xkikbxr

Hi, I have an 02 Silverado 1500 4x4 I belive it's the small 4.8L Auto. The problem I'm having is Now that the cold weather is here, the engine started knocking for a couple of minutes when I start it. Once it's warmed up it goes away. I've tried different weight oils in it with no improvement. Any thoughts would be helpful. Oh It has 82,000 miles on it. The other problem just happened this morning. I started it and the idle would go all the way down to just having the engine chug almost dying to raising up in idle to about 3000 rpm's. Like I said any thoughts would be helpful. Thank you.

cams 98 silverado

the knocking sound is your exhaust chattering like your teeth do when your cold. mine does the same. when your engine is cold it idles differently when its a summer day cold start. the idle goes up more to warm it up faster and that idling is sort of matching the vibrating frequency of teh exhaust. i thought i had major problems too... but after crawling under my truck and listening carefully, i found the tubing to be the noisy culprit. as for the rough idling that sounds a little weird. mine on winter cold start idles at 980-1000 rpms and my problem is my cooling system is SOO sexy that it stays at like 160 deg. or so... and no matter the driving... it will go up then cool down fast. ill go 75 down a road. hit the normal temp. hit it in neutral and the temp falls to 160 lol. i think i gotta swap out thermos for wummer/winter. 190 winter 160 summer... dunno yet. but yea. hope it helps.

xkikbxr

Thanks Cams98,
I'll crawl under it and check it out. But you think it may be the exhaust?,So if I install a heavy gauge exhaustwhether it be wolmanized or stainless, would the knocking go away??
As for the cooling. I'm sitting at right about 200 degree. I have no problem in summer or winter. If I have to get out quick and have no time to warm the engine it still only takes about 2 miles for the heat to start and at about 5 miles I have full heat.

cams 98 silverado

well the difference in your cooling is because of our year trucks. when an engine is cold it uses more fuel to warm up and such thus the reason of a high idle. so auto makers put in different thermos to regulate this and to get sales up with these fuel prices, they make the engines run hotter. a hotter engine runs more efficient in the way of exhaust emission and so on. you get a hotter running engine you burn more exhaust gases and accompanied with better cats you get better emissions. trucks like mine run cooler. todays suburban run at blazing 210 running temp and over heating is at 260. also... since my trans cooler line goes through the radiator. my transmission is running cooler. its running at just the right temp. any lower would be a little bad for me. transmission temps are critical. you want your trans to run between 140 or so and 190. youll get hotter with towing an so forth but that is a good temp range. and as for your chattering exhaust. i dont think it will make a difference in your gauge of tube used. its just the engine being cold shivering and that shivering matches the resonant frequency of the exhaust. and i was wrong to say vibration frequency. its resonant. good ol physical science. my truck with its open engine bay takes a tad longer than yours to warm up. and it cools down so much faster. but. perhaps... and this is only theory. but if you installed stiffer polyurethane motor mounts. it wont chatter. your chassis will absorb the vibrations. but then again thats goin pretty far to get some chattering away. and its only theory. but. try it out. on a cold start get under and check. listen very very carefully.

xkikbxr

Thanks for the advice, I'll crawl under it tomorrow. But as for the hotter it is the better fuel mileage I'm not sure about. I get about 12 - 13 intown and I only get a max of 17 on the road. I also drive it very very easy. I don't even exceed 1500 rpm on take off. Thanks again.

cams 98 silverado

not fuel mileage. emissions. its the fact that your engine runs hotter to burn more exhaust fumes and get your cats hot enough to burn more carbon an such.

jkgray80

Your noise is piston slap. Common problem w/the earlier 4.8,5.3,6.0. No ill effects, dont worry about it.Sometimes 5/30 synthetic will quiet it up some.