Who Runs a 15W40 when 20W50 is Spec'd?

[M.D. Holloway]

I have had this in the back of my mind and it won't leave. I have had a bunch of customers whose gearboxes, hydraulics and air compressors run hotter than what they would want. They look for a solution and many oil companies will suggest using a thicker oil, but I have actually gone in the other direction and went thinner and they all end up running cooler. So why not apply that same idea to engines? By design, our engines run hot. I want to run a 15W40 instead of a 20W50. Problem is two fold - I just changed my oil 500 miles ago and 2) I'm a pussy - I know it won't F up my engine but I'm still a pussy.

Anybody use a 15W40? If not, anybody want to get involved in a case study? I will supply the oil you just have to provide some info.

[stlrj]

15W40? I'm on 5W30 and my trombone cooler barely heats up.

Joe Garcia
74 w/ 86 3.2

[jasonq]

my very qualified porsche mechanic uses 15-40 when he does oil changes on early cars. He recommended 15-40 to me over 20-50, if i could find it. Its just a lot harder to find 15-40 than 20-50. The only place i have found it locally only had chevron 15-40 "diesel" oil so i still use 20-50.

go ahead, use it, the only down side might be a little more oil leaking.

[M.D. Holloway]

the "diesel" oil may actaully work better for you. The TBN may be higher which will inhibit varnishing and oil oxidation.

[..P]

Guys, since a 911 is really "oil cooled" to a certain extent, I would think you would want to stick to what the owners manual says, and not experiment with going to a thinner product. Also, and I think this is VERY important to know, a given designation like 20W50 says nothing about whether it is a mineral oil or a synthetic, and oils with this same 20W50 designation will differ GREATLY in many ways if you compare one that is synthetic, to one that is not.

Therefore since we can buy a 20W50 in a mineral oil and a synthetic, what is the basic difference you ask? Well, you may be surprised to know a synthetic like AMSOIL 20W50 will cold flow down to colder temperatures than some 10-weight mineral oils will, simply because synthetic is an engineered product with all molecules the same general size, while mineral oil has clumps of differing sizes of molecules. Synthetic will also provide better heat resistance, better lubrication, and LOWER RUNNING TEMPERATURE due to lower frictiion.

I'm a water cooled guy visiting the 911 board because I'm in the market for a 1973 911 for my collection. I'm on the hunt. I don't know all that much about the 911 except that it puts very big demands on oil. Therefore I would think all 911 owners would be using a synthetic.


Here is a link you may find of interest. I posted it on another thread, but I want to share it with everyone so I want to post it here too. It may be buried in the other thread.
http://www.network54.com/Forum/message?forumid=426130&messageid=1125341697
You will note, at the end of this thread I provide a scan of the owners manual for my 928. It stipulates a 20W50 for that particular car over a specific temp range. It does not stipulate a synthetic over a mineral oil. Since I've done considerable research on oil for my various cars, clubs, boats, etc., and since I also know what my oil pressure gauges are reading, I highly recommend going to synthetic for anyone who wants to keep good equipment in good condition.

Sincerely,
P


Anyone out there with a 1973 911 or similar model for sale, send me a note !

[kenikh]

Synthetics on older 911s, especially ones that have run dino oil for years typically leak like sieves. That's pretty much the only caveat to running synth on early 911s. Usually there are no probs on a fresh rebuild.

BTW, early cars for sale:

http://www.early911sregistry.org/forum/forumdisplay.php?f=8

[..P]

I agree with that, thanks for the note.

The synthetic oil, as I'm sure you know, will not "cause" a leak, but because it flows so much better it will leak out an existing leak faster than the other stuff will.

Perhaps this is why they call the 911 an "oil dripper"? In any case, thanks for the link, I'll be checking it in a moment.

regards, P

[M.D. Holloway]

I strongly disagree on several fronts. Automakers, transmission OEMs, and even bearing OEMs really know very little about lubrication and tribology. Their recommendations are meager at best and only come close in their attempt at the proper viscosity to use.

Do you know how the proper viscosity is actually determined for an engine? a transmission? or even an oil lubricated bearing? I think you will spend many an hour doing an on-line search only to be disappointed.

As far as using a synthetic over a mineral based oil, I can show you reams of data that shows how a mineral based engine oil has out performed some of the best synthetics on the market and then turn around and show how a synthetic can achieve unheard of longevity and resist thermal breakdown compared to anything else. That should leave you confused because at the end of the day, the oil plays a role in part failure prevention but too many other factors weigh in.

As far as the low temp performance of the AMSOIL product is concerned, the molecular size is a factor but a rather small one actually. The molecular size distribution plays an important role more so but the real factor rests with the percentage of parafinns in the oil and these are abscent in synthetics but can be readily found in Group I base stock and to some extent in Group II's. These are the molecules that are actually forming solids that inhibit flow. But here is another thing to consider, these are also the compounds that provide increased lubricity!

For you to highly recommend synthetic would be like a doctor recommending an anti-biotic over the phone. Not a good idea without first understanding the engine. There are no no-size-fits-all oils.

[M.D. Holloway]

Originally posted by ..P
I agree with that, thanks for the note.

The synthetic oil, as I'm sure you know, will not "cause" a leak, but because it flows so much better it will leak out an existing leak faster than the other stuff will.

Actually, that is not really correct either. Many synthetic oils actually mimic the molecular arrangement of commonly used plastisizers of the day namely d-octyl phalates. These plastisizers were/are used in many different polymer components including seals. The synthetic oil actaully will pull them out of the rubber matrix leaving behind mico fissures for oil to seep out of.

You know how I know this? I used to work for Parker Seal as a bench chemist many years ago.

[jhora]

Mike,

Back to your original thoughts and idea...

I think you may have something here...
you know in the Porsche manual "Vehicles for Sport Purposes" it recommends for the 2.0L S engine to use SAE 20 and for racing use SAE 40....they did recommend using Valvoline Racing Motor Oil for the SAE 40
So that is 20-40.....more like your thought of 15-40

I think you have an interesting idea.

John

[KobaltBlau]

Originally posted by kenikh
Synthetics on older 911s, especially ones that have run dino oil for years typically leak like sieves.

Is this what has happened to you?

[donstevens]

Mike,

Don't be such a puss. As an oil guru you should be the first to experiment in your own car and pass on your experience to others. Besides, if you asked someone else to experiment because you pussed out and they had an engine failure, just think about how you would feel?

I have used Amsoil 15W40 in my old SC and it worked fine. I lost track of that car after it had well over 200,000 miles and had never been torn down. It was a hot running motha too. It did run cooler on the 15W40 vs mineral 20W50.

I am running Amsoil 20W50 in my car now and it actually runs hotter than it did on Mobil-1 15W50. Mobil-1 is typically on the thin side of the viscosity range as well where Amsoil is typically on the thick side. So, your experience with "thinner is cooler" seems to have a parallel to mine, at least in this one case.

I agree with your statements that one cannot deduce cooler operating temperature between synthetic an mineral oil of the same viscosity primarily because of viscosity range. According to CTC lab results 50 weights fall between 16.3 and 21.9 cSt. So a 16.3 cSt mineral will most likely run cooler than a 21.9 cSt synthetic. It may be a coincidence that ..P experienced cooler temps with the synthetic but there are too many factors that affect oil temperature, regardless of oil composition, to draw a blanket conclusion that all synthetics run cooler than a mineral oil of equivalent viscosity. Having said that, historic data shows that the synthetic oil will have more stable thermal properties at temperature extremes over time than the mineral oil but that is a different story.

I question you comment about "The synthetic oil actaully will pull them out of the rubber matrix leaving behind mico fissures for oil to seep out of. " Is that still true today? For all oil belnders? I thought they were over thise issues with modern synthetic oils. If not, wouldn't every car leak? Why would anybody use them?

Don

[MichiganMat]

I saw this same situation with my SC engine:

15-40: car never got over 180 with trombone cooler except under extreme 20min redline hill-climb circumstances
20-50: car was into 210 in traffic with an updated radiator cooler with fan.

I've chimed in more than once on this board to threads where owners are wondering why after an oil change their car is suddenly running 30degrees hotter. "Did you go to 20-50?" Answer is %95 YES.

I still run 20-50 but unfortunately it was changed about 100 miles ago.

Im also suspicous about using oil data as suggested from 20 or 30 years ago. Have there not been major improvements in oil technology since then? Take me to school...

[drsimonwong]

No data to back anything up but my mechanic puts 15W40 mineral oil in my engine since it came under his care about 6 years ago and he's been using this weight for ever as far as I know. He's been working on 911's since the early 70's so I guess that's enough real world experience.

No leaks what so ever in my 120k car. Hardly uses a drop, except after a hard track session the dipstick mark drops a 1/3. Our summers are hot and winters mild to give you an idea of the environment.

I do remember looking back at the service history where 7 years ago one owner switched to Mobil 1 and " leaks attended to" was noted on the next service entry roughly just when new owners bought it and took it to it's current mechanic.

Simon

[wholberg]

My 3.2 would run up to about 250F sitting in traffic on a 95+ degree day with Castrol 20-50. I now run Mobile 1 15W-50, and the car runs 20-30 degrees cooler under similar conditions.

I don't know why it runs cooler, but pumping a lower viscosity oil through the system probably helps a little.

[Brother]

When I ran 5w-40 synth, I could barely get the temp up to 180-190.

I always get up to 200 during my 20 minute commute now running Amsoil 20w50.

[RoninLB]

I use M-1 15w-50 based on the higher temps that it can handle before toasting. Upper piston ring land heat makes me nervious.

based on a 5yr old comparison chart that I lost.

[M.D. Holloway]

Originally posted by donstevens
Mike,

Don't be such a puss. As an oil guru you should be the first to experiment in your own car and pass on your experience to others. Besides, if you asked someone else to experiment because you pussed out and they had an engine failure, just think about how you would feel? Don

Your right! Coming to grips with it, I do not lack confidence but there is something else at play here. To give a little background, I formulated a 20W50 to have a head to head comparison to the Mobil 1 15W50 to see if I could get the temps down with just changing oils and keeping the same relitive viscosity - and it worked. The formula is stout and I wanted to go to production with it but the minium production size is several hundred gallons - and thats in a pilot plant kettle. Needles to say I can't make the numbers really work out because the market is not big enough for a true product introduction (needs to be >$1M) for costs to be in line. So I have the qualifications, the physical data and even some field data to support the technology but the customer base is real smal in comparison. I can't justify keeping the baby!

Its not that I'm skeerd per se, just that I put work into the 20W50 and I now I may have to let go.

The great news is I do have a 15W40 that uses the same stout technology and is commercially available in qts, gallons, 2 1/2 gallon jugs (and drums and totes and tankers. ) I have great confidence in my 15W40 - used it in my Volvo and got over 40K before I changed and I only changed because the TBN went down to 4 but I still had no signs of wear metals and the additive pack was somewaht intact.

[M.D. Holloway]

I guess I wanted a bunch of guys to come back and say DONT DO IT - STAY THE COURSE OF THE 20W50! But that did not happen - if it did, I would have the rationalization in my meager little brain to try to make the numbers work. I'm glad I dont have to engage in that rationalization.

[Mike Bonkalski]

If you want to send me some of your formulated 15-40, I would be more than happy to test it out and report my findings.