Thin vs Thick Discussion Midterm Examination

Status
Not open for further replies.
Joined
Jan 9, 2005
Messages
1,625
Location
Sarasota, Florida
Motor Oil Midterm Examination
Answer questions without looking back. This is a closed book exam. Base your answers on the information provided in these past chapters.

1- At normal operating temperature, 212 F, a straight 30 grade oil has a viscosity of around how many centiStokes?
A- 3
B- 6
C- 10
D- 20
E- 30

2- While racing at 95 F, mid-summer in Florida, which of these synthetic oils gives the best protection at 302 F oil temperature?
A- 0W-40
B- 5W-40
C- 10W-40
D- Straight 40 grade
E- They are all exactly the same

3- While starting up your car at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight 10 (ten) grade motor oil?
A- 3 cSt
B- 6 cSt
C- 10 cSt
D- 20 cSt
E- 30 cSt or higher

4- The biggest problem with mineral based motor oils with long term use is:
A- Thinning
B- Thickening
C- Loss of VI (viscosity index) improvers
D- Both A and C
E- None of the above is correct

5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
A- 20 grade
B- 10 grade
C- 5 grade
D- All of the above
E- None are too thick





Answers to the Oil Midterm Exam
I feel these were all difficult questions. You would be doing well to get 3 correct.

1- At normal operating temperature, 212 F, a straight 30 grade oil has a viscosity of around how many centiStokes?
A- 3
B- 6
C- 10
D- 20
E- 30
The correct answer is C- 10 cSt.

2- While racing at 95 F, mid-summer in Florida, which of these synthetic oils gives the best protection at 302 F oil temperature?
A- 0W-40
B- 5W-40
C- 10W-40
D- Straight 40 grade
E- They are all exactly the same
The correct answer is E- They are all exactly the same.

3- While starting up your car at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight 10 (ten) grade motor oil?
A- 3 cSt
B- 6 cSt
C- 10 cSt
D- 20 cSt
E- 30 cSt or higher
The correct answer is E- 30 cSt or higher.

4- The biggest problem with mineral based motor oils with long tern use is:
A- Thinning
B- Thickening
C- Loss of VI (viscosity index) improvers
D- Both A and C
E- None of the above is correct
The correct answer is B - Thickening

5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
A- 20 grade
B- 10 grade
C- 5 grade
D- All of the above
E- None are too thick
The correct answer is D - All of the above
 
On paper I am a B student for this exam. In real life I decided to stop using 10w-30 mineral based oil and last oil purchased was 5w-20 PUP. So maybe I am a A student in real life where it counts?
 
5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
A- 20 grade
B- 10 grade
C- 5 grade
D- All of the above
E- None are too thick


Answers to the Oil Midterm Exam

5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
A- 20 grade
B- 10 grade
C- 5 grade
D- All of the above
E- None are too thick
The correct answer is D - All of the above
😂 ... the correct answer is actually "E- None are too thick".
 
Last edited:
I feel like real answers arent the right answer to this quiz.

2. what does florida have to do with anything?
there is no straight 40 syn
0w40 would have more additives and VII so depending on the oil 5w40 or 10w40 would be the answer.

4. Depends on the motor and use. Long term use could mean 10- 5k oci's or anything really. not specific enough.

5. since your engine wont self destruct on any of those.. I'd argue they are all adequate. so E.

too thick would be 15w40 at -30f in BC.


Also in chapter 9 you refer to
"the numbers are not exact but they show clearly that the ”0” represents different startup viscosities. This is unlike the 0W-30, 5W-30, 10W-30 and straight 30 grade oils that all have the exact same viscosity in a Hot engine = 10 cSt."

0 is the winter rating not the viscosity, all those oils you mention none are exactly 10 its a viscosity range.. and there will be as much as 20% difference between oils

Also, none of these OIL discussions seem to meet the bar of being a white paper or Technical discussion.. being in general inaccurate, far too simplified, and contradictory.
 
Last edited:
I thought we had established that the primary reason for startup wear is not that oil is too thick, it's that it's too cool. Viscosity is mostly irrelevant unless it's too thick to pump. Oil needs to reach ~80c to for best properties.
 
I thought we had established that the primary reason for startup wear is not that oil is too thick, it's that it's too cool. Viscosity is mostly irrelevant unless it's too thick to pump. Oil needs to reach ~80c to for best properties.

And context is key. By the author's logic, OTR truck engines with 15w-40 in them meet two of his criteria for excessive wear:
1. Too thick on startup/craptacular winter rating (15W)
2. Too heavy of viscosity (40)

Yet they are the longest lasting engines on the road. Doug Hillary did tear-down testing of OTR trains in the Aussie outback with Delvac 1 5w-40 and both liner and bearings spec'd "as new" after 1.3 million Km. I'd like to see how the OP's Ferrari would compare in a tear-down on 0w-20 for even 1/10th the mileage.

The million mile Ford van was run on like 10w-40 or something, the GM truck on 15w-40. OPE don't self destruct on SAE 30 and gensets that go from off to WOT and full load don't last one operating cycle. Marine engines which are regularly run both cold and on wickedly heavy oil under full load last thousands of hours.

@Shannow has provided countless amount of data on these subjects in years past.
 
Dr. Haas,

Please explain your logic with #5, as you haven't given enough information. Are you saying they are too thick if the engine is started cold and immediately run at wide open throttle?
 
Dr. Haas,

Please explain your logic with #5, as you haven't given enough information. Are you saying they are too thick if the engine is started cold and immediately run at wide open throttle?
Correct. And "cold" need not be sub zero but rather 75 F. Also, one must remember that oil warms slowly compared to engine water temperature. It takes 20 minutes or so to get an engine oil temperature from 75 F start up to 212 F operating temperature with normal driving.

The problem will be obvious when you read the next and final chapter.

AEHaas
 
Correct. And "cold" need not be sub zero but rather 75 F. Also, one must remember that oil warms slowly compared to engine water temperature. It takes 20 minutes or so to get an engine oil temperature from 75 F start up to 212 F operating temperature with normal driving.

The problem will be obvious when you read the next and final chapter.

AEHaas
Yes, all oil is thick at room temperature compared to operating temperature, but we make oil viscosity determination based on climate and requirements at operating temperature. You're example, while true, has no practical application. We don't put 1 cSt oil in an engine because we don't want startup oil viscosity to be higher than operating viscosity.
 
Yes, all oil is thick at room temperature compared to operating temperature, but we make oil viscosity determination based on climate and requirements at operating temperature. You're example, while true, has no practical application. We don't put 1 cSt oil in an engine because we don't want startup oil viscosity to be higher than operating viscosity.
Yep, and when those “change oil hot or cold“ threads roll by … my answer is I pop it right up on the ramps and change the oil. Before I installed a Fumoto valve … lukewarm oil splashed everywhere …
And I’m to believe that oil has a mobility problem ?
 
Yes, all oil is thick at room temperature compared to operating temperature, but we make oil viscosity determination based on climate and requirements at operating temperature.
Just to add ... oil viscosity determination is also made on the climate lowest expected temperature, by using the correct "W" (Winter) rating. Owner's manuals clearly show to use a lower "W" rating as the temperature gets colder. There are literally millions of vehicles starting up at temperaures way colder than a balmy 75F that last many 100s of thousand miles. SAE J300 and the recommended "W" ratings to use per the engine manufacturers are there to ensure no engine damage occurs to millions of vehicles during cold starts.
 
There was no mention in question 5 of the oil being "too thick if engine is started cold and immediately run at wide open throttle" - implying revved to redline. Nobody in their right mind that knows anything about engines would do that anyway. As question 5 stands, the "correct" answer given is wrong.
 
Last edited:
I think someone is recently retired and got bored. I think bitog should have more tests, then everyone can put their gpa in the signature block. that way we can know who is spouting rubbish or qualified info. :) j/k of course
 
2- While racing at 95 F, mid-summer in Florida, which of these synthetic oils gives the best protection at 302 F oil temperature?
A- 0W-40
B- 5W-40
C- 10W-40
D- Straight 40 grade
E- They are all exactly the same
The correct answer is E- They are all exactly the same.


The one with the highest HTHS

A 15w, 20w, or 25w /40 and a straight grade SAE40 will have an HTHS >3.7
A 0w, 5w, or 10w /40 with could have an HTHS of 3.5

All else being equal(additive package and basestocks), the answer is D which will usually and hopefully have the highest HTHS.

3- While starting up your car at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight 10 (ten) grade motor oil?
A- 3 cSt
B- 6 cSt
C- 10 cSt
D- 20 cSt
E- 30 cSt or higher


There is no 10 grade oil. There are 10w, 8, and 12 grade oils, but no 10.

5- Which of the following mineral based motor oils are still too thick at a 75 F startup temperature?
A- 20 grade
B- 10 grade
C- 5 grade
D- All of the above
E- None are too thick


There is no 10 or 5 grade oil. Again, there is a 10w and 5w grade. And there is a 20w and 20 grade.
And, if the engine starts and maintains oil pressure, none are too thick. At 75F, I wouldn't worry about a monograde SAE30 or SAE40 for my climate, and definitely don't even think about it with a 10w30 or 15w40 in the sump. -25F outside, and then I fill it up with 0w

Attached is a SAE J300 listing the grades.
Engine-Oil-Viscosity-Classification-J300-.jpg
 
Status
Not open for further replies.
Back
Top