C36 intermittent overheating

[deeuutee]

1996 C36, 214xxx kms, engine rebuilt by previous owner 4 years ago, recent new water pump, thermostat, expansion tank and cap (6 months ago), hoses are in good condition and coolant level is normal.



Over the last week I have noticed sometimes the water temperature increases from the normal 80-85 range to up to 100. The last time this happened I was on the freeway and unable to pull over and then shortly after the needle went back down.


My initial thought was a faulty sender or guage, but I used an infra red thermometer to check the temperatures of the radiator and hoses and they seem to reflect the guage. There is a temperature difference between the top hoses and the bottom one, and both top hoses are similar.


The fans seem to be operating normally, and when the temperature rises the high speed kicks in.


So, this only happens sometimes, other times the temperature is in the normal range.


My usual mechanic is short staffed and I can't get in to him for three weeks, so I'm hoping for some insights from the forum members.