Thermostat Replaced...Now what?

[vdesigner99]

My tale of overheating Fiat". This is a compilation of my overheating problem, how I tackled it, the time and money I spent and of course a good conclusion. It started a short time after I bought her, she had 120k miles but in fairly great shape. I noticed coolant beads on the upper radiator welds.
I kept an eye on it but she ran fairly cool, normal for a year. Well three months ago I took her out on a short run and smelled the sweet smell of coolant and of course noticed the temp gauge redlining. Luckily I was several blocks from home. Yep the radiator had finally burst. I wasn’t too worried I knew it was time for it to be repaired or replaced. I scanned the web for replacements and of course called a local rad shop for an estimate. I decided on a new aftermarket one from VAS, not original but new. While I was at it I might as well replace the thermostat and hoses and add a new 14” fan. The pump seemed OK and I also the added a t-fitting to the heater supply line. The install was easy and straight forward. I have owned a 77’ 124 many years ago and had done much work on it, even rebuilding the motor so I wasn’t new to this. I added the coolant she overheated, OK what’s up? I noticed that the fan didn’t come on. Oh boy is the fan faulty? I added power to the fan but it came on, OK it’s not the fan. Next several days I scanned all over this forum, “heating”, “thermostat” and “radiator” topics to find answers. I also pinged my local Fiat club. It all pointed to the burping process. So for additional weeks I tried this over and over, several trips to Auto Zone for more coolant. I added coolant from the new t-fitting, the t-fitting near the radiator, the lower rad hose and the preheater, raised front end etc. I even decided to change out the rad switch just in case. Still over heated. But once in a while she ran OK and the fan came on. Next day overheat again, over heat and reservoir filled and bubbling. OK I’ll change out the pump, what the hell everything related to this is new anyways. While I was waiting on the pump I tried the burping one more time. I was adding coolant to the heater-t and noticed that it kept taking more and more water, never filling up, but wait the reservoir was filling up? Is this normal? Isn’t there a pressure plunger on the rad cap that restricts the hose unless over pressure is applied? I assume it should only open to allow fluid to escape to the reservoir only after a certain pressure? I compared the new cap from VAS to my original one. Of course they were similar but maybe not. I did notice that the new cap had less resistance to compressing the spring. Same 1” length but different pressure tolerance maybe it’s not seating correctly? I pinched off the hose with v-grips and filled the heater t-fitting till over flowed. Seems ok, ran car, eureka no over-heating, fan turned and temp gauge registered back down to below 90! I tried this for several more times on different days with no problems and same good results. Finally had confidence to drive further distances in fear of being stranded. I replaced the new cap with my original and that’s where I am now. All this time and it was the radiator cap, at least that what I concluded. I have a new pump that I will use one day but for now I’m cool!

Hope this was informative.
Stay Cool!
Victor