2003 impala cooling system problems (HELP)

I have a 2003 impala with the 3800 and lost most of my heat a few months ago. I took it to a radiator shop and they told me I had CO in the radiator fluid and needed to replace head gaskets. My concern is I have no CEL I am not blowing any white smoke and the engine is running fine (no miss fires). I was wondering if it is in fact a head gasket or could there be other issues causing CO to enter the radiator fluid? Possibly lower intake gaskets.http://chevroletforum.com/forum/images/smilies/confused.gif

I have a 2003 impala with the 3800 and lost most of my heat a few months ago. I took it to a radiator shop and they told me I had CO in the radiator fluid and needed to replace head gaskets. My concern is I have no CEL I am not blowing any white smoke and the engine is running fine (no miss fires). I was wondering if it is in fact a head gasket or could there be other issues causing CO to enter the radiator fluid? Possibly lower intake gaskets.http://chevroletforum.com/forum/images/smilies/confused.gif
Lower intake gaskets going out usually result in coolant in with the oil. Stuff always flows from high pressure areas to low pressure areas. The head has higher pressure at the top of the pistons than the coolant system. You can get a second opinion, but if you are loosing coolant and the shop says you have CO in your coolant, probably a head gasket.

Were you low on coolant? Any external leaks?

Were you low on coolant? Any external leaks?

I was a little low on coolant and did find that my upper intake was leaking. I have replaced the UIG and retested with a block tester and got no signs of exhaust gas in the radiator. I have never had oil in the radiator or anti freeze in my oil, but I still cannot get good heat. The engine has never overheated and maintains a steady temp at about 180. I get about 50% heat at highway speeds and no heat at idle. Any suggestions ?

I was a little low on coolant and did find that my upper intake was leaking. I have replaced the UIG and retested with a block tester and got no signs of exhaust gas in the radiator. I have never had oil in the radiator or anti freeze in my oil, but I still cannot get good heat. The engine has never overheated and maintains a steady temp at about 180. I get about 50% heat at highway speeds and no heat at idle. Any suggestions ?

Well, CO is a product of combustion......only way you get that is from a cylinder leak, like a head gasket/crack.....or was it really present?

Can you give us a better timeline? Now we find out you replaced the upper plenum gaskets.....was the EGR hole on the upper plenum checked for degradation?

When was the radiator replaced(was it leaking?)? When was the upper plenum gaskets replaced? Who did both jobs? Was thermostat ever replaced(usually done when upper plenum or gaskets are replaced)?

If your temp on gage or scan tool reading, is only reaching 180F on the highway, this should have set a P0128, and thermostat should be replaced.....

At this moment in time, is coolant level ok? when car is at normal operating temp, it the upper radiator hose hot? Are BOTH hoses to the heater core hot or is one cooler than the other?

If BOTH are hot, then the temp door(doors if dual system) movement has to be checked.....

If the outlet heater core hose is cooler, then you need to backflush the heater core.....