overheating when at highway speeds

check your compression first on those two cylinders and see if they are low . for the overheat problem, after your rv is warm/hot, shut motor off and check rad for coldspots. if it has them thenthe rad needs to beredone, it should be the same temp all over. as far as stuff for sealing head gaskets/cracks , it will also seal up rad and heater cores.

WHAT IS MEANT BY DOING THE RADIATOR IS TO REMOVE IT/ HAVE IT REMOVED AND PROFESSIONALLY TAKEN APART, "BATHED", AND THE VANES RODDED OUT.........IF THIS IS AN ORIGINAL PART, WITH ITS AGE, YOUR RIG MAY DESERVE A BRAND NEW ONE. DEPOSITS AND BUILD-UP ADHERE TO THE INSIDES OF A RADIATOR AND IT'S ABILITY TO RADIATE IT'S HEAT TO THE OUTSIDE AIR IS DIMINISHED GREATLY. A OLD RADIATOR IS ALSO MORE LIKELY TO SPRING LEAKS DUE TO CORROSION AND BREAKDOWN OF THE MATERIALS USED TO CONSTRUCT IT.

AUTO PARTS STORE "MIRICLE" COOLING SYSTEM FLUSHES WILL NOT PUT A DENT IN SOMETHING THAT IS TERRIBLY CAKED UP WITHIN

THERE ARE SEVERAL OTHER POSSIBILITIES THAT MAY BE EZ TO FIX, AND COULD HAVE BEEN OVERLOOKED.....WITHOUT TEARING INTO YOUR ENGINE WITH EXPLORATORY SURGERY

TWO THAT SOMETIMES ARE OVERLOOKED ARE

A RADIATOR HOSE, WITHOUT AN ANTI-COLLAPSE SPRING, S.UCKING FLAT DUE TO WATER PUMP SUCTION (USUALLY THE LOWER ONE) IT MAY ONLY DO IT AT HIGHER RPMs......BASICALLY WATER CANNOT CIRCULATE TO THE RADIATOR TO BE COOLED

ANOTHER IS IF YOU HAVE A MECHANICALLY DRIVEN COOLING FAN, THE FAN CLUTCH MAY BE MESSED UP AND THE FAN CLUTCH "SLIPS", IN TURN, THE FAN DOES NOT SPIN AT CORRECT SPEEDS TO DRAW AIRFLOW THRU THE RADIATOR.

JUST THOUGHT I MIGHT THROW IN SOME STUFF THAT MAY HAVE BEEN OVERLOOKED ON YOUR END

THE MEDIC