SM465 eternal rattle (spark knock) on highway

[JoeliusZ28]

Well I thought I had the truck "dialed" but the trip proved otherwise. I was hauling about 2,000 lbs worth of stuff this weekend and she didn't like it one bit. Had to turn the dist back 10 degrees and switch to premium fuel and she was still rattling a bit. Starting to think this mediocre steed is just tired because i don't think putting a load on the engine should affect the timing requirements that much.

 

[diesel4me]

2000 lbs = 1 ton,and thats a lot of weight,especially for a 1/2 or 3/4 ton truck..
It could be the 305 is just struggling too hard with the weight and gearing,its simply under powered ?..
(I forget what you have for gear ratio,anything under 3:73 with a manual will make the engine work hard,especially under a lot of weight,and larger tires will make it worse)..

If the engine is running hot,it'll be more likely to ping too...not "overheating" hot, but close to it will encourage pre-ignition..

 

[JoeliusZ28]

yeah its a 3.08 gear and thats definitely a big part of the problem. The spark knock was a bigger concern to me than the lack of power i knew it wasn't going to be an all-star tow vehicle. But I also didn't think it would struggle that much considering I don't have an overdrive, and the truck seems to pull like a mule in any of the lower gears. My 98 half ton (350, 3.73s) had an easier time pulling 5k pounds at highway speed and it would maintain 80 in overdrive (Id leave it in 3rd under 80mph).

As far as heat goes, I was definitely pouring the coal to it, but the engine stayed cool. Has a 180 t-stat, and I have a 3-row radiator that probably has nearly double the cooling capacity of the original. The temp gauge never budged. I did notice however the spark knock was worse during the heat of the day, so you are probably correct about heat in the combustion chambers.