348 Odd Overheating Problem

All's well that ends well, glad it worked out for you.

 

I have exact the same problem as you had. I will start with checking the Radiators Fans if are working properly

 

Hi very interesting threads on Ferrari 348 running hot! I am over in the UK I had a 308 GTBi for a couple of years and earlier this year I picked up a 32,000 mile 348ts Which is a lovely car but over the last few weeks it started to get a bit hot, After taking the R/H rear arch liner out i noticed a small leak along the top of the radiator, I removed the radiator and took it to a local radiator repair shop who did a repair then leak tested and pressure tested it all for £50. My next step was to fit new water temp and oil temp sensors on the radiator, Then fit two new coolant temp sensors and the temp gauge temp sensor which is in between both coolant temp sensors, I fitted a new thermostat then refilled the system with both bleed screws open until I got coolant coming out, I had also noticed an E5 error code on my heater display so I stripped out the luggage bay around the bulkhead and removed the Bosch motor and heater valve, these I took into work and gave to one of our bench electronics engineers and he took the Bosch unit apart cleaned it and tested it and is all ok he said I found the heater valve a little stiff this was lubed and now works freely, I refitted this today and I am glad to say it opened and let the coolant through so I fired the car up with the heaters now working and no E5 code it did not take long to bleed the system, A quick test drive and the car was faultless the needle pointed just below the middle mark and when I left the car stationary just on tick over the fans were cutting in and out which was a joy to hear so I now have a 348 that does not overheat, Thanks to this great forum and tips it was quite an enjoyable task which would have cost a small fortune at a main agents.

 

Sorry I haven't read all of the replies but I thought I would chime in I had a similar problem with my reply older 328. 1st of all I recommend you go to Harbor freight and get an inexpensive infrared thermometer that way you can check each radiator each cylinder head water jacket and even the coolant tank for correct accurate temperatures you can't always trust that your gauge on your - is not off. And finally what I wound up doing is I took the thermostat and removed the "disk" or gits which gives it some restriction but allows the water to flow freely in other words making the thermostat think that it's open all the time I know this isn't the greatest but it solved my problem.

 

I'd recommend you examine # 13 on the same diagram. On my '95 355 these hoses looked fine on the outside, but checking past the nipple connector, they were almost closed from age/swelling, not from sediment.
Slicing it open mid length confirmed the problem and they're easy enough to replace and that greatly helped cooling.