Go Back  PPRuNe Forums > Ground & Other Ops Forums > Engineers & Technicians
Reload this Page >

Low Oil Level, rise in temperature?

Engineers & Technicians In this day and age of increased CRM and safety awareness, a forum for the guys and girls who keep our a/c serviceable.

Low Oil Level, rise in temperature?

Old 18th Jun 2009, 18:12
  #1 (permalink)  
Thread Starter
Join Date: Jun 2005
Location: near an airport
Posts: 157
Low Oil Level, rise in temperature?

Hi tech experts,

Just wondering your view on the following:

You operate a jet engine at very low oil level, say 1 QT. Would oil pressure increase noticeably, resp. pressure drop significantly?

Thanks for your insights.
galleypower is offline  
Old 19th Jun 2009, 11:19
  #2 (permalink)  
Join Date: Dec 2008
Location: lefthand side of the screen
Posts: 133

a drop in OIL pressure, and a rise in temperature..
subsonic69 is offline  
Old 19th Jun 2009, 12:36
  #3 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
This depends on the system. I have had several occasions to lose all oil, and didn't experience any indication of an increase in temperature. Temperature may be sampled at one of several points in the oil system, ranging from return oil from an oil cooler to oil entering a cooler, to oil in the sump, etc. Temperature is generally sensed and measured by a probe inserted into the oil. If there is no oil to flow over the sensor probe, then the sensor probe either won't detect a temperature at all, or may indicate a false reading.

I experienced a complete oil loss in a TPE-331-10, and the engine ran perfectly...just no control over the propeller due to lack of oil. There was no change in oil temperature indicated in the cockpit. Later conversations with Honeywell revealed their data which states the engine will run for 30 minutes with no oil on board. In my case, I noted neither an indicated oil pressure loss or temperature increase until a loss of torque occured. With the loss of torque there was no attendant rise in temperature. Shortly thereafter a forced landing occured (as the failure was in a single engine airplane).

Just a few days ago I experienced a complete oil loss in a light piston twin, in which all the oil exited the engine through a failed drain plug. The cockpit indication was both a loss of pressure, and a loss of temperature.

In other cases involving nearly complete oil loss in large radial engines, the oil loss has been physically observed as an engine and a wing covered in oil, and the engine subsequently shut down, without any significant increase in indicated oil temperature most of the time; just a loss in pressure. Generally only in cases where a gradual loss has occurred have I seen an increase in temperature.

Elevated temperatures have more commonly been due to failed vernitherms or other regulatory devices, in my own experience. Stuck oil cooler bypass valves, failed thermal regulation devices, etc, tend to contribute more to high oil temps than low oil quantities, though a low oil quantity certainly can be a cause of a high temp.
SNS3Guppy is offline  
Old 19th Jun 2009, 16:49
  #4 (permalink)  
Join Date: Aug 2006
Location: Paranoid Delusion
Posts: 32
I've had several experiences of oil pressure decreasing with oil temperature rising on piston engines. This has been indicative of engine internal failure with a oil filter full of metal.
Like the previous post says, on the radial pistons there is usually a hell of a lot of oil spewing out of the engine which indicates oil system problems.
I've had a jet engine loose all it's oil on me, but I've chopped it before oil pressure and temperature became an issue as the quantity gauge was dropping off during the ground run. Made a bit of a mess.
Yoth is offline  
Old 15th Jul 2009, 16:41
  #5 (permalink)  
Join Date: Jul 2009
Location: Tampa Florida
Posts: 15
Your question: You operate a jet engine at very low oil level, say 1 QT. Would oil pressure increase noticeably?

How can oil pressure increase if the oil is low? Of course, the oil pressure will decrease and reach 0 when the oil supply will reach 0.

The oil temp is not the critical engine parameter on Jet engines so you should not worry about it too much. The critical parameter on jets is the ITT (Inter Turbine Temp).

On pistons the critical engine parameter is the oil pressure. If the oil supply is low the oil pressure will be low and the oil temp may increase
airflorida1 is offline  
Old 15th Jul 2009, 21:12
  #6 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
Your question: You operate a jet engine at very low oil level, say 1 QT. Would oil pressure increase noticeably?
The value, 1 qt, is irrelevant without knowing the specific aircraft engine in question. The measurement is also irrelevant, as the engine may be measured in gallons, litres, pints, quarts, etc.

Would oil pressure increase with very little oil? Generally, no. Typically temperature will increase. However, oil pressure may increase, depending on the condition and temperatures involved. Larger volumes may cause a bypass to open, dropping pressure, whereas low volumes may not have that capability, even under pressure.

The type of cooling system, place the temperature and pressure is measured, etc, also vary the answer to this question.

How can oil pressure increase if the oil is low? Of course, the oil pressure will decrease and reach 0 when the oil supply will reach 0.
Not necessarily. I've had zero oil with pressure still indicated, and yes, it can happen. This is one reason why all parameters must be considered, including temperature, and ancillary or supported accessories such as CSD temps, engine operation, annunciators, chip detectors, etc, to determine what is really being seen. Conversely, it's quite possible in some systems to get a zero oil pressure indication with a fully functioning, full oil system.

As stated previously, some engines will run a long time with no oil, and may indicate accordingly.

The oil temp is not the critical engine parameter on Jet engines so you should not worry about it too much. The critical parameter on jets is the ITT (Inter Turbine Temp).
Oil temperature is a very critical parameter on a turbojet aircraft, whereas some of the most critical components use high pressure oil jets for lubrication and cooling: the turbine bearings.

Many turbojet engines don't have ITT. Other temperature measurements such as EGT and TiT are also used. Again, you must specify the specific powerplant.

Oil temperature on a turbojet engine can be extremely critical: a high temp on one powerplant, for example, may indicate an impending CSD failure. A CSD failure can lead to an uncontrollable engine fire in some cases...a magnesium fire you can't put out. Oil temp may be your first, or even your only warning before that failure occurs.

On pistons the critical engine parameter is the oil pressure. If the oil supply is low the oil pressure will be low and the oil temp may increase
Numerous parameters may be said to be critical on a piston engine, but then again, it really depends on the engine and which particular parameter it is to which you're referring.

Oil pressure does not decrease in proportion to oil level in most piston engines, nor in most turbine engines, either. If that were the case, we would be able to tell the oil level by the oil pressure at any given time. With a very low oil supply, so long as the temperature has not increased significantly enough to drop oil density and pressure, the oil pressure will remain a general regulated value until such an insufficient quantity exists that the pump cavitates. At that stage, temperature will generally be a good indication of the oil loss, provided the loss is not catastrophic in nature.
SNS3Guppy is offline  
Old 16th Jul 2009, 00:46
  #7 (permalink)  
Join Date: Jul 2009
Location: Tampa Florida
Posts: 15
SNS3guppy said - "I've had zero oil with pressure still indicated, and yes, it can happen."

No way. Your as always wrong. What you are saying contradicts the law of physics. If there was no oil then what was creating oil pressure? Air? Water? Maybe your imagination? If you were getting oil pressure with 0 oil in the tank then the only what could be wrong there was the stuck or broken oil pressure indicator or wiring.

I am not an A&P mechanic but I know some things about engines. Just go and check the engine manuals. All of them say that when the oil is low the temp will rise and the press will go down.
here is the link on PT6 turbrop engine. Check it out. It clearly says that - low oil pressure? check the oil tank, high oil temp? check the oil supply. These are the first things all mechanics should know by heart.

pt6 engine troubleshooting
airflorida1 is offline  
Old 16th Jul 2009, 11:22
  #8 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
You're not a mechanic, but you know what a mechanic should know by heart?

You've just told us:

I am not an A&P mechanic
But in your first post on this site stated:
I absolutely agree with the guys above me. I worked on Let410 airplanes as a mechanic. If you have any technical questions about this plane I will be glad to help you.
You've also recently told us you are an avionics technician who works on airplanes and has test equipment and publications, etc...and let's not forget you're working on your buddy's Cessna 150, too.

Taking a shot in the dark here...you're not a chiropractor from Chicago, are you? No? Not the same guy who came on here posing as a helicopter pilot, airplane pilot, jet pilot, under a dozen different names? You sound very much like the same one.

But despite the fact that you claim to be a mechanic, you've finally come clean and admitted that you're not. While your credibility here is shot, at least we know where you stand. You're not qualified.

No way. Your as always wrong. What you are saying contradicts the law of physics.
Which laws of physics would those be, exactly?

Do you understand the difference between an oil pressure indication, and oil pressure?

Have you ever seen zero oil pressure indicated on an instrument, but know full well that oil pressure is present in the engine? Are you aware of the differences in the way oil pressure is sampled, and how each method of sampling may produce errors? Clearly not.

That the engine oil pressure gauge indicates pressure may or may not mean there is engine oil pressure. A sensor may be involved which may stick, the oil pressure gauge may require aircraft systems power and mail fail, stick or provide a false reading, a bourdon tube (do you know what that is?) may plug with sludge or other material and give a false reading, a leak in an oil pressure line may cause a false reading...there are many reasons that the indication in the cockpit may not match what's going on in the engine. Most certainly an engine may have no oil pressure, but still have an indication of pressure. It may also have nearly no oil remaining, and still show normal pressure. I've seen both personally, and have experienced it as discussed before during an engine failure...with no oil remaining in the engine.

Just go and check the engine manuals. All of them say that when the oil is low the temp will rise and the press will go down.
Without any need to debate the foolishness of this notion, why don't you quote the "engine manuals" that show this, and demonstrate it's universal application to all situations? I'm intrigued.

Check it out. It clearly says that - low oil pressure? check the oil tank, high oil temp? check the oil supply.
You don't read very well, do you?

For low oil pressure, a low supply is listed as one possibility. It's a troubleshooting chart. If you read on, you'll also find that the other possible causes are...

A defective oil pressure indication...the user is instructed to verify what's being seen using a direct reading gauge rather than the cockpit gauge...because the cockpit indication may be wrong. Imagine that...shoots your theories apart, doesn't it?

A pressure relief valve malfunctioning. We've covered this in a previous post...you just didn't read or comprehend very well.

An internal oil leak...also already covered...and it's not just a low oil supply. Surprise, surprise!!

A failed heat shield and excessive temperature...the pressure may have absolutely NOTHING to do with volume or pump capability...but with temperature. This can also occur with a failed oil cooler bypass valve, or one stuck in bypass. You didn't know that, either, did you? Of course not. You googled the PT6 and became an instant expert. Problem is, you shouldn't attempt to dole out counsel based on your lack of qualifications and experience...and google doesn't make you an expert.

Oil pressure follows the power lever, and is acting as a function of RPM, leaking oil past a cracked housing under higher operating pressures...nothing to do with supply, but everything to do with other mechanical problems. But what was it you've told us? Low pressure, it's got to be the "tank?" (Of curiosity, do you understand the difference between a pressurized oil supply or tank and one that isn't, and the difference this can make in operation and indications)?

Here's a favorite...you cleverly boiled your troubleshooting down to two choices: low oil pressure check the tank, and high oil temp, check the supply? The last item on the troubleshooting list you provided, but obviously didn't read, is zero oil pressure (even though the engine is producing normal oil pressure)...check to see that the oil filter isn't installed backward. Do you suppose that somehow violates the "laws of physics," too?

But wait, there's more...

Again, you stated:
Check it out. It clearly says that - low oil pressure? check the oil tank, high oil temp? check the oil supply.
Let's see what we find under the troubleshooting guide for high oil temperature...

Yes, certainly a low oil supply could be one possibility...though you cited "check the tank" for low oil pressure, when the guide YOU provided clearly states "check the tank" for high oil temp, too. Do you think before you speak (or write)?

Of course, other problems may be present, having nothing to do with a low oil supply, and a low oil supply may not cause a high temperature...and a complete loss of oil will generally show a drop in temperature (depending on the engine, of course) because there's no hot oil over the temperature probe to give an indication any more....you didn't know that either, did you? I experienced a complete oil loss on a test flight of an aircraft several weeks ago, and saw both a pressure loss and temperature loss at that time due to a catastrophic oil loss. No temperature increase at all.

So...the trouble shooting guide provides other solutions to a high temperture...such as a stuck vernitherm or thermostat. Imagine that...a high temperature that has nothing to do with oil quantity. Does that violate the laws of physics, too?

Then again, excessive idling with the propeller in feather, providing little cooling airflow to the oil cooler, is next on the list...a rise in oil temperature caused by engine operation, rather than low oil quantity...but didn't you tell us that every mechanic should know by heart that high oil temperature is always due to low quantity...and then prove it by giving us this reference? You are wrong, of course, and the reference you provided proves it...but then you're the same one who claimed to be a mechanic and then told us outright you're not...so this is no surprise.

The last one on the troubleshooting guide is amazingly identical to the third-to-last on the pressure problems...a failed heat shield. Yet another case of a perfectly functioning oil pump with good output, a full oil tank, and still the potential for low pressure and/or high temperature. But what's that you say? A mechanic must know by heart that with low pressure one must "check the tank," and with high temperature one must "check the quantity?"

Of curiosity...when one has this low pressure situation and checks the tank as you say all mechanics know to do by heart...what is it one is looking for, other than quantity? Do you realize that "checking the tank" and "checking the quantity" are the same thing? You do not, because you simply posted without knowing what it is you posted...and given that you're now fully exposed, perhaps you'll drop this charade and refrain from further embarrassment and providing poor counsel to those who might not know otherwise.
SNS3Guppy is offline  
Old 16th Jul 2009, 12:13
  #9 (permalink)  
Join Date: Apr 2005
Location: Stockholm Sweden
Age: 71
Posts: 570
I've had zero oil with pressure still indicated, and yes, it can happen
So have I.
Oil qty is measured in the oil tank. You can have zero qty in the tank, but the engine is still full of oil.

Try starting an RB211 in sub zero conditions.
The oil is very viscous. The indicated oil qty will drop to zero as all the oil is pumped out of the tank. It ends up in the gearbox but doesn't scavenge back to the tank. The oil pressure indicates off scale high. But the engine starts, and as the oil warms up everything returns to normal.

Pilots are usually taught to ignore oil qty readings. Let the engine keep running until you get a low pressure indication. The oil qty may be misreading., and again on the RB211 oil hiding in the gearbox is not unusual, even in flight.
Swedish Steve is offline  
Old 16th Jul 2009, 15:35
  #10 (permalink)  
Join Date: Jul 2009
Location: Tampa Florida
Posts: 15
SNS3guppy, it seems to me that you have ZERO hand-on aviation experience. I am sure you never worked as a mechanic if you have no idea what the A&P license is. You should know what I meant by saying “I am not A&P mechanic”. I am an airframe mechanic with no powerplant ratings. You are probably a college teacher with some theoretical knowledge of engines, aircraft and aviation. I also very much doubt that you are a pilot at all.
About the oil temp and oil pressure and engine troubleshooting:
If you ever worked on engines as an aircraft maintenance technician or engineer you should know that the number 1 rule for all maintenance technicians and engineers is to follow the manuals and troubleshooting charts. The engine manuals and troubleshooting charts are created by the engine manufacturer and the technicians should follow the charts step by step starting from step 1, not from step 3 or 4. If the troubleshooting chart says that if there is low oil pressure FIRST check the tank oil level (first thing to do on all engine troubleshooting charts {what basically confirms the relationships between the oil level and its press} ) you should go and do this first even if you think that you know more than the manufacturer. If it says if there is high oil temperature FIRST check tank oil level and replenish supply (again shows the relationships between the two) you should do this first again no matter what you think about the manufacturer.
If you disagree with the manufacturer and think that there is no relationship between the oil pressure, oil temp and oil quantity it is your problem. But who does give you the right to confuse other pilots and maintenance technicians with your inventions and “creative” thoughts? It is dangerous.
If you know of any cases when there was an empty oil tank and the oil pressure was in the green arc with all other aircraft systems functioning properly, please, provide the link and then we will talk again professor SNS3guppy

Last edited by airflorida1; 16th Jul 2009 at 15:54.
airflorida1 is offline  
Old 16th Jul 2009, 16:17
  #11 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
Having thoroughly discredited airflorida1, he's hereby relegated my ignore list with the other pretenders and liars...almost certainly the same person who has been exposed everytime. The pattern of speech, the language, the inexperience, the same level of ignorance...I know this poster, and he's back, once again. Shortly he will be banned again, and will resurface under a new name...but for now we may safely discount anything further airflorida1 believes he may have to offer.
SNS3Guppy is offline  
Old 21st Jul 2009, 02:11
  #12 (permalink)  
Join Date: Mar 2006
Location: Elgin
Age: 44
Posts: 8
Well just to add to it, I know that an RB199 when low on oil will give an oil P caption on the CWP. So for long sorties they are always filled to spill to account for loss of oil during the sortie.
rb199 is offline  
Old 21st Jul 2009, 19:27
  #13 (permalink)  
Join Date: Dec 2004
Location: Jeddah, Saudi Arabia
Age: 56
Posts: 30
As the oil qty decreases the volume will be cycled through more often, reducing the cooling time. In turn this increases the load on the oil leading to 'cracking' of the oil molecule chains. However there are a number of other factors also playing a part: oil cooler efficiency, outside air temperature, precipitation, engine power settings, to name a few.

Bear in mind when the oil qty is down to 1qrt (1gallon, whatever), there is a distinct possibility for the pump to momentarily take in some air as the oil sloshes around in the tank. This will normally be indicated by oil pressure fluctuation.

The engines I work are the RR Allison T56/501's. The only thing I see regularly, is a slight decrease in pressure as the oil comes up to operating temperature. I have on occasion run the engine with as little as 4gallons in the tank (10 - 12 gallons full), but never seen higher than normal temperatures on decreased quantities

Hope this helps in the quest for knowledge .....
pjvr99 is offline  
Old 21st Jul 2009, 23:03
  #14 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
SN3 Guppy
Low oil quantity (specifically down to one quart indicated) in the system does or does not give low oil pressure?????
Low oil quantity does or does not give rise in oil temperature?????

Spare the rhetoric about false indications, the man was asking for the actual.
As has already been given in enough detail, the oil pressure indication may decrease, or may remain the same...and in some systems, may actually increase. Low quantity may produce a higher temperature, or may not, depending on what else is going on and the nature of the specific system.

Point is, you really can't simply state that low quantity means a high temperature, because that's often not true. You can't simply state that low quantity means low pressure, because that's also often not true.

I'm not sure how many times we need to keep saying the same thing here, but this material has been given before.
SNS3Guppy is offline  
Old 21st Jul 2009, 23:32
  #15 (permalink)  
Join Date: Aug 2007
Location: Godzone
Posts: 391
Don't block florida dude - he's so much fun to laugh at

I believe you Guppy - and I have a few formal aircraft qualifications, although having only 1 would be more than florida (and his multiple IDs..)
toolowtoofast is offline  
Old 22nd Jul 2009, 00:38
  #16 (permalink)  
Join Date: Jul 2009
Location: Tampa Florida
Posts: 15
pjvr99, I think 4 gallons on T56 engine is still enough oil to provide engine lubrication. It is the minimum. You will see the oil press and temp rise only after the oil quantity falls below 4 gallons. Please, correct me if I am wrong.


Last edited by airflorida1; 22nd Jul 2009 at 00:49.
airflorida1 is offline  
Old 22nd Jul 2009, 00:43
  #17 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
There does seem some reluctance to accept the idea that an engine can be low on oil yet not experience a temperature increase. An engine with a 40 gallon oil tank, for example, may well be at 20 gallons and show no increase. The oil cooler continues admitting or bypassing oil as needed, and unless some change occurs with in the engine to cause abnormal temperatures (bearing failing, for example, or a bearing oil jet plugged), the temperature may not provide much clue.

Likewise, as the quantity falls, so long as the pump doesn't cavitate, it's output will typically remain constant, and you will very likely see no pressure change. As temperature gets higher in some engines (and it may get higher due to less oil, or it may not) depending on the system, pressure may decrease...or it may remain constant. The type of oil system and pump makes a difference.

In some systems, excess oil, especially early in the operation of the engine before systems are warm, can cause oil bypasses to open and you'll actually see a drop in pressure, rather than an increase...the same may be true of oil quantities in a given system; less oil doesn't necessarily mean less, or more pressure.

We've seen from the example provided by airflorida1 that many causes can be responsible for a given engine indication. As a mechanic, we generally start with the most simple and easiest/least expensive, and go from there...checking quantity is simple, easy, and inexpensive. However, one should not make the mistake of assuming that once a low oil quantity is found, the problem is solved. What caused the oil quantity to be low?

Some engines inherently burn large quantities of oil. In our R2600's, for example, I routinely put in 20 gallons of oil each time I added fuel. In a TPE-331 turbopropeller engine however, oil is added by the pint and the engine shouldn't be using oil. The competition, the PT6A, does use oil, and it's to be expected...but in either case a loss of oil may or may not show up as high temperature or low pressure. Such an analysis is far too simplistic, and not enough information is provided.

We can expound on this all day, but at the risk of being accused of providing "rhetoric."

Last edited by SNS3Guppy; 23rd Jul 2009 at 10:13.
SNS3Guppy is offline  
Old 26th Jul 2009, 10:34
  #18 (permalink)  
Join Date: Jul 2009
Location: omaa
Age: 38
Posts: 9
High Oil Temp

Oil Temp Is A Vital Parameter In Jet Or Piston Engine Operation. Temp Is Sensed Just Bfore Oil Jets R Outlet Of Oil Cooler. Ofcourse Low Oil Level, High Oil Temp. High Oil Temp Leads To Engine Seize.a Constant Flow Rate To B Maintained To The Bearings.lack Of Flow Causes Bearing Seize.so Many Ifsd's Happend With High Oil Temp.high Oil Temp May B Blocked Cooler Inlet R Out Let But Chk Tsm Always.

Last edited by prattgamco; 27th Jul 2009 at 20:23.
prattgamco is offline  
Old 26th Jul 2009, 11:48
  #19 (permalink)  
Join Date: Oct 2005
Location: USA
Posts: 3,218
Low oil level may lead to low oil pressure or high temperature,but in a properly functioning system, it generally does NOT.

Oil temperature may be sensed at any number of places in the oil system, depending on the system in use.

High oil temperature does not lead to bearing seizure. It may be symptomatic of an impending seizure, but does not of it's own accord lead to bearing seizure. Lack of lubrication, failed bearings, and high bearing temps lead to bearing seizure.

I can't understand the rest of your post. Complete sentences will help.
SNS3Guppy is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.