Originally Posted By: Jim Allen
At the risk of belaboring this, some comments:
1) I didn't catch how hard you work your truck but if you fit into that "normal usage" category as shown in your visc. example, the 10W30 would be fine. There are are people here, me included, that run 10W30 in diesels with good results long term. And if it's in the recommendation, and you are using the vehicle within those recommendations, then you have nothing to worry about in or out of warranty. If you fit that "normal" category, there is really no benefit to going to heavier, though no loss, except perhaps slightly in mpg.
2) The day-to-day differences between a 10W30 and 5W40 aren't huge in any practical comparison. Neither are the long term differences. We can debate lots of "what-ifs," most which never happen. Most people don't work their trucks hard enough or often enough to really "need" a heavier oil or to overwhelm the lighter oil, especially some of the very good stuff we have available now. If you work the truck a high percentage of the time, then the needle swings more into the 5W40 camp.
3) Since you just had the engine partly apart and it never hurts to flush out any potential contamination.
4) We've been having this soot-stained xxW30 vs XXW40 for diesels debate for a long while and neither side can produce much in the way of studies or data to support either argument absolutely. No one-size-is-best-for-all magic bullet. It all comes down to matching the viscosity to the operational characteristics and oil temps of the engine. But any plusses and minuses may even out in the long run, whichever camp you are in, making this debate a waste of bandwidth. But then, we simply can't stop ourselves!
Good thoughts, Jim.
But my question isn't so much about performance when loaded as it is about cold starting.
If I could find a 5w30 CJ4 rated diesel oil I would probably use that! Unfortunately I haven't seen anything like this anywhere, so in order to get 5w oil I have to spend the money on synthetic 5w40.
My question was whether or not 10w30 would adequately protect the engine for cold starting down to -25 F.
Bad News, I hadn't already decided anything when I posted this. I wanted to know if 10w30 would suffice for the winters we have up here. What made me decide to get 5w40 was going through historical data and seeing the week they had up here last January where the lows were near -20 and the highs were around 0.
This is my first winter up here so I didn't know exactly what to expect.
