Originally posted by ehoe@Mar 19 2006, 09:44 PM
Anyone out there with an old E34 still using fully synthetic oil. Any problem with oil consumption with the thinner fully syn oil?.
My 90 E34 on fully syn oil consumes approximately 2L of oil in between every 10K service. So I am assuming perhaps the oil seals aren't so good anymore so perhaps using a thicker oil (semi syn) would be better.
Also with the thinner oil the tappets are noisier too. With semi syn, what would be the ideal service internal? Can the semi syn go at least 8k km? Any comments or feedback appreciated ya.
How long any kind of oil be it dino oil or semi synth or fully synth, depends on how you drive the engine and the surrounding environment factors.
A rule of thumb, sem-synth probably about 7000-10,000. Fully synth 7,000 and beyond.
Also how long the oil will last also depends on the TBN level of the oil to begin with and how long it can neutralize the acids before the TAN get higher which deems the oil as unusable any longer.
Some fully synth engine oils will burn off and some don't. Why? The oil doens't burn off, its the VII that burns off. Some oils are resistant to this as they contain some secret additives that stops it from burning off or possesses a high film strength. The issue of consuming engine oil boils down the additives in the oil package and mostly its coz of the viscosity index improvers. Example..same brand XYZ...a SAE 5W/20 will burn off less than a SAE 5W/30..why? coz to convert the 5 centistoke oil to a 20centistoke oil from cold temperature to 100 degrees centigrade(kinematic viscosity) requires less VII hence it will burn off less. An oil that posseses less VII will be much more stable hence the most stable are straight grade oils like SAE30, SAE40,etc. Multigrade oils offer protection at startup and at running temperature. A multigrade oil such as a 5W/30 meaning at cold startup, it is 5 centistoke hence its light enough to circulate around the engine FAST hence offereing good startup protection which is where the most wear and tear occurs. and once at the operating temperature, it is a 30 centistoke KV oil weight. An SAE 0W/40 will offer extremely good protection at startup but contains a lot of VII and the tendency to burn off the 'oil' is high unless that oil has got some sort of secret additive that prevent the phenomena to occur lesser. In your case, using a thicker oil is just to cover up the problem of consuming oil. The oil dictates the majority performance of the engine and why do you want to cover up the problem by using a thicker oil that effects the performance? find and fix the problem, don't cover it up.
I have never had any experience by using thinner oil that will render the hydraulic tappet to go noisy, it's not the kind of oil that give the protection, its OIL PRESSURE, make sure you have enough oil in the crankcase, protection is never about the type of oil, it's about PRESSURE as our lubrication system is forced fed.
Also semi-synth oil contains no more than 30% of synth compounds, you are lucky if you can find a semi-synth oil that can even have 20% synth compounds. One can claim this particular semi-synth can contain 30% synth compound but how you know? send to lab test for verification?? Synth compound oil give better protection in terms of ADDITIVES in the oil that is added in, you can never have a 100% synth oil as additives needs group III oils to mix. Advantage of using synth oil is longer drain interval due to higher TBN and some additives that will give the engine better protection.
