For the first time in my 2 years of owning "Bob the jeep" he has brokendown, recovered by the AA. Since changing a water pump approx 1000 miles ago he has not lost any coolant but has ran slightly above normal temp when travelling over 65-70mph. Then yesterday on the M1 having covered approx 60 miles the temp climbed a little more than usual about 2/3 before danger sector, I slowed down and the temp went back to just over 1/2. approx 20 miles later the temp started going up rapidly and I lost power gradually I pulled over and switched off, the temp just short of danger. My initial reaction was head gasket. I checked the oil cap and dip stick no sign of water both are normal. The expansion resevoir and rad were both still at normal levels, this was confusing. The AA patrol tested the water for exhaust gas, none were present. Following various other electrical checks he diagnosed a possible injection problem, making Bob run weak and causing hotter running before finally packing up.
Has anyone experienced similar and can possibly identify what the failed component maybe?
What sort of mileage do head gaskets do?
All the belts are relatively new and well adjusted, timing belt was replaced at last service along with plugs (NGK), air filter, and I change oil every 5k. Current mileage is 86k
Any help would be appreciated.