Burping Problem

[Switchrider]

1996 LT1- I am sure someone else has had this problem. I replaced the thermostat and coolant and now cannot get good coolant flow through the heater core. Followed all of the proper procedures as described in the Factory service manual even tried to jack up the front and get the radiator up in the air above the thermo. Tried the air bleed etc. Only heat I get is when the car sits and idles for a while but turn on the fan and she soon gets cold. No overheating issues just no heat!

[maxwedge]

Welcome to AF. Let it sit overnite with th cap off, try jacking the ftont up, I assume you felt both hoses and one is not hot to the heater, no water control valve on this right?

[tractorboy]

what does your temp guage read durring this. There is some wax sticks that you can get that will melt at diff temps. You make a line on the thermo housing and it will melt when the thermo opens. So you can check the system out So you are not getting hot air in the car compartment ? what about a duct door not closing or opening / blocked heater core .

[Switchrider]

There is no control valve. There should not be a problem with a control door because this started right after the coolant change (Only change). Car runs with the gauge at normal and the electric fan runs with the car idling and the air on when it gets hot. I just can't get the coolant to burp through the heatrer core.

[tractorboy]

...so you think there is a bubble ? I use that term because I use to work for a company that we drove 4 cylinder dodge caravans. There were 8 of us and we all had basically the same . I am sure that the head gasket was leaking into the cooling. The dealerships reply was " it had a bubble " ... you could take the rad cap off ,start the van and see the bubbles in the coolant.

[Blue Bowtie]

LT1/4s are notorious for air entrapment. I had to raise the front of mine and start it that way, bleeders open, then let it cool, refill, restart and warm up, etc.

Make sure the small coolant return line is unobstructed and flowing coolant, and that coolant is flowing through the throttle body passage. Those are about the only paths for air in the heads to escape.

[tractorboy]

air entrapment

How do you know if you have air trapped in the enginge block or where ever. Wouldn't the fact that the cooling system gets pressurized push the bubble to the rad or would the bubble get pushed around inside the cooling system. ? I just changed the coolant in a 3.4L LA1.
It was supposed to hold 11 quarts, only about 8 - 9 came out. I drained the rad and took out the bolt in the block to drain the block. I refilled and only about the same amount went back in. I used the bleeders as describbed in the factory manual. Was there still a few quarts left somewhere or do i have a bubble ? heater works fine, temp guage shows between 180 to around 200 degrees.

[wtousand]

Originally Posted by Switchrider

1996 LT1- I am sure someone else has had this problem. I replaced the thermostat and coolant and now cannot get good coolant flow through the heater core. Followed all of the proper procedures as described in the Factory service manual even tried to jack up the front and get the radiator up in the air above the thermo. Tried the air bleed etc. Only heat I get is when the car sits and idles for a while but turn on the fan and she soon gets cold. No overheating issues just no heat!

Usually driving a car for a bit gets rid of any air, so that is not likely the problem. The temporarily trapped air is a shop-handoff-to-a-customer problem more than anything. A radiator can suddenly appear low as the customer gets home.

If you haven't gotten it fixed by now, it sounds like you may have flushed the system (or caused debris to break loose anyway). What happens is that people often flush their systems which loosens scale etc and it immediately flows to the heater core where it plugs it partially up. So the commendable attempt at good service practice ends up making things worse. Note that flush kit directions often say to hook to the heater inlet hose. Doesn't do a darn bit of good cleaning the core out.

The heater core acts like a filter in the cooling system, sometimes a plugged filter. The clue is that there is so little water flow that any air increase quickly cools the air to cold.

A TEST: When the air flow is off, you should feel both heater inlet and outlet as the same water temp. But when the blower is turned on high, the outlet will be noticably cooler to the touch because all the heat is sucked out of the meager trickle. A correctly working system has very little in-out difference to the touch with the blower on high, almost indiscernible.

The solution is to back-flush the heater core. If you catch the back-flush in a bucket, you will be surprised at the amount of gunk that comes from it. The inlet to the heater core is usually a hose from the top of the engine. The heater hose that goes to the water pump is usually the heater outlet. You would want to force garden hose water backwards up the outlet hose. If in doubt, flush both ways.

Unfortunately, a clean heater core flows fast again, good for heat output, but bad for debris. New debris gets there extra quick because of the increased flow. So it would be a good time to flush the motor again with these hoses off and let loose debris hit the ground.

There is also a possibilty of having knocked a vacuum line off a heater water flow control which would also restrict flow but the plugged core scenario is the most likely problem.

Hope this helps someone.