Expert: Roland Finston - 2/6/2012

Question
QUESTION: 1998 Cirrus 2.5L V6

Found a small leak at one of the original heater hoses at the engine outlet so I replaced both the hoses and flushed out the heater core. Before replacing hoses a noticed neither of the hoses was getting hot (or warm) as the engine reached operating temp. I suspected the heater core may have been clogged.

Now after completing the new hose install I find there is still no circulation in the heater hoses - they are not warming up as the engine reaches operating temp. Also the upper radiator hose is hot (after the thermostat opens) but the bottom hose remains cool.

I see no signs of coolant leakage anywhere. The water pump/drive belt were replaced about 12,000 mi ago ( less than 18 months ago). Could it  fail already? No leakage from seals or noise though.

Related to my hose replacement: when I restarted the vehicle I seem to have lost the power to my brakes. I don't believe I disconnected anything brake related when I removed the Intake Plenum.

Help!

ANSWER: Hi Gary,
I would suspect that your heater core is clogged. So try to backflush it with water from a garden hose connected to the domestic water supply. On the brakes, I suspect that the vacuum line to the power brake canister is not attached tightly to the intake manifold.
Roland

---------- FOLLOW-UP ----------

QUESTION: As I noted in my question I have back flushed the heater core when I replaced the heater hoses. I flushed several times to produce a steady clean flow. The initial flush did really produced any debris, just some discolored coolant.

So I'm baffled why I can't get circulation. Any thoughts on why the bottom radiator hose isn't warming up when the top hose is very hot.

Thanks for the suggestion on the vacuum line, it was not reinstalled when I reattached the intake plenum.

ANSWER: The bottom radiator hose is the outflow so that would suggest that your radiator core flow is impaired (if the engine is also running hot) or that the radiator is very "open" and doing a good job. As both the inlet and outlet hoses are on one side of the radiator you should find that the other side's 'tank' is also somewhat warm, and if not then the flow is indeed impaired. That would reduce the circulation in the system and might well explain the lack of flow through the heater core or alternatively you might simply have air trapped in the heater core. Be sure the radiator is full and the overflow bottle is at the 'full' line. Also run the vehicle and cool it down several times to allow any trapped air to be driven out of the system.          
Roland

---------- FOLLOW-UP ----------

QUESTION: re: "you should find that the other side's 'tank' is also somewhat warm"

I'm not following what you mean by this.

This morning I will follow your suggested procedure for removing trapped air in the system. I'll be back to you if this can'y cure the problem.

Answer
The flow in the radiator is from the side with the hoses to the far side and then back, in a sideways U pattern. If the radiator is partially blocked the far side will be fairly cool compared to the income/outgo side. If the flow is good, the two sides will be more comparable in temperature.