engine overheat and cold air: thermostat?

Head gasket. (And it's through, not threw)

A thermostat stuck in the closed position will cause the engine to overheat and can cause a no-heat condition if the coolant is not circulating.

With the engine cold, you can remove the radiator cap and watch to see if coolant circulates when the thermostat opens.

Other things that can cause overheat but generally do not cause a no-heat condition are clogged radiator, leaking head gasket, and bad cooling fan clutch. A bad water pump usually leaks before it causes an overheat condition.

You are much more likely to get the correct thermostat from the dealer than from an aftermarket source. When you purchase a thermostat, also purchase additional coolant and a thermostat housing gasket. Drain the coolant from the petcock at the bottom of the radiator into a bucket or pan. Remove the bolts on the thermostat housing and remove the thermostat, taking careful note of the orientation of the thermostat, i.e., spring side down.

Place the old thermostat and a thermometer in a pan full of water, place the pan on a stove, and turn on the heat. Note the temperature at which the thermostat opens, it should be around 60 C. If the thermostat does not open, then that was the cause of the overheat.

Clean off the old gasket material on the thermostat housing and engine side, install the new gasket and thermostat, and replace the thermostat housing. Turn the heater control to hot and fill the radiator until it reaches the bottom of the radiator neck. Start the engine, and as the thermostat opens, the coolant level will start to drop. Gradually top off with coolant until the level no longer drops. Replace the radiator cap and top off the overflow bottle.

I was wondering the same. ISTR that when a car of mine blew its head gasket, there was oily froth in the radiator water, caused by oil leaking from the oily side of things into the watery side within the engine block. (FWIW, the head was warped and had to be skimmed to flatten it again. FWIW-2, that was around 1980.)

All was fine in that same morning, over the past few days, I have been noticing varying lengths of time for the heat to kick in, sometimes works well, other times, not so good. The temp guage has been also been rising to just below the red and then it drops dramatically to well below the normal mark. Have not paid attn to where it leveled off.

I assumed that it was the thermostat that was sticking and that was my explanation.

head gasket sounds expensive. I will start with the thermostat and rad flush. Any other advice to rule out the head gasket would be greatly appreciated. Some say to run the engine and tab on the thermostat housing.

On reconsideration, the oily froth may have been in the breather pipe, meaning the leak was going in the opposite direction. Sad news, either way.

if there is oil mixed with the coolant or coolant mixed with the oil, then the head gasket is suspect. If you do not have either condition, then a bad head gasket is less likely.

Sounds easy enough. Thank you.

You're welcome (if you're responding to my post) ;-)

Thanks Ray O

You're welcome! Hopefully, it's just a thermostat.

What sounds easy enough?

So it seems there is a leak or at least no antifreeze to see in the rad and little to none in the overflow. The oil is not milky and the antifreeze overflow ( what little there is) does not seem contaminated either. Water pump seems fine (no noise, no visible leak, no movement of pulley), now the question of finding the leak and I have still not ruled out head gasket --can you lose that much antifreeze via exhaust?? I have noticed some white exhaust but it is cold presently and I see many cars with similar white exhaust.

For the moment, I am going to top up the existing fluid with a economy antifreeze 50/50 mix with distilled water with the intent of flushing the system once I figure out where the leak is. Of course, there is no pool of fluid under the vehicle which is good and bad.

The responses have been very helpful and if anyway would like to offer suggestions for the next step, it would be greatly appreciated.

Yes, you can lose a lot of coolant through the exhaust if there is a head gasket problem. The white exhaust should be reduced as the car warms up. If it doesn't and the exhaust has the odor of anti-freeze, the head gasket is the likely cause.

The low coolant level can also cause the lack of heat.

Someone with an exhaust gas analyzer can stick the probe into the radiator and check for exhaust gases bubbling through the radiator.

What does the oil look like?

Oh, and what's coming out of the tail pipe.

If the head gasket is damaged near a cylinder, it could miss an oil jacket. The antifreeze would leak into the cylinder and mostly burn away.