Ok so about Thursday of last week on the way to work my G35 Temperature gauge starting going up. Pulled over immediately and called a tow. Once I made it home I checked my coolant level which was completely dry. Refilled with some new coolant, made sure the air was out and took the car around the block a few times and the temperature gauge started climbing again after a while. Decided to leave the car alone and waited for Friday. Checked the coolant levels which did not seem to have decreased. So I'm not thinking it is a coolant leak. Decided to check the fans which I noticed then that they didn't seem to be running (although it could've been that I hadn't noticed them kicking on or giving them the chance to) I checked the fuses and relays. Decided to do another test drive and this time I noticed that the fans were running. This time the temperature gauge didn't climb up and I thought the car was fine. That was until Monday. Did some driving all day then by the end of the day thr temperature gauge started climbing up again. I've been looking at the car all day today. Fans are running fine. No coolant loss that I can see. I thought maybe the thermostat is bad, but coolant does seem to be circulating as I can feel the upper radiator hose is filling up so I'm assuming it is circulating. I tried to see if anymore air was in the system that may have been missed the first time. I'm literally at my wits end right now. If anyone has any ideas of what this could be. Please lmk. Thanks so much!

 

Did you check the lower hose? It should get hot as the car reaches operating temp.

 

If your thermostat stays closed it will get too hot rise above normal and overheat, if it stays open it won't get hot enough in the colder months for cabin heat. If you aren't loosing any coolant I would probably change the thermostat out since it's only a $20 part. They do fail, mine went out at 128k miles.

 

just checked it this morning and no it doesn't seem to be getting hot

 

yes I was thinking of it being the thermostat except those 2 days that I was able to drive with no issues kind of put me at a loss and those were about an hour drive each way

 

Change the thermostat, should fix the issue. A cold lower hose is a clear symptom of a failing thermostat

 

thanks I'll do that and see if that works

 

well went ahead changed out the thermostat after bleeding the system. Put in new coolant made sure I got all the air out. Tested the system. Lower radiator hose was heating up and then tonight same thing again. Car started overheating and lower radiator hose was not heating up again.

 

Gotta ask, was the thermostat oem? Or aftermarket? Many stories of thermostats not working right out the box if they are aftermarket.

 

it was an aftermarket from motorcraft one that I got from Autozone.

 

I would honestly get and oem one. Then go to the next troubleshooting step which might be a complete radiator flush

 

I went ahead and did a flush when I put in the new thermostat. Do you know where I'd be able to purchase an OEM thermostat? Also noticing that the reservoir tank is filling up more as well

 

Oem from the dealership, should be 30 bucks or so. Is the reservoir filling up after the car reaches operating temp?

 

Yes, it's filling up after reaching operating temp

 

Well that's nomal because coolant expands when it's hot so that's what the reservoir is for. To catch the expanding coolant that the radiator can't hold. Once it cools down the reservoir will get lower as the radiator sucks coolant back into itself.
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