CK-4

O

OilzGood

Joined
Dec 2, 2025
Messages
24
Hello all, long time listener first time caller.

I have a feeling my type of question has been asked before but didn't find anything exactly like it when I used the search function so please forgive my ignorance if it's already been asked.

I've been looking at CK-4 oils for my truck (L5P Duramax) and looking at the HTHS numbers on the listed oil specs. I've been thinking about switching oils to something with a higher HTHS number than what I currently use and I've contacted some of the brands I plan to use and a couple of them don't recommend using there oil for my truck even though it's a ck-4 rated. I assumed that all ck-4 rated oils were good to go for modern Diesels but maybe not? One of the oils in question is the Amsoil dominator 20w50 with a higher zinc content. Aside from having higher zinc (couldn't find a voa of that specific oil so I don't know how much higher it is compared to what I'm currently using) would there be any negative affects to the after treatment system using this oil?

I appreciate in advance any info you can give me even if it's telling me I'm dumb for wanting to run a 20w50 oil lol
 
Welcome to BITOG!

I don’t think you need a 20W50 - and I mean that with all sincerity. What does the engine specify? If you want to go up a grade from that spec, no worries, but jumping all the way up to a 20W50 isn’t necessary and won’t give you better life or “better protection”.

I would worry more about the oil quality, what specs it meets, than the HTHS alone, as long as the HTHS is sufficient.
 
Amsoil dominator competition diesel 20W-50 oil wouldn't last long in there. And a regular 15w-40 which is usually 4.1-4.3 for non boutiques would be more than enough for it.

For the most part a true race oil sacrifices almost all if not all detergent/dispersant additives since those interfere with the antiwear additives. Some race oils claim race and could be used in those applications like Mobil 1 15w-50 but are normal in their detergent/dispersant composition and still provide adequate protection. I don't think i would use that in the L5P.

I'd run any good 5/15w-40. Mobil 1 Extended Performance 5w40 is a great oil. If it doesn't go below 20f a 15w-40 would crank normally. Below that they can begin to slow down but not much. Delo XSP and Delvac extreme are great off the shelf oils. I'd skip rotella. There's also Valvoline heavy duty diesel oil and the full syn states 4.3 hths which is nice for a budget off the shelf full syn diesel oil but has to be ordered but walmart ships it for free. I run Mag 1 15w-40 in my gas engines since it's sufficient.
 
Last edited:
Plenty of 15w-40 grades but must look at companies HTHS if they share it. I'm going to add some info I posted but give me a few. 🙂
 
SAE 40 has two different HTHS limits minimums. If you want to make sure you get a small bump minimum than stick with a 15w-40.

  • For SAE 0W-40, 5W-40 and 10W-40, the HTHS limit is 3.5, whereas the limit is 3.7 for SAE 40, 15w40, 20W-40 and 25W-40.

Splitting hairs... I don't think so. There are 15w-40 over 4 or more like @JavierH19 suggested. I do with VOA threw in HTHS test though. 👍😀
 
Wow thank you all for the responses. I probably should've added that I'm running an oil bypass kit on my truck as well which has dropped oil pressure a little bit. And by little bit I'm talking about 1 psi. I was thinking a thicker oil would help keep pressure in a good sweet spot.

The only reason I'm even looking into HTHS numbers at all is because of this forum lol and I mean that with the upmost respect. So I figured the higher the HTHS number the better. I plan to keep this truck until I die lol.

One thing that I've been surprised by is how I can find gas engine oils that have HTHS numbers into the 5+ range but can't find a ck-4 spec oil in that range unless I go to multi grade 50 weight and even then it's hard to find Diesel oil in that grade, at least ones that share there HTHS numbers and other typical specs you would expect to find on a data sheet.
 
OilzGood said:
Hello all, long time listener first time caller.

I have a feeling my type of question has been asked before but didn't find anything exactly like it when I used the search function so please forgive my ignorance if it's already been asked.

I've been looking at CK-4 oils for my truck (L5P Duramax) and looking at the HTHS numbers on the listed oil specs. I've been thinking about switching oils to something with a higher HTHS number than what I currently use and I've contacted some of the brands I plan to use and a couple of them don't recommend using there oil for my truck even though it's a ck-4 rated. I assumed that all ck-4 rated oils were good to go for modern Diesels but maybe not? One of the oils in question is the Amsoil dominator 20w50 with a higher zinc content. Aside from having higher zinc (couldn't find a voa of that specific oil so I don't know how much higher it is compared to what I'm currently using) would there be any negative affects to the after treatment system using this oil?

I appreciate in advance any info you can give me even if it's telling me I'm dumb for wanting to run a 20w50 oil lol
Click to expand...
https://www.amsoil.com/p/amsoil-5w-40-heavy-duty-100-synthetic-diesel-oil-ado/

1764714590990.webp
 
Rand said:
What is your location for climate purposes? Is the truck stock?
Click to expand...
PNW area but it very rarely gets below freezing except for maybe a couple days in the winter. Truck is all stock emissions wise but I do have a oil bypass system which lowered oil pressure ever so slightly.
 
Z28racecar said:
Amsoil's Max Duty line would be my choice. HTHS on their 15W-40 is 4.5. HPL also offers HDEO.
Click to expand...
Yeah I noticed that too. Thats probably the route I should go with. In my mind I just keep thinking more is better but I know that it's not even necessary after a certain point.
 
I use Castrol Vecton 15w40 in my turbo diesel. It's approved by some truck manufacturers for an OCI of up to 75000 miles. Given that I change my oil every 3-4k miles, it should have plenty of reserve oiliness left when I change it out.
 
20W-50 won't damage your Duramax, but really, it's not needed. I would use a good quality, high HTHS 30-grade before that.

Delvac Extreme 10W-30; HTHS=3.6
 
OP, if the HT/HS value is not listed in the Technical data sheet, then go by the manuf. approvals (formal approvals,not "recommended for..." or "satisfies the demands of...") :

Volvo VDS-4, Mack EO-O PP,Renault RLD-3, Volvo VDS-4.5 ,Mack EOS-4.5, Detroit 93K214 , 93K218 and 93K222 all demand min. 3.9cP HT/HS "after shear" visc. (90 cycles per ASTM D4683 or CEC L-36-90 "shear stability" test) for SAE xw-40 oils.


All these mandate min. 3.4cP "after-shear" HT/HS viscosity for xw-30 oils.
 
I'm actually going to be running that oil next run. Amsoil states to still follow manufacturers oci so it will be fine. You could run the diesel truck and marine if you want higher zddp and stay 15w40. Im hoping to bump oil pressure slightly at idle. My truck is a 19 3500.
 
20w-50 on its own is not a bad grade to run in these. The problem is that finding a good 50 grade diesel oil is hard. I only see conventional 20w-50 hdeo or race diesel oil but nothing i'd run in a daily driver whereas with 15w-40 you can get tons of solid full synthetic off the shelf or cheap and free shipping options left and right and i'd rather run a great full syn 15w-40 than conventional 20w-50 hdeo which is likely to cost more and be harder to source while still being less good.

Only HPL makes higher viscosity diesel oils that one of the best and great for a daily driver. Hdmo comes in 10w-50 which is good for days where it's at 0f.

https://www.advlubrication.com/products/heavy-duty-motor-oil?variant=31346080645143

https://www.advlubrication.com/coll...4-heavy-duty-motor-oil?variant=40506655047873
 
Last edited:
Running Amsoil ARO Premium Protection 20w50 in the tractor so that would be another good option. Higher zddp than comp.
 
Viscosity @ 100C not HTHS determines oil pressure at operating temperature.
Shop for a higher KV100C if you’re worried about oil pressure, or drop down a gear instead.
Gale Banks runs 15w40 on the dyno in L5Ps producing over 800 hp.
Petro Canada has two choices in Duron 20w50. They work great in motorcycles and lawn tractors and maybe in an old Detroit two stroke.
 
You must log in or register to reply here.

Similar threads

O
MPL Thirty-K 15w40
Replies
12
Views
430
kschachn
O
A3/B4 in HDEO application, what would go wrong?
2 3
Replies
54
Views
1K
JavierH19
V
L5P Duramax Oil
Replies
7
Views
2K
FreedomOne
F
Walmart Rotella T4 HDEO 15w40
2
Replies
22
Views
2K
FlyingTexan
V
Hard to find a CI-4 5w40 in Sweden
Replies
12
Views
445
Snagglefoot
Back
Top Bottom