UK Car Repair: Temp guage, temp guage, temp gauge

Question
Christian.  I have a 1988 escort gl. 1.9. while under normal driving the temp gauge works fine. i deliver newspapers at night and there is a lot of stop and go and slow speeds. ive noticed that the temp gauge will spike all the way to hot for a split second, the electric fan kicks in and the temp drops to mid normal level just as fast. the gauge only stays at hot for a second then drops. this is a sporadic issue. i have noticed in listening to the engine that the fan doesnt always kick on. this is when the temp gauge shoots to hot. there is no sluggish to the engine or hesitation while the temp is at hot. Fluid level is fine. My question is what may be the issue? the thermal switch, temp sensor or something else. i am a novice when it comes to engines. I can check electrical issues and some other minor things. Thank You in advance for any help you may be able to give me. Tom.

Answer
Change the temp sender £7 or so.



if it really is a second the temp spikes then its electrical, the coolant really cant get hot like that so fast, unless the water pump is failing, then it can spike... check the temp of the pipes on either side of the radiator and if theres a greart difference between the temps then change the water pump £35-£70 (scrap/ford), do the thermostat at the same time as part of good practice £6.