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Old 05-25-2016, 06:38 PM   #1
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DA50R Over Heating

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OK Guys;

I am having a bit of an odd problem with my DA50R – so far it has caused two crashes due to over-heating – and I cannot figure out a solution!

So here we go;

Fresh gas, Low octane, mixed 32:1 (lots of oil)
Prop; Mejzlik 22 x 8 – but the problem is consistent with other props.
Cooling – it failed last year with a cowl in place and it failed today with no cowl.
Tuning – factory spec to start and then minor tweaking (Low 1 3/8 turns, High 1 7/8 turns)


Fired up and tuned with no problems! Low idle goes down to 1.6K, High end is up to 7.1K. the throttle is very sensitive but it has a smooth transition – it is at maximum revs with the throttle at half.

I am afraid that in the air it will unwind to 7.8K or better and cause damage so I richened up the high end with little to no effect until the engine died. (I took the High end up to 2 ˝ turns with no effect, beyond that the engine died)

After going through a tank of gas in the tuning the engine started to over-heat and ran poorly above mid-range and then stopped. This is what happened last year, in flight… and lead to a nasty landing.

Before I tear the engine completely apart looking for some minor flaw… (I’m thinking a carburetor problem).

Has anybody had a similar experience or a solid suggestion?

Thanks for your time!
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Old 05-25-2016, 07:30 PM   #2
Mike Sebastien
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Re: DA50R Over Heating

Why are you concerned with the engine unloading to 7.8 k? DA engines are very robust and can take it. Sorry to be sarcastic but have you ever heard of the throttle. If your engine is unloading you must be a dive and good pilots come back on the throttle.

What is your Gas/oil mixture?

Last edited by Mike Sebastien; 05-25-2016 at 08:37 PM.
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Old 05-25-2016, 09:41 PM   #3
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Re: DA50R Over Heating

In your details you said "low octane"? You should only use high octane With no ethnol in the fuel. The ethonal ruins your motor.
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Old 05-25-2016, 10:18 PM   #4
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Re: DA50R Over Heating

Sounds frustrating (been there)

I have an engine that was always reliable until it started overheating suddenly a few minutes into each flight. Bearings seemed good to me but a friend and small engine expert felt worn bearings were the issue.

$20 and a case of beer later it stopped overheating and still runs great. Might be worth a shot.
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Old 05-25-2016, 10:53 PM   #5
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Re: DA50R Over Heating

How can you tell that the motor is stopping because of overheating? I've had a motor act very similar to what you described and it had nothing to do with the motor overheating. In my case it was a carb issue (fuel inlet screen somewhat plugged). Since the issue happened again with your motor completely uncowled I would really have second thoughts about overheating being the issue.
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Old 05-25-2016, 10:55 PM   #6
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Re: DA50R Over Heating

Not sure that I got that right , you say running a case of beer thru the engine cured the overheat problem.....must have been the 5% ethyl alcohol.

Sorry the devil made me say it !
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Old 05-26-2016, 03:14 AM   #7
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Re: DA50R Over Heating

OK, let's see if I can respond to everyone in order...

Mike - as I said in the initial post ... the gas blend is 32:1. Lots of oil - mainly for break-in but it works just fine. it has been my experience that engines gain 6-800 RPM once airborne - the extra RPM would take the engine to it's max and I don't need to replace an engine just now so I try to keep the engine speed with in tolerances. The throttle control is a fine idea - but not always practical...

Brodie - DA recommends the lower grade of fuel (87 octane) in their manuals and specifically says NOT to use High Octane.

Danno - a bad bearing?? I had not thought of that - I don't have much run time on this engine - but that doesn't mean too much - I'll keep it in mind when I have tried a few other fixes.

Gordon; GOOD POINT! I was planning on taking the carb apart - you have confirmed my main suspect and given me a good place to start looking at.

Thanks to all for the input - the collective knowledge of the RCC forum has been fantastic once again!

I'll get to work and let you know the results!
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Old 05-26-2016, 07:57 AM   #8
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Re: DA50R Over Heating

Rob, I would be looking for an air leak of some kind. It appears that your engine is running lean. (No reaction to the high speed needle 2 1/2 turns out and overheating). Possible areas I look would be around the intake system gaskets or the front bearing. If you have any vibration from a unbalanced prop, bent prop hub or crankshaft (Previous prop strike) can cause front bearing to leak over time due to bearing failure. Best of luck with your troubleshooting.
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Old 05-26-2016, 07:58 AM   #9
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Re: DA50R Over Heating

Hey Rob - you already have suggestions but just a couple of comments.

Rare for a DA50 to overheat unless it is run lean or not enough air flow through the cowl. Excessive running on the ground without enough air flow over the fins in a cowled engine can make it run hot. But running hot with no cowl seems very unlikely.

Based on your needle settings you are around factory standard so hard to see them causing the problem. You also said you richened it up.

As you already noted do not run high octane, follow the recommendations in the DA manual - I think octane 87 or 89 is fine but no need to go to 91-93 etc.

32:1 oil is lots of oil. You did not say what kind but I cannot imagine that the oil is causing the problem.

DA's that overheat tend to get a pinkish or purplish colour to the fins. Nothing dramatic just a tint of colour. Does not mean permanent damage but indicates running hot, again usually due to lean running.

Bad bearings could cause a problem. Usually you hear something when flipping the prop.

I would have a close look at the carb and inlet screen as per Gord. Even if your needles are right, if you have crap partially blocking the inlet screen that cause cause lean runs. If you have the carb off to look at the screen I would take the needles out and blow out the seats and jets with carb cleaner just to make sure there is nothing partially blocked.

As Jeff just said a bad carb gasket or loose carb then is sucking in air will also cause it to run lean.

These engines are usually solid but I have had one blow bearings causing a dead stick. If you hear any clicking when you flip the prop that does not seem right then the only solution may be to pack it up and send it back to DA for them to go over.
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Old 05-26-2016, 08:44 AM   #10
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Re: DA50R Over Heating

A couple of things: Make sure that all the air coming in the front of the cowl has to go over the finns. I use blocks of balsa or foam to block all the empty spaces. I also blocked the L/H cowl intake with a piece of thin plywood painted flat black. The standard clearance on a piston to cylinder is about .001". When I was rebuilding ultra-light aircraft engines with snow machine parts I would set the clearance at .003". Try increasing the clearance to between .0015" and .002", then install a new ring. When I did this seized engines were a thing of the past.

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