My heat stopped working. It runs hot driving over 30mph. Cools down at idle. No leaks. Replaced thermostat. What's wrong?

 

Did you replace with oem thermostat?? If so if you have drive up ramps or the ability to get the front end up a little turn car on heat on high with rad cap off you may have to blueprint system. It might have air pocket in it. A little more info and we might be able to help more.

 

Blurp the system

 

Yes. I installed an oem thermostat. At idle it was great. The fans come on perfectly. Driving at 30mph the fans are on but the temperature gauge goes up. It noticed the coolant in the reservoir had some bubbling. Also, my heat doesn't work.

 

Blueprint the system? Burp the system? Raise front end with radiator cap off and what's next?

 

next is to start your thread titles with a much more descriptive title. It will help the right people help you.

other than that, be more descriptive in your problem, there are two different heating units in these cars etc. etc.

 

thanks prophecy99

 

if the coolant reservoir is bubbling but you bled the system, your headgasket is probably blown and throwing combustion gas into your radiator. bleed the system again, if youre still constantly getting air i would look towards HG

 

Exactly how do u bleed the system?

 

Raise the front end up 6 to 12 inches.
Remove radiator cap (while engine is cold)
Start engine and allow to run so that thermostat opens and coolant circulates
Allow to run for another minute to allow air to escape
Fill radiator to the top and put radiator cap on
Lower car.
Check level in over flow tank and correct if needed
Go wash your hands and have a cool beverage of your choice.

 

heater full blast hot, rad cap off, fill rad with coolant, run engine at 3000rpm and top off the coolant in the radiator until the coolant gauge goes halfway like normal on the cluster or the radiator fans come on and air quits bubbling to the rad. put cap back on, thats it

only car ive worked on that needed the front end jacked up was some POS Ford Taurus and those things are a pain to bleed anyways

 

The FSM for some reason says to leave the rad cap on when bleeding the system but that goes against common sense. Air pockets need a place to rise and escape from. So like others said, leave the cap off. Before taking the rad cap off, turn the key to the run position, set the heater to 90 and AC and other accessories off. The blower always is on with these cars. Let the heat run for 10 sec or so then turn it off. The point of this is to allow coolant to circulate through the heater core so any air can be subsequently bled out. Then turn off the car, go take the rad cap off and start the bleeding procedure. Start the car, bring it up to operating temp and then race the engine to 2500 RPM for 10 sec several times. This will kick on the cooling fans faster. Keep an eye on the temp gauge and top off coolant as needed. Boom, you're now done.

 

Engine coolant always flows through the heater core regardless of how you set the controls. The 1994 Maxima was the last year to use a coolant cutoff valve.