The outside temperature was -2 *F when I started my engine and it has always had a slight tick when the engine was cold (like many engines do). That'* not the issue though. the issue was when I put it in drive to take off.. The engine sounded like a pop can full of tiny pebbles being shaken about slowly when I pressed the gas to accelerate. The noise increased with engine RPM.. I have no idea what would make my engine start knocking, especially with only 51,000 miles! The oil pressure was 115 PSI during all of this as well and I let the engine warm up for about a minute and a half before driving off. I didn't go over 2,000 RPM. The sound slowly went away as the engine warmed up and by the time I got home it was completely gone... Ideas? What would cause an engine to knock when it was cold, but to sound almost normal once warmed up? My gas mileage also went from about 40 MPG instant @ 55 MPH to 21 MPG instant @ 55 MPH.

what kind of oil do you have in it?

Check out this site

I think the 4LV8 is close enought to a Northstar that it could still be considered.

http://www.pistonslap.com/

Does it display any of these problems, if so thats what it is.

In the past, before I started using full synthetic engine oils, cold temperature starts would cause lifter clatter. Especially when the temp was below 0 and the car had sat overnight. I've also had it with synthetic oil after a sub zero start-shutdown-start while the engine was still very cold. The Northstar has hydraulic lash adjusters that still need oil lubrication to operate quietly. Piston slap (which I had on my '02 T/A LS1) is usually lower pitched and sounds like a diesel engine. Lifter clatter can sound just like a can full of marbles, high pitched and "rattlely". Try switching to a full synthetic oil which are supposed to "pour" at -50 F.

Did you check out some of those pages on there pretty funny, fell bad for them but kinda funny.
http://www.pistonslap.com/photos/tahoe_ad.jpg
http://www.pistonslap.com/photos/tahoe_ad_2.jpg

You are right it could just be lifter noise

For some reason, I think you put some nice 40 weight in it. The reason I asked this:

Was because of 1) The high oil pressure - 115psi? More is not better here, I'm thinking you've got molasses for oil. 2) Cold temps causing high pressure and poor pumpup of the hydraulic lifters.

That gives you the slack in the valvetrain, your "pebbles in a can" sounds, and poor running (valves aren't opening all the way)

By the way, a minute at -2 degrees is not going to warm anything up. In extreme temps like that, I'd say you need 5-10 minutes minimum. The best way to warm up the car however, is to drive it... but it'* your gas money.

When its that cold the oil becomes thicker. Thats why there are multi-vescosity oils. His oil was probably as thick or thicker than 40 weight would be at that temp, which would explain his oil PSI and the ticking. But after a few minutes of warming up that should thin out and the ticking should go away.

Shawn

I only run 5 W 30 in my engine. The place that changes my oil doesn't even carry any 40W oil.. I asked what all they had and basically they limit their supply to 5 W 30 and 10 W 30 unless specifically asked to put anything else in.. They said they put 5 W 30 in it though. (my manual calls to use 5 W 30 year round.)

Some good points above but here'* another idea;

I've seen quite a few engines that really disliked 10W30 oil when used instead of the recommended 5W30. Maybe they put the wrong weight in your car last time thinking it wasn't a big deal.

It might be a long shot but I have seen this before.

Cheers,

They had to have. 10W30 has a pour point of "around" -20degrees F. But it'* pumping point (the point where it'* thin enough for the oil pump to get pressure) is about 0F. Just another reason I don't take it to quick lube places. I have a friend that drove out of one of those places where they didn't tighten the drain plug enough, and it rattled out within a couple miles of leaving. Dumped all the oil out, and burned up the engine. He'* still working on a lawsuit to get a new engine from them.

Anyways, if you'd like to see your engine running for some time, I'd suggest draining out what you have, and refilling with synthetic 5w30. Good to -40F to -70F.