Which oil is thinner at start up?

5-20 or 0-30? I know that the 5-20 is thinner at operating temperature but I dont know if 5-20 is thinner at start up. I know 5-20 is thinner than 5-30 at start up. I know that 0-30 is thinner than 5-30 at start up... what i dont know is if 5-20 or 0-30 is thinner at start up and by how much... and if 5-20 is thicker at start up at what temperature do they have the same viscosity.

 

The way to read the oil viscosity grading for multi-vis oils: the first grade number is the "viscosity a single-weight oil of that grade would be" at low temp (0 degrees F IIRC) and the second grade number is the "viscosity a single weight oil of that grade would be" at high temp (212 F IIRC). It stands to reason the 0w30 is thinner IF the starting temp is 0 F.

But then it's equally logical to conclude that at some temperature between 0 and 212, the 5w20 is thinner. But to say a 5w20 is thinner than a 5w30 is only 'guaranteed' true if start-up temp is "something" above 0 deg F.

In other words: it depends on temperature at start up.

Since viscosity grades at temp's other than 0 and 212 aren't specified (and my guess is the curve isn't linear since there are multiple things going) it could be anyone's guess where the 'start up' viscosities are the same. It's also probably safe to assume the crossing point could vary from one manufacturer - or formulation - to another; there could even be multiple crossing points or be essentially congruent for a huge range of temperatures.

 

o-30 better at start up..5-20 better for mpg

 

x2

Although both have crappy shear number

 

shear.....

 

its interesting you brought up sheer for the oil. iv been doing some reading on it. here is a good read: http://www.bobistheoilguy.com/oilshear.htm

 

thanks fixed

I seen that but he is confusing....
I was told that best oils have high HTHS numbers. I had been sticking to oils with high HTHS numbers and never had problems, Tacoma is first one that I am not sure what to do in part due to VVT-i in it. Otherwise I would be running Shell 5-40 which supposed to be near 4.7 More then even Mobil Delvac.

 

There's ever so much more to a good oil than one single dimension like high shear numbers.

Isn't Delvac a diesel engine oil? If it is it could have a boundary layer additive in high proportion that mfr's of gas engine oils have been reducing or eliminating because it poisons catalytic converters - ZDDP. I'm not sure that's the case, but it's something one could lose track of if pursuing a single dimension of perceived quality to the exclusion of all others.

 

Well Delvac and Rotella are both rated for gasoline engines too. The only difference supposed to be that, as you point out they still should have higher levels of additives to combat wear. Gasoline only oils, had been told to reduce additives to lower the strain on catalytic converters. Problem with that is oils like Mobil 1 5w-30 are no longer as good as they were before the change. Which happened I believe sometime around 2006 -2008. Personally I was wondering what happened with Mobil 1 since I could feel the difference, until I found out that, yet again California had forced the rest of us to use crappy oil.
First I thought I bought a bad batch of oil, after getting oil from different sources and still having engine becoming noiser as oil was wearing out, it was clear that something had changed drastically in formula.
Now here is what I gathered from interweb...
Toyota, GM and some other company did test to figure out what is the lowest HTHS number they can go before engine will have possibility of catastrophic failure, their number was HTHS 2.9
Mobil 5w-20 is ... 2.62
Mobil 0W-30 is 2.99

oils like 5w-20 or 0w-30 are on the border line of what even Toyota deems to be a safe number so I am not sure if I want to run them.

 

Give us a link or it's...well...as they say... "(The internet) is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind- boggling amounts of excrement when you least expect it."

I simply can't believe that Toyota says the oil they require us to use (doesn't a 30 wt have minimum HTHS of 2.9 per SAE spec?) is almost going to lead to 'possibility of catastrophic failure'. Just makes no sense.

Also, from what I've read HTHS doesn't seem to be as important with synthetic oils since they exhibit much greater "Newtonian" properties than do petroleum oils that rely on VII's. In other words: they don't change viscosity in high-shear conditions.

 

so then whats the best oil weights for our trucks BlueT?

 

Honest answer is ...Dont know.
I am waiting for Toyota to tell me why Tacoma does not have xW-40 in its book. Most likely as some others point out its VVT-i. I am running Mobil 1 5W-30 as others but I do change oil as soon as the sound of the engine changes which is around 3500-4000 miles. It could be my engine but I doubt. It runs super quiet on fresh oil.

 

Well HTHS comes into play at the highest revs and hottest engine oil working range. If you do lots of WOT driving then you need 2.9 or higher. Your oil wont break down and casue issues if it is at least 2.9 and that figure wont even come into play unless you have high oil temperatures to begin with. My WOT use is limited so I am totally NOT concerned with HTHS numbers. I also have the aux engine oil cooler.

 

That makes sense about WOT use. I think it makes a very good case for trailer towers using synthetic since they stay in grade so well even with extended drain intervals. If anyone should doubt it just check the UOA's at BITOG. With a synthetic oil it's rarely the loss of viscosity that drives the decision to change oil, it's the loss of TBN, accumulation of contaminants an/or other factors.

But none of this has anything to do with the original question: which oil is 'thinner' at start up, an entirely different conundrum.

 

I have discovered for Mobil 1 the 5-20 is the thinner oil at pretty much all temps above freezing.

 

The best oil is whatever the owners manual recommends. There are reasons they recommend it.

 

Probably reasons that have more to do with 'entrenched conservatism' than anything else...

 

the funny part is you could've used the cheapest walmart brand oil and you still would've never 'had problems'

 

and you've discovered this how??

 

By using Mobil 1's viscosity and density data and bibistheoilguy's viscosity calculator I can interpolate down to 15 deg C and makes educated guesses down to freezing. This is just for ONE of the 5-20 formulations and the 0-30 Advanced Fuel economy formulation. I didnt test out ALL the Mobil 1 5-20s but it appears the results would be similar.