Engine running too cold?

[pmccarthy]

My 912ULS runs very cold in cold winter weather. Oil and CHT both run just above the bottom of the gauge in cruise ie say 60 -70 degrees. On start up and then warm up oil will climb to 60 degrees only but CHT stays pinned at the bottom. On gradual descent say 4000 rpm both may pin at the bottom of the gauge.

 

I could blank off part of the radiator but I have the opposite problem in climb. Even on the coldest days, more than 5 minutes at the recommended climb settings takes CHT to just below the limit ( top of the orange and just below the red zone on my gauges), so I have to level out in steps.

 

I am wondering whether running cold will do harm.

 

 

[fly_tornado]

Yes it does

 

 

[Guest Maj Millard]

PM, this problem has been discussed at length before . Rotax does publish engine temperature 'operating ranges'.. which should be marked on the appropriate gauges.

 

The 912 in most applications does generally want to operate on the cooler side, except where being used in some trikes or gyros in my experience .

 

The stated temp ranges are listed by Rotax as being the 'normal operating ranges', I don't see anywhere where the use the words mandatory, or recommended are used. Read that as you may.

 

Regardless, it is wise as an operator to observe these ranges, and do everything we can to operate our engine within them.

 

The coolant temps in my Lightwing (912uls) have always operated at the bottom end of the green , and the oil temp generally sits at 85 which is 5 below the bottom of the green. It will go higher right after takeoff, especially with a heavily loaded extended climb. This is with both coolers blanked 50% during the cooler months, and with the coolant radiator blanked 50% year- round, as it is now. Rarely do my temp rise to an alarming level, and rarely do I ever see them up above mid range either. Oil pressure is always steady as a rock at mid range, and always has been.

 

Am I concerned that the oil temps operate 5 below the range ?....not really, if it was 10 below I would be. My old 582 in the Drifter always operated at the bottom of the coolant temp range. I was told many times, that's not good for the bottom end bearings, yet it was retired still in great shape at 700 hrs + and never once did it ever show sign of letting anyone down.

 

My current 912 now has 760 hrs on it and just keeps getting better. Until I get any indication that things may change, it'll stay just the way it is thank you.

 

By all means do what you need to, on your particular installation as I have done, to maintain operation within, or close to the 'normal operating range'.....and yes one should alway avoid operations way below the cool end. But even assuming our gauges are anywhere near accurate, I'm not about to stress about that minus 5 deg on the oil temps. As my coolant temps sit at mid range most of the time, I am happy that my engine is suitably warm and content during most operations..........Maj....

 

 

[Ultralights]

i have half of the oil cooler covered in winter, and 1/3 covered in summer... usually runs around 90degC it might see 11o max on a long climb max rate from sea level to 4500 ft, and will drop to about 60 on a long descent from about 5000ft to sea level. water temp and hence head temps are thermostat controlled and always at around 100degC,

 

 

[alf jessup]

Are you boys using Evans NPG as coolant? When I got the Tecnam it had a glycol mix and used to run way low about 70 deg, changed to Evans and it went up to 95 deg and stays constantly around there now, rises to about 110 on a 37 deg day on a prolonged climb to 7500. also helped the oil temps a fraction too

 

Alf

 

 

[Ultralights]

i use Evans NPG.

 

 

[alf jessup]

i use Evans NPG.

Always used it since owning the aircraft??

 

I was amazed that the coolant temps rose so much for the better when I changed to Evans.

 

Alf

 

 

[Ultralights]

the evens stuff has been used since new, almost at 1000hrs now.

 

 

[Willborne]

I use it to with the same result

 

 

[alf jessup]

I use it to with the same result

As in temps went up ?

 

 

[facthunter]

That will happen if the material doesn't cool as well (as water /glycol) While this doesn't seem an advantage, the waterless allows a much higher temp without steam and hot spots occurring . Water cooled engines don't really run hot enough for maximum efficiency. Nev

 

 

[alf jessup]

That will happen if the material doesn't cool as well (as water /glycol) While this doesn't seem an advantage, the waterless allows a much higher temp without steam and hot spots occurring . Water cooled engines don't really run hot enough for maximum efficiency. Nev

Totally agree Nev,

 

Always felt better once the Evans went in and the head temps went up, I was always a little concerned with lower temps than what Rotax recommended but the temps now are far more stable, still use some tape at during winter months on the oil cooler but the radiator never needs tape during normal operations throughout the year.

 

Alf

 

 

[Willborne]

As in temps went up ?

Yeah Alf sit around the same as you have quoted

 

 

[pmccarthy]

I will make the change and see how that goes.

 

 

[jetjr]

Thermostasis make a oil thermostat for rotax and others

 

 

[Guest Maj Millard]

The part you leave on the ground, is the part that'll never give you a problem........kiss theory applies...keep it simple stupid !

 

 

[David Isaac]

Excuse my lack of knowledge, but I thought that Rotaxes ran thermostats in the coolant ... and please don't give the line they are more trouble than they are worth, because that is simple BS if the installation properly designed. After all by blocking off part of the radiator you are effectively reducing the cooling effect which is what a thermostat does in a far more temperature constant manner. Running a liquid cooled motor below optimum temps will increase the wear factors and one day it will show. If combustion temps are not optimum you will suffer the long term consequence either side of the optimum.

 

 

[facthunter]

I would go for simplicity. The coolant path is complex on the 912 with pipes to and from all cylinders and I could see a variation of temp possible as the flows are in parallel. a shutter on the radiator and the waterless would be the best bet for reliability, then you can get the temps up without the worry of a hot spot . My opinion only. Nev

 

 

[David Isaac]

A pilot 'inflight adjustable' shutter would be an excellent alternative as long as you weren't asleep at the stick.

 

 

[facthunter]

Easier than having to land and adjust a piece of foam when the green stuff starts coming back on the top of the cowl. Nev

 

 

[JUSTNUZZA]

What temps are you showing ?

 

Totally agree Nev,Always felt better once the Evans went in and the head temps went up, I was always a little concerned with lower temps than what Rotax recommended but the temps now are far more stable, still use some tape at during winter months on the oil cooler but the radiator never needs tape during normal operations throughout the year.

 

Alf

[alf jessup]

Just Nuzza,

 

Since changing over to the Evans from the water/glycol mix my CHT now run constant 95 deg in cruise at 4800-5000 rpm, used to run at about 70 deg, oil temps 85-95 deg most times depending on the OAT.

 

Cruise climbed out last summer on a 37 deg day to 8500 to cross the great divide from Yarrawonga to my home base at West Sale and the CHT's never exceeded 110 deg and oil was in the top of the green at 110-115 deg.

 

Normal temps on a 25 deg day poking around are CHT 95 -100 & 85-95 deg on the oil.

 

Usually place a small bit of tape over part of the oil cooler in winter to keep the temps up and off in the summer months.

 

Cheers

 

Alf