Oil and oil line info:
Selecting a lubrication oil.
Heres what u need to do : first, get a feel for what the lubricant is supposed to do for your engine and what special requirements your situation imposes on the lube. These data will tell you what type of oil will bes fit your needs. Second, consider the climate and operating conditions the lube must endure. This info tells you what viscosity and level of severity luve will best do the job. In gerneral it is best to avoid wide range multiviscosity oils, as the materials added that create the multiviscosity capability are the same materials that cause coking. Thus 20w-50 is clearly better turbo oil thean 10w-50. a straight viscosity is best of all, with a ten point higher viscosity in summer. If it is possible to determine the detergent tating and antioxidizing rating, good turbo oil will be high in these two categories.
Now you know the type and grade of luve that is best your best choice. The one remaining factor is the brand to buy. This boils down to availibility, price, and what your R&D efforts tell you is the trule the lubricant for your engine. One can be relatively certain that an oil formulated for turbo use, and so advertised, will be an adequate lubricants.
Types of lubricants.
There are two choices here: synthetic based or mineral based lube.
Synthetic lubes are manufactured fluids in which the basic structure of the lub is much more rigidly controlled than in standard hydrocarbon oils. The resultant product is a very consisitent stable fluid with uniform molecular structure whose properties are highly predictable. Sunthetics have clearly demonstrated their capability with the respect to frictional losses, high temperature stability and basic toughness of the molecular structure. Mineral based lubes are less expensive and more likely to coke.
Water cooled bearing housings
The turbo bearing housing with a water jacket around the bearing chamber has virtually eliminated the problem of oil coking. The cooling capability of the watyer is such in that the oil seldom reaches the temperature at which it begins to break down. Of course all oil subject to high temp use breaks down slowly over time so the need for periodic oil changes still exists. The oil change interval thus becomes slightly less than with an atmospheric engine.
What is coking?
Coking is nothing more then than charred oil residue accumulating in the turbo bearing section to such an extent that the proper flow of oil to the bearings is eventually blocked. The seriously compromised oil flow will kill the turbo in no time. Four things gang up on the turbo to cause a coking problem.
-Oil with inadequate high temperature capability
-Oil with a wide multiviscosity range
-Extended oil changes
-Excessive heat in the bearings
Oil flow and pressure requirments.
The turbo survives with surprisingly low oil pressure and flow. Is is virtually certain that all engines in production have enough excess oil pumping capacity to adequately take on the additional load of a turbo.
To much oil pressure can creae problems with turbos. It is possible to force oil past the seals that are in perfect condition if oil pressure exceed 65-70psi at the turbo. If your engine has these high of oil pressures a bypass or a restrictor (needle valve) can be used.
Problems of oil pressure over powering the seals are evident in a frequent smoking problem.. anytime oil exceeds the 65-70psi and smoking arises put a needle valve or bypass in.
Don't be hasty and just go buy these cause every other kid has one. Oil prefers to operate in a given temperature range that supplies the viscosity needs for protecting the engine, doesn't overheat the oil in the high end and when cool doesn't add more drag to the system then necessary. These requirments are all easily met by the right oil type and viscosity operating in the correct temperature ranges.
Mineral bases oils are not as tolerant of high temps as the synthetics oils. For street engines, both synthtic and mineral based oils have the same lower temperture requirement (150F min), but synthetic can operate about 40F higher (270F) therefore, you may need an oil cooler if you use mineral based oil and perhaps not if you use synthetic.
It need to be understood that oil temperature below the these mininum will degrade durability just as surely as exceeding the maximum. The installation of an oil temperature gauge will tell the whole story. Do that before installing an expensive oil cooler system. There are occasions when both oil and water temperatures are on the high side but neither is out of bounds. The best oil cooling system would be a system controlled by a thermostat that directs oil to the cooler when at a certain temperature.
The turbo creates no special filtering requirments.
Oil to and from the turbo
The plumbing that feeds oil to the turbo and drains is back to the gnein is perhaps the weak link in the entire scehem of turboing. This is definalty the place for a fifteen cent part to fail and have oil spewing all over the ground and wreck your entire motor. Don't cheap on on the feed and return lines, if you do you could pay in the long run.
The oil lines feeding the turbo must meet pressure and temperature requirments it will endure. Also make sure it is hydrocarbon proof because this can cause the line to deterioate fast if not. The best lines to use is a stainless steel braided line with a teflon center, this line is very tough and durable. Another thing to take into consideration is where u have ran your stainless feed line. DO NOT have it rubbing on anything because the line will eat right through whatever it is.
The drain line is often overlooked and cheaped out on, this line is very important as it is just as vital as the feed. If this line is not straight down towards the pan it will foam up and cause smoking in the turbo. Make sure the drain line is matched with the hole in the turbo. If the exit hole is ? your hose should be ID of ?. When drilling in the pan for the drain hose nipple, make sure this hole is above the oil line of your engine because it will cause backup bad if its not.
Shopping list for a turbo feed line on a peugeot (or other) engine:
- [T - connection between oil pressure sender and engine oil outlet]
- [Straight male (I used M10x1.0) to -3 braided hose fitting.]
- [Length of steel braided teflon hose from T to turbo banjo fitting]
- [-3 braided hose to extended bend neck (M10x1.0) banjo fitting]
Links of interest to people building there own oil system for TurboChargers.
[ThinkAuto] - All the parts you'll ever need to build your own custom oil system
A note on turbocharger oil requirements by MembersPage/RichardChwiendacz:
I found that document I was referring to on the oil flow specs from Garrett. This is for a Garrett T3. When reading this, note that most people consider the Mitsu turbos to be undersized in bearing/shaft size when compared to the Garrett turbos of equal airflow.
1.7 liters/min oil flow @ 2.75 bar, 90 degrees C oil temperature.
As Jorgen mentioned though, restricting oil flow TOO much is indeed dangerous. Try beefing up your drainage system as much as possible first, becuase extra drain capacity will never hurt the turbo, whereas too little oil flow/pressure can. Also note that many turbos don't have seals in the traditional sense. I'm not sure about the Mitsubishi turbos, but many have what are called "dynamic seals", which use some combination of a small labyrinth of passageways to stop the oil from leaking out, sometimes along with a little passage to vent compressor boost pressure into the turbine side, to provide pressure against oil leakage. It's possible of course that your turbo uses just a normal system of (sintered?) carbon seals, and those can indeed break down over time. The dynamic seals I would think would be very difficult to have just "wear out", though - and a rebuild might not help your problem if you choose to go that route. Anyway, just my thoughts on the matter. Best of luck!
- Richard Chwiendacz