Gen2 heat fades hot and cold while driving

[JohnnyB]

2010 ST - electronic climate control dual zone

The heat is fading from hot to cool/cold. When I am moving it is working fine then when i come to a stop either to pull over and idle or sometimes just waiting for a light to change it starts getting cold. When I start moving again it goes back to hot.



When I push the button from hot to cold and back to cold I hear a creaking/grinding noise as the temperature blend door moves. I am going to get the blend door motors changed next week under my warranty direct extended warranty at my local repair shop.



I am concerned if that is 100% the problem or if vacuum is involved. I took out that little check valve under the hood and blew into it and sucked air and it seems to work. I know when i hit the button to close the vent from outside air I hear that vacuum sound so I assume the vacuum is working. It is weird that the blend door would automatically move to hot when I am on the gas driving and move to cold when I slow down and stop.



any ideas?

 

[Gavin Allan]

Have you watched your temperature gage? Does it stay in normal and stay pretty still? If your gage is not getting up to the normal zone pretty quickly or if it is moving all over the place I would check for and underfilled engine coolant and/or a faulty engine thermostat.

 

[RedRanger 7]

If its going to the shop for warranty im sure the mechanic is going to diagnose the problem before the shop starts playing guessing games with their time and money :driving:

 

[JohnnyB]

The Temp gauge raises up normally and stays in the middle the whole time. I was considering a possible thermostat also but it is way to erratic for it to be that. It is like driving for a block or two heat comes on and when I let off the gas to slow for traffic or a light it cools off. Then when I get on the gas again and am moving it starts coming out hot again. Very strange. Thats why I was asking about vacuum, maybe I build enough vacuum while on the gas reving at a higher rpm then when I get off the gas at a lower rpm I am getting less vacuum.. Maybe a vacuum leak?



The mechanic said it is all electric and the blend door is opened and closed by the temp blend door motor. Maybe a temp sensor is bad? giving the signal that it is no longer cold and to move the blend door to the cold side?



The mechanic has had it on the computer and no codes are popping up.

 

[Todd Z]

Vacuum is strongest at idle or when your off the gas.



Check the blend door, the thermo sensor or could even be a clogging heater core.



Todd Z

 

[Tim Holt]

What is the coolant level IN THE RADIATOR? It could be that you have a small leak. Coolant is pushed out when hot and air is drawn back in through the leak as the engine cools as there is less resistance than drawing coolant back in from the expansion tank.

At higher revs the waterpump is pushing enough coolant that it goes through the heater core at idle it tends not to resulting in cool/cold air.



There is another guy on FB that has the same problem, he doesn't seem to want suggestions from Todd and I.

 

[JohnnyB]

Thanks guys. I will check those.



I found that the radiator was a little low. I only added about 2 1/2 QTS of water. Will see if heat works better.



Anyway of checking the heater core without removing it?

 

[Vic Sorlie]

2 1/2 quarts is more than a little low IMO. Now that you've corrected the level are you seeing improved heater operation? That much coolant loss is not normal thought - I'd do (or have done) a pressure check to see where your leak is. I've got an '08 STA with just under 90K miles; had to replace my radiator about 10K ago.

 

[Taylor Corn]

+1 That is a lot of coolant loss. Anticipate that being the root cause. Definitely need to source that much loss.

 

[Yardsale]

Check those plastic radiator side tanks.

 

[JohnnyB]

Thanks again guys.



Not going to be easy to find the leak. I dont see any signs of coolant in the engine compartment. It must only leak out under pressure when the engine is hot. Maybe spraying out and evaporating?



Will check what you said.

 

[Vic Sorlie]

JohnnyB, back to my question: Is heater working better with topped-up coolant level? Other things to check: 1) Pull oil dipstick without wiping it. See any whitish deposit above the oil level? Hope not - that is indication of coolant leaking into the oil. 2) Notice any white smoke from the exhaust? 3) Check passenger side carpet for wetness.

 

[JohnnyB]

Passenger side carpet is dry, no white smoke from exhaust, oil dipstick is good nothing but oil.



Heat is working better with coolant topped off.



thanks

 

[Vic Sorlie]

That's good news then. A system pressure test will show you where the leak is. Search YouTube for DIY videos.

 

[Todd Z]

Its normally the bottom Pass side of the radiator that leaks Only when hot. I found mine showed up when the truck was Med warmed up and nosed down on a hill..



I let it run on my driveway facing down and finally Drip, drip, drip.



Radiators are notorious on the gen 2 v8 for failing.



Special transmission line tools are needed. Unless you just cut and double clamp but that's a hack job.



Todd Z

 

[JohnnyB]

The radiator had a leak on the drivers side of the radiator. Also the rods or arms that open/close the temp blend door were rusty and keeping it from closing all the way sometimes. Got it fixed just in time for the snow coming to the north east.

Thanks

 

[Todd Z]

Typical Gen 2 rad leak....



Glad its fixed.



Todd Z