Which viscosity oil for 1991 BMW 735

[Bluestream]

Hello, I have a 1991 BMW 935iL with 50,000 KM on it. The owners manual suggested to use 15W40 for the temperatures -5F to 90F (It also recomends 10W30 for temps of -25F to 40F, and 20W50 for 15F to 120F) I went with Castrol RX Super 15W40 this summer. This is a diesel oil API rated CH-4, CG-4, CF-4 CF/SJ I don't know what these ratings mean, but it does say that this oil can be used in gas or diesel engines. I do not want to be bothered with synthetic oil due to the cost, and the fact that this car is only used about 3-4,000 KM per year, in the summer only. I only change the only once per year. Is Castrol RX Super a good oil to be using in the car? I would also like to know if BMW has canged their oil recommendations for this car since 1991 of anyone has this information.

edited to fix title

[ October 01, 2003, 05:07 AM: Message edited by: Patman ]

 

[Cary]

I assume that you have a 735il, since there is no such thing as a 935il. That uses the M20 Big Six motor, and 15w-40 is fine. In fact you should consider using 20w-50 if you don't use that car in tempuratures below 40F. One thing to watch on that engine is the banjo bolts for the oil sprayers on the cams backing out. They should be checked when the valves are adjusted.

Cary

 

[buster]

Amsoil ATM 10w-30, Delvac 1 or Amsoil 10w-40 would be my choices.

[ September 30, 2003, 07:09 PM: Message edited by: buster ]

 

[Bluestream]

Yes, it is a 735iL (it has been a long day!) The dealer would install 20W50 for summer use, and 10W30 for fall/winter. I assume that 20W50 would result in slightly higher fuel consumption. Any comments on the quality of Castrol RX super? I decided to use Castrol as it was very popular on a BMW forum that I found

 

[Doug Hillary]

Hi,
your choice of Castrol RX Super 15w-40 was an excellent one. It is a great product and would probably be OK year round. I have a lot of happy experience with that oil as do most Truckers in OZ

If you wish to go to a synthetic, Mobil delvac 1 5w-40 is as good as they get and it works very well in Euro cars

I use this in all of my cars including a MY98 Z3 2.8 manual

Regards

 

[Dr. T]

I'll second the Castrol 15-40 recommendation...or you could easily use Castrol Syntec 5-50 year round for a cleaner running engine.

 

[Patman]

quote:

---

Originally posted by Dr. T:
I'll second the Castrol 15-40 recommendation...or you could easily use Castrol Syntec 5-50 year round for a cleaner running engine.

---

I fail to see how a group 3 oil in 5w50 form that is loaded with VII could possibly keep an engine clean in the long run?

Do you actually know anyone who has run this oil for 200k or more and opened up their engine to see how clean it is (or isn't!)

 

[Doug Hillary]

Hi,
yes I must say I had some difficulty reconciling "better cleanliness" with the Syntech 5w-50 than with the CI/SJ Castrol RX Super
RX Super is probably recognised here as the Delvac 1 of Mineral oils and a very clean oil

Putting Delvac 1 in my BMW Z3 2.8 ( VANOS ) ( 50000 kms ) has made the engine considerably quieter than it was previously with M1 0w-40

Regards

 

[Dr. T]

That's easy...Syntec contains esters. This together with a better base oil ie. Group III vs. Group I or II will allow for a more oxidatively resistant oil providing for a cleaner engine. I have found Syntec to "clean" close to or as good as Delvac 1.

Yes, there are VI improvers to allow for the viscosity spread....it's unfortunate that Castrol doesn't offer the Syntec 20-50 in Canada...else, I'd recommend it as well. In either case, make no mistake a synthetic (group III, IV or V) will keep your engine cleaner than dino. Period.

 

[Patman]

I agree that esters will help keep an engine clean but do we know for certain that Syntec's 5w30, 10w30 and 5w50 really do contain esters? Or is it just a rumor?

And if it does have esters, is that addition alone enough to keep things clean if their 5w50 is thinning out severely due to rapid degradation of it's VII?

 

[Dr. T]

Aside from smelling like "Tide" laundry detergent, the board's expert, Molacule confirmed that Group III's contain esters...

Aside from the VI's (which all oils contain), synth's contain less of them than dino and contain less impurities than dino oils as well...thereby allowing for less deposits over dino.

Although, it is hard to compare a dino 15-40 with say, Syntec 5-50...but, I would still wager to bet that the synthetic will keep things cleaner, longer...because you're starting off with a better base oil.

 

[Primus]

Bluestream,
You have M30 engine and may use any oil except xW-20, xW-30 ACEA A1/B1, A5/B5 and pure diesel.

First you have to decide: synthetic or semi-synthetic (no mineral oil for BMW, please). Use of PAO synthetic oil now may cause seal shrinkage and therefore oil leakage. This may happen with 80 % probability and usually the rear seal of crank-shaft starts to leak first. But nothing serious: all 6 cylinders owners experienced this sooner or later despite M30 is still considered as the most reliable and succesful engine.

I am not familiar with Amsoil, Redline or Neo, so cannot give some comments. As for non exotic for me brands available on N.A. market, depending on weather and application the choice would be (in alphabetical order):

- 5W-40: Havoline Synthetic, Liqui(Lubro)Moly, Motul 6100 Synergie or its new version 8100 X-cess, Valvoline SynPower, 76 Pure Synthetic (all PAO + group III);
- 10W-40: Motul 6100 (PAO + III), 4100 (III +PAO)
- 5W-50: Castrol Syntec (mainly III + E)
- 15W-50: Mobil1 (PAO), Motul 6100 (PAO + III)
- 10W-60: Castrol TWS Motosport (PAO + E)
- 0W-40: Mobil1 (PAO+AA+E), Motul 8100 E-Tech (E + PAO)
- 0W-30: Castrol Formula SLX (PAO)

I would avoid 0W-30/0W-40 for summer and be careful with CH-4/SJ oil use in high revving engines due to high ash content. No way for CI-4/SL where the ash content may be even higher.

My personal choice for M30: 1. Castrol TWS 10W-60, 2. Mobil1 15W-50, 3. Castrol Syntec 5W-50.

And don't worry about spread and engine cleanliness: with any of a.m. oils the engine will be clean more then enough. Just follow
recommended 7.500 km or 2 times a year drain
intervals.

To make a compromise you can use

If it is not a problem and you are are more interested to engine protection

 

[Bluestream]

In the early seventies when I was in High School auto shop classes we were given a project to rebuild an engine. The local junkyard would drop off about 12 engines from their stock of wreaks. These were Buick, Ford, and other V8's from 60's era cars. Each group of two people were given an engine to work on, and first thing that I noticed was how much sludge was in these engines. The valve covers were totally covered with 1/4 to 3/8 of an inch of black sludge. The heads, and all internal parts of the block were covered with this stuff. All of the engines taken apart were in the same condition. Now fast forward to 1996, and I had to change the valve cover gaskets on my 1991 Ford explorer; the inside of those covers were practicaly like new with 150,000KM on the engine. There was maybe a thin film of sludge in one area that could be seen by wiping a finger down the inside surface. This is how far oils have come in 25 years. I don't think sludge is anything to worry about anymore.

Also, we did the "oil filter" study long before there was an internet. The first thing that our teacher had us to was to remove all the oil filters from the Junk engines that came in, and to cut them open and measure the length of the paper inside. He would use this information to purchase the brand of filter that was best for the coming year. I still remember the results from 1972 in anyone gives a **** . The best filter was a Mopar with 12 feet of paper, and the worst was a Sears filter with 4 feet of paper element.

 

[Bluestream]

Primus, thanks for your reply. I am not sure why you say no mineral oil for BMW? This car has had mineral oil for the past 11 years, and I don't know why I should change, given that I use the cars very little from May to October. I am going to change the oil before I put this car away for the winter. The oil will stay in the car over winter, and then be in use for next summer. I have been changing the oil only once per year. We get high temps of 90F to 95F for only a few days in the summer. Most temps are 75-85F in the summer.

I have heard of people on other web sites getting 300,000 to 400,000 miles out of these engines, but I don't know if this is true. At the rate I use the car, it will last longer than I will.

[ October 01, 2003, 11:25 PM: Message edited by: Bluestream ]

 

[Doug Hillary]

Hi,
if you are storing your car it may be worth considering an oil with a Vapour Phase Inhibitor ( VPI )to prevent corrosion above the oil line

Such oils are made for Agriculture/Farm equipment, suitable for all vehicles and Castrol's AGRI TRX 1540 is here sold in OZ. Perhaps its sold there too

This oil is at least rated as a CG-4/SJ and has a viscosity of 15w-40

Regards

 

[Cary]

Although I am a big synthetic fan, I still believe for this application, a good 15w-40 or preferably 20w-50 will work fine in this application. The one writer is correct, that the M30 motor will easily go 300,000 miles with regular oil changes on mineral oil.

Just for the record, my mechanic just rebuilt his M10 2002 motor after 200,000 miles. This motor ran 20w-50 mineral oil its entire life (california with temps down to Mid 30F). Some people would say only 200,000 miles. The catch is this was a 10:1 compression, 304 schrick cammed motor with 45 weber sidedrafts running NO air filters for 20 years. This engine saw regular 7000+ rpm use and countless lapping days at the track.

Cary

 

[sprintman]

20W50 eh? Must be one of those large clearance non American engines, probably an import from Australia.

 

[Bluestream]

quote:

---

Originally posted by Doug Hillary:
Hi,
if you are storing your car it may be worth considering an oil with a Vapour Phase Inhibitor ( VPI )to prevent corrosion above the oil line

Such oils are made for Agriculture/Farm equipment, suitable for all vehicles and Castrol's AGRI TRX 1540 is here sold in OZ. Perhaps its sold there too

This oil is at least rated as a CG-4/SJ and has a viscosity of 15w-40

Regards

---

I have never heard of this stuff, but I am sure it is available here also.

I have never done anything special for storage, but I should probably fog the engine with storage oil, and use some fuel preservative. I did think of buying some of the cheap Walmart oil in the 20 liter pails, and pouring the whole pail into the engine. Then draining it out in the spring. I guess it could be saved and reused year after year, or used in my 1991 Explorer.

 

[Primus]

quote:

---

Originally posted by Bluestream:
I am not sure why you say no mineral oil for BMW? This car has had mineral oil for the past 11 years, and I don't know why I should change, given that I use the cars very little from May to October. I am going to change the oil before I put this car away for the winter. The oil will stay in the car over winter, and then be in use for next summer. I have been changing the oil only once per year.

---

Just thought about something more usual in 3.5 l BMW given drive style of their European owners. For M30 engines BMW recommends to change the oil twice a year: before and after the winter. So, if to change only once a year, then probably CH-4/SJ mineral oil may be better then SJ/CF or even A3/B3 synthetic in preventing from internal corrosion. If the appropriate conservation is not made, then it may be recommended every 2-3 weeks to make the engine work (better to drive) 15-20 minutes after the temperature reachs 85-90 deg C.

I would be happy to buy the car from owner like you or my father (car of 1978 with 76K km, perfect state). Here owners which do not use their cars during the winter are called "snowdrops". Another categorie of owners (with well maintained cars too) are called "gladiators" (from Russian verb "gladit" that means "to stroke") - those who takes the car out from garage, wipes the dust and puts the car back. Probably in English it should sound like "strokers" or "irons". All others, including myself" are called "kettles".
Good luck !