older 912 ul heating up

[oldfox]

ok guys need some help just got the old bird back in the air flew great hands free but as I made the 4th lap around patch EGT (1530F) CHT (251F) stared to get on the high side oil temp was good 185 F I do have a in line coolant temp sensor and it was at 230F oh sorry RPM at 5100, I back off RPM everything drops back down . So I know lean right I check the needle setting was good even drop them down still heating up ?? check the jet size 158 right to the book has any of you guys gone richer then 158 ?? oh by the way pulled the plugs they are white in color after wot shut down . I'm burning 100 LL this cause problem ?? just pulling my hair out trying to fix . thanks for any help

[Norm]

Not sure because I just fly mine and have never had to adjust but "drop down the needle" wouldn't that make it leaner as less gas is being allowed in the carb. Not sure on the 912 but I know that is how the 582 would work.

[oldfox]

Nope I drop the clip down that takes needle up and makes richer. I’m looking to see if I can maybe change the timing?

[jiott]

Have you checked the entire coolant system including radiator for free flow?

[Av8r3400]

How about the sender or gauge?

[kmach]

Are you using 50/50 antifreeze/water or Evans water less coolant? There is around 25F difference between them in coolant temps.



Do you have all cylinder's exhausts monitored for egt ?



Carbs out of sync can cause different egt readings on different cylinders .



High egts can mean inefficient burn in the heads. Proper plugs? gapped at what?



Prop pitch can affect heating, over pitched and you will generate heat. lugging the engine will do this also.



Did you try increasing rpms ? to 5300- 5500, sometimes this will make the engine run cooler.

[oldfox]

Ok guys I have not flushed the coolant system good idea will do only have two egts one in the front and one in the back other side of motor. Carbs are synced right on the money and by the way brand new carbs not old ones also brand new spark plugs, have not try to run high RPM . I get if the coolant is a problem but would that send the EGTs through the roof again has anyone gone fatter on the main jet ?? I have 158 jet size and a 2nd through would be to much exhaust restriction could cause this also ?? Again hair pulling shi”” thanks for the help guys anything more you guys come up with let me know.

[Dave S]

Oldfox,


Just a thought. Many times when I have done engine diagnosis (not necessarily aircraft engines) especially when a symptom can have many causes such as this puzzling situation your are dealing with, I have found it useful to go back and check cylinder health first....meaning compression - reason being that no amount of work on the ignition or fuel systems will dispatch a problem if there is a mechanical problem such as an exhaust valve developing a leak.



A cylinder problem can translate into high EGT or high CHT due to lack of cylinder efficiency. Ruling this out could help reduce the number of things you would want to consider.


Again, just a thought.

[Russell320]

Before all this started, what were the original readings?

[Xengineguy]

ok guys need some help just got the old bird back in the air flew great hands free but as I made the 4th lap around patch EGT (1530F) CHT (251F) stared to get on the high side oil temp was good 185 F...

A couple things to consider, Float level, carb vent line location. Check your
Egt gauge and sender. Do you have an oil cooler? Do you have a heater installed?
Make sure you not more than 50/50 on you antifreeze mix. Do you have a thermostat installed.
Drain your cooling system and refill using a vacuum refill system. Very important if you have a heater and thermostat.

I have a speedster with an early 912. I’m at 160 on the mains but I also have the zipper big bore kit.

[jrevens]

Could you provide some details, and possibly pictures, of using a vacuum refill system? Thanks!

[Xengineguy]

Could you provide some details, and possibly pictures, of using a vacuum refill system? Thanks!

The unit I’m currently using is the snap on Svtsrad272a. Check out Utube
They have some nice demo videos of it in use. :)

[efwd]

That thing looks like a piece of cake to replicate at home. Certainly John or Merril can do it.

[jrevens]

Thanks for that, Mike. I think that it would be even more ideal to draw the proper vacuum at the distribution tank at the top of the engine, then draw the antifreeze into the system at the drain plug on the radiator. That would seem to be the ideal technique. Some plastic tubing, a couple of valves, and a "jet-pump" or aspirator type vacuum source using air pressure from your compressor would be very easy to build.

[Xengineguy]

I’ve been filling systems this way for years. When you draw a vacuum on the
System there is very little air left in the system. The rubber hoses even collapse.
Refilling from the top works fine.
For best results drain the system before you pull vacuum,trying to top off a system has mixed results.

[oldfox]

ok guys looks like I have the wrong sensors or the wrong EIS for this motor talk to Rotax guy he said the motor would not even run if the EGTs where that high showed him the spark plugs and he told me they were burning great so stay tuned for more and thanks again guys for all the help.

[oldfox]

Ok just got back from the airport all fixed now. 1. changed out exhaust prob was and was still too F*** high check the plugs again and again and again running lean so after 100th time I changed the main jet to 170 :eek: I know right But I want to see black plugs not white ones and man did it do the trick drop the temp right down EGTs 1250 F CHT 230F and coolant 215 F flew the plane for over 1.5 hour top speed 120 mph . I pulled the plugs and nice and brown. I'm going to keep my eye on plugs and see what happens thanks again for all the help will post some picture

[Av8r3400]

I don't know what you have going on there, or who your 912 Rotax guy is, but 170 jets are way, way, WAY too much fuel.

1250º is way too cold of EGT. Normal is 1472º F, redline is 1652º F with the EGT probe 4-6" from the exhaust valve.

Also, for the record CHT redline is 300º F.


I really wonder if you are chasing a non-problem.

[oldfox]

Well you could be right but I have not stop looking for the issue just trying to move the needle motor gets too hot it will sink a valve seat and then we start spending big money I think if it runs too rich I will see that on the plugs I will say I do believe the problem is in the carbs everything else is right on the number

[jrthomas]

Just a thought. I had a similar problem with a 503 years ago. After changing jets and adjusting my floats so that my carb bowl gas level was right, I happened to notice what should have been obvious, that my floats were barely floating. I ordered new floats and went back to stock jetting. Problem solved! James Thomas

[oldfox]

Ok guys here is the update have about 20 hours on the old bird have 168 main jets in carb EGTs at 1550 F at max, coolant temp at 230 F max , cylinder head temp 260 F runs great. Still not sure why I had to open up jets to get to right temps?? Here are some pic of the plugs, one from each side what do you guys think of color of plugs . Still looking for cause

[jiott]

Color looks about right to me; if anything maybe a tad on the hot (lean) side.

[jiott]

I don't see any sign of the white thermal paste you should be using. Definitely use it, it will cool the plugs somewhat.

[Danzer1]

I think the color is darn near perfect. The gaps seem to be a little different but that may just be the different photo angles. I do agree that the larger jetting is compensating for a different carb problem. Such as incorrect fuel float level and/or sinking floats.

[oldfox]

The carbs are brand new ?? But I will check height of floats and adjust to the heavy side and see if I can get to run rich. thanks for the help guys love flying this plane.

[Av8r3400]

Just because they are new doesn't mean they don't have bad or badly adjusted floats in them. There have been several series of bad floats coming out of Rotax (Bing) in recent years.

I agree with Danzer1, those jets are unnecessarily huge and masking a different problem. What about the rubber boots between the manifolds and carbs? What about the o-rings on the intake manifold to head seam?

[Dusty]

It has been suggested before, but have you checked your vent lines.
These make a huge difference.if they are vented into the K&N type filters like mine you will need to be up a jet size or two.

[jiott]

Mine are vented into the K&N filters and needed no jet change from the standard.

[jrevens]

Same here.

[oldfox]

I need to check the float height but seems to me if floats were low you would run out of gas at WOT on take off I have replaced all the rubber O rings and carb flange boots and ran motor spray down intake manifolds looking for leaks it is good but I’m not giving up . Guys have a great 4th holiday

[Dusty]

Maybe the exact location of the vent pipe in the air cleaner is the reason there can be variables.Me engine runs at 1550f egt,vented internally,but lower when clipped to the carb.