My little truck has overheated twice in recent weeks. Both times in city traffic, which was pretty annoying. Last week I was spending so much time looking at my temp gauge that I drove thru two 40 KPH speed cameras at around 60 KPH, so am expecting two big fines in the mail anytime now. The cooling system has always been suspect, it had some sort of cooling system sealant in the radiator when I bought it that may have been related to the issues I'm noticing now, but I never had the temp gauge go higher than the middle mark, where it usually sits. What has happened a couple of times though, is after a long-ish drive in traffic, when I get it home, I could hear the coolant bubbling away, so flushed the cooling system and replaced the thermostat.
I replaced the MAF sensor a couple of months ago. I wasn't happy that while the picture on Ebay was of a genuine Mitsubishi MAF, the one I received was a chinese copy. Also, when I installed it, the car didn't run as smoothly. It was only after installing the MAF sensor that the overheating events happened, so even though I've bought a new water pump and radiator "just in case", yesterday I removed the MAF sensor, gave the old OEM sensor a clean and reinstalled it. It ran like crap initially, but after 10 minutes or so started running smoothly, and after 25 minutes or so was back to normal. I drove it to my local shopping centre on my way home and bought some Chinese food for lunch, and when I came out the little truck started right up and ran like a charm. I purposely drove it in slow moving traffic to see if it would overheat, but no, the temp gauge needle didn't move.
My theory (which could be completely wrong) is that the "new" crappy Chinese MAF sensor made the engine run too lean, which was the cause of the overheating. I could be wrong, but I'm hoping that I'm not. In a couple of days the temps will be double what they were yesterday, so will be a good opportunity to either prove, or disprove my theory, but the good thing is that if I'm wrong and I have a bad water pump or rad, I have them here to install. Hopefully they won't be necessary.