would just like to know what heat is normal on the head after a flight... in F? yesterday I bench tested my Rossi R65 and it got hot... but there are leaks... what is danger zone for head temps?

Beginners should really rely on the techniques to set the needle properly, and learn to judge the needle setting in the air.

The problem with quoting head temps is that almost nobody knows a number that works with all the different engine sizes, fuel mixes, prop diameters, prop pitch, plane weights, etc etc. Also, the process of reading the temp is not simple. Different head types also dissipate heat differently, some do better than others so the cylinders underneath are feeling it differently. Engine size also matters. The smaller engines actually have problems keeping enough heat in them to run well without higher nitro fuels. As size goes up in the larger engines, they hold/lose heat longer/slower.

4strokes have lots more head and run hotter temps than 2strokes. Did you know that the temps in the top of our engines vary by location. And of course, vary by how different areas are cooled by airflow.

There doesn't seem to be a database anywhere and there's a fairly good reason. Actually, as you see, there are a number of reasons.

The best one can be that the temp some guy remembers for his model isn't reliable for yours.

Some techniques can work for experienced flyers, but some aren't really the best for beginners.

will 25% maybe be a better content than 20% to have cooler running temps? or could I try a colder plug? also I see that Sidewinder 20% uses 12% oil as to 17% by Omega... how much effect will the 5% more oil have?...

Nitromethane doesn't actually burn, it really only carries oxygen into the combustion chamber so it's basically a chemical supercharger so I would imagine (this is just reasoning, I don't know it as a fact) that more nitro would either be wasted (assuming the engine's already burning fuel efficiently) or would raise the temp rather than lowering it (due to more fuel being burned if it was running inefficiently at lower nitro content).

The temp rating of the plug won't have much effect on the running temp of the engine either. Plug temp is a way of changing the timing of the engine... a hotter plug will cause the fuel to ignite earlier in the cycle (advancing the timing), a cooler will have it fire later (retarding the timing).

If your glow engine's overheating there's really only three possible reasons...
1: The cooling fins are clogged with debris. Clean your engine.
2: The engine's encased in a cowl or similar which does not allow sufficient airflow. Allow sufficient inlet holes, and outlet holes 2-3 time as big as the inlet to avoid a high pressure area.
3: The most common (and easiest fixed) reason - your engine is running lean. When setting your mixture, tune to the peak RPM then detune the engine rich by about 1/4 turn. This allows for the engine to lean out in the air due to lower air pressure at altitude and the prop "unloading".

FYI, an engine will always run hotter when bench tested than in flight, due to the lack of "blast cooling" from the aircraft moving through the air - the same as if you let your car run long enough without moving it, it'll eventually overheat whereas driving it will keep it cooler.

I like to keep my engine temp to about 220F to 230F if I am pushing hard. For sport flying I like to keep it below 220F.

how do u measure ur temps?

How true. When I used to build VW powered sand rails once in a while someone would put a head temp gauge on there car. Being used to water cooled engines these people would go nuts when they saw what there little air cooled engines were running.
For the OP, engine temp depends more on correct tune plus enough oil content in the fuel. Most glow fuel has 17 or 18% and that is plenty. On the bench and during break in an engine will tend to run a bit hot anyway, that's one of the reasons we start breaking them in at a very fat setting and lean as we go. Prop size is also another little thing you may want to check.

Get one of those IR temp sensors made for pets that are being used for RC now. Alternatively, put a single drop of water on the head, if it evaporates within 3-4 secs she is fine. Less than 3 secs and its starting to get hot.

I mailed Rossi... I was just using the incorrect fuel... or not incorrect but here is explanation... with higher nitro content I have to use an extra shim for the head to decompress engine... they recommend Omega 10%... I used 20% and didn't add the shim so that could explain the leak at the head? and also why it got hot Sidewinder uses 12% oil and Omega 17-18%... the oil content can it make difference to heat?

Leak is a leak. Just tighten the screws on the head, once you do that it will be fine, careful not to over do it. On Rossi's you will need to shim it if your nitro content is high. My Rossi 53 was running fine on 5% nitro then I went to the field with 15%, brought the wrong jug. It would not tune at all with the 15%. That's Rossi for you but they are lovely engines.

so what plug would you recommend... I checked that the OS #10 plug says its good for 60size engines and up... what would you say?

I was running the Rossi plugs, I think mine was the cold or extra cold one. I never tried OS plugs on mine.

do you know how I can see what size engine I have?... I bought it from someone that said its the 65... but nowhere on the box it says anything, just on the engine or mount it says 67...