Oil Viscosity

[Plimbob]

Chris,

Thanks for the education - much appreciated. Sounds like I ought to look at 'Ester' oils due to the oil leak in 0-30 vis?

Thanks,
Tim

 

[HiHoeSilver]

Science time on why *SOME* synthetics cause leaks, or how that may have started

tl;dr early synthetics didn't play nice with old school gaskets. Since then, material compositions and understanding has changed such that it's a non issue. The notion that synthetics cause leaks was never a myth, but you need to look at it with a relevance to the time.




There are 3 base oil types that can be used and be marketed as a fully synthetic oil

1. Hydrocracked - Basically ultra refined conventional oils such that the molecular weight is homogenous and offers the advantages of synthetic. Most cost effective

2. PAO - Polyalphaolefin - longest service life, resistant to breaking down, fuel dilution, water contamination.

3. Esters - Best wear protection, does not play nice with short trips or other scenarios where water contamination is a concern. "sticks" to metals on a molecular level. Also innately acts as a detergent as is extremely effective at breaking down sludge/varnish.

Now onto the leak bit: Esters cause seals to soften slightly by the nature of the molecule. Redline is notorious for using esters in their oils. May also explain why folks with 30+ year old cars say to use redline in the transmission and don't have any issues w/ leakage. It's a group V base stock - the most recent one

Hydrocracked oils, for all intents and purpose, behave as would a traditional dino oil. If you're looking for a 1:1 swap over to gain the benefits of synthetic, this would be your best bet. Rotella uses it in their synthetic lines, and it's fairly common to see house brand synthetics use this base stock.

PAOs: The group IV base stock. These provide the longest service life - Amsoil signature series, mobile 1 annual, etc. However, this particular base stock causes seals to shrink slightly. In the early days of synthetics, this wasn't quite understood. So you'd fill your crank case up w/ a good quality synthetic oil only to find it leaks like a siv. What gives??? Well, your seals shrunk. That's since been corrected and manufacturers have a good grasp on it now, and add some seal conditioners to the oil to counteract this property. Ever hear of anyone recently switching to synthetic and having their seals shit out? No? That's why. Just took some development. These also didn't play nice with the old school cork gaskets and started making rounds during the transitional period when we were moving to more modern nitrile gaskets. So that could have played a big part in the whole leak issue.






Also of note: This same relevance is why I hold the personal belief that 5w30 is an out dated oil weight and 0w30 should be used instead. We started using SAE30, because the 10w30 of the time would shear down to it's 10 weight base stock rather quickly. The same happened when 5w30 came around. Vehicles stuck with a 10w30 recommendation for years after until the tech matured and we came up with better viscosity modifiers. And now we're at the point were 0w30 provides much more desirable cold flow characteristics while still maintaining the appropriate viscosity at operating temperature. That has matured for long enough that shear down is a non issue for even extended oil change intervals.

If you don't know, 5w30 is composted of a 5 weight base stock with viscosity modifiers added such that it's an effective 30 weight oil at operating temperature. What you end up with is an oil that's thinner than an SAE30 when cold, but still maintains the appropriate viscosity when hot. The lower the first number (15, 10, 5, 0, etc) the lower the viscosity/temperature curve. i.e. the less the viscosity will change across a temperature range.

Awesome info. I didn't know a lot of that.

Let's not forget, though, that the science /data doesn't always translate into real life the same way every time because there are lots of variables to consider. Different temp ranges, pressure changes, material compatability, etc. How about condition of the seals in the first place, or the manner in which they were installed?

I work with solvents and equipment that uses them. Gasket material is important. Some need to take a set, some need to see a bit of heat, some have a memory, etc. Viton was (still is, at times) a good option. However, it swells. I have seen both of the following scenarios:

1. The swelling Viton helps seal up an otherwise not-so-great mating.

2. The swelling Viton causes the gasket to move, resulting in a leak.

James has experienced the "synthetic leak" and he's not the only one, so we know it does and can happen... sometimes. This wouldn't stop me from trying (especially backed up by your science lesson), but I'd still use high milage as a source of added confidence (real or not, lol).

Some say once you go "high milage" you can't (shouldn't) go back or you'll leak. I haven't owned a vehicle with under 100k in more than 20 years. I use high milage, and believe that the seal conditioners have probably helped mitigate some potential leaks (just a hunch).
What are your thoughts here?

 

[08grey]

I went from using only high mileage to using the GTX start up oil one and immediatly had oil spitting out the front crank seal. Same oil weight.

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[SnowDrifter]

Which one? My wife's car or Grumpy's?

Yours

What are your thoughts here?

Personally, I've never subscribed to the whole high mileage thing. Don't run it; don't plan to. I'm of the opinion that if a vehicle has a leak, or other issue for that matter it should be addressed directly and not cobbled around with any bottled fixes. That said I also have yet to experience any leak or changes in leaks with synthetics and run them in every piece of equipment I own from small engines to passenger vehicles. I feel it's also worth mentioning I do my own work where logistics allows, so my cost of repair for these things is lower than you'd typically see from a shop.

Here's a smattering of vehicles I either own myself or are in charge of maintaining - family members rigs. Worth noting in all cases, that on purchase - every fluid on the vehicle was changed. Coolant, engine oil, p/s, trans, brake fluid, diff fluid, etc. Coolant was either OE formulation or univeral stuff. Brake fluid is all DOT4, changed at 2 year intervals, lubrication fluids are all synthetics from name brands unless otherwise specified.




1999 vw passat, got it at 155k, sold off at 180k. Wet everywhere, no drips by some miracle of god. Sludged motor on account of conventional changes every 10k. Ran Rotella t6 the whole time I owned it and just changed the stuff when it got visually dirty. Managed to clean up the sludged but it still quite varnished everywhere.

2002 jeep wrangler. Bought it at 18k, though to be entirely frank I think that's a lie. How many miles it really has are anyone's guess. That one was also sludged up. Ran rotella, changed when it got visually dirty, then transitioned to whatever name brand 5w30 syn was on sale. Local shop switches between half off M1 or Valvoline. Rebuilt front differential directly after purchase. Pinion bearing and seal were shot. Few years into ownership (this is 2014 era now) the valve cover and rear main began to leak. Replaced both of those, no other leaks to this day.

2003 subaru forester - bought at 98k, sold at 124k. Unknown service history. I ran every which oil in that one ranging from 0w20 to 15w40, synthetic, conventional, high mileage, name brands, house brands. That car had some loud ass piston slap when cold, was playing around trying to determine what quiets it. This one got me playing around with lab tests and viscosities. I found that it was quietest on a Xw20 or 0w30, but 0w30 posted the best wear numbers overall compared to any of the other weights I ran.

2005 chevy tahoe - bought at 115k, has 140k on it at current. Regular service history every 5-7k, unknown what grade of oil was used previous. I've run a mix of redline, amsoil, mobil 1, and amsoil. Settled on M1 0w30 esp due to availability. No leaks, nothing wet underneath; it's dry as a bone. Only gasket related stuff was to change the transmission cooler lines at ~134k due to a wet spot developing. And the valley pan gasket as part of the knock sensors while I was doing the intake gaskets.

2008 toyota highlander, purchased new now has 115k - syn from day 1, no leaks to this day

2010 jeep wrangler, purchased new now has 50k. Was traded in last week for a newer model. syn from day 1, light valve cover gasket wetting near end of ownership.

 

[swathdiver]

Yours

2004 Pontiac Montana with about 170K miles. Mobil 1 5W30 (regular or high mileage, don't remember). Back in the '80s and '90s this happened whenever we bought a car and switched it over to synthetic fairly regularly. Since we were racing and always tearing into motors it was not a big deal to do a rear main back then. When these minivans have a rear main or transmission failure, that's usually their death knell as the labor is great to pull the motor or trans from this type. It'll be less expensive to go out and buy another one.

 

[SnowDrifter]

IIRC M1 uses PAO as a portion of their base stocks. I'm curious to see what would happen if you ran redline (ester) in there for an OCI

 

[swathdiver]

IIRC M1 uses PAO as a portion of their base stocks. I'm curious to see what would happen if you ran redline (ester) in there for an OCI

I thought M1 reformulated their oil back around 2010 to Group III base? In a couple of weeks I'm going to put it back on Mobil's conventional oil and see what Lucas has to swell up the seals. I reckon that will be its last oil change in our stable.

 

[SnowDrifter]

I thought M1 reformulated their oil back around 2010 to Group III base? In a couple of weeks I'm going to put it back on Mobil's conventional oil and see what Lucas has to swell up the seals. I reckon that will be its last oil change in our stable.

That's entirely possible

I'll check in on it and get back to you

 

[steve45]

Personally, I think you should have gone to a higher viscosity when you bought it. Low viscosity oils don't increase engine life, they improve the almighty fuel economy. Who care how long the engine lasts as long as it meets government fuel economy standards and it's out of warranty when it blows up?