Hello everyone! Well, it happened again. My original engine committed suicide at around 122,000 miles a little over a year ago, so I went with a 70k used engine that is already on it's way out. Specifically, the engine is exhibiting almost zero oil pressure at idle and makes a knocking sound over 1700 rpm.

I don't understand what I am doing wrong with this truck. She was always pampered with the finest wine (Royal Purple/ Mobil1) and the finest steak (Shell 93 RON). What gives?

Could it be that these 4.3s aren't designed to be driven over 2500 rpm? I am asking this because my truck developed a knock both times (1 year apart) when I had travelled two hours on an interstate where anything below 80mph is a death sentence. Usually this truck never sees any action above 2000 rpm because I just don't drive fast.

Since I always need a "dirty truck" handy, I am left with two options--either to get another used engine (and never travel over 60mph even if it means death) or just run a 100 miles away from GM (this is the only GM product in the family and it's asking for a third engine already). Please enlighten me with your wisdom.

Thanks.

 

i think its just bad luck, i see cars at work with 50k on the clock with bad transmissions or knocking engines. the 4.3s have always treated me right i have one in my offroad truck and for the last 7 years this thing gets red lined all the time trying to climb hills

 

My girlfriends blazer soon to be mine has 2002000 miles on the engine and transmission and I red line that engine on a daily basis but I also follow routine maintenance on it to the T. No burning oil no smoke on start up no knocking. Drives smooth to since I put some manroe sensa track shocks on it. The only major repairs done to it was I had to replace the rear axle at 175000 do it. The oil never being changed in it

 

My first thought is LIM gasket failure causing premature bearing wear. Did either of the engines have mysterious coolant loss before failure? IMO tight LIM gaskets are key to getting these engines to live long healthy lives.

 

Sir, I just don't know what to say to that. I always replaced my oil at 3000 mile intervals, replaced cap and rotor at 7000 miles with Ac Delco units, replaced radiator with the Ac Delco unit at every 45,000, replaced oil after any continuous driving of 100+ miles (sometimes twice a week!), and still I had to witness failure twice. Mine was never an oil burner and always got around 24.5 - 26 mpg on highway (on shell 93 RON).
Funny thing is that I was almost beginning to like this truck before the knock developed the second time around. I have a QX80 and a 08 Navigator L as my primary and secondary trucks, but this little Bravada was somewhat special. Last winter it easily traversed miles of ~2ft snow when no other stock truck could I don't think I'm going to get over her anytime soon..

@KM346
I was well aware of that issue with both engines so no, there was never a LIM gasket failure situation. The first engine had it replaced around 90k, and the second engine got the Felpro problem solver kit right at installation. I was also aware of the absence of priority main bearing lubrication in these engines, hence why I was so **** about oil changes..

 

Alright friends, I have an update for you! By some weird trick of nature I met a guy at an autoparts store a while back and his 97 Blazer had once encountered similar issues under similar circumstances. To summarize him, he insisted on never filling up with 100% 93 RON.

My degrees in Mechanical Engineering and MD become null and void at understanding this. However, my Bravada did pickup a tonne of power after filling up with 89 RON this weekend. The knocking sound is somewhat occasional now. This phenomenon is different from the last time around where my original engine would knock at every rpm everyday everytime.

I dont have much experience with pushrod engines, but my research has revealed that this might have something to do with the top end. I'd use a mechanic's stethoscope to isolate the problem area, but the stupid bugger wont knock at any rpm on neutral

BTW: Would a fingernail size gray goop on oil drain bolt be of any concern? The oil was only 1500mi old when the knock developed and I changed it. I have had spun rod bearings before and this time I was diligently looking out for shiney speckels in the oil, filter, and on the drain nut but I found none. My coolant level seems fine and cant be thinning out the oil. I could pay a mechanic to get the truck sorted out ASAP but where is fun in that? I need to learn everything about this 4.3 pushrod, and I consider this thread my group project

 

Trans slipping?

 

I think its just bad luck with getting other peoples junk.

Ive had 8-10 blazers. all 4.3s. I beat the living poo out of them. 5k rpms everday. heavy foot,dont care.

Ive done 2 transmissions,but not 1 motor. Do a oil change every 3k,and treat it like you want too. they deal with it.