Joined
·
15 Posts
Hey, graycaddy08. I just signed up, but I also welcome you to the forum as well. I just purchased my '09 a couple of weeks ago. Mine sounds exactly like your description. I did start using premium to see if it helped the noise; I cannot say that it does, but my mileage appears to be 2 to 3 mpg better with premium. And, yes, I always buy Top Tier fuel. I also wondered if there could be carbon buildup in the cylinders, so I shot a bottle of Lucas cleaner into it. I purchased the car from a local Cadillac dealer; the sales person did not hear the noise that I did. Even with the noise, I jumped into the purchase head first. I have driven the 3.6 and the 4.6; I still believe that nothing beats a V8 for sound and performance. The 3.6 is pretty zippy, however, and I did not hear any unusual noise form the engine. My STS has 70k miles on it.
 

·
Registered
2008 STS
Joined
·
11 Posts
Discussion Starter #6
Thanks for the welcome NCgator8. When I brought this to the dealers attention, they thought it might be carbon and old plugs. They agreed to cover this service as well as a fresh oil change afterwards. Glad they did this because it was over $450 in service. After the service, the noise was slightly less noticeable. I am very tuned into car noises. I mess around with classic cars and do most of the service on my other cars. Once I was convinced that the engine was as clean as possible and that I wasn't doing any damage to it by driving it, I started paying less attention to the noise. The car has a few other electrical gremlins that I will be chasing down after the cold is gone here in Ohio. The driver outer heated mirror is not heating but it is still auto dimming. The TPMS for the passenger rear tire is throwing warnings daily. Probably a bad battery or sensor. And the driver door handle stopped unlocking upon pulling the handle. Probably a bad micro switch. Not sure if I can just by the switch or if I need an entirely new handle. Plus, the heated steering wheel does not work. Probably won't dismantle the steering column for this one. I have to keep the car outside for now since the garage is too full. No messing with these things until spring. I have to say that overall I am very happy I waited until I found the V8. Lots of torque and very peppy for a large car. I had nothing against the V6 but have always felt better about V8's with a reputation like this era of Northstar.
 

·
Registered
2014 Cadillac XTS, Former 09 STS and 07 CTS
Joined
·
223 Posts
The 3.6L Require Plus Fuel and the 4.6L Requires Premium. I know this because My uncle has the Escalade and it says so for the V-8, I had the non DI and now the DI version of the V-6 and the non said plus and the DI says regular, I don't trust the new standards so I use plus even with the DI now.
 

·
Registered
05 STS4
Joined
·
4,241 Posts
The 3.6L Require Plus Fuel and the 4.6L Requires Premium. I know this because My uncle has the Escalade and it says so for the V-8, I had the non DI and now the DI version of the V-6 and the non said plus and the DI says regular, I don't trust the new standards so I use plus even with the DI now.
All bad info there...

The DI does NOT require anything more than 87 octane.

The LH2 Northstar is recommended 91 octane for best performance but can run on lower (though I don't suggest it).

Also for the record being a V8 (even a Northstar for that matter) does not mean it requires high octane. The 00-05 FWD L37 and LD8 N*s were tuned specifically to run on 87 octane.
 

·
Registered
2014 Cadillac XTS, Former 09 STS and 07 CTS
Joined
·
223 Posts
All bad info there...

The DI does NOT require anything more than 87 octane.

The LH2 Northstar is recommended 91 octane for best performance but can run on lower (though I don't suggest it).

Also for the record being a V8 (even a Northstar for that matter) does not mean it requires high octane. The 00-05 FWD L37 and LD8 N*s were tuned specifically to run on 87 octane.
Well if you read I said I put in plus but I also said the manual says regular.
 

·
Registered
05 STS4
Joined
·
4,241 Posts
framedforlife said:
Well if you read I said I put in plus but I also said the manual says regular.
I suggest you read it too. You state the "3.6 requires plus" and v8s needs supreme just because the Escalade, which uses a Vortec V8 that stares NOTHING with the Northstar used in the STS, needs it.

All wrong.
 

·
Registered
2006 STS 1SG & 2007 STS 1SE
Joined
·
7 Posts
What's more, there are over a hundred blends of gas in the US. Your car, driving habits and local conditions may vary. Here, in SE Wisconsin, premium unleaded is $0.40 per gallon or more higher and just has a little more octane; no more energy, no higher quality, and no real difference I can tell in my V8 STS.

'Framed...' probably realizes that specs, recommendations and owners manuals for one vehicle have no bearing on the best choices for another. Unc's Escalade is no reference to an STS, whether powered by 4.6 V8 or either form of 3.6 V6.
 

·
Registered
2014 Cadillac XTS, Former 09 STS and 07 CTS
Joined
·
223 Posts
I suggest you read it too. You state the "3.6 requires plus" and v8s needs supreme just because the Escalade, which uses a Vortec V8 that stares NOTHING with the Northstar used in the STS, needs it.

All wrong.
I was wrong with mentioning the Escalade but you jumped to conclusions and did not fully read my post.
 
1 - 13 of 13 Posts
Top