oil viscosity question

[moveoverGM]

This will be my first winter with my 73'. It has a 360 V8 and up until now I have been putting 40W oil in the engine. We have had a long hot summer here and that weight oil made sense. That is because it is technically still going through a "break in" and seating of the rings since having a total teardown and rebuild 6 years ago. Estimate the miles on the engine since the rebuild at 2K. But winters can be cold here in Tennessee especially in the mornings. Would I be safer now to switch to a synthetic oil? Perhaps 10W-30? Don't want the engine to suffer due to thick oil especially first start-up in the morning.
Thanks, Donald.

 

[Jasperrc]

This is a subject that may have opinions that are all over the place so I'm curious to see what folks think.

Personally, I wouldn't change oil types, just maybe the grade. Maybe switch to a 10w-40 for winter? But I wouldn't switch to synthetic unless you are making that change permanently anyway.

 

[fatherdoug]

You're correct. There will be lots of personal opinions. I don't know what the original recommendations were for the truck, but I'm guessing in '73, they were still big into single weight oils that were swapped from summer to winter.(20W and 30W) I also think 2K miles is well past the break in period for an engine. I was told not to tow anything on my engine rebuild until after 1K.

You could go with a multi weight oil like 10W-30 and call it good.

 

[BigNate]

I'm of the opinion that the modern synthetics are amazing and unless you have leaks, I think now that you've broken it in, it would be the perfect time to switch to a full synthetic. I usually run AmsOil now (became a dealer) but there are a few that rate pretty high.

 

[Ozzie]

Here's one more view.
If the break-in is complete it should be O.K. to switch to a synthetic.
I don't have the manual for the '73, but I do have one for the '75. Here's what it says on viscosity and ambient temperatures:

Multi Viscosity oil:

consistently below +32F: 5W-30 (unless operation is sustained above 60 MPH; then use 10W-30 or 10W-40)

consistently -10F to +90F: 10W-30 or 10W-40.

consistently above +10F: 20W-40


Single viscosity oils:

consistently -10F to +32F: 10W

consistently +10F to +60F: 20W-20

consistently +32F to +90F: 30

consistently above +60F: 40

Whatever you decide on viscosity, always use a reputable brand rated appropriately, and if the engine has flat tappets be sure that there's enough zinc compound in the oil as you have no cat converter to consider.

 

[CowboyBilly9Mile]

Multi Viscosity oil:

consistently -10F to +90F: 10W-30 or 10W-40.

^^^^ My vote, and good for any max temperature you encounter where you live despite the +90F. Besides, the recommendations don't cover over +90F, lol.

......... be sure that there's enough zinc compound in the oil..........

Zinc, something that is being added to oil in smaller and smaller doses in recent years.

 

[BigNate]

^^^^ My vote, and good for any max temperature you encounter where you live despite the +90F. Besides, the recommendations don't cover over +90F, lol.



Zinc, something that is being added to oil in smaller and smaller doses in recent years.

I'm on the other end of the thermometer concern. I once rebuilt a Buick v6 for a Toyota SR5 and while it was still in the break in period, temps dropped to -20 and I ruined the fresh rebuild. I don't do many rebuilds anymore, but learned from an engine builder one tip after this.

He said" build it to run it, don't build it to wear into running it." Much to do about clearances but his method established a good local rep with the dirt track and IMSCA crowd. He would start one up and run it up to full rpm as soon as it was warm.

The fresher the engine the more I worry about the colder temps in the winter. I'd run nothing heavier than 10-30 in the winter unless it's synthetic and even then no more than 10-40.

Depending on test criteria they all claim to be best but AmsOil, Royal Purple, Redline, Schaffers, Mobil 1, Castrol full synthetic, and now even Pennzoil Platinum. are pretty valid. Any of these would be a better choice in cold weather, more money up front, big savings later.