Ahhhh I almost blew my engine by accident but the NHC250 seems tough. First I tightened the thread on the coolant reservoir cap, which is what probably saved me from blowing the head gasket.
Since I used to make special race fuel mixtures with my bike when I raced a little bit back in the days, I proceeded to see what worked or did not in the NHC. It seemed to run smoother on oil and start better with marvel and tranny fluid. So, I thought, what about some aircraft 5W level grade turbine oil?
Big Mistake.
This stuff is synthetic and had a purplish color, and it does NOT combust. It is more like hydraulic fluid. Result is that I did not notice that I my engine was almost hydrolocking. I am going over a bridge uphill and man was the truck going, she was like accelerating whereas before she would just slow down to 35 mph struggling. I think that the higher compression resulting gave it a few horsepowers.
Then I stop at a kerosene station to fill her up and it is when I started sweating balls. I cranked her back up and she went half a crank and stoped cranking, completely locked in. Once I let go of the start switch she all of a sudden cranked over and started with just one that one crank. I assume some of the cylinder blow by space might have saved it from complete lock in. The exhaust gave out this strange and possibly toxic wettish mist too. Yikes.
Since I added kerosene mixed with some Howes lubricant at the station, I did not have a repeat of that half crank once I got back home. I had coolant leaking out my water pump though but nothing indicating the gasket was blown since then. I gave been checking the oil for 2 weeks and no water nor overfill signs there and she is back to her old ways since then. The leak at the fuel pump shaft stopped too. I might change it, though.
In any case, I found a way to boost the engine compression accidentally, albeit at the risk of blowing my engine. I think I put 3 quarts of that turbine oil for about 10-15 gals of diesel. I changed the fuel filter since then.