High Point in Oil Line

You need to bleed the air out of the suction line before you start the engine for the first time. There is a procedure in the Rotax installation manual. I just disconnect the oil return hose to the tank, seal off the tank inlet and pressurise the tank via the breather hose using a foot pump. You may need to make a gasget to seal around the cap, I just use a polythene bag. If you then slacken the hose from the pump inlet, pressurise the circuit and when oil starts coming out, reattach the hose to the pump inlet and the return hose to the tank. You then need to rotate the prop in the normal direction about 50-60 turns and then switch the master on and check that the oil pressure has started to rise. Once I see that I crank it on the starter for a few seconds just to see that the pressure increases normally. Once done you shouldn't get air in that line again.

Hi Kevin,

I am glad I asked this question. Your advice on bleeding the air out of the inlet line will solve the issue of the air in the high point that has been bothering me since I installed the line. Your procedure sounds goood.  I believe I could have missed this step and been confused about why I could not get oil into the engine by just doing the prop rotation by hand or why I did not get immediate oil pressure. Its great to know one can see a little oil pressure rise before actually cranking the engine.

Thank you so much for taking the time to answer my question. I am finding this site extremely helpful for questions specific to the Rotax 912 as I get closer to first engine start.

Regards,

Perry

I would strongly recommend downloading the installation manual and having a read through, there is a lot of useful info. The oil pump is not self-priming, you have to get the oil up to the pump and it will only tolerate a small amount of air in the line. The last time I had to purge the line it took me a couple of goes to get enough of the air out for the hand-propping to show an increase in pressure. I would definitely not start the engine until I had oil pressure come up during cranking.

Hi Kevin,

I do have the manual downloaded on most of my devices, iphone, ipad, laptop and Imac. I have read through it once and a few sections more closely, but need to go back and review each section thoroughly, with particular interest to the oiling section.

I have the homebuilt help videos on the 912 installation for CH-701 and 750 but I don't recall them taking such care with filling the oil inlet line. It  could have been Zeniths placement of the oil cooler which I diverged from. I won't touch that starter switch until I am sure I have oil pressure. I know it will be much harder to convince my wife I need another new engine.

Regards,

Perry

A lot of aircraft have some high and low points in their oil hoses. It isn't a problem. When you drain the oil tank during an oil change the fittings on top drain too. This small amount of air isn't an issue. When you take the tank off for cleaning the fittings on top don't have any oil in them. It's just a small amount. Same thing with the oil filter. It will always have a small amount of air during the change. It's the huge amounts of air that gets induced like at a hose change and all the hoses get drained that we do an oil purge. Small amounts of air just pass through the system.