I am at the end of my rope with the Jabiru #5 cylinder!  I thought I had the problem fixed in early June and flew it to get it painted (a horrible story) and had no trouble.  The temps outside were cool, so the temps on the engine were fine.

I picked up the plane after 2 months at the painters!!!! and again had high temps on the way home.  My wife and I spoke to Pete at Jabiru and he said I could bring it down there and they would fly it, but that is an issue, since it is running hot and the trip is 425 nautical miles!

Has anyone installed a Jabiru 3300 in a 750, using the Continental type plenum?

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Doc,

How hot is hot? Is it right at the red line on that one cylinder?

I second Mark's comment, Ed. Give us some data! CHT's, EGT's, and oil temp at what power setting and what altitude? How many hours on the engine now?

I think if you jump to a totally different cooling system, you'll still be starting from scratch with a totally experimental cooling system with scant experience from others to help you.

 

 

John,

I've given the temps in reply to Mark, but the corresponding oil temps were 314, 316, and 315 on Thursday.  Tonight, they stayed below 200, but I only flew for .3 hours.  The engine has 33 tach hours and 44.6 hobbs hours.  I'm tempted to just fly it and see if things go down.  It has great power and runs very smoothly.  Only thing I've noticed, is that my fuel flow seems to be higher than when I took it to the painter?  I don't believe he did anything to the engine, so I'm hoping it is just bad gauge readings?

Ed

I'm assuming you meant the oil temps were 214,216,and 215, not in the 300's.

What's the EGT on #5 in cruise and where is that (hotter, cooler, average) relative to the other cylinders?

Is the oil sump cooler connected?

With the unpleasant experience with the painter, no chance some masking material, etc., has been ingested in the right ram air duct?

It's been my experience that the Jab is "happier" at cruise at a little higher rpm's - around 2900, even 2950 seems OK - the cooling is just a bit better.

Be sure and re-torque the cylinder head bolts per the engine installation manual schedule. A hot cylinder will loosen them more than the other cylinders.

The Zenith demo 750 with the Jab has always seemed to run cool without issues. One thing I noticed looking at it at AirVenture was the right ram air duct has a ramp running up from inside the bottom lip of the inlet to the top of the fiberglass dam. It also has the dam extension over the #1 cylinder fin and the curved ramp over the #1 barrel which I think you already have. That ramp would be easy to install.

Are you running the Sensenich wooden prop? They seem to cool better with the "fat" blade in front of the inlets vs. the composite and adjustable props which are "skinnier"/less chord near the hub.

Do you have the vane insert just before the carb and smooth (most use rubber radiator hose) duct between air box and carb? The insert evens mixture distribution even more and cooling seemed to improve just a bit.

Keep the oil level just barely over where the hash marks on the dipstick begin. Jabs don't like high oil levels - it will definitely affect temps

I burn about 6 gal/hr at 2900.

Your observation to keep flying it is a good one if you can keep temps reasonable. I always thought that mine was fully broken-in at about where you are, but it just kept getting cooler and cooler with time and probably stabilized another 50 hrs later!

Hang in there! As you know, I'm at 1 year and 160 hrs. Temps in hot weather 250-300 and oil around 192 usually. Just did the diff comp test yesterday on the annual and cyls range from 74 to 80 over 80. It's very smooth, very dependable and totally without issues. You CAN get there!

John

N750A 

 

John,

You are correct, they were 214, 216, and 215!  The #5 EGT was 1349, 1301, and 1345 at the cruise RPM's I noted.  I took off the ram airs and checked for debris and there was none.  And yes, the patented John Austin oil cooler is working fine.

I have retorqued the heads and they were fine.  I also had the ramp in before, and it made no difference.  I have the vane in the carb and am using the wooden prop.  I have my oil up to the half way mark on the dip stick, so I'll take some out.

I was burning around 5 per hour at 2800, so we will see what happens.  

Did you have a good time at OSH?

Ed

Darn it, Ed, you've about used up my bag of tricks! HA! When the ramp was installed, was it used in conjunction with the raised air dam (to cover more cylinder fin on #1) and curved ramp over #1 barrel? If not, it might be worth a try to reinstall it. (Although I don't have the ramp installed, that's the configuration the Zenith demo has).

I don't remember, did you extend the duct down the backside of #5 cylinder fins? That seemed to help on my 3300.

I never fill beyond about a quarter of the hash marks on my oil dipstick.

5/hr seems reasonable fuel burn to me!

I had a great time at AirVenture! The weather was perfect and although (to me) it seemed that overall AirVenture attendance was relatively light, there was a huge turn-out for the Zenith builder's banquet. At the Zenith display, I think I let my enthusiasm get away from me ... I "sold" at least two people on getting a 750 kit!

John

N750A

John,

Yes, I did extend the duct down behind #5.  I will try out the ramp again.  I have to do a fuel check to see if I'm still at 5 gph, my Dynon is showing more.

One of the guys who helped a lot on my build has decided to go with a 750 also.  He was looking at an RV, but after OSH, he is ready to get going as soon as he sells his Challenger.

Ed

Mark,

at 2760 RPM, CHT 368, at 2820 RPM, CHT 367, at 2790 RPM, CHT 366 - this was on the flight home last Thursday.  Tonight, 2800 RPM, CHT 350 to 360.  Jabiru calls for 356 max continuous.

Ed

Hi Ed, sorry to hear of your continuing heating problems. I was just looking at the paint job in your recent photos (which really looks great), and was wondering about the size of the air outlet at the bottom of your cowl. It looks much smaller than mine which is 9 inches from front to back ie (the bottom of the fire wall to the lip of the lower cowl opening). I see you've got a nice big lip there which should help to create that negative pressure needed in the bottom cowl.

As a rule, the opening at the bottom of the cowl needs to be (at the very least) 3 times the size of the air inlet openings behind your prop. 

Gary 

Gary,

I think I have plenty of opening, but I will measure today.

Ed

I suspect you are running too lean.  At 7-8GPH, I stay cool.  Try carb heat to richen the mixture and see if the CHT's and EGT's don't fall.

 

My advice is worth what you paid!

Jerry,

Mixture is hard to change on this engine, what did you do?  I've already turned the carb @ 5 degrees as suggested by Pete.

Ed

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