Sudden surge on engine temp gauge to 260 then back down - Cause?

I've got a slow leak in my coolant hoses which requires me to top off the coolant levels every week (Until I can get it fixed). I've noticed the engine to be running slightly hotter than 210 on average even though its 20-30 degrees here in the Boston area. This morning I refilled the coolant bottle, started up my car and went back inside for

5 minutes while the car warmed up. When I started driving the car I noticed the temp gauge to be between the 210 and 260 mark. Since the engine showed no signs of overheating I was puzzled. All of a sudden the temp gauge surged to 260 and the "Check engine Light" came on. I pulled over and waited for the steam to come pouring out of the engine, which never happened. The funny thing was all the fans were working. I turned off the car, let it sit for a while and turned it back on. When the engine warmed up it was back to 210 again and showed no signs of moving above that.

What could be the cause? Clogged lines?

97 Cherokee Sport 4 x 4.

You are describing a set of valve guide seals getting cooked due to being steam baked. I personally have turned a perfect engine into a bad oil burner that way and have seen others do it too.... Idiot light instead of gauge eh...

When you have a 'small' leak, the coolant goes into the overflow bottle like normal, but when you shut it off, it is easier for it to suck air through the leak that to suck coolant up from the overflow bottle so your engine top or head gets full of air.

You need to fill it from the radiator cap, not the overflow.

This air bubble turns to steam and spikes the temperature sender that sits in the head area or at the top of the engine somewhere until the thermostat opens and coolant starts flowing which will make the temp gauge go lower.

Eventually this steam will also kill the thermostat too usually. On my CJ7 that sprouted a small air leak last summer, it blew my thermostat into fail-safe open mode. I at the time knew what happened so shut it down quick and got fluid into the 'radiator' saving my valve guide seals.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >