I have a 2001 Montana with the 3.4L engine. I replaced the head gaskets and the van is running fine except for it doesn't have much heat coming from the vents. The temp gauge is also reading very low. I forgot to add coolant to the engine before I first started it up so the system was quite low, but not so low it overheated.
Can air still be in the system? I have bled the system, but to no avail. What is the proper method for bleeding the cooling system?
If I leave it idling it will come up to temperature, but when I start driving, the temp goes back down and cool air comes from the vent again.
I am also getting a code for the knock sensor. Can this be associated with the heating issue?
Many Thanks for the help,
Ian
You could still have air in the system....but, did you replace the thermostat when you did the head gaskets? Did you do them yourself? So, you replaced the head AND lower and upper intake gaskets, right? Just trying to get a better picture.
The best way I have found to bleed the system from experience on all of these motors (3.1, 3.4, 3.8) is as follows:
Put your heater control to cold. Once you are ready to fill the cooling system, remove the brass vent from the heater bypass pipe. It`s the metal pipe running across the front/top of the motor. The brass plug is screwed in to this pipe above the water pump. Pour your coolant mixture into the rad slowly. Also fill the coolant resevoir to the 'Max' level. Once the rad seems full, squeeze the upper and lower rad hoses gently a few times to help 'burp' the system. Add more coolant...burp again until ONLY COOLANT comes out of the vent. Replace the brass plug. Now, continue trying to burp the sytem squeezing and releasing the hoses until you cannot put anymore coolant in the rad. Start the van and run for 10 seconds. Add coolant as necessary. Repeat once. Now, start the van and let it idle with the rad cap off. Squeeze and release the upper hose several times during the next couple of minutes. Add coolant as necessary. Replace the rad cap. Now, raise the idle speed to around 2500 RPMs by using the throttle on the throttlebody in the engine for about 20 seconds. Check the temp gage. Keep doing this until the temp gage begins to rise. Check the upper rad hose for heat. If it`s not hot, the thermostat has not opened yet. Raise the idle again for 20 seconds, then loosen BUT DO NOT REMOVE the rad cap to allow air to escape. You should see bubbling in the overflow bottle. Tighten the cap again. Repeat this step until 1: the upper rad hose is hot, and 2, there are no more bubbles comming out in the overflow. Now, if the upper hose is hot, raise the idle again with one hand on that upper hose for about 30 seconds. You should feel it collapse slightly while revving the motor a bit. This will cause the system to 'suck' in coolant from the resevoir. Add coolant to the resevoir as needed.
Finally, you will know when the system is free of air when the rad cap is hot. If not, theres still some air in the system. This should eventually come out on it`s own or you can carefully loosen but DO NOT REMOVE the rad cap to allow more air to escape. ALLWAYS WEAR GLOVES AND EYE PROTECTION!
Check heater function.
Just so you know, I`ve done the head and lower intakes on 8 GM vehicles so far including a Transport and Montana, as well as several rads and heater cores on these vehicles and this seems to be the best way I`ve found.
There may be other ways too. This isn`t the ONLY way.
Let me know.
Ian
