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Synthetic oil for turbos?[ALL/1998] posted by Brian Feltovich on
Wednesday, 10 September 1997, at 3:36 p.m.
A recent post regarding a 740 turbo stated that synthetic oils are superior because of their improved lubrication at high speeds and because they don't degrade as quickly. The author also stated that with a synthetic oil you wouldn't need to let the turbo cool down before shutting off the motor.
Is this true?
I thought that the reason for letting the motor idle before shutting down was to let the cooling system have a chance to even out the temp between the turbo and the rest of the engine. How is this affected by synthetic oil? Does the turbo run cooler all the time? Are we talking about intercooled turbos?
Thanks.
Re: Synthetic oil for turbos?[ALL/1998] posted by Ray Hartle on
Wednesday, 10 September 1997, at 10:12 p.m.
Brian,
I posted the comment about synthetic oil being the best for turbo engines. My '87 740 sedan is intercooled but that simply means the air being pushed by the turbo is passed through an intercooler (infront of the radiator) to cool it down before it enters the intake manifold. This permits a denser air/fuel mixture, less detonation and more power.
Turbos are actually connected to the exhaust manifold and reach temperatures much higher than the rest of the engine block. These temperatures are mostly a function of exhaust gas temperatures and not lubrication.
Synthetic oil will however reduce the amount of friction produced heat from your engine and lower the cooling demands on your radiator. The thermostat will maintain a normal operating temperature.
In simple terms, turbos have two turbine fans on a single shaft. On one side, the exhaust gases turn the exhasust side turbine when the engine rpms go up and the wastegate closes. The exhaust tubine then turns the air side turbine which creates a pressurized manifold condition or "boost". The shaft(and bearing) which carries these two tubines rotates at incredible rpms and operates at exhaust manifold temperatures.
Water cooling the housing around the turbo shaft bearing reduces the operating temperature so that the oil will not "coke" and extends turbo life. Idling the engine for a minute or so after higher rpm operation (aka "normal driving") allows the cooling system to reduce the turbo housing temperature enough that when the engine is shut down, no coking occurs...supposedly.
Since synthetic oil does not coke under extreme temperatures ( recall the frying pan commercial) you don't have anything to worry about.
All of the commercial airlines use sythetic oil in their jet turbine engines for this reason.
I hope this answered some of your questions.
Ray
Re: Synthetic oil for turbos?- Ray Hartle[ALL/1998] posted by John Brabant on
Thursday, 11 September 1997, at 12:22 p.m.
Ray, I have never used synthetic oils, a major reason being the high cost of the oils. I remember Mobil -1 costing in excess of $5 per quart. My questions are:
1. If I use synthetic oil, can I offset the higher cost through less frequent oil/ filter changes? If so, what would the oil change frequency be?
2. How many brands of synthetic are out there? Are there any you recommend or any that should be avoided?
3. Where can they be purchased at a discount? Any mail order places around??
4. Can this oil be disposed of with regular motor oil collection programs?
Re: Synthetic oil for turbos?- Ray Hartle[ALL/1998] posted by Ray Hartle on
Thursday, 11 September 1997, at 11:18 p.m.
John,
Answers to your questions:
1. Synthetic oil is more economical even though it costs more per quart. I use Amsoil because they are the leaders in synthetic lubricants and they have a filtration system that is an essential part of the program. A conversion to Amsoil sythetic oil in a "clean" engine costs about $30 for 5 quarts of oil and around $18 for 2 special filters, for a total of around $50. I mention the "special" filters because proper filtration is the key to extended drain intervals. Since sythetic oil doesn't break down keeping it clean is the only concern. This oil can be used in you car for 25,000 miles or 1 year with only a filter change at 6 months. And yes Amsoil has a warranty to back it up.
Campare this to say 8 oil changes at every 3000 miles at say $10 each (if you do it yourself) and you've spent $80, and a lot of time. Sythetic oil also provides a 10% boost in fuel mileage and 70% less wear on engine parts. If you did put 25,000 miles on per year, at 23 mpg and $1.3/gal, you would save another $141! So far you would be $171 ahead and I have barely scratched the surface of the benefits.
2. There are several brands, Mobil, Castrol, Pennsoil, *Amsoil*. All are fundamentally the same (mineral oils)with sightly different recipies. Only Amsoil has the filtration products to permit extended drain intervals. Most companies also sell blends of sythetic and petroleum.
3. I can get you all the sythetic Amsoil you need and have it shipped directly to your house. I've been an Amsoil dealer since 1985. I don't use anything else in any motor I own. I could send info if you like.
4. Synthetic are completely compatable with petroleum based oil and collection centers accept it. ( you would only have to go once a year!)
Where ever you are, there is probably Amsoil dealer near by.
Ray
Re: Synthetic oil for turbos?[ALL/1998] posted by sherman on
Friday, 12 September 1997, at 12:02 p.m.
it always amazes me when someone is not willing to spend an extra few buck a year on syn oil. Look at the money you have tied up in a car and the real cost per year for synthetics even if they only serve to extend the life of your battery by easier cranking in the winter (in my city) and the cost is a no brainer.
I buy Mobil 1 at BJ's wholesale or Sams club Whols for about $20/cs of 6 and mobil always has rebates going on which knock a buck/quart of final cost. Do the math and there is no reason not to use them (I even run syn in my beater car jnsut for the winter cranking. Forget the extended drain debate, it is not worth wasting time on, just use the stuff like regular oil and change it every 5K.
Check out Mr Moly additive too, my favorite. Made in UK or Canada, mailorder thru importer in Rochester