10w30 vs 5w30

Joined
Jul 14, 2020
Messages
520
Ok, to start, let me tell about the vehicle. 98 mustang v/6 3.8. with 81k Sits in warm garage, so is never started at less than 40 degrees F. And rarely that, as it is usually stored for the winter, from October till April or may. But in the summer it does get interstate runs in 100 degree weather. My question is would the 10w30 be better for that summer use than the 5w30. Both Valvoline high mileage. Yes I know ford back speed it to 5w20, but the owners manual says 5w30, and I have always been more or less a thicky anyway. In the old days I used a lot of STP in my old cars.
I do know that at hot temps, that they are both suppose to be the same, but I have read somewhere that the 10w30 actually holds its viscosity better than 5 or 0 w does. Is there any truth to that? Or would I have to go to 0 or 5 or 10w 40 to make any difference?
 
Does your manual show temperature ranges for 5w30 and 10w30? If so, is 10w30 recommended at/below 40°F?
 
Does your manual show temperature ranges for 5w30 and 10w30? If so, is 10w30 recommended at/below 40°F?
Doesn't say, only says 5w30 , and besides It NEVER gets started below 40 and hasn't been started at even 40 in the last 3 years since I have owned it.
 
Yes, 10w30 will shear less during the OCI
That is what I had heard, but then maybe that doesn't matter much since it will never be run more than 3000 miles between changes, and usually more like 2000
 
Plus it's completely dependent on whether your engine has a problem with mechanical shearing, which most engines do not. And not all VII are the same either. A modern oil from a reputable blender is not going to have the same problems with mechanical shear as did the 10W-40 of old.
 
Plus it's completely dependent on whether your engine has a problem with mechanical shearing, which most engines do not. And not all VII are the same either. A modern oil from a reputable blender is not going to have the same problems with mechanical shear as did the 10W-40 of old.
Bingo.
 
It's not necessarily all about the shearing. Most 10w-30s also have a higher HTHS, which is important if you run the engine hard. For example, M1 5w30 HM has an HTHS of 3.2, 10w30 is 3.5. That's a significant difference. If the engine is not run below 40F, you could actually use a straight 30 (not that you really have that choice). Running a 5w30 is using a weaker base oil with more additive for no gain when you use them over about 10F or even a bit lower. So yes, I'd run a 10w30 (I do in all my cars) were I you. A 5w30 is probably just fine, but why compromise when you don't need to?
 
It's not necessarily all about the shearing. Most 10w-30s also have a higher HTHS, which is important if you run the engine hard. For example, M1 5w30 HM has an HTHS of 3.2, 10w30 is 3.5. That's a significant difference. If the engine is not run below 40F, you could actually use a straight 30 (not that you really have that choice). Running a 5w30 is using a weaker base oil with more additive for no gain when you use them over about 10F or even a bit lower. So yes, I'd run a 10w30 (I do in all my cars) were I you. A 5w30 is probably just fine, but why compromise when you don't need to?
You might want to check that, most SN/SP GF-5/GF-6 5w-30's an 10w-30's have the same or similar HTHS numbers. Mobil doesn't list HTHS for their 10w-30 BTW (or the 5w-30).

When you start looking at HDEO's, that's when the HTHS will be 3.5cP and higher.
 
Ok, to start, let me tell about the vehicle. 98 mustang v/6 3.8. with 81k Sits in warm garage, so is never started at less than 40 degrees F. And rarely that, as it is usually stored for the winter, from October till April or may. But in the summer it does get interstate runs in 100 degree weather. My question is would the 10w30 be better for that summer use than the 5w30. Both Valvoline high mileage. Yes I know ford back speed it to 5w20, but the owners manual says 5w30, and I have always been more or less a thicky anyway. In the old days I used a lot of STP in my old cars.
I do know that at hot temps, that they are both suppose to be the same, but I have read somewhere that the 10w30 actually holds its viscosity better than 5 or 0 w does. Is there any truth to that? Or would I have to go to 0 or 5 or 10w 40 to make any difference?
My opinion is today most 5W-30 uses better basestock than 10W-30. I would think the ML 5W-30 has more GIII so it's natural VI is higher so the amount of VII difference is likely minimal so that the shearing should be to. In the real world likely little difference between the two for your uses.
 
One other question, I have several gallons of Traveler brand (TSC) 15w40 conventional HD oil that I would like to use up. It would take me 20 years (and I won't live that long) to use it up in my lawn mowers etc. I am not going to use it in my 2017 Nissan Frontier, so that leaves the 65 6 cylinder mustang or the 98 v/6 3.8 Mustang. I have no qualms using it in the 65, but wondering about the 98 as it has cats. I do also have a couple gallons of Rotella t5 10w30 that is the stuff from a few years ago with high ZDDP, and wondering if I could use that in the 98?? I know the viscosity is good, but is the high ZDDP problem?
 
One other question, I have several gallons of Traveler brand (TSC) 15w40 conventional HD oil that I would like to use up. It would take me 20 years (and I won't live that long) to use it up in my lawn mowers etc. I am not going to use it in my 2017 Nissan Frontier, so that leaves the 65 6 cylinder mustang or the 98 v/6 3.8 Mustang. I have no qualms using it in the 65, but wondering about the 98 as it has cats. I do also have a couple gallons of Rotella t5 10w30 that is the stuff from a few years ago with high ZDDP, and wondering if I could use that in the 98?? I know the viscosity is good, but is the high ZDDP problem?

I wouldn't worry about it unless you have a significant amount of oil consumption.

Even then often times you will find lower consumption with increased viscosity. 800 ppm phosphorus at 1 qt per 1000 mi is the same as 1200 ppm at 1 qt per 1500 mi as far as your cat is concerned
 
Last edited:
One other question, I have several gallons of Traveler brand (TSC) 15w40 conventional HD oil that I would like to use up. It would take me 20 years (and I won't live that long) to use it up in my lawn mowers etc. I am not going to use it in my 2017 Nissan Frontier, so that leaves the 65 6 cylinder mustang or the 98 v/6 3.8 Mustang. I have no qualms using it in the 65, but wondering about the 98 as it has cats. I do also have a couple gallons of Rotella t5 10w30 that is the stuff from a few years ago with high ZDDP, and wondering if I could use that in the 98?? I know the viscosity is good, but is the high ZDDP problem?
If the cars were mine, I would absolutely run the 15w40 in both. If my vehicles stayed above 30 or so degrees (they do not) I would be running 15w40 HDEO in all besides the BMW.
 
  • Like
Reactions: wlk
Run the 15w40 until out then switch to 10w40. I run 10w30 and 10w40 in my old cars all the time w no issues.
 
I run 5 and 10 w30 in my cars and it all sounds the same during start up (coldest temp where I live so far is 44 degrees). The vehicles run the same, no difference in gas mileage w either weight.
 
So it seems most everybody is saying to use most anything I want in that 98 3.8. Sounds good to me. Of course I will probably not change it again till this fall, as it now has only 1600 miles on the Havoline 5w30 high mileage and TG filter. 99% highway miles. All warm to hot weather.
 
Back
Top