I tried it and spoiled an engine

Since then I use the "prevention is better than cure" approach. What I suggest is, if your engine is open and the "natural aluminium" finish, clean it every weekend after flying is done for the week with some soap water and a toothbrush. This will keep the engine exterior clean and your model looking good too. I do it on my Tiger that way.

If the engine is cowled, you may consider taking off the cowl and doing the above once every month. This will require more effort as the castor on the head will have baked on, but it will allow the engine to run cooler. I did this on my Topstar (UCD60 clone) till I got fedup with it (and had engine tuning problems with the inverted 2C engine) and started to fly without the cowl, hence open engine.

I believe that this cleaning externally regularly will offer better engine life as subsequently there will be lesser "heat soak" effect. I believe you clean your model every weekend so why not the engine? Only ensure that once you scrub it, dry it thoroughly with a heat gun to prevent rusting of any parts. Also, plug close the carb during cleaning to prevent water from entering the crankcase.

Just my two cents, no offence meant

Ameya