Hey guys. I'm looking for some input as to what could be causing my car to never fully warm up and periodically overheat. The heating system never seems to blow enough air to adequatly heat the car up and everyonce in a while when driving it completely overheats. We bled the coolant twice and replaced a thermostat to no avail, so two nights ago I took it to Mr. Lube to do a coolant flush. The car began to overheat the next day, so I dropped it off at Mr. Lube who bled the system even more. It was blowing hot at idle when I left the shop, but after letting my car sit it began to blow cold air at idle again. This morning I took it to Mr. Lubes warranty shop that was going to bleed the system even more, but on the way the car overheated and was towed there. They bled it following the Nissan FSM, and although the car seems to blow warmer air now, it's still not hot inside. My old blew much hotter, along with almost any other car I'm in. I'm wondering if my heater core may need to be flushed. The car has a new thermostat. new coolant andhas been bled by a shop/Mr Lube a total of three times now. What's next? Does the heater core need to be flushed? If so, is it an east DIY? Sorry for the long post, I just wanted to make sure you had all the info.

 

Your first mistake was taking your car to a place called Mr. Lube, IDK, lol!

Honestly sounds like air in your cooling system or not bled correctly, cooling systems are very fickle.

 

Thanks for the reply. I would have prefered to take it elsewhere, but the car was overheating so I took it where I could get it in right away. The shop guarunteed there was no air in the system, so I'm wondering what's next?

 

You might have a screwed up "new" thermostat. I'd take it out, throw it in a pot of water on your stove along with a high-temp thermometer, and bring it to a boil to see if the thermostat opens at the appropriate temperature, and then if it closes again at the appropriate temperature. Test it a few times and replace it with another new one if necessary(or exchange it if they'll let you)... you may have just gotten a defective unit.

How old/dirty was your coolant when they changed it? Did they put in red or green coolant? if they put in red, it might have mixed with the OEM green coolant... and when that happens, your car is pretty much screwed. When you mix red and green coolant, it gums up and forms a nasty crystal-like substance that blocks coolant passageways in the system. If this happened, you could be having a situation where chunks of that crystallized coolant are breaking off and temporarily blocking the passage of coolant to certain areas of the car...which would explain the erratic not-heating up, and overheating problem.

 

I could always check the new thermostat, but the same issue was occuribg with the old one in the car. I've watched all of the flushes and bleeding sessions first hand and the coolant was all green. I couldn't tell you how old it was. I bought the car at 61000 miles and now it's at 68000. I could dig through the maintenance records for you.

 

Oh.. hey.. I just thought of something else. There is a warranty issue with the radiator fan on our cars not turning on in some cases due to hardware failure of the fan assembly. They extended the factory warranty on this particular item from 60K to 100K miles because they were failing and causing a lot of 2003-2007 G35 Coupes to overheat when the fans failed in warm temperature environments when the car wasn't moving very fast. This doesn't explain why your car would take a long time to warm up, but it is something to consider after all else fails and you still can't find the problem.

 

Thanks for another response, but I've checked both fans and they're running normally. The shop disconnected the inline coolant heater, as they said it could be causing the car to overheat due to a restriction of coolant flow, but I won't know if that made a difference for a few days. I'm mainly concerned with the lack of cabin heat at this point.