: 2005 Northstar Knock on Start Up

11-23-12, 07:15 PM
Hey guys,

I have a 2005 Cadillac STS, with the Northstar under the hood. The car has 77K on it, and has bene a pretty good car since I have had it. Yesterday, I went out and started it up, and got a pretty severe knocking sound at startup and it pretty much went away immediately. I had my wife start the car while I listened to the engine, and it appears to be coming from the front of the engine. If you turn it off and start it up again without letting it sit for a while, the noise isn't there. This makes me think something hydraulic in the engine. Is it possible a timing chain tensioner is failing? Could this be the sound of carbon rap? I haven't heard it before, and the day before it first happened we took it on about a 140 mile freeway drive up to the in-laws for Thanksgiving. Any tips or what to look for are much appreciated.

thank you,

11-23-12, 08:54 PM
Cold Carbon Rap is more of a tick rather than a knock. Sounds just like lifters and goes away in 30-60 seconds. If that's the problem, a good dose of WOT usually cures it.

Chain tensioner problems are almost unheard of, especially at only 77K.

11-24-12, 11:08 AM
No, this is not a slight tick. This sounds more like a bag of marbles near the front of the engine. It goes away pretty much immediately, about the time the starter is done cranking. The car has been sitting overnight, and I plan to move it into the garage today. I will try and get a video w/audio of it today.

Is it possible to have piston slap for a few seconds right at start up? Thanks for the input.


11-24-12, 11:25 AM
Its the VVT

My 05 does it dads 07 does it, cold weather makes it more pronounced.

11-24-12, 11:52 AM
also it could be the AIR pump but VVT seems more likely since it goes away so quickly

11-24-12, 12:11 PM
Hmm. I guess it caught me off guard, because I have had the car over a year, and all through last winter never heard it. We were up in Sedona AZ, overnight lows were around 50, and the car was parked in the garage. I really hope it is something normal.


11-24-12, 12:34 PM
well you could be a bit low on oil ... when's the last time you checked the dipstick?

VVT works on oil pressure ... thats why it doesn't happen if you shut the car off and start it up again

11-24-12, 12:47 PM
Rippy, I didn't realize that it also operates on the oil pressure. To be honest I am not too sure how the VVT functions, time to make a google search :) Checked the oil right after hearing the noise, and the oil level was good. I actually check the oil level at every fill up. May be a little paranoid, but 30 seconds to check oil is much cheaper than replacing an engine :) And the OLM is showing 80% currently. I also read a little bit more into the piston slap/carbon wrap, and found a mention that on the Northstar carbon build up can cause some slap on start up. It may be time to do some WOT clean out.



11-24-12, 02:36 PM
I assume you are using synthetic oil? Because the VVT is hydraulically operated, synthetic oil is a must during cold starts (not that I consider 50 degrees cold, but the engine might).

11-24-12, 03:08 PM

You are correct. I use synthetic in all vehicles. My choice is Mobil 1. And I use the Mobile 1 Oil Filter as well. Sometimes a NAPA Gold, but where I live now a NAPA is a bit far away.

11-24-12, 04:57 PM
It could be that someone changed the oil and filter and replaced the filter with one without a drain back prevention valve. At shutdown all the oil in the system drains back to the pan and it takes longer at the next start for the pump to pick up the oil and build pressure. Meanwhile the valve gear, VVT, and chain tensioners all sound off. The OEM filter has a built in check valve that prevents drain back.

11-24-12, 05:30 PM
I thought about the anit-drain back, however, I thought that all Mobil 1 oil filters had the anti drainback valve. I will have to verify this however. I do the oil changes myself, so unless someone swapped it out while the car was parked, it should still be the M1 filter :)

11-24-12, 06:50 PM
Unless you're getting a good deal on the M1 filters you might want to just use the ACDelco OEM filter (PF61 or PF61E) next oil change. Besides the anti drain back valve all filters are pretty much the same and the 61's are so common that they aren't pricey at all.

11-24-12, 08:04 PM
A lot of times the local parts store will have a 5qt jug of M1 with an M1 filter for $29.99. I have 3 cars and all of them are running M1. And not one of them uses 5 qts on the dot, so I always have residual that I end up carrying over till the next change. Works out pretty well in the end.

11-24-12, 08:31 PM
Where I get my filters I can't even find a PF61 anymore. All PF61E's.

11-24-12, 10:54 PM
What is the difference between the PF61 and the PF61E?

11-25-12, 12:02 PM
New "E-Core" filter.

use the proper WIX filter - probably 51522.

11-25-12, 12:25 PM

11-26-12, 11:56 AM
nothing wrong with the newer "E" filters

11-27-12, 05:42 PM
I agree. There's no good reason to avoid the Delco branded filter, no matter who manufactures it, e-core or not.