Ok, I Just bought a 91 Sedan Deville with ~93k miles in California and drove it back to where I live in Tennessee. This car was my bestfriends, grandfathers car. It had always been to the dealer every 3k miles, with the instructions from Larry (the first owner) being "just do whatever it needs boys", so it has been well cared for. For the most part ive driven mainly 300k-400k mile Isuzu cars and always ran 5/30 Mobil one synthetic in them with much success. When I had an 84 Eldo with a 4100, I ran 15/40 in it. I know Sal reccomends the 15/40 in these engines, but I'm a die hard synthetic fan. My question is would the synthetic for 15/40, which comes as a 5/40 made by Shell, protect the motor in the same manner that 15/40 does, but with a synthetic advantage? Would I be safe to run 15/50 Mobil 1 synthetic? I always use a quart of Lucas in my engines as well as an O.E. filter, I want to do what is best for this car, as I plan on keeping it a long time, the white leather and symphony sound are too sweet to give up anytime soon. How does this transmission respond to the use of synthetic fluid? I know its been changed every 15k, so when i change it and put in my lucas i was thinking of using Mobil 1 synthetic in it aswell, any ideas? :stirpot::cloud9::burn:

remeber , that 15w40 isnt regualr old 15w40 but the devlac and shell rotella flavors , which are primarily for diesels and dont have the friction modifiers in the "other" oils ....this is beatter for your distbutor gear and for the oil pump you have in that car , not as important for the 4.9s (dont you have a 4.5?) but pretty much what should be run in the 4100 ,4.1,4.5,4.9 cars

syntheitc is really only beneifical if your seeing high oil temperatures , like track duty or towing ....

id rather run a can of gm engine oil suppliment in the place of the lucas every once in awhile .....

Well, the mobil 1 might be ok, maybe someone else has more experience with the 15/50. I do know that I tried chevron 20w50 a few years back, but changed back to 10w30 afterwards and it felt like it had more 'peppiness' (and mpg probably).

But one thing you might want to try is the Amsoil 15w40 synthetic diesel/marine oil. :hide: It has some of the best protection properties available and my HT4100 really likes it-- nice clean oil changes. It's the pure synthetic equivalent to Mobil Delvac and Shell Rotella, etc.

As with any synthetics, you may have some minor oil leaks after switching to synthetic from a dino-only car, but if you want to seal it up you can change the gaskets and you shouldn't have any more problems.

The topic of oil here has been much discussed. Do a search on the subject. Bbobynski has laid down some pretty good techinical attributes to oils.

He, as well as I, highly recommend the 15W40 oils for use in these engines, such as Rolella T, Delo or Delvac brands.

Synthetics do not really give a lot of advantage over these oils. I have always been of the school, use a good quality conventional oil and filter (AC/Delco) and change it often. I have been using 15W40 oils for more than 20 years and have yet to have any issues with engines at all.

Mike

The theories on synthetics are old, they don't hold "weight" to the newer modern oils (SL and SM for gas engines).

All the technobabble out there on synthetics is comparing them to old SE and older oils, which did suck. So take what the oil salesmen preach and take it with a gain of salt. When you see cars like the old Turbos and Diesels from the 70's and 80's specing you to run 30W, that is a clue that they needed the best protecting oil out there. Now, look, my dad's 496 Chevy RV at 30000#, takes 5W30. It used to be you didn't touch 5W30 below 60F, and NEVER tow with it. Now it is just as good as anything else.

All the tests that show that this oil has been wear than another, again, where does this apply to an engine? No where.

I have been running Mobil 1 10W-30 in my '93 DeVille with the 4.9 since I got it.

That was at 79,917 miles, she now has 107,800 and is as clean as could be inside. I now use the Extended Performance, 6 bucks a quart, but with the gas prices now, it is more money to fill my tank with gas then it is to change my oil using synthetic.

I change it according to the OLM, which is about every 5k miles.

Ok, I do understand that the oil quality and grades of today are much better than that of yesteryear, however, like I said, I used to drive 300k-400k mile Isuzu's. They ran perfect, no leaks, no smoke, all clearences within new spec, the only thing stopping me from continuing to drive them is that people like to hit me in them and they are fairly rare and hard to come by and with a lot of miles they book at nothing, despite that they run so well. I have no probelm with spending $6-$10 per quart, I just want the best protection that will allow this 4.9 to perform like my old Isuzu's did. Btw my Isuzu's had either 1.6 or 1.8 twin cam 4cyl. with shim on bucket valves with shims for adjusters, and I never had to touch em.

My 91 Deville (sold) had been run on Amsoil 10W30 then later 0W30 with 25K oil changes from around 60K miles to 142K miles. Then went Mobil 1 due to cost. At 180K it looked awesome inside. No sludge, no dark oil residue, no burned residue, just clean metal, aluminum colored aluminum....

remeber , that 15w40 isnt regualr old 15w40 but the devlac and shell rotella flavors , which are primarily for diesels and dont have the friction modifiers in the "other" oils ....this is beatter for your distbutor gear and for the oil pump you have in that car , not as important for the 4.9s (dont you have a 4.5?) but pretty much what should be run in the 4100 ,4.1,4.5,4.9 cars

syntheitc is really only beneifical if your seeing high oil temperatures , like track duty or towing ....

id rather run a can of gm engine oil suppliment in the place of the lucas every once in awhile .....
A 91 would be a 4.9.

Blaze

in my experience, synthetic oils are just plain more "slick" than conventional motor oils..i bought an 89 eldorado with 68k miles on it, and changed the oil using regular motor oil at the dealership( they were running a $20 special:)). I didnt believe in the "superiority" of synthetic oils at the time either, but on the suggestion of a friend who used exclusively Mobil 1 syhthetic and got 400,000 miles on his 2.8L citation v6( and it was CLEAN as a whistle when he tore it down to rebuild it ), I switched to synthetic motor oil, mobil 1 10w30, and instantly saw about 3 to 4 MPG improvement in economy on the highway and about 2 mpg in the city..

I will likely be testing it soon. I have it down on my DOE, but I haven't decided the best way to implement the test. Any Six Sigma Green or Black Belts out there that can advise? Sorry, I am only a GB in Training.... Just tacking up some more experience in Minitab, not to mention, paying close attention to what works and what doesn't in the fuel economy catagory.

http://www.cadillacforums.com/forums/showthread.php?t=51616

I honestly do not believe synthetic is any slicker (that was Penzoils Synthetic ad campaign aim), I do feel that there is a potential for better ring sealing, as the oil film strength may be stronger and resist shear better. But with better and better oils out there, this gap seems to be closing. With a better ring seal you will see a potential for better mileage. Again, potential. Claims as high as 4 mpg are pretty far out. What is the long term data to back it up? I have long extensive records on my cars (dummy me sold my old car with them....), so I am back at it again with the FWB. I have 20K+ miles now with tons of details on my driving over the last 7 months. (yeah, I drive a lot) Not much has a REAL effect on mileage. But testing goes on. If anyone has recommendations, I will work it into the DOE if I can.

Up coming are:
K&N Filter
Synthetic (5W40, need to keep to 40W on hot, as that is where my current baseline is, possibly later to a 30W oil, but we shall see.)
Ongoing is air pressure. Currently at 35/35, soon to go to 40/40, was at 30/30 for a short time, and it did have some detrimental effects.
Winter Tires go on soon too. So that will be in there for this year.

As for synthetic lasting long, there isn't a valid control group to validate the validity that the synthetic helped the Citation live that long. Was it a fluke? Do all last that long? Claiming the oil was the reason isn't a valid claim, doesn't matter the credentials of who claims it. There isn't statistical data to back it up.

Am I saying synthetics are bad? No, as we have learned time and time again on this forum, the reasons for it aren't needed like they used to be. I hope to prove the claims of synthetic for fuel economy sometime soon!

Yes if you are a "Real enthusiast" you can feel the differance in synthetic to nonsynthetic. I dunno im the kinda guy who can drive a car, and get out and say the left front tire feels about 3 psi off from the right. I feel everything in a car, i can be one with it. I finally changed my oil, using what i figured to be the best of both worlds...5/40 rotella synthetic and a delco filter. These are the smoothest quietest cars, and I bet you think they cant get any smoother or quieter, well they can, switch to synthetic, and you wont regret it, especially with the rotella being so reasonably priced, you cant beat it. Havent got to test the milleage yet, but i would imagine it would go up a hair, now to you this hair may not be worth the extra money, but if it is making the engine perform noticeably on the output end of the spectrum, it must be working wonders inside!

I'll second the remark on synthetics being smooth.. I switched to Amsoil 15w40 Diesel synthetic on my 4.1L, and whether its the weight of the oil or the synthetic nature, it runs smooth and quiet and sometimes I have to check and make sure it's even running ;-)

Mt 94 FWB LT1 is smoother than any other car I have seen at idle, with 15W40 and also even 5W30 (which was in it when I got it). I honestly cannot hardly at all tell if the engine is running when I am at a stoplight.

Yup, I am one of the sick puppies that seems to notice everything on the car. Air pressure being a big one.

Popular Hot Car Crafting magazines have done some tests showing some HP gains at higher rpms. Honestly, I would take thier results with a grain of salt, as there is no control to the experiement. Now, if they would have run with dino oil then same weight synthetic, then back to dino, and then back to synthetic and proven some increase then on the same dyno, then i would put more stock in the theory. No change not returning to baseline is 100% valid. It might show some trendyness, but for real validation, there needs to be more control. Follow some of Jim Hand's testing on camshafts. Amazing. His dyno? The 1/4mile track. And is that man rock solid on the reaction time. And he will return to baseline to prove the experiment is valid.

So, yes, oil is going to be in my fuel economy testing, hope to see some results. As for now, 5W30 vs 15W40 shows very little. Considering 1 is "engergy conserving" and one is not.

Take a look at my results http://www.cadillacforums.com/forums/showthread.php?t=51616&highlight=analysis+15W40+5W30