What CHTs are flying RV-12s Seeing?

What cylinder head temperatures are you seeing in flight? I have done a few short ground runups to 122F oil temp and by then I am just going over the 248F CHT alarm limit.

The top hose of the radiator is warm and the expansion tank's coolant level has moved down to midway between min and max after the first run so I am reasonably sure the coolant is moving. Scott expressed the idea that ground run may not push enough air through the radiator to get 'regular' cooing and he well may be correct, but what are you seeing in flight?

As an aside, I at first thought the CHT max of 248F might be an error because that is the max for the oil temp also..a real coincidence...and looking around on the internet some Rotax 4 cylinder engines have CHT max given as high as 284F (a number reversal that led me to suspect an error in the instructions but I guess it wasn't.)

JohnF said:

What cylinder head temperatures are you seeing in flight? I have done a few short ground runups to 122F oil temp and by then I am just going over the 248F CHT alarm limit.

The top hose of the radiator is warm and the expansion tank's coolant level has moved down to midway between min and max after the first run so I am reasonably sure the coolant is moving. Scott expressed the idea that ground run may not push enough air through the radiator to get 'regular' cooing and he well may be correct, but what are you seeing in flight?

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John, I was just mentioning that the cooling will not be near as good as in flight as a general comment.

I have about 75 hours of flight time in RV-12's and I have never seen the CHT's get anywhere close to limit just running on the ground waiting for the oil temp to get to 122 F. A typical temp in flight is 180 - 190 F in OATs of about 60 F..

I think you have some type of a problem but it is impossible to tell without more information.
How long are you running the engine?
At what RPM?
At what outside air temp?
Do all of your indicated temps match when the engine is cold (I.E. when the engine is totally cold from sitting over night do your oil temp and both CHT's read very close to the shop/hangar temp on the D-180)?

too hot

My temps have been like 203-201 with 93 degree outside air temps. Very Close.

My rightside EGT is somewhat cooler, perhaps from air blowing in, maybe by 20 degrees.

My oil pressure stays in the green, near the top in 90 degree long climbs.

My oil pressure seems to bounce around erratically sometimes like between 40 and 80 psi, maybe the sensor is getting hot. I pull back power and it seems happy.

Has there ever been a case of vapor lock? Mine was sitting on the runway after a cross country. When I took off, there was a brief loss of power as soon as i got to Vy. As soon as I put the nose down, it was running strong again. 8 gallons gas in tank .

Thanks Scott.

okiejohn said:

My temps have been like 203-201 with 93 degree outside air temps. Very Close.

My rightside EGT is somewhat cooler, perhaps from air blowing in, maybe by 20 degrees.

My oil pressure stays in the green, near the top in 90 degree long climbs.

My oil pressure seems to bounce around erratically sometimes like between 40 and 80 psi, maybe the sensor is getting hot. I pull back power and it seems happy.

Has there ever been a case of vapor lock? Mine was sitting on the runway after a cross country. When I took off, there was a brief loss of power as soon as i got to Vy. As soon as I put the nose down, it was running strong again. 8 gallons gas in tank .

Thanks Scott.

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That's good feedback John. Can you comment on what you are seeing for oil temps after long climbs at 90 degrees OAT.

Scott,

Does the static WOT have anything to do with the oil temps? Mine is set at 4900 and my oil temps run 195 to 203 in Texas all day long and have for close to 90 hours.

Peterk said:

Scott,

Does the static WOT have anything to do with the oil temps? Mine is set at 4900 and my oil temps run 195 to 203 in Texas all day long and have for close to 90 hours.

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I think it is likely to only have an effect if you are flying at the higher pitch settings and subconsciously climbing at slower speeds because of the poorer climb performance. In reality this wont really improve your climb rate, but pilots can tend to do it if the climb performance isn't good (trying to help the airplane go up faster). With the slower climb speed it will effect your oil temp some.
Once I have reached pattern alt., I usually cruise climb at 80-85 kts. It only causes a slight reduction in ROC but improves cooling.

My opinion is you should adjust for a bit more RPM unless all of your flying is at low altitude and from low elevation airports. I would recommend at least 5000 static.

What OAT do you get those oil temps? (that info would make your 3's much more useful to other RV-12 owners)

Those of us in the CT community have found that pitching our props to give 5500 RPM in level flight with WOT at the altitude we normally fly gives excellent results. For me that gives a take off RPM of 4900. This gives a good compromise between cruise and climb performance.

However, Rotax SL-912-016 states that take off RPM should be no less than 5200. That seems a little high and most of us flying CT's don't pitch for 5200 on take off.. Each of you should read the SL, play with prop pitch a little bit, then pick what you are comfortable with keeping in mind what the SL says and why.

My static RPM is around 5,000 RPM, WOT at altitude I can hit 5,650 RPM. Seems to be a good compromise for a prop setting.

My CHT's are around 200 - 210 when flying around 5,000 RPM.

With the warmer OAT temps of 80F my oil temps are getting a little high for my liking. If I push the engine 5,300 RPM they will rise to 230F. 4,800 RPM will drop the oil temps back to 205F.

I avoid the long climbs by gaining altitude faster when the oil is cooler, then leveling off for cruise around 3,000 MLS. We are at 1,500' MSL here.

I'll be looking for other solutions to keep the oil temps lower. Any ideas?

Geico266 said:

With the warmer OAT temps of 80F my oil temps are getting a little high for my liking. If I push the engine 5,300 RPM they will rise to 230F. 4,800 RPM will drop the oil temps back to 205F.

I avoid the long climbs by gaining altitude faster when the oil is cooler, then leveling off for cruise around 3,000 MLS. We are at 1,500' MSL here.

I'll be looking for other solutions to keep the oil temps lower. Any ideas?

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Look for evidence of zero air leaks on the seals at the coolant radiator. This is where builders that didn't take the time to get that interface accurate, will pay the price.
If the 1/4" dimension is accurately held and the seals are installed per the instructions, it makes for a good seal because the air pressure inside the plenum actually pushes the seals tighter. I am aware of some builders with construction errors in this area choosing to use a different seal. This puts them in an experimental situation as to how good of a seal they actually have.
Any amount of leak at this location causes a drop in the pressure delta across the oil cooler and the coolant radiator.
I have inspected one RV-12 that was about ready to fly. The builder had not trimmed the extra fiberglass flashing from around the perimeter of the oval air inlet. This effectively reduced the inlet area and would likely cause some cooling issues. This indicates that there are a number of different things builders can have done that would have an effect on engine temps.

Testing on the prototype would indicate that an oil temp of 230 in cruise condition with the OAT at only 80 degrees should not be expected.

High CHTs

Any update on others experiencing high CHTs?

My CHTs went high enough to trip the Dynon alarm at the weekend. Slightly longer than normal taxy/hold before takeoff, with a strong crosswind while holding. Engine was still hot from a previous flight.

I cancelled the takeoff and taxied into wind for a couple of minutes. Temperatures dropped into the green, so I went back to the runway and took off. Temperatures dropped further when airborne, into the normal range.

I checked coolant levels afterwards, all normal.

Cheers...Keith