Won’t burp cold

When you say cold, do you mean the engine hasn’t run, or the OAT is unpleasant.

Can you feel the compression when rotating the prop? You need to be able to build pressure in the cylinders so that this then pressurises the crankcase and returns the oil to the tank. If your valves only seal when the engine is warm that that would explain your problem. You may need to regrind the valves if that's the case.

to have a good return of the oil in the tank you must have a perfect seal of crankcase pressure. 

there are a lot of places where 91X seals can leak. For example o-ring in pushrod oil return tube, in valve covers etc.

In the maintenance manual there is also a test of crackcase pressure using a manometer 

If crankcase pressure is marginal with cold , dense oil the return can be difficult.

Engine hasn’t run outside temperature is probably Not a issue 40 to 70°

Hi John,

40F (4C) is cold by my standards. Even with a multi grade oil, like AeroShell Sport 4, it is likly to be a little "gluggie". This combined with cold engine clearances being high/wide,  reducing your ability to get good compression, will make Burping more challenging.

70F (21C) is a much more civilised temperature. You should have no Burping problems.

Burping Technique;

Burping is not a sprint activity. Slow turns of the prop, rather than going for max speed, with a pause at each max compression, is generally a more effective way of raising crankcase pressure and forcing the oil into the oil tank for a Burp.

I have adopted a slightly diffrent approach (I read in this Forum);

Burp your engine after flight when engine/oil nice and hot. I find that Burping is very quick doing this. You can check oil level at this time however I prefer to follow up with a cold engine Burp, before flight and then check the level. By doing both hot/cold, I feel that I get a very good oil level reading.😈