I have a 2001 Rodeo, 5 speed manual transmission. On startup the water temp rises quickly all the way to hot and the cools right back down and runs in the middle the rest of the time.
I have a friend who is a service writer for an Isuzu dealership who has taken a look at it. Cooling system is functioning properly. No air in the cooling system as they did a pressure test and put the car on angle and worked any air out that way. Did block test to see if exhaust was getting into the coolant which is inconclusive. He gave me back the truck today to drive it and see if there is any changes.
Immediately went hot and then cooled right back down. My fear is the head gasket is shot but curious if any other Rodeo owners have experienced a similar issue. A head gasket is not something I am comfortable doing myself.
I just bought this and really like it, hoping it will be something I can drive my 15 miles a day for a few years.