OK, my Dad's 98 Chevy Blazer had the 4.3L V-6 with around 110,000 miles. It has had 3,000 mile oil changes relisiously since new and runs fairly decent still. However, it has what I think sounds like moderate rod knock on cold starts. It's definetally not piston slap, I know what that sounds like from my 3.4L Grand Am. It doesn't sound like a lifter because those "tick" more than knock. The sound goes away after about 20 -30 seconds. Oil pressure is still normal and comes right up instantly after you start it cold. Should I be concerned at all? I'm thinking maybe auto-rx might help, but it has had 3,000 mile Pennzoil changes without fail. Is it normal to sometimes hear rods hammering away wwhen the engine is very cold? Thanks for any info.
Rod Knock?
- Thread starter Drew99GT
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Drew, I doubt it's a rod knock. If a rod bearing was that loose, it would also knock when hot. However, it might be from loose endplay in the crankshaft. When the side/thrust portion of the main bearings get worn, the crank will move back and forth when first started, and this movement causes a knock.
If this is indeed the cause of the knock, I would put it in the same catagory with piston slap. Annoying and irritating but not really serious.
If this is indeed the cause of the knock, I would put it in the same catagory with piston slap. Annoying and irritating but not really serious.
Hmm, what oil filter? And what viscosity? The only time I had any noise(same engine) was last winter it had a change done at Pep Boys with 10w30 GTX and their ProLine filter. I'm assuming it was from the filter. I've never heard it again. I always used AC filters and M1 once.
It probably has a Pennzoil oil filter, aka fram, with Pennzoil Conventional 5w30 oil. That's what they use at the place he takes it to. I doubt the noise has anything to do with the oil filter. The oil pressure instantly comes up tp 60 psi on cold starts. But sometimes the knock sounds downright disturbing when started cold.
Yeah but I don't know how accurate factory guages are.
I'd try a different filter.
I'd try a different filter.
The gauge on the dash in most GM's is fairly accurate. I've had a mechanical oil pressure gauge hooked up to his truck before when trying to diagnose low oil pressure (turned out to be the lines that go to the oil filter) and it ways exaclty what was displayed on the dash. Seriously, it probably isn't the filter at all, it would be in bypass anyhow when cold. And the bearings do have oil pressure. So, hmmmmmmm, what do I do? Or should I even worry about it?
Hey guys, thought I'd bump this one up for an update. Knock is getting worse, but still goes away completely after warmed up. LoneRanger, you may be on to something. When I changed the oil a while back, there were some pretty large chunks of metal attached to the magnetic drain plug. Yea, not good to say the least, but one of the chunks resembled the "thrust" portion of a main bearing insert. Main bearings usually have a ridge on each side, and the piece stuck to the drain plug looked like half of on of those ridges, broken in half.
This vehicle did have the infamous intake gasket changed; perhaps coolent contamination has finally taken it's toll on the bearings? Also, the truck has run 5w30 always, even in the hottest of weather; seen a few trips to Pheonix in the summer with the 5w30 Pennzoil. That probably didn't help things I would imagine. Any more thoughts? Dad isn't ready to believe that his beloved GM engine may be on it's way out
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