Straight 40 to thick?

[TJ's GMC]

Well I was able to get oil filters for my 305 V6 for $2.88 a piece so I stocked up on some. I already changed the oil a few months ago, but will be changing again as my custom for older engines that have had old oil in them for years. I keep changing the oil frequently until it stays clean for longer than before. Anyhow...my question....winter is on its way...and I have a large stock of Straight 40 Napa oil. Is that gonna be a little thick? Seeing as how this is a fairly high mileage engine I thought it should be fine. Don't have an oil pressure gauge on this thing so I have No idea what I'm running at now. Seems to be fine with the 15w-40 I have in it...so I don't think the straight 40 would hurt anything.

[FetchMeAPepsi]

If you're not in a hurry it won't hurt to wait till summer for the straight 40w. I use 10w40 Rotella in mine and she starts up great in winter, but that's variable viscosity.

[TJ's GMC]

Originally Posted by FetchMeAPepsi

If you're not in a hurry it won't hurt to wait till summer for the straight 40w. I use 10w40 Rotella in mine and she starts up great in winter, but that's variable viscosity.

Ok, I found a 5 gallon bucket of fresh 15w-40 that I have so I'll use that. lol. Mine cranks over just fine with the rebuilt starter. haha

[George Bongert]

Greetings TJ!

Take it from an old farm boy, straight 40 is way too thick for winter. You are far better off using the 15w40 oil for winter weather. 10w30 Amzoil Synthetic Oil would be even a better choice over the 15w40. Straight 40 is fine for summer, but running straight 40 in winter, you might as well have molasses in your engine because straight 40 flows just about the same. If you are lucky enough to get the engine started on a zero or below zero day (most engines will fail to start in temps that cold even running a straight 30 oil,) you run the risk of engine damage since you will have a lot of parts starving for lubrication until your molasses thick oil gets to them.

[TJ's GMC]

Originally Posted by George Bongert

Greetings TJ!

Take it from an old farm boy, straight 40 is way too thick for winter. You are far better off using the 15w40 oil for winter weather. 10w30 Amzoil Synthetic Oil would be even a better choice over the 15w40. Straight 40 is fine for summer, but running straight 40 in winter, you might as well have molasses in your engine because straight 40 flows just about the same. If you are lucky enough to get the engine started on a zero or below zero day (most engines will fail to start in temps that cold even running a straight 30 oil,) you run the risk of engine damage since you will have a lot of parts starving for lubrication until your molasses thick oil gets to them.

Thanks for the input George! Napa 10w-30 is going at a good price right now so I may pick up some of that. Trying to flush the system out....then run a good oil. The oil I put in was dirty after a couple months. lol So any new oil will be better than what's in there.

[Foley]

10W-30, 10W-40, 15W40 and so forth. I'm not a chemist but I learned that the multiple viscosity oils are blended for all weather use, and the "W" means winter.

So you get 10 weight on the start up when the oil is cold (or 15 weight) and then it does all that magical chemical heat business as it warms up inside your engine. West coast states and southern states not need to worry about that so much as you folks in Montana, the Dakotas, and Maine, etc.

Foley

[Clyde]

The owners manual states:
SAE 30 32 degrees-120
SAE 20 32-90
SAE 20W 10-80
SAE 10W -10-60
SAE 5W -30-10
In South Carolina I use Shell Rotella 30 weight oil in my V6's. At the time these engines were made multi viscosity oil was available but the engineers choose to recommend straight weight oil. In 1964 I purchased a new GMC 1500 with a 305E V-6 and ran 30 weight oil year round in Massachusetts, put 100,000 miles with a camper and towing an enclosed trailer with my Top Fuel dragster up and down the East Coast, the engine never missed a beat or used any oil.