Those "thin" numbers like 5-40 scare people unnecessarily. That oil when at temperature for the 5 rating, will actually be thicker than when at the temperature of the 40 Rating, so there should be no fear of ruining trans or engine based on the fear of too thin an oil when cold .

I understood what you meant. It was around 4°F at the beginning of this month at my house. The "W" in oil viscosities stands for winter. It's the viscosity of the oil when it is cold. In the case of a 5W-40 like I run, it has a viscosity at -30°C of an SAE grade 5 oil. This will significantly help with a cold start environment and will allow the oil to flow more smoothlyon startup preventing dry starts. But when it gets up to operating temp is where the second number comes into play. So you'll have the viscosity of an SAE grade 40. Hence "5W-40.

If you wanted to retain the heavier viscosity at operating temp, do a little research and lok for a 5W-50 or something similar. I believe redline makes one. But I duggest doing research before that. I've personally run my 5W-40 in -15°F temps with no issue. I like to let at LEAST the coolant get up to operating temp before driving though.

By "cold out" I mean around -10 or so ( I imagine that's around 10 F ).  

I run my 5W-40 year round. It doesn't hurt to run the lower winter rate year round. If you understand how oil viscosity is measured, then you'll understand why it's not a concern.

I'm always looking for a better oil. But currently, Rotella T6 is a great full synthetic with ≈ 1250ppm Zinc and ≈ 1100ppm Phosphorus, the main two components of wear resistance in an oil. This is in contrast to the beloved Castrol that everyone says you should run which has ≈ 1100ppm Zinc and ≈ 800ppm Phosphorus. And the Shell oil has some really advanced V.I. additives that have proven to not break down in higher heat. And by proven, I mean in my oil analysis it showed after 3000 miles I still had 9.8 TBN. This means I still had PLENTY of life left in my oil. Blackstone finds that below 1 TBN unacceptable.

Another hot topic of debate is that "Synthetic oils are bad for your seals". This USED to be true for almost all synthetics, and is still relatively true for Group V synthetics. But you won't be buying any Group V syn at autozone so you can simply forget the argument.

AMSOIL full synthetics are generally Group IV and thus are less compatible with seals. They have a lot of additives that make them more soluble and retain their compatibility with seals. In an older car with pretty worn seals you MIGHT see an issue, but the chances are so low that it's a moot point.

What I personally like about the Shell Rotella T6 Full Syn is that it's actually derived from a base oil that is a Group III. This means it's completely compatible with all of your seals. It also has a good amount of detergents necessary for street cars that are often not included in race oils.

So Shell Rotella T6 Full Synthetic has:

1) Full compatibility with your seals just like a dyno oil does because its base oil is a Group III.

2) Advanced Viscosity Enhancers that reduce sheering to a point that it's not even a worry (Proven by my oil analysis after 3000 miles)

3) Higher Zinc and significantly higher Phosphorus than Castrol GTX

4) Great thermal protection and consistent oil pressure above 100°C

So can anyone tell me why I shouldn't be running synthetic?

Does anyone run anything thinner than 20/50 when it's cold out? ( manual gearbox )

So much great information.  

I agree with MtyMous that it would be nice to hear from the anti-synthetic camp what the *specific* wear concern is. Info we can take to the bank instead of 'concerns'.

Otherwise it's tempting to become a rebel again - until the next time I tell someone I run synthetic.  And watch the guy pass out, have a seizure, cross himself and wave garlic at me.

I was using Valvoline Racing oil in the '70s since it was free at the Valvoline truck at the race track along with hand cleaner, brake cleaner etc.  No body was using redline in their Minis as there was concern about what it would do in the trans.  I had determined that the ester based synthetics were the best, and Redline was the only one I knew about except for Klotz for the 2 strokes.  I did a dyno test comparing the two and found 4 ponys by changing the oil and filter.  That was 101 to 105 at the wheels, about the same increase as going from single 45 Weber to split 48s.  That sold me as far as racing was concerned.  After a few years I noticed about everyone racing a Mini was also using Redline.  On the track I observed lower oil temperatures, lower water temperatures,  higher oil pressure even at the end of a race on a hot day, no wear on the bottom or top end.  The biggest problem I had with Valvoline dyno oil was on hot days the oil just gave up at about 225 degrees.  I could still buy EN40B cranks for $200 back then, but DNFs were a bummer.

The Amzoil product is also an ester based synthetic formulated specifically for old flat tappet cars (vintage types) and ones that may sit for long periods.  I also use their 0W20 oil in my Honda Insight 3 cyl motors, and 10W40 in my Bini.  They will try to get you to sign up as a dealer...it's free...and the only thing that happens is you get a big discount on all the products.  Haven't  tried any of their other products.  Have been tempted to use their gear oil in the Bini.

Ran full synthetic Shell Rotella T6 for 3 years in my mini. Never had an oil leak after I fixed the original oil leak when I bought the car. Never had a problem shifting, never had a problem with overheating or underheating. I sent my oil out for an oil analysis by Blackstone Labs once a year and found no excessive wear characteristics, no signs of overheating the oil. Low soot levels, significantly less breakdown than the dino oil I sent in for my first analysis, and it simply "looked cleaner" to me every time I drained it. This was proven by the oil analysis.

When I pulled the head, I found no deposits or sludge. And when I broke down the transmission, I found absolutely no signs of wear on the gears or bearings.

Please don't take my comments as "You're all wrong", but instead, try thinking of this as someone who'se done a significant amount of research and spent a good amount of money trying out something different. If you would like to stick with non-synthetic, by all means... go for it. Make sure you get something with a decent amount of ZDDP, but there is so much emphasis on "Make sure it has a high ZDDP content" that people tend to just grab the one with the highest number and not look at ANY of the other oil characteristics.

Has anyone else got hard evidence that would prove that synthetic is bad for our cars? I'm truly asking because if you can prove that it's bad for my new motor I will avoid it. But I think I'm the only one that has ever posted that they have sent their oil out to a lab for analysis. haha

I was running the GTX 20/50 in my car, but was told by my mechanic that the best oil to use is the Valvoline VR1 Racing Oil because of the ZDDP content. I'm no expert, but this is from their site:

Valvoline VR1 Racing Oil: Contains 75% higher zinc than SM motor oil with a balanced additive package designed to work in both racing and street-legal applications. This product will protect older style push-rod and flat tappet engines. Valvoline provides this product in both multi and mono viscosity grades: 20w50, straight 50, 10w30, straight 30, straight 40, and straight 60.

Announcing my next genius idea...

An aluminum box to cover the top of the gears, separating the engine oil supply from the tranny.

Allowing us to run whatever oil in the tranny and whatever in the engine.

I put mobil-1 synthetic in one of my minis. I gradually started having trouble shifting between gears, both up and down (fourth down to third was the first symptom). I was sure my synchronizers were going bad. But then put two and two together. The Mobil-1 was so effective as a lubricant, the synchronizers couldn't get a bite when shifting. I switched back to Castrol 20/50 and things got better in the transmission almost immediately.

OK I'll bite.  And there's an Amsoil guy just up the street though I hate the constant sales pitches to open an Amsoil franchise.

Last I heard is that we're not supposed to run synthetic because of 1. zddp and 2. The gears.  

Thus, I thought most guys were settled on GTX 20/50.

So a synthethic with zddp is still ok on the gears...?

thanks for the input. Going to look into it further and see if i have a local distributor.  Cheers,  Bill

I use it.  Seems to be made for Minis.  Cling additives good for infrequent starting on cars in storage.

//www.amsoil.com/shop/by-product/motor-oil/gasoline/z-rod-20w-50-synthetic-motor-oil/

Does it have any ZDDP additive?

has anyone ever tried AMSOIL Z-Rod 20w50 synthetic oil?

Its advertised as "modern technology for classic cars".