No Heat .. Sometimes?

[jeffdemara]

When the car is cold and started up, you can hear the coolant flowing through the heater core.. and once the engine is warm heat starts coming out fine. However, when the engine is warm, and you turn it off and come back to it 5-10 min later and start it up again, it wont blow hot air.

Also, when the engine is hot, the upper rad hose is not hot and has no pressure when you squeeze it. I have replaced the rad cap and it has not made a difference. I tried to do a coolant flush, and the car would only take about 3-4 liters of coolant, so i put the cap on and let it run, and it started overflowing out of the reserve resevoir.

Wondering if I need a new thermostat or maybe a water pump?
The engine seems to stay right in the middle of the H and C mark on the temp gauge, and doesnt overheat.

On another note, the cruise control only seems to turn off and on within the first few minutes of the engine being first started when cold. Would anybody know if it is due to a vacuum problem? Not too sure what the problem could be.

Any help would or suggestions would be appreciated.
Thanks!!

 

[Quin]

The only reason I can think of that explains the cold rad house is a thermostat that's stuck closed.

Have you or a previous owned bypassed the VSV? That kind of sounds like what you're describing, as far as the heat is concerned.

 

[Dan_Gyoba]

The automatic climate control will not turn on the fan until the coolant in the heater core is above a certain temperature. Not sure what that temperature is, but when my VSV failed, the system wouldn't turn on the fan, let alone get heat out of the system.

You can check if the VSV is working by cranking the heat all the way to the top, and looking at the valve position when the car is off vs when it's running. When it's off (No vacuum) the valve will be closed. When running it should be open. (I have the Merceded Benz VSV in my car currently.)

If the valve is opening, this means one of 2 things.

1. Your heater core is full of air, not coolant.

2. Your heater hose lines are blocked, so the coolant isn't circulating through the heater core.

In the first case, this is a bad thing, and you need to purge the system of air.

In the second case, you need to determine where the block is, and remove it.

By the way, you should not be able to hear coolant flowing though the heater core. This means that you've definitely got air in the cooling system. If the system is full, there should not be any audible noise from the coolant passing through it, so you need to take care of this first.

 

[jeffdemara]

Will do, I am about to change the thermostat and bleed all the air out. It would not cycle through last time i tried so hopefully its the thermostat.

Thanks for your help ill let you know if it works out or not.

 

[shaeff]

check your heater valve. probably the most common problem is that it gets stuck closed because of a bad vacuum source, no vacuum, or the diaphragm is ripped. it's located on the passenger's side of the firewall. here's a pic:



and at the end of this arrow is the plunger for it. pull it up and secure it in that position. if you get consistent heat, that was the problem.

 

[jeffdemara]

i checked that heater valve, it seemed to work okay, lots of vacuum. when i pulled the hose off, it would close, and open again when i put the hose back on. i just put in a new 192 degree thermostat and now there is pressure in the upper rad hose.

 

[IJ.]

Sometimes the CC fries an amplifier and won't let the heater door open so even if the VSV is open and the Heater core is full of hot water you still don't get heat.

 

[jeffdemara]

i attempted to do a coolant flush, and topped it all up etc... i dont believe it took 8.7qts and when i start the car when cold, i still hear coolant rushing through the heater core for about 30 seconds.

thermostat is replaced, rad cap is replaced.