I have a pair fo these motors on my rig. A couple months back, both were rinning hot only at low (below 1500) RPM's. Changed out Poppit Valves and 1 engine corrected. Of the remaining possibilities (water pump or T-stats) which is more likley to be the culprit, or is there something else to consider. When above 1500 RPM, the engine runs normal temp. per the temp. gauge.