I have just purchased a 03 350.... had it for a week and everything has been great. Just got in this morning and noticed it was over heating before I could get 5 miles down the road.... heat was first blowing out of vent cold and then started to heat up after I turned to full blast. It’s 3 days before my son receives his Christmas gift/ dream car, and all the shops in small town USA are closed. Any idea where I can start? I know nothing about this motor....

 

Go touch radiator hoses. Is one hot and one cold?

Could be as easy as a thermostat

 

lower is warm, upper is cold

 

My best guess is that the thermostat is stuck. You can test it by taking it out and put it in boiling water to see if it opens.....or just replace it

 

That's strange given the fact that, IIRC, the coolant flows from the block, through the upper hose, through the radiator, then back through the lower hoses to the thermo/block. The upper hose should be hot and the bottom cold, not the opposite .

Do you have an OBD2 scanner with live data capability to monitor coolant temps? Or is an Advance Auto Parts or Autozone near you to rent one?

 

So, double checked coolant levels and went around the bypass (stop and go for about 15mils) and no issues, normal temps.... ugh

 

if working normally now, then sounds like thermostat.

I'd make sure the fans turn on when it gets too hot

 

How many miles are on the car and how well do you know it's maintenance history?

If the thermostat has never been replaced then you could swap it out just to see if it fixes the problem / rule it out.

I'm sure your local Nissan dealership will be open on Thursday. The swap is easy and you could definitely have it done in about 2 hours.

 

140k was one owner, fella had it til his 30s. He’s upgraded some parts (fly wheel, clutch, intake, etc) so I’ve only assumed he’s kept regular maintenance per his word. I’ll probably take around the block few more times just to keep eye on it and go ahead and start small with the thermostat. I can hear the fans on when I come to park. Did notice the air will fluctuate between hot and cold even though I got temp set to hot.... this just plain baffles me. My first 350, and just wanting to make sure son don’t have a ton of work to since he has to drive it back 3.5 hrs home...

 

Thermostat is on the block, so if it's not opening, no hot water will be in the upper hose.

Does the hot/cold air temp fluctuate with RPMs? If so, and it's warmer with higher (2k+) RPMs, you also likely have air in the coolant system.

 

He mentioned in his first response to Travlee that the bottom hose is hot and the top hose is cold. That goes against the flow of the coolant through the radiator. A thermostat that is stuck closed should display symptoms of a hot upper hose and a cool lower hose if coolant is even entering the radiator.

 

Brain fart... Yeah, for some reason I had in my head the thermostat in the upper hose.

Yeah, that's odd.

 

It's all good. You had me questioning myself there for a bit! Haha

 

replace the thermostat. if it stuck once. it will do it again.
if you are diligently watching the temp gauge its a quick way to blow a head gasket.

cheap swap. or just remove it.

 

It only takes a few minutes of distraction for that needle to shoot through the roof. I'd rather replace a thermostat than an engine any day. Much cheaper and easier.

OP, do you have any further updates?

 

Also could easily have an air pocket from prior work.

 

mid the car went back to normal temps as I saw back on your edit, and if the overheating is Intermittent(meaning off and on) you definitely need to replace your thermostat. You also need to keep in mind if the heat is on etc. causing it to overheat when on and not when off, then you could be chasing down some other issues, but this definitely sounds like a thermostat issue, especially with the heat blowing comd
temporarily. Hope this helps! Good luck!