I had the same thing with my 2 OS 21 RG's, OS 18 cv-r(x) and my 2 OS 15 cv-r(x)'s. By tank 2 or three, the temps came up to around 200 though and I didn't have any problems from there on. I leaned them out a bit after tank one. I used a break in process that I wrote up after reading a few of other peoples.
On both OS 21's and 15's, I got over 9 gallons out of the engines before requiring a pinch or rebuild. The OS 18 I never ran more than 20 tanks through it. I sold the truck it was in around tank 15. Now the engine is in a baggie all AR oiled waiting for me to by a 1/10 something again.
My break in process:
I use the heat cycle method with all my engines. It takes a couple hours and about 10 - 12 tanks of fuel before it’s tuned for good performance. You should have a temp gun.
Some engines take a gallon or more before they are completely broken in and you start realizing the kind of power they produce. While others only take a quart.
First, pull out the glow plug and slowly rotate the flywheel until you know the piston is at the bottom of the stroke(This is known as BDC). Mark the flywheel with a dot of fingernail polish or a permanent marker so you know where it's at what at BDC without having to pull out the plug.
Also, I always use Trinity MHP 20%/12% oil in all my engines. It's been the most consistent for me. I’ve used Blue Thunder 20%, Wildcat Eliminator 20%/16% oil, Byron 20% and Trinity MHP 20%/12% oil.
Tank 1
You want it to run rich and with most engines the temps will range from 120-180 in the first tank. All you do is let it idle through the tank with the wheels off the ground giving the throttle an occasional blip to keep it from loading up too bad. When it runs out of fuel, position the flywheel so the piston is at BDC. Let the engine cool to ambient temps before you fire it back up.
Tank 2
You should start driving it on concrete or pavement of some sort in large figure 8's. Your not only breaking in the engine, your breaking in the driveline as well. You shouldn't get above 1/2 throttle through this tank. Start leaning the High Speed Needle about half way through the tank. You should be able to get to 160 - 180 or so by the time the tank is empty. Again, when it runs out of fuel, put the piston at BDC and let it cool to ambient temps.
Tank 3
Do the same as tank 2. Keep leaning a little bit to get the temps up. A good operating temp range for most engines is between 210 and 260. By the end of tank 3, you should be getting up to 200 or so. Again, when it runs out of fuel, put the piston at BDC and let it cool to ambient temps.
Tank 4 - 5
You should start leaning it to get the temps up above 210. If at any point in time, your temps spike up over 260, you got some issues or your being to aggressive with your leaning of the needles. Normally, as the tank empties to about ¼ tank, I refill while it’s running and keep it running. Through tanks 4 and 5, you can start opening up the throttle a little more to about ¾ for a couple seconds at a time. You still don’t want to peg the throttle. That comes later… After tank 5 empties, put the piston at BDC and let it cool to ambient temps.
Tank 6 – 9
I normally keep it running through these 3 tanks of fuel. All the while leaning a little bit every tank. Make sure your temps are within the safe range. By tank 8, you should be able to hit WOT for short 2 second bursts. After tank 9 empties, put the piston at BDC and let it cool to ambient temps.
Tanks 10 on up
Keep an eye on the temps. Nitro engines don’t like to be held wide open for extended periods of time. They are built for high RPM’s, but can’t withstand them for too long without overheating or causing some damage. Putting your piston at BDC every time you shut it down will help prolong the life of the engine. Keeping the air filter clean will also help. Keep the temps above 210 and below 270 and your engine will reward you with a long life and as much power as it will give you. Also, if your going to store the vehicle for more than a couple days, a few drops of after run oil will help keep corrosion down and again, will help extend the life of the engine.
This is how I break mine in and I get typically over 9 gallons of life out of my engines.
