PT air from heater goes from hot to cold to hot.

I notice that the air coming from my heater when set on hot will come
out cool then back to warm, to cool, and so on.
The heat gauge is normal. What could be causing this? The PT is a 2001

 

Check the coolant level, especially if it's correlated with engine
speed. On our Intrepid (I know, completely different vehicle) when the
radiator tank cracked we learned about it because at low RPMs water
wasn't getting into the heater core, so the heater went cold at
stoplights. Temperature gauge read normal.

 

I agree with Joe - low coolant/air bubble in coolant. If it has a
bleeder, open that after the engine is warm and see if any air comes
out. If so, leave open until only coolant comes out. Check level in
reservoir and top off if low before and after you bled it. If the
reservoir is the pressurized type (I don't know about the PT), don't
open it to add coolant while the engine is warm/hot - let it cool down
and de-pressurize first.

If coolant level is OK and no trapped air, the heater core may be clogged.

 

Since you do indicate that you sometimes have some heat, probably ignore
my last sentence there.

 

Thanks all!

I checked the coolant in the radiator. I can not see into the
resovoir. I added about a quart of 50/50 antifreeze. It bubbled as it
went into the radiator. I figured this was air being replaced. Seems
to have solved the problem.
One more question. I wonder where the missing fluid went. Nothing on
the engine, under the car. And the oil pan has nothing but oil in it.

 

First place I'd look is the easiest: pressure test the system and
radiator cap (you can borrow a pressure tester from Autozone). If it
passes that, I'd get worried about the head gasket and related
problems.

 

Once again, Joe and I agree - couldn't have said it better. The
pressure caps have a sneaky way of leaking and not leaving a trace.

 

Would that also apply to non-pressurized system caps also? My 41
Chrysler radiator level goes down, but no leaks on the floor or anyplace
I can see. The cap was new earlier this year, but could it have gone bad?

 

Not sure. The coolant systems back then (10 years before I was born)
weren't pressurized? The fact that I ask that question shows that I'm
the wrong guy to ask on that one.

 

Wwhen a pressurized system's cap goes bad it doesn't maintain pressure,
which results (through a long chain of explanation) in steam escaping
through it. I've got no experience with non-pressurized systems, but
I'd assume by definition that you couldn't have the same failure
mechanism.

 

It was probably just low a low coolant level. If the 2.4 in the PT is
like it is in the cloud cars, the the radiator cap is the highest
point in the cooling system. The AA cars had a bleeder on the head to
get the air out. If the system was not bled correctly, it would take
out the headgasket. I know this from experience.

I would suggest checking the coolant level on a regular basis. When
the water pump failed on my cloud car, it would leave puddles of
coolant on the garage floor. I would also suggest checking the engine
oil and transmission fluid for coolant contamination. Has the water
pump and timing belt ever been changed on your PT? It may be time
since it is a 2001, depending on the mileage. The belt change on cloud
cars was 101,000 miles.

KM

 

Don't know about a '41, but my '49 had a pressurized system. Pressurized
to a *whopping* 4 psi vs. the ~15psi common today