Like the title says, I started as synth blend until about 17k (never burned a drop of oil) then switched to mobile 1 and started burning oil. I'm now at 23k and still burning oil, so my thought is that the blend was better with the VQ can I switch back to blend or will this mess my engine up completely?

 

Yes, you can switch back and forth between synth and dino oil without any problems

 

anyone disagree

 

No problems will result from switching, but what is happening is unexpected if you are using the same grade (5W/30) for both formulations. The blend (Mobil Clean 7500) has a viscosity of 10.6 @ 100C and a flash point of 200C.The Extended perf. has a viscosity of 11.0 @ 100C and a flash point of 230C. Both #'s should point to less consumption and volatility. This means less "burning".

If you were going the distance (15K miles on the full syn), then it makes sense that more may be used near the end of the interval as the viscosity index drops. But with equal intervals, I don't know why your engine would want to eat more full syn. Mine has 78K miles on it and uses a qt. about every 4500 miles. Always has no matter how I drive it. Mobil 1 full syn since 2200 miles.

 

I've mostly run M1 and oil consumption was fairly high1.5 to 2qts per 5K miles. Since switching to Pennzoil dino or MC7500, I've seen the consumption drop to approx 1 qt per 5K miles... my G has 74,000 on the odo. Through oil analyses, I've also discovered that my G doesn't like any of the Mobil branded oils, dino, synthetics, nor blends... I'm switching to Pennzoil synth for a few fills to see how it works out.

Switching back and forth between synth or dino or blends will not hurt the engine nor have any negative effects whatsoever. In fact today's synths are even safe to mix with dinos; the oil bottle labels often state it.

 

+1, I agree.

 

M1 is a great oil but it sucks on our car... I run German Castrol Syntec 0w-30.

I have seen many Used oil analysis on the VQ with GC and M1.. GC is much much better. The M1 seems to run really thin and has high lead deposits in the VQ engine. GC is only available at autozone.

 

its fine to use the 0w?

 

Thin Oil Myth
Created: April 10, 2006
Last Edited: Never

Disclaimer:
All the temperatures here are in celcius.

Short answer:
0w-30 and 5w-30 can be thicker than 10w-30.

Long answer: Read below.

Really Basic (but not so intuitive) information:

I'm sure we have all seen 5w-30, 10w-30, 10w-40, 20w-50, but what does it mean?
When talking about viscosities, you must state the temperature.

Lets break this up into two categories: hot and cold.

Xw-20, Xw-30, Xw-40, etc (HOT!)
This is your oil's hot viscosity. The viscosity is measured @ 100c.
This number is relative when the engine is warmed up.
The most common unit is cST. The larger the number, the "thicker" the oil.

Examples
A "30" weight is between 9.30-12.49 cST @ 100c.
A "40" weight is between 12.50-16.29 cST @ 100c.

Here's a table.


0w-XX 5w-XX 10w-XX, etc (COLD!)
This is your oil's cold viscosity. A 0w, 5w, 10w, etc, are not measured at the same temperature!
This is number relative when starting your engine.
The most common unit is cP. The larger the number, the "thicker" the oil.

Examples
A "10w" weight must have a MAX viscosity of 6600 cP @ -30c
A "0w" weight must have a MAX viscosity of 6200 cP @ -35c

Here's a table.
It never gets to even -15c here, so what's the start up viscosity for me?
Great question! A lot of us don't live in super cold temperatures.
Unfortunately, the oil companies don't have to tell you. All they need to specify are the extremes.
Can I know an oil's viscosity at different temperatures?
Yes! Aside from actually measuring the viscosity, you can do some calculations.
With a viscosity calculator and enough data, you can piece a graph together.
You can usually get all the data from the manufacturer's datasheet.
Take the calculator with a grain of salt. They are decently accurate in most temperatures, but I wouldn't trust them below -15c.
Why do they measure the cold and hot viscosity (cP vs cST) in different units?
Something about dynamic vs kinematic viscosity.
I won't go into detail here, because I haven't researched this.


Back to the point, "Why isn't 5w-30 or 0w-30 thin?"
I think a real-life example will help.

Lets compare Mobil1 5w-30 to Mobil1 10w-30.

First the Hot (100 c) setting
Straight from Mobil1's datasheet (Looked on April 4, 2006):

5w-30 = 11.3 cST
10w-30 = 10.0 cST

Looks like the 5w-30 is thicker! (Notice how both oils are a "30" weight)


Now lets look at the cold setting
Based on the 5w and 10w specifications:

5w-30 = 6600 cP or less @ -30c
10w-30 = 7000 cp or less @ -25c

Looks like 5w-30 is thinner than 10w-30!
We can conclude that:

5w-30 is thinner than 10w-30 at -25c.
5w-30 is thicker than 10w-30 at 100c.

The above implies that 5w-30 thins out less than 10w-30 as temperature increases.
Still confused? Maybe this graph will help.
The graph is just a learning tool, don't use it as an actual reference.
Reminder: this example refers to Mobil1. If you're curious about other brands, you will have to look at their datasheets.


Finally, my concluding remarks.

My main points are:

5w-30 can be thicker than 10w-30.
0w-30 can be thicker than 5w-30.
Unless you have tools to measure viscosity, you need to at least:

Specify a temperature.
Check the manufacturer's datasheet.
The cold viscosity tells you NOTHING about the hot viscosity.
Some things you might have noticed:

I haven't claimed an Xw-30 to be thicker than an Xw-40. At least at operating temps, any Xw-30 will be thinner than any Xw-40.
Everything I have said can apply to other weights within the same hot viscosity.

It's possible for a 0w-40, 5w-40, or 10w-40 to be thicker than a 15w-40 at certain temperatures.
It's possible for a 0w-20 to be thicker than a 5w-20 at certain temperatures.
MANY other factors about oil were not discussed here. Please don't base your oil preference on viscosity numbers only.
When in doubt, follow your car's manual. At least you won't void your warranty that way.