Chevy 305 Knock

Hey guys... Well, I've been cruising around in a 1996 Silverado with the 5.0

I love the truck, its low and comfortable, and gets a whopping 14 mpg (better than the 9 mpg the 2006 f150 I used to have got), but as soon as it got cold last winter, it started knocking when it was cold. The knock always goes away as the engine warms up and/or you accelerate. I figured it might have been weather related, but it did it again as I was coming home from school on a 70 degree day earlier in the week.

Idk what it is, since it always goes away. Any ideas?? Its always started, the truck has 115k miles on it, and its stock except for flowmasters and a cold air intake. I also have the typical 17 year old lead foot, and I always keep the oil changed in it. Idk if any of that makes a difference, but whatever.

I'm wondering if its that serious, or what?? It needs a new starter and an alternator, and if the things about to blow up or it needs a ton of work,maybe it would be cheaper in the long run to put a 350 in it or something??

First of all what is the engine oil pressure when you start it and what is the oil pressure when it is at operating temperature. If the oil pressure drops a bunch when it is warmed up you have a problem in the crankshaft area. I would say that you have piston slap and it is going away when it warms up because the pistons expand and get tighter. Which would bring it nearer the origanal tollerance. All and All it is a very simple engine to overhaul. Just my opinion Dave Thompson jr.

You have the infamous GM piston slap problem. Google it and learn more. I have a 99 Chevy with the piston slap. Motor has 75,000 miles on it. I just don't pay attention to it anymore. GM screwed up the tolerances in those engines.

Can't say what your problem is.. What I can say is my dad's brother has a 94 with a V-8 (I am unsure, always thought it was the 350 though) that "knocks" at startup.. Has for 11 years (over 100k) that I know of.. It shows strong oil pressure once running, just the cold start.. Truck has just about 300k on it now. I don't know when it started knocking, but I know it has done it pretty well ever since they moved up here from Georgia in 1998/99

Seems like when I was a kid, mom and dad had a 4.3 v-6 in a astro van that did it from about the first oil change.. The solution the dealer/GM came up with was a larger oil filter, and seems like they used a different viscosity of oil too maybe (If I recall correctly, they bought the van around 94, and sold it in the very late 90's, so i was a young teenager when they bought it) But I don't recall if it actually fixed it or not.

You might try Lucas oil additive on your next oil change.. It would help keep the oil "in place" when sitting (or so the product claims)

Brad

Put a bullet in it's brain and go shopping for a vehicle that gets at least 30 mpg. You can't afford that gas guzzler at $80 a fillup every week.

Its called the 305 death knock!

True, but I can't haul scrap with a honda civic...

I think it would be really cool to have an impala or like a 90s mustang or something, but I like this truck... Its great for tools, junk, etc, and the gas mileage could be worse. My mom pays for the gas it takes to get to school and back, and I don't do very much more driving than that, so its not that bad.

Back when I was with my dad in Michigan, I drove his F150 around. It got 9mpg in town, with the 4.6 V8, totally stock. On the highway trip from near Cleveland, OH to Port Huron, MI, it got something like 12.5, which is a record (at least to my memory). He's one of those people that draws ignorant conclusions based on one or two experiences, and was convinced that all american vehicles get bad mileage and are poorly built (that one came after the air conditioning went out, warranty covered it). The idiot ford dealer in town said there was nothing wrong with it, and since I wasn't buying gas for it, I didn't make a big deal out of it. But, if it were my truck and/or gas, I would have found a real mechanic. But, thats just me.

Thats re-assuring... I don't plan on putting 11
more years on this one, but getting me through
school and then some would be pretty nice... And
then maybe it'd be a shop truck or something, if
I'm ever lucky enough to start my own welding/fab
shop somewhere.

I'll definatly try the Lucas oil, I'm probably
changing the oil in it again this weekend (its
about that time). The larger filter is new to me,
but I don't really see how that could help
anything... But, I'm no mechanic.

Whew, thats what I was hoping to hear

Hmmm, thanks for that. I guess thats what the radio is for, after all...


"I have a GM 3100 that has cold-slapped from day one. It now has over 200k on it. It is well known in low-friction, short piston skirt engines and is not associated with engine failure, damage or lack of durability in any way"
Website

No, its got really good pressure... When its cold, about 60-70 psi, and then 20 or so when idling, and 30-40ish when just cruising down the highway, or whatever...

Is that bad? It seems kind of normal to me...

The filter trick is actually a filter with a good anti drainback flap to keep the oil in place for start up.

I agree with Lanse. Those engines had really short piston skirts and were noisy from day one in many cases. The short skirts let the piston rock just a little rattle. GM did that to reduce internal drag in the engine. It worked, but they tend to be noisy. On the up side they seem to run for ever without issue. I would not worry about it.

Greg

no answers here ... thats why i will not buy GM anymore., THIS IS My EXperience ... starting with pontiac and olds gutlas V SICKS in the mid 80s, , My wife and i Loved their Styling , but in Spite of My Best efforts , Every one of the 4 GM JUNK that i have owned ,.. Were ready for the junkyard when they left my drive. that INCLUDES a 1994 NORTHSTAR Cadillac !...bUT . I still got a fine 1958 Chevy Viking grain truck With a 283 that is a total Sweetheart //That GREAT Generation of Chevys made it possible for 2 decades of sales and Decline by putting junk in the driveways of Many Loyal GM believers that were hoping for Qaulity their parents enjoyed .. btw, every Ford I ever Sold after I thought it reached retirement age went on to continue service in the community for many Years for the next owner,. I still OWN Every Chrysler Product I ever Bought , AND I WISH I HAD BOUGHT MORE ...

You should be getting over 20 MPG with a 305. 6.0 litres are known as gas guzzlers and will get 14 MPG.

How often do you haul scrap? How much can you get in a pickup? I haul two loads a year, 7x16 trailer,3000 lbs, Geo Tracker, 4th gear, 30 mpg. I know 95% of your driving is two people or less, no load, no scrap.
You are a smart kid, Sit down with your phone calculator and figure it out.
How many dollars are you puring into that truck a week?

Real synthetic oil (Amsoil or Mobil1) will make it go away sooner or occur at a lower temperature. My '98 5.7 does the same thing. The syn oil gets there (skirts) quicker.

20 at idle and 40 at hot cruise is what mine carries.

I have 103K and it is slowly getting worse, occurring at warmer temperatures and lasting longer.

Hey Lanse, there is a GM technical service bulletin (TSB) that sounds like it might pertain to your noise. The number of it is 99-06-01-003.
The thumbnail sketch is you need to measure the main bearing clearance. All L30 (5.0)and L31 (350) engines were built with a .001 undersize main bearing in the #5 position (the very back one). What happens is the crank flexes and you hear that deep knocking noise. What you need to do is pull the oil pan and check your main bearing clearance with the "green" plastigauge. Ideal clearance you want to see is .002. What I'd do if it were mine is slip in a new set of bearings. Unless it's been worked on, it probably still has the std size bearings in it.
Measure the clearance on the rear main. If it's greater than .002 but not more than .0025, retain the original .001 bearing in the block and install a .002 undersize in the cap.
If it's .0025 to .003, install a .002 undersize bearing in the block and cap.
If the original clearance is .003 or greater, install a .004 undersize bearing in the cap and retain the original .001 bearing in the block.
Next go to the connecting rods and check them with plastigauge. You want to get a clearance of .001 to .002. If the clearance is greater, replace them.
All of this info is straight out of GM Service info.
I would also get a new oil pump and pick up tube for it. The tube is a press fit into the pump. I've always heard people say they weld them in after installation. The pump is cast iron and the tube is steel. Since welding to cast iron is an art form, I made a bracket from a piece of steel that is welded to the tube and is secured to the pump under one of the bolts that holds the pump together.

Your oil pressure sounds about normal. I just built a 383 for my 98 that runs about 75 cold 45 hot. It drops off to about 30 at idle hot.

you"re smarter than the average 17 yr old, paying attention to your vehicle, most 17 will turn up boom=box and never hear any noise. could find a used 305/350 with less mileage and drop in rather than tear old one apart. time you spend tearing old one apart to check it out, might as well overhaul it. if truck is in super shape, two decisions to make.

i have 1997 gm that i use as service truck it has 350 gas with over 700000 km or 420000 miles has had that knock since i got it with 225000 km still good pressure and runs good

Howdy,
Lanse, as long as you are doing an oil change anyway use an AC oil filter (not a chinese ripoff) and a quality oil & throw in a can of STP and turn up the radio. The 305 is my second least favorite engine right behind the 4.3.
Bob S.

its a normal thing in the chevy trucks i got a 97 silverado with the 5.7 and it does it too its got 273000 miles on it and i just ignore it id keep on drivin it.

Just drive it!
I had a 92' Cadillac Eldorado with the 4.9 engine that had the imfamous 'cold knock'. I bought it dirt cheap because the former owner was not about the invest $3,000 in a new long block for it. Between myself and my daughter we managed to eeek another 10 years and 76,000 miles out of this without ever removing a valve cover. I sold it last fall with 235,000 miles on the clock and as far as I know, the guy that bought it is still driving it. As soon as the temperature readout on the dash reached 105 degrees, the engine sounded like new.