mineral oil

[105viking]

anybody care to give a brief description of the difference in mineral oil and ashless dispersant. particularly what properties of mineral oil make it prefereable for break-in situations?


additionally, what would happen if a quart of mineral was accidentally mixed with regular oil and flown for a few hours?

all of this discussion on breaking stuff in has caused me to wonder?

 

[avbug]

Mixing oils won't hurt a thing. Mixing straight mineral and straight AD oil won't hurt, mixing brands won't hurt, and mixing weights or single and multi weight won't hurt. All aviation oils meet the same basic specifications, and may be mixed without ill effect (excepting synthetics, which should preferably not be mixed)

Ashless refers to non-metallic oil additives. Dispersant refers to the oil’s ability to suspend combustion by-products, keeping them dispersed until the oil is drained. All AD aviation oils contain oxidation inhibitors as part of their standard additive chemistry. All AD aviation oils use the same base stock and additives.

AD oils can be mineral oils. Multiviscosity AD mineral oils are available for break-in. Multiviscosity mineral AD oils "seat" piston rings in approximately half the time of a straight grade oil. Multiviscosity mineral AD oils reduce the chance of break-in cylinder glazing, a risk pilots take when breaking in an engine with a straight-grade mineral oil. The lubrication provided by multigrade mineral AD oils is more immediate than that provided by straight grade mineral oils. A good single or multigrade AD mineral oil will suspend debris that is created during the "dirty" time of break-in, keeping it from being deposited inside the engine.

If you use a multigrade AD mineral oil, you can then go right to regular AD multi grade after break-in. You can do that anyway, but will experience greater benifits by going with the multigrade AD first, instead of just the straight mineral oil.

If you're already using an AD oil, continue using AD oil when breaking in a new cylinder; use AD mineral multiviscosity oil. It is a good practice to continue using a multiviscosity AD oil after the cylinder has been replaced because the cylinder will run hotter until the piston rings have seated. Engines run hotter during a replacement cylinder’s ring seating process just as they do during the initial engine break-in period. This is due to increased friction between the cylinder bore and the piston rings and less heat transfers to the cooling fins. The metal-to-metal contact necessary for ring seating causes temperatures to rise within the cylinders.


You should plan on changing oil after the first ten to twelve hours of operation during breakin, then continuing with multiviscosity AD mineral oil out to the interval specified by the manufacturer; typically 25 or 50 hours, with an oil change at the 25 hour mark.

A word on synthetics: synthetic oils show no benifits in piston aircraft engines, and never have. Additionally, synthetics are unable to break-in an engine.

 

[mar]

I'm no good with a wrench

These engine and oil discussions have been good reading for me because I'm hopeless in the shop.

Since we're talking about oil I have a question for Avbug about oil temps on the R-2800.

Per the book (Douglas and/or Pratt and Whitney?) we have our automatic oil coolers doors set at 70C.

Most of the engineers will run the doors in manual during cruise. I have no problem with this as it's taught during IOE.

But the FEs are taught to *maintain* 70C.

We have one FE who likes to maintain 75C because somewhere along the line someone told him that water would vaporize out of the oil better at the higher temp...

...so, is any of this necessary? I suppose 5 degrees is no big deal but the yellow arc starts at 80C. Redline at 100C. I just don't dig it very much.

I hate non-standard procedures. I hate it when crew members start trying to reinvent the airplane. I want to tell him that Douglas and Pratt and Whitney have been running the oils temps at 70C for 50 years for a very good reason.

So. What would be that reason? You know, just for my own edification.

Thanks.

 

[105viking]

"These engine and oil discussions have been good reading for me because I'm hopeless in the shop."

me too. thanks avbug. that was just the info i was looking for.
-105

 

[A Squared]

mar,


It sounds to me like he's misapplying something he heard in another context. With a low utilization engine (one that sits for weeks at a time without running) it is good practice to make sure that when it *is* run, the oil temp is allowed to get quite warm ....180 degrees F (82 C) is the figure I usually see in the publications. The reason for this is that as the engine sits, moisture from combustion condenses on the inside of the engine. When the engine is run, that moisture winds up in the oil sump as droplets of water. If the oil temp remains low, that water remains in the oil, together with additional water from the combustion. More water, more condensation, more corrosion of steel parts as the oil film slowly thins over weeks of inactivity. If you run the engine so that the oil gets hot enough to evaporate the water droplets out of the oil, the moisture is vented overboard thru the crankcase breather. There will always be some moisture left inside the engine, but if you heat the oil up well, at least the quantity of moisture remaining in the engine doesn't *increase* each time you run it.


Now, how does this apply to your engines? It doesn't, at least not as far as I can see. It's a corrosion preventative measure, and an engine which is run several hours a day, 6 days out of the week, just isn't going to have the corrosion problems that a chronically inactive engine has. The oil film on the internal parts is replenished on a daily basis, and it takes weeks for it to thin to the point where rusting occurs. At any rate, an 1-1/2 hour flight with an oil temp of 70 C is probably sufficient to evaporate any water droplets in suspension in the oil. I seriously doubt that there's substantially more moisture remaining in your oil after an hour at 70 C than there is after an hour at 75 C The problems occur when the engine is run for half an hour every month or so and never reaches full operating temp, not when the engine is run for several hours every day at full operating temp.

I understand that above 85 degrees the oil is thin enough that it may be pretty tough to get a prop feathered, especially with a well worn feather pump. (ask Fred, he's been there) At 75 degrees you've already given away 30% of your safety margin.

Regards

 

[avbug]

Mar,

Oil should be heated beyond the boiling point of water, to remove the condensation that forms in the water. However, above that point, there is no benifit to increasing the temperature. Actually reaching that temperature isn't necessary to remove the water, either.

You're running with a remote tank, and are measuring the oil temperature as returned to the oil tank, I believe. The temperature probes are more than likely original issue probes, long out of date, not calibrated, and probably never tested before installation. (only get tested if abnormal readings occur, and even then, usually only replaced). That's standard, but the bottom line is that the temperatures may not be what is being indicated in the cockpit.

This becomes a problem if the temperature of the oil is higher than what is indicated; if the FE elects to run the temperature up to the caution line, he may actually be running temperatures much higher.

Your vernitherms may or may not cycle at the appropriate temperature; it's all relative. It's for that reason, plus varying ambient conditions that may affect temperature cycling, manual control is sometimes necessary. (I've had vernitherms stick with carbon particles too many times, requiring manual control, etc).

My own recommendations would be to follow the manufacturers recommendations as strictly as possible. Once your engine reaches operating temperature, you're going to burn off that condensation regardless; modulating the temps higher than set at the vernitherm and/or as recommended by the manufacturer won't help anything, but can only contribute to the thermal breakdown of the oil. Heat is the enemy to oil, and the higher the temperature, the harder it is on the oil.

You're right, Mar. The FE should stick to accepted practice and policy, and stop trying to invent the wheel.

 

[mar]

The Safety Margin

ASquared--Thanks. Good explanation. I've been trying to figure out why it's buggin' me so much--except that it's different from how I did it.

But I think it's, as you put it, the compromising (unnecessarily) of the safety margin of having cooler oil.

I suppose we get comfortable with the needles parked in a certain spot and when they're different it's sort of a nuisance.

I suppose I'll just keep my mouth shut--unless a Capt points it out first.

You know, I'm out of the training business now.

 

[mar]

And thanks to Avbug

It's true the tank is remote but the oil temp bulb is located at the tank outlet.

The thermostat for the oil cooler door is located at the inlet to the tank as the oil is returned to the tank from the oil cooler.

How certain are you that these temp probes are not calibrated? As you say, heat is the enemy of oil and it seems to me that the company would take certain lengths to ensure maximum life of the engine.

On the vernitherm topic: I've also experienced sticky oil cooler doors in 'auto'. Usually just a bump into 'manual' and then back to 'auto' does the trick....but I've never heard the term 'vernitherm'.

Can you write out a quick "Vernitherm for Dummies".

Thanks.

 

[avbug]

A vernitherm is a thermostat for your oil. It's usually cylindrical, and serves to either flow oil to the cooler, or bypass it to the tank. On aircraft of your vintage, the vernitherm is usually a coil of bimetalic metal, which serves as the spring to open and close the vernitherm. It's a rotary device, with the bimetalic spring coiled inside. Sometimes bits of carbon will get stuck in the rotating barrelof the vernitherm, causing it to stick open, or shut. Open, it's seldom a problem, but closed, and oil doesn't make it to the cooler. You can leave the doors open all day, and it won't help, because oil isn't getting to the cooler.

The vernitherm is what gets adjusted to set the oil temperature. It's independent of your temperature gages, competely. When a mechanic sets the oil temperature, he's adjusting the manual spring tension on the bimetalic spring, which in turn adjusts the point at which the vernitherm will open or close. It's usually a double screw, or offset screw arrangement at one end of the vernitherm assembly.

The temperature you see in the cockpit is probably being read by a thermocouple probe; a bimetalic probe that is about four inches in length, and appears brass in color. (some silver or aluminum in appearance). These probes in theory will send a particular voltage value to the gage based on any given temperature, but the actual values read by the same meter will often vary. Accordingly, adjustements made to the vernitherm to compensate, vary, and the actual oil temperature is seldom what is indicated in the cockpit.

This is common. The truth is that most of the information received in the cockpit is only rough and approximate, modern FMS units excepted. Your voltage values are on ten cent gages that don't indicate accurately; they're only there as a rough approximation for the flight crew. From a maintenance point of view, most indications in the cockpit are really just idiot gages to keep pilots happy. What is actually going on with hydraulic pressure, voltage values, electrical loads, temperatures, pressures, torques, etc, is often not what you're seeing in the cockpit.

Some measurements are tested to be within certain tolerances, others are not. Often not.

I would be very surprised if your company tested their temperature probes during installation, or verified that the temperatures indicated in the cockpit are true measurements of what's occuring at the probe. Only if gross misindications occur would there ever be a reason to test the probe, and only then to determine if it's an instrument problem or an actual temperature problem. Generally the probe just gets replaced. I've seen multiple probes go bad, one after the other. Calibration of the probes is sometimes done at the instrument, sometimes it's measured prior to installation using temperature and voltage.

 

[mar]

Idiot gauges

Avbug--That was perfect. Thanks again.

The vernitherm pretty much fit the picture in my head (something twisty...like the vernier-style controls).

Back to our policy of running the oil coolers in manual during cruise. The reason they teach this is that we would be able to detect rising oil temp much faster (say, in the case of a main bearing failure) then if we ran them auto. True enough, I suppose. I agree the oil cooler door would cover a rising oil temp to a degree but at some point it would fail to keep up.

You wrote: "The vernitherm is what gets adjusted to set the oil temperature. It's independent of your temperature gages, competely."

In fact when we run all engines in auto the oil temps on the gauges are all a little different. I guess that speaks more to the inaccuracy of the gauges then what's actually occuring in the engine because I can pretty much assume all of the vernitherms were set to the same temperature.

So here's my question:
Given that the mechanic is the true setter of oil temps wouldn't it be more prudent to run the oil coolers in auto all day long and save the manual operation for a day when the oil cooler failed?

I mean if all the vernitherms are set for 70C but we're getting indications in auto like: 65C, 70C, 70C, 75C....well who cares right?

But if my favorite engineer wants to indicate 75C straight across the board he's gonna increase the temp 10C on #1. Then he'll fall asleep while we're slowing down in ice or mountain waves and the oil temp will creep up to 80C (indicated) but that's really 85C as far as the vernitherm is concerned.....

Do you or anyone else, ASquared, think the oil cooler should be run in auto all day?

I don't believe my company has ever seen a main bearing failure. Of course it could happen but I'm beginning to think we should just leave the stinkin' door in auto.

Set it and forget it.

 

[avbug]

In manual, you're running the actuator, and this places wear on the actuator and doors only when you're actually moving the controls. In auto, those doors and the actuator are fluctuating all the time. The actuator has a limited life. It may not be expressely stated in the maintenance paperwork, but that actuator will only cycle so many times before it dies a sudden death.

The real reason why the company probably prefers manual is that they're already paying a flight engineer to monitor and work those doors, and it's a lot less expensive than constantly replacing the acutators when run in auto.

Once the actuator goes, you don't have any more control, beyond the capability of the vernitherm.

When the mechanic sets the vernitherm, typically he isn't setting it according to an actual oil temperature reading. He may be running the screw all the way in one direction, or he may be approximating it. Don't count on it to cycle at the same temperature; it's all rough and approximate. No vernitherm of cooler assembly is going to run the same temperature every time, even with the same assembly on a consistant basis. It does require manual modulation as a matter of function.

We used to run into the same thing on the C-130. The FE monitored the oil temps and worked the cooler doors (usually closed in cruise, open for landing), rather than letting them run in auto. It just wore out the actuators, and somewhat negated paying the FE to be there.

 

[mar]

That makes sense

Thanks for taking the time to answer my bonehead questions. Your answers make a lot of sense.

I've always wondered why the plane was designed with automatic oil coolers but the cyl head temp control is only manual.

Now I know. We're paying that FE to *do* something besides bring the coffee!

 

[A Squared]

A little modification to what Acbug said, the DC-6 system is a little bit different.

On the DC-6 the Oil temperature is not regulated by a vernitherm. There is a Oil flow control valve on the oil Cooler which operates similarly to that which Avbug described. It may be properly called a Vernitherm, I don't know I've not heard that term before. In the DC-6 I beleive that it is a poppet type valve, not a rotary valve. It's primary purpose is to prevent oil cooler rupture due to excessive pressure resulting from congealed oil in the oil cooler. If the oil is cold enough that congealing in the cooler oil is a possibility, it routes the engine return oil through the oil cooler shroud, which allows it to heat the oil in the core without subjectiong the more fragile core to excessive pressure. Once the entire oil cooler is heated, the oil will be routed through the shroud and the core for maximum cooling. The valve also provides a pressure controlled overpressure bypass of the entire oilcooler. At lower temperatures it does provide some regulating, but my understanding is that once the entire lubrication system has reached normal operating temp, that valve remains fully open continuously routing all oil through the shroud and core of the oil cooler. The actual regulation of the oil temperature is accomplished by controlling the airflow through the oil cooler, not the flow of oil through the cooler. The air flow is regulated by the position of the oil cooler doors. The door position may be controlled manually, or by the automatic regulation system. The automatic regulation system has a temperature sensor (I assume some sort of bi-metallic element) which closes a contact, this activates the cooler door postioning motor briefly. There is then a delay. if the oil temp trends into the proper range, there is no further action, if after the delay, the oil is still too hot or too cold, the door is adjusted another increment and there is another delay.

If you've ever been outside the plane on the ground when someone has left the master on and the coolers in auto, you may have heard a periodic click and bzzz, as the system gradually closes the doors in a vain attempt to keep the temp up on a cooling engine.

As far as running in manual or auto in cruise, I think it's a very good idea to use manual. Auto can completely mask an uncontrolled oil temp rise until it's too late. Presumabley the FE will alert the crew if he's made several adjustments to a particular cooler door and the temp is still rsing. A main bearing failure is rare, but not unheard of, and it is by no means the only failure which is accompanied by an uncontrollable oil temp rise. One that I've encountered a number of times is a nose case failure. The first signs are rising oil temp and gradual increase in BMEP. You see that and there's a good chance your nose case is self destructing. The next step is usually a rapid decrease in oil quantity.

If you're in auto, you may not be aware things are going south you notice your oil is gone. I think it's a really good idea to run them in manual mode



Wait a minute...your FE's bring Coffeee???????

 

[mar]

I'm sold on the manual thing

Actually I won't drink that guy's coffee. In Bethel we'd call it 'village coffee.' In Rome they'd call it 'espresso'.

At any rate, thanks, I'm sold on running them in manual.

I'm not really too hung up on the guts of the matter. You know me, when someone asks where the batteries are, I point to the battery switch and say, "At the other end of that switch."

I have limited greymatter to commit to stuff that's gonna work with or without me.

But still I appreciate a little theory.
Thanks again.