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Operating Temperature
What is the normal operating temperature for glow engines? I am sure this varies from engine to engine based on size and mounting dynamics (cowels). I am running two O.S. .91FX two stroke engines in my tightly coweled P-38 and was wondering about cooling. Over 65 flight so far but I had an engine out a few weeks ago and it got me thinking. What is too hot? The engines are generally in the 165-200 degrees Fahrenheit range after a flight. Is this acceptable?
Thanks!! Dom |
RE: Operating Temperature
Aluminum cools very fast.
I think you will need to measure temperature while the engine is running at full throttle and the temperature will generally be over 200* F. Bill |
RE: Operating Temperature
I have seen anything from 225F to 375F listed as acceptable temps for a 2 stroke .90 size engine (the latter is from Dave Gierke's book on two stroke r/c engines), but as far as I'm concerned over 300F is getting pretty hot. The general answer I've gotten has been that it's going to vary from engine to engine due to manufacturing differences, glow plug, fuel/lubricant variance, mixture, etc., and just because your engine is a little hotter than some, that doesn't mean that it is too hot for that particular engine. I know this is vague, but I hope it helps.
Dave |
RE: Operating Temperature
This is not a personal shot here but whenever I see someone pointing a temp gauge at their engine, I make sure those around who are new stay very clear from these guys. There are no published specs and if there were, there are hundreds of scenarios to force varying temperatures.
I have seen countless overheated engines to include many of my own. This was brought on by bad tuning, lean runs due to airleaks and a half dozen other things. With this, they all had one thing in common, and overheated engine will lose power in flight after a couple minutes. It may up and quit immediately or in most of what I saw, simplly lose power and if you lucky enough to land , the throttle will be full forward yet the engine is only near and idle speed. I have recently read here, MY ENGINE TOO HOT TO TOUCH!" Well yeh!!!!!! Engines get that way[sm=bananahead.gif]. I have seen absolutely no use for a temp gauge. If your worried about a hot engine, need to learn to tune it right. |
RE: Operating Temperature
Amen to that!
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RE: Operating Temperature
Cowled engines tend to run hotter on the ground compared to flight. Plane's speed helps cooling.
Hence, measuring temp on the ground means nothing for the flight. However, as a general rule 250-300 F would seem OK to me at the hottest point of the engine for 4-strokes on the ground. Stelios |
RE: Operating Temperature
ORIGINAL: Cyclic Hardover This is not a personal shot here but whenever I see someone pointing a temp gauge at their engine, I make sure those around who are new stay very clear from these guys. There are no published specs and if there were, there are hundreds of scenarios to force varying temperatures. I have seen countless overheated engines to include many of my own. This was brought on by bad tuning, lean runs due to airleaks and a half dozen other things. With this, they all had one thing in common, and overheated engine will lose power in flight after a couple minutes. It may up and quit immediately or in most of what I saw, simplly lose power and if you lucky enough to land , the throttle will be full forward yet the engine is only near and idle speed. I have recently read here, MY ENGINE TOO HOT TO TOUCH!" Well yeh!!!!!! Engines get that way[sm=bananahead.gif]. I have seen absolutely no use for a temp gauge. If your worried about a hot engine, need to learn to tune it right. Dave |
RE: Operating Temperature
Seems like measuring temperature is another tool to assist with tuning. Cannot have too many measuring instruments that assist with problem solving.
NASCAR folks use temperature probes during testing. Bill |
RE: Operating Temperature
An infrared temperature gauge can be a valuable diagnostic tool, but primarily for comparing from one day to the next. At least on a single cylinder engine.
As BillS said, in racing we used them to compare the exhaust temps from one cylinder to the next to check cylinder balance. And in this use, if you have a multi cylinder engine, a temp gun is really a good tool to have when setting the two (or more) cylinders to match. Bill. |
RE: Operating Temperature
Exhaust Gas Temps (EGT) are extremely important on Turbines. Without constant monitoring, you can destroy a $4000 engine in no time at all.
So from what I am reading here, you need a temp gauge to tell you the reason for you engine overheating is lack of airflow? I hope those who are reading this thread are not mislead by any of this. These temp guages should have warning labels that read, "for entertainment purposes only." In certain areas of R/C yes and maybe, for glow engines, I see no use for it at all and it could also give you a false sense of security. If an engine runs like crap and on your list of diagnostics is to whip out a temp gauge, I hope nobody's watching. There is another thread on this here right now and as far as picking the right Temp Gauge, it really doesn't matter since they all tell you the same thing-nothing. |
RE: Operating Temperature
ORIGINAL: Cyclic Hardover So from what I am reading here, you need a temp gauge to tell you the reason for you engine overheating is lack of airflow? Dave |
RE: Operating Temperature
I use temp gauges. So sue me! :)
I like to know how much the temps are. I also like to compare between one prop and another. Between one glow plug and another. Between one fuel and another. Between one day and another. Between one click on the needle and two. As Bill said, between one cylinder and another. Why not? Once the engine is in the air flying, those ground temps don't matter. But it sure as hell does when you have the engine on a test stand and are breaking it in! [sm=thumbup.gif] |
RE: Operating Temperature
As long as the engine is being tuned for crisp and clean running and not lean running, the engines on your P-38 will run whatever temp they run at when they are happy. There is no hard set of rules to follow with two stroke glow engine temps. If they are getting too hot and fadeing or sagging in flight then richen them up, especially if airflow is a concern. You mention that you have 65 flights? did I read that correctly? If so, you are tuning them just fine (regardless of temp) as long as they have not been deadstick landings.
For a non competition single cylinder glow engine, the temp gun is merely a device to satisfy curiosity, nothing more. |
RE: Operating Temperature
For my son's recent school science assignment & for my own personal interest, we ran some tests using an old OS35 engine (cross flow) & varied the castor oil % in the fuel - the ratio ranged from 40% right down to 10%. The purpose of the tests was to see what would happen to the general performance, power output & operating temperature of the engine. The engine was fitted with a control line venturi & a MA 10 x 4 prop with spinner. The engine was placed on the test stand, standard muffler fitted & run in our back yard.
We monitored the head temperature by attaching a thermocouple probe to the rear left hand head bolt (when viewed from the rear of the engine). The probe was then connected to the multimeter. As we were concerned about seizing the engine on the lower oil %'s, we did the 40% test first then worked our way down in 5% increments until we arrived at the 10% mix. The dear old engine was then ran at FULL POWER for a total of 3 mins on each fuel/oil mix & recorded the head temperature every 20 seconds. Ambient air temp was around 16C or 61F. Briefly, the operating temps ranged from about 185C or 365F for the 40% oil mix & peaked at about 265C or 510F for the 10% test. At this lower %, the engine was clearly HOT HOT HOT - even after only 3 mins - and your nose could easily detect that "hot metal" type of smell. As other readers have noted, the tests can be a bit meaningless comparing one make of engine to another. However it is useful for ongoing monitoring of a particular engine & also if you like to experiment with different fuel mixes - eg: varying the % of oil & altering the mix of synthetic/castor oil within a fuel mix. If there is enough interest, I will publish in full my findings/results on RCU for information & comment. |
RE: Operating Temperature
ORIGINAL: Bone If there is enough interest, I will publish in full my findings/results on RCU for information & comment. |
RE: Operating Temperature
ORIGINAL: Bone For my son's recent school science assignment & for my own personal interest, we ran some tests using an old OS35 engine (cross flow) & varied the castor oil % in the fuel - the ratio ranged from 40% right down to 10%. The purpose of the tests was to see what would happen to the general performance, power output & operating temperature of the engine. The engine was fitted with a control line venturi & a MA 10 x 4 prop with spinner. The engine was placed on the test stand, standard muffler fitted & run in our back yard. We monitored the head temperature by attaching a thermocouple probe to the rear left hand head bolt (when viewed from the rear of the engine). The probe was then connected to the multimeter. As we were concerned about seizing the engine on the lower oil %'s, we did the 40% test first then worked our way down in 5% increments until we arrived at the 10% mix. The dear old engine was then ran at FULL POWER for a total of 3 mins on each fuel/oil mix & recorded the head temperature every 20 seconds. Ambient air temp was around 16C or 61F. Briefly, the operating temps ranged from about 185C or 365F for the 40% oil mix & peaked at about 265C or 510F for the 10% test. At this lower %, the engine was clearly HOT HOT HOT - even after only 3 mins - and your nose could easily detect that "hot metal" type of smell. As other readers have noted, the tests can be a bit meaningless comparing one make of engine to another. However it is useful for ongoing monitoring of a particular engine & also if you like to experiment with different fuel mixes - eg: varying the % of oil & altering the mix of synthetic/castor oil within a fuel mix. If there is enough interest, I will publish in full my findings/results on RCU for information & comment. My own boy is in his last year in Mechanical Engr and I really feel this is a great project for your boy and you. However knowing what an operating temp just for the heck of it does nothing. The main concern (IMHO) of engine temp is to see how hot it's going to get before damage can occur. You showed at one point 510F but so what if the engine got hot and it smelled. If you have the time, do this and it will mean something to me. Run that engine on any fuel you like but stick with the same fuel. Tune it good and run it and get that baseline range. Then run that thing lean and get that thing hot enough to lose power. So much so that the engine is barely running and the throttle is darn near wide open. Get a reading then and to me, would be very useful information. Then it is possible for somebody to use a remote thermo couple and some for of an alarm could go off when the temp if approaching a certain range while he is up in the air. |
RE: Operating Temperature
Cyclic,
Thank you for your thoughts and opinion. As I said, the tests were done for a school assignment & also for our own personal interest, nothing more, nothing less. The objective was not to destroy an engine but to demonstrate how the general overall performance was affected by different oil % in the fuel. We mix our own fuel & had complete freedom as to the oil % in each fuel mix. The engine we chose was a 1970's OS 35 & the oil was Castrol M Castor - 2 items that are likely hard to come by for most modellers in all parts of the world & therefore, they could not perfectly duplicate our results. They would need to use their own preferred engine & fuel/setup etc & draw their own conclusions from their results. I repeat, the tests were done by ourselves for ourselves. The outcome of the tests showed that the manufacturer's recommended oil % was the optimum amount that gave an acceptable operating temp, good power & smooth running. This was then considered to be the baseline value & gave us the normal operating temperature for that particular engine. Too much oil and the engine was down on RPM, very smokey exhaust & low temp. Too little oil - certainly beyond the lower limits of what the manufacturer recommends - resulted in greatly elevated temps. These high temps combined with a hot summer's day (very common in my part of the world) may push the engine past the point of no return. Armed with this knowledge about operating temps & oil % for their particular setup, the modeller can go flying at any time of the year & providing the needle valve is set correctly, correct prop size etc, no damaging engine overheating should occur. |
RE: Operating Temperature
I think one of the reasons that temperatures vary so much is that many engines vary on the fin cooling areas. Older engines had less and the newer square engines have much more. This results in cooler temps for the newer engines. Most modern engines can be converted to gas without overheating, despite running much hotter temps. Many gas engines have that hot metal smell as a normal course of their running, maybe not as much, but I have noticed it. So maybe the main damaging factor with running lean is not overheating, but lack of lubrication.
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RE: Operating Temperature
ORIGINAL: Cyclic Hardover If you have the time, do this and it will mean something to me. |
RE: Operating Temperature
ORIGINAL: MaJ. Woody What is the normal operating temperature for glow engines? I am sure this varies from engine to engine based on size and mounting dynamics (cowels). I am running two O.S. .91FX two stroke engines in my tightly coweled P-38 and was wondering about cooling. Over 65 flight so far but I had an engine out a few weeks ago and it got me thinking. What is too hot? The engines are generally in the 165-200 degrees Fahrenheit range after a flight. Is this acceptable? Thanks!! Dom --------------- Believe me, if you were cooking them for over 65 flights, the pistons would be a dark black and the rings would have lost their tension long ago. Of course, this is not to say that it is impossible for something to have failed in the fuel delivery system, resulting in a radically leaned mixture at any given point. I'm an old schooler, as you may have guessed. You don't need to take the engine's temperature in order to know whether it is running hot or not. When engines run hot habitually, they consume glow plugs at a much faster rate than normal. Then there is the buildup of carbon on the piston that I mentioned previously. They also smoke for a while after being shut down. Electronic tools are wonderful, if you know how to read them correctly - and I'm not just talking about the display/readout. They can also cause unwarranted concern and confusion when not understood in their proper context. |
RE: Operating Temperature
I think temp probes etc are useful ... let's look at the RC car scene, in the 1/10 touring car we really need to monitor the temp if not the engine will definately break a crank shaft or conrod because its running too lean.
We usually run the engine in the 130C (sorry I do not have it in F) range if you are being compatitive and if you want to push it then in the 140C-150C. Difference in life span? Well at about 110C it lasts about twice as long as 150C. This is info we gather from other drivers over a couple of years. I still check my plane engine temp when I land, I want my engines to last. Temp created by 'friction' (be it due to lack of oil or bad tuning) will kill an engine. When properly tuned my engines are reading about 230F just right after I land, sometimes with my SA72 its only about 220F only. |
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