There is no exact match between these letters and an actual temp in C° as it also depends on the make and model but for a standard car, I mean not a racing car, you have something like C=30, N =85 to 95 and full H above 100. If the engine is equipped with an expansion bottle on the cooling circuit C could be up to 100 and H above 120. maybe someone else might have a better answer to your question. Hope it will help you. What car and engine are you asking for?
Hi hillman, Thanks for your reply. This is on my 1725 Rapier Fastback. When I first got the car the temp gauge ran around the N mark. Then I changed to just an additive (Penrite Classic coolant) and de-mineralised water. This had the effect of having a very clean system and the temp now sat at halfway between C and N. I thought this was pretty good but have been told it should run hotter than indicated. I had purchased a new thermometer bulb so decided to replace the original one. Now the car ran at halfway between N and H?? Wrong thermo bulb? I have another new one which I shall install and determine if the gauge still reads over N. Then I guess I'll start on the thermostat. The car does have a "recovery" bottle in the system. Trial and error ??
Hi, Changed the thermometer bulb this morning, went for a drive along the motorway and, guess what? the temperature sat on the N mark for the whole trip. So it looks like that has cured the problem of faulty readings and am most happy now. Thanks for your interest.