I’ve been having a vexing problem on my 2001 LS with 160,680 miles. I’ve had several winters where I’ve had little to no heat. What’s weird is that when it’s warm (50+), my heat is usually pretty good (not as good as it should be though). When it drops into the 30’s and below, it’s anemic and sometimes is absolutely zero.
Things that have been done to the car that relate to the HVAC system recently:
Flushed heater core several times (mostly clean, no rust and good flow) - hoses are warm (not hot like radiator hoses)
Replaced top Quick-Lock hose connector to heater core (old one cracked when taking off hose)
New water pump (changed at 158k miles a month ago) - new GM rotor vane style
New serpentine belt (Goodyear Gator)
New radiator hoses
New s-bend hose at top engine by bleeder valve
Checked for air in system at bleeder valve
Thermostat changed at 60k miles during intake manifold gasket change
Flush of system (twice over the last 3 years) - filled with DexCool
If I do get any heat, it’s only when I’m on low fan, and maybe an outlet temp of 60-65. At higher fan speeds, the heat is sucked out of the heater core faster than it goes in so it blows cold.
I visually checked the heater blend door actuator and it’s working (at least the shaft is turning - I didn’t remove it).
One odd symptom is that when the heater knob is all the way on hot, the air flow is about 1/2 that when it’s all the way on cold (one reason I checked the actuator).
Of note, first time I noticed it was when I had a flush at 100k miles (done by a mechanic at work). I checked for air in the system and also flushed my heater core and it got better for a bit.
This is really no fun. I live in the northeast and when it’s 10 degrees out, it’s like driving a freezer to work (45 minutes). Driving to VA last weekend was even worse - 6 hours with it being about 45 degrees in the car.
There should be a coolant shut off valve in the system some where that shuts the coolant flow off when the air conditioning is on. I’d be checking that valve to make sure it is opening all the way.
There should be a coolant shut off valve in the system some where that shuts the coolant flow off when the air conditioning is on.
What vehicle has a design like that? Many vehicles have a design that the AC turns on automatically when the defrost is on. If the coolant is shut off when that happens during winter months in NH…the cabin would be freezing.
Since it started with the flush, air in the system would be my first guess. If it has a radiator cap have it off and let the air escape. If not, loosen upper radiator hose clamp and stick a screw driver between the radiator and hose and let air bleed out. Jack up or raise the front end and get it up to temp. Turn on the heat full blast. If this doesn’t work, than you’ll have to try the other suggestions.
Feel both heater hoses when the engine is up to temp, heat is selected with the fan on mid-range. If both hoses are hot, then check the blend door for proper operation. If neither hose is hot, then re-bleed and change thermostat if bleeding doesn’t help. If inlet is hot but outlet is cold, likely need a new heater core.
@Pylot Two questions for Pylot - What is your temperature gauge indicating? Also - When you flushed the heater core was it a chemical flush or a water only flush and did you do a reverse flush?
Bing I was pleased that my 1996 Miata had a temperature gauge until I was informed it was actually an analog idiot light. It may have been an oil pressure gauge.
The oil pressure gauge on a Miata is a fake. The temp gauge is real.
But the question from the OP is valid. To me it sounds like a bad thermostat, but that’s just a guess of course. The old trick of putting a piece of cardboard over half the radiator might do something useful, but if you try it keep a sharp eye on the heat gauge. And burping the air out of the system makes sense too.
MikeinNH, My 1971 Maverick had a vacuum operated coolant valve in the heater line that closed the coolant off of the heater core the first time the AC was used, it rarely ever re-opened that valve when heat was needed. You had to manually open the valve. Not one of Ford’s better ideas.
My new Subaru Legacy does not have a coolant temp gauge. It has a useless and distracting MPG gauge but not a more useful ECT gauge. You have to buy the top of the line Limited model to get that gauge. Not one of Subaru’s better ideas either.
You have 100,000 miles on the existing thermostat. If I had this problem, that would be the first thing I’d do, replace the thermostat. Especially if it is a bypass type. That design can sometimes fail in a way that still maintains the proper coolant temp for the engine, while fail to provide adequate heat for the passenger compartment.
No heat? 100,000 miles on the thermostat? It’s a no brainer, since on most cars it is such a simple and quick procedure, first thing to do is replace the thermostat.
OK, I didn’t know what an LS was. I thought it was GM. If it is a Lincoln, 2001 LS, I’m not giving up on the coolant control valve. Just Google it and it sounds like a common problem. That or there is an inside temp sensor or a problem with the climate control system itself. Check for codes. Has this gone to a Ford dealer and they couldn’t trouble shoot it for two years??
I had a caddy with the valve Bing is referencing. IIRC it was a vacuum actuated valve with a small linkage to the valve and the actuator had failed. The heater valve was stuck in the open position and roasting me out of the car. I might be wrong, but I think that was the way they accomplished the blend operation.
Historically, the lack of OP involvement has never stopped the conversation.