CHT temp after maintenance

by Arnaldo Pessina in 912 / 914 Technical Questions 12 years ago

Hi. I leave in SÃ£o Paulo-Brasil and have a stol ch 701 with an rotax 912 ULS. The engine hours is 890 and the mechanic did the cleaning and adjust of valves, and reassembly (500 hour maintenance). After a flight test of 25 minutes, where i climb 1000 feet and level i observe a higher CHT temperature of about 30Â° F, others parameters egt, oil temperature and pressure exactly the same as before the maintenance.

During the test the external temperature was 26Â° celsius( not hot day ).

The usual CHT temperature before the maintenance was 185/195 Â° F in level flight, after maintenance is 220 Â° F .
I know that max CHT is 275Â° F , but i donÂ´t understand why this increase in my CHT.
Any possible explanation ?

Thanks,
Arnaldo

Re: CHT temp after maintenance

by Roger Lee » 12 years ago

Roger Lee

128 5.28k 4.98k

Hi Arnaldo,

What adjusting of the valves? There is nothing to do with the valves. Do you mean the carbs? Check the CHT connection and make sure it has a solid connection on the probe. If it is loose it will give an erroneous reading. On a 70F day the 220F is a little on the high side. Check the coolant level and the coolant cap. Check any air flow entry points into the cowl for a reduced air flow. Out of curiosity what are the EGT and oil temps? On climb out what is the max rpm and what is your wide open throttle (WOT) rpm when you are flying flat and level at your average altitude? If the prop pitch is too course it will cause the engine to be overloaded. reducing the pitch will reduce the load on the engine. If you are using a 50/50 mix for anti freeze I would not let my CHT's get even close to 275F. The coolant temp isn't that far from the CHT and 275F is too high and may cause a vapor spot in the head that isn't getting any liquid coolant. I wouldn't allow over 248F-250F CHT or coolant if you have both gauges and your using a 50/50 anti freeze mix.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: CHT temp after maintenance

by Arnaldo Pessina » 12 years ago

Arnaldo Pessina

16 16 25

Hi Roger. First of all excuse me for my poor english. I use only avgas 100, because of alcool (25%) in our automotive gasoline. So in this maintenance they remove 4 cylinders for cleaning inspection and resettle the valves. People here in Brazil refers to this maintenance as "top of heading". According to then this is necessary in order to remove the carbon in the pistons. They also check, clean the propeller gear box and change ball bearing disk springs and oil seals. We didnÂ´t change prop pitch.

This afternoon i will re-check all the itens that you suggest, after that fly and take notes of rpm CHT oil pressure and temperature in climb and after level. After that iÂ´ll post the result

Thanks

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CHT temp after maintenance

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