motor oil
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Racer
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motor oil
My 68 327/350 original specs call for 10W 40W motor oil. these days that's not easy to find specifically ones with high levels of ZDDP. I live in a warm climate and have been using Mobil European blend synthetic oils with a viscosity rating of 0W 30W and 5W 40W, I see oils out there with 20W 50W that have high ZDDP levels. Any opinions on running a higher viscosity vs lower viscosity?
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My 68 327/350 original specs call for 10W 40W motor oil. these days that's not easy to find specifically ones with high levels of ZDDP. I live in a warm climate and have been using Mobil European blend synthetic oils with a viscosity rating of 0W 30W and 5W 40W, I see oils out there with 20W 50W that have high ZDDP levels. Any opinions on running a higher viscosity vs lower viscosity?
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Racer
Joined: May 2009
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The question was since I live in a warm climate is it better to run a higher viscosity oil eg. Valvoline ZR1 20 50 or Mobil 1 15 50 as opposed to the thinner viscosity mobile oil I am using now. As I said 10W 40 with high ZDDP is hard to find. I know royal purple sells 10W 40 but Im not up to spending $60 + dollars for an oil change.
Drifting
Joined: Aug 2016
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From: Arizona
The question was since I live in a warm climate is it better to run a higher viscosity oil eg. Valvoline ZR1 20 50 or Mobil 1 15 50 as opposed to the thinner viscosity mobile oil I am using now. As I said 10W 40 with high ZDDP is hard to find. I know royal purple sells 10W 40 but Im not up to spending $60 + dollars for an oil change.
Race Director
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The question was since I live in a warm climate is it better to run a higher viscosity oil eg. Valvoline ZR1 20 50 or Mobil 1 15 50 as opposed to the thinner viscosity mobile oil I am using now. As I said 10W 40 with high ZDDP is hard to find. I know royal purple sells 10W 40 but Im not up to spending $60 + dollars for an oil change.
Le Mans Master
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I ran Valvoline 20w50 racing from birth until Maxlife came out about 20 years ago. Switched to 10w40 around 60k....still purring at 78k...
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The question was since I live in a warm climate is it better to run a higher viscosity oil eg. Valvoline ZR1 20 50 or Mobil 1 15 50 as opposed to the thinner viscosity mobile oil I am using now. As I said 10W 40 with high ZDDP is hard to find. I know royal purple sells 10W 40 but Im not up to spending $60 + dollars for an oil change.
What weight is best for your engine depends not only on high temp viscosity but how often the engine is started without needing that upper end temperature protection - i.e., shorter trips here and there without sustained high rpm driving. If you are not spending the majority of driving time at highways speeds, then I'd rather go with lower weights overall (10w-40).
If you know, how many miles ago did your engine get new bearings? A looser engine can tolerate heavier oils without issue while a tight engine may not get the flow and coverage needed.
Last edited by barkingrats; Aug 16, 2025 at 07:27 PM.
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I ran 15w50 and 20w50 in both my 327 and 427. The viscosity is not an issue and will only add benefits. The thicker oil will stay in the bearing oil barrier longer and will increase the oil pressure on high mileage and older engines. You cant have too much oil pressure in these older engines. They do not run the tighter clearances that require an 0w weight which in an older engine will compromise that oil film barrier.
Buy it, run it and enjoy
Buy it, run it and enjoy
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I've ALWAYS run 20W-50 in my 77. Always. Even back when I lived in Wisconsin. But keep in mind I never drove it in the winter months in Wisconsin.
Who says the factory spec is 10W-30? For what weather?
I do not believe 20W is to thick for start ups.
Who says the factory spec is 10W-30? For what weather?
I do not believe 20W is to thick for start ups.
Race Director
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From my Factory service manual. Clearly shows 20W-50 is a recommended lubricant for temperature's above 20F.
So, I've always run with that.
Le Mans Master
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Greg,
You don't have to spend $60+ for changing your oil / filter.
Another option is to use crap brand oil with a crap brand filter.
Then, when you wipe a couple lifters and a few cam lobes, see if that event comes out cheaper.
You don't have to spend $60+ for changing your oil / filter.
Another option is to use crap brand oil with a crap brand filter.
Then, when you wipe a couple lifters and a few cam lobes, see if that event comes out cheaper.
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Yes, but... from 10w-30 to 20w-50, they all show the same upper protection. What I mean is the chart doesn't show any reason to choose one over the others for the upper end.
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I have however attended oil seminars and received a great deal of education on the topic due to my vocation.
But obviously, not everyone has. The topic of which oil to use comes up on here frequently, and opinions very widely.
I can not understand why people regularly use such thin oil in these engines.
And others can not understand why I run 20W-50.
Yet I am firm in my convictions.
Race Director
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Also published by the factory back in the day. And still overly simplistic.
but. 5W-20 oils not recommended for sustained high-speed running.
Overly simplistic yes. But certainly points in the direction that thinner oils and higher loads is a bad idea.
well, you take from it what you wish.
This thread started with basically, can I safely run 20W-50 motor oil.
I say yes.
