Chief complaint: The car’s heater only blows out warm air when the temperature gauge shows that the car is very close to overheating (just before where the gauge turns red). Then it blows out warm air for a bit until it gets to about the midpoint of the gauge (which is where it usually would be after the car has warmed up when operating normally). Once it gets to this midpoint, the heater resumes blowing out cold air again until the precipice of overheating, at which time the whole process repeats. This happens in both stop-and-go traffic as well as at highway speeds. Sporadically, and for relatively brief periods, the coolant light comes on.
History of the present illness: Last month, something similar was happening. Although at that time, no warm air would come out. Also, the gauge didn’t get quite as high. And driving at highway speeds would tend to bring the gauge back down to the midpoint (without blowing out warm air, as my car does now). I suggested “Maybe the thermostat needs to be looked at.” But I think the repair that they did was (i) replacing a coolant sensor, and (ii) something with a hose.
Review of systems: All other complaints re this piece of shit car are likely non-contributory.
I welcome any consults on this very interesting case.
Have you checked the coolant level? Sounds like it might be low.
ETA, I didn’t even notice the part about the coolant light being on. Go check the coolant level. If it’s low, add coolant, or at least fill it up with water and see if that clears things up.
The symptoms described are very typical of having a sizable air pocket in the cooling system, or in other words significantly low coolant level. This is caused either by careless servicing (e.g. failure to get all the air out, or opening the cap when the engine is warm/hot) or by a leak. If the symptoms were largely unchanged after the repair last month, I’d suggest finding a more competent shop.
If it is indeed caused by low coolant, the next symptom will be severe engine overheating with a likelihood of doing further expensive damage. If possible, check the coolant level under the pressure cap (i.e., in the radiator or surge tank, or with some cars on the engine), not in the overflow jar. Top up if it’s low to forestall worse damage. Have it checked out ASAP to get to the root of it.
ETA: If the outside temperature gets below freezing where you are, avoid adding a large quantity of water to the system so as not to suffer a cracked engine block. It’s always best to add a 50/50 mixture of water and antifreeze.
Coolant levels were topped off last time. Now that you mention it, I remember the shop owner saying “You have a compressor leak. But I bled out an air pocket.” And I was like “Yeah, I know [Ed.: I do have a compressor leak], but this ain’t an A/C issue, son.”
But now I realize he has something of an accent and was saying “You have a compression leak.” Which can be brought on by a blown head gasket.
Just some info from experience. I had a 91 Deville that had similar issues with the heater. The malady turned out to be a vacuum leak caused by my putting a lead light onto the plastic vacuum box that was attached to the firewall. The bulb melted a small hole in the box and my mechanic … who I called on the phone … told me to check the “tank” … and after I told him I found a small hole … had me mix up some epoxy and patch it.
I had a Buick about 6 years ago that had a internal coolant leak and I didn’t feel was worth tearing down and used a stop leak product. That stopped the leak, but the heater core ruptured about a year later and I plugged off the lines and then sold the car as is for six hindered. The party I sold it to is still driving it today! It is his work car.
One of the frustrating things about some cars is how difficult it is to purge the air out of the system. Just the way a car sits on the street or drive makes it dificult. Having the radiator fill port at a high point helps. Sometimes squeezing the upper radiator hose slowly and releasing will help. A thermostate with a jiggle valve helps but filling the block as full as possible when changing a thermostat helps also. And don’t forget the bleeding valves on the coolant components when provided.
Thermostates without jiggle valves usually have bleed notches but to my belief don’t work as good. Maybe I don’t give them enough time to bleed?
I seem to remember the Ford Aerostar was particularly bad. IIRC the accepted method was to raise one front corner of the vehicle with a jack prior to coolant fill.
Thanks Gary T for that nugget of knowledge.
I do think patients is a great tool and realize a shop would loose there shirt if to much is used on the customers dime. :dubious: