I know this is probably the millionth thread about this topic, but I have a lot of specific things to explain about this one. So a bit of backstory:

Got the car (06 G35, completely stock) with my dad from a guy I met on Facebook marketplace (this was my first car). Its been running PERFECTLY for 2 years now, sitting at around 100k miles. Only minor issues, had to replace a few old parts, camshaft sensor went bad, etc. But recently in the past month it started overheating. yay.... Noticed it got all the way up to the H when I was driving home from work one day. We came to the conclusion that it was the head gasket, and I don't have a lot of money so I decided to do head gasket sealant, the car wasn't blowing white smoke out of the exhaust and still isn't to this day, but the sealant actually fixed the problem for about a month and a half. Fast forward to about a week ago, its overheating again. Still no white smoke. Tried the sealant again, didn't fix it (obviously). I've rea d some threads that I could've possibly clogged my heater core with the sealant? I don't know if that would cause the overheating? So my question is:

What could possibly be wrong with it? I've never heard of situations where there is no white smoke coming out of the exhaust and the head gasket / heads / engine block is cracked / blown. (But if I'm wrong about that please correct me) I am new to all of this as this is my first car, so if anyone could explain the possibilities of what could be wrong I would really appreciate it!

 

You need to pressure test it.
Could be a hose clamp issue.

 

How did you come to the conclusion it was the head gasket? Did you do a leak down test, radiator pressure test, compression test, or block test? Did it overheat while actually driving or when you were stopped at a light or something?

 

Ok..take it easy on the guy.
He came to that conclusion, because every other clown says it is the head gasket..usually homeless guys and guys with more money than brains...same thing...only homeless guys are smarter.

Also when our **** is not working we all tend to "awefulize" until we train ourselves out of the hardwired fight or flight response.

Let's give him a plan of attack on this problem and train him to be the thinking aggressor.

 

Look up "combustion leak tester" it's a two part deal, first you put the dye solution into the little test bottle. Then use a turkey baster or siphon/pump to suck out some of the coolant in the radiator.

Next put the combustion leak tester bottle solidly onto the radiator while the engine is running and there's a little squeeze pump at the top that you use to suck air from the radiator for the next minute.

The dye will turn color if there is exhaust gas present in the coolant. It's a pretty simple device and only costs like $25-$35 if you get the cheapo Harbor Freight one which works fine.

You can test which color the coolant will change but taking the tester over to the exhaust pipe and sucking air from right near the exhaust.

This is a pretty basic but QUICK, EASY, AND CHEAP way to test for an obviously blown HG. Alternately you can do a leakdown (or do one if it passes the combustion gas test) which requires the leakdown gauge and an air compressor and a little more mechanical knowhow.

 

Just to add to the above...pay close attention to taking out a decent amount of coolant from the radiator, because your kit is going to act as a overflow tank, and you don't want it taking up coolant, just the gasses in the coolant.

888888
If it doesn't indicate a possible head gasket leak, you need to pressure test the system to look for a leak somewhere else, like the radiator, hoses or a clamp.

Also you can run the motor with the hood up, until the motor comes to temperature and then listen for gurgling or hissing after you shut her off. That means you are taking air into the system. Get your ear in under the hood.