Any auto mechanics-heating question

[replicant_argent]

Stat, control/blend problem (maybe), partially plugged core, water pump vane erosion, a few possibilities.
when it sits at idle, can you get to the return line from the heater core? if it is warm, you can isolate it to behind the firewall, whether a heater core, or a HVAC problem, rather than pump/radiator/stat/etc.

I would toss a stat in first, as it is cheap, easy, and if you haven't done one in a couple years, might as well. Especially since you had a cooling problem recently, and it may have boogered the stat.

[Blueface]

Thermostat vote here.

[jmsremax]

I had a similiar issue with my first car and my problem was the thermostat wasn't closing. I think I paid $15 to get a new one at Autozone. Hopefully this is the case with you.

[68TriShield]

Low coolant level again or bad head gasket/cracked cylinder head.
Which could be why you lost coolant in the first place.

[Blueface]

Originally Posted by 68TriShield

Low coolant level again or bad head gasket/cracked cylinder head.
Which could be why you lost coolant in the first place.

Oops.
Missed the "coolant" part.

[BloodSpite]

I always vote cheapest solution first. I use a 180 degree thermostat in pretty much everything

[jmsremax]

Originally Posted by jmsremax

I had a similiar issue with my first car and my problem was the thermostat wasn't closing. I think I paid $15 to get a new one at Autozone. Hopefully this is the case with you.

I meant to say it wasn't opening

[357]

Originally Posted by Blueface

Thermostat vote here.

Disclaimer: I am not a mechanic. I have however done a lot of work on my own cars out of financial necessity.

A bad thermostat is most likely and is cheap/easy to replace. <$10 usually. It sounds to me like it is sticking closed and requiring a hotter temp (more pressure) to open it. I recently had the exact opposite issue. My thermostat was stuck open and my engine often wouldn't reach the proper temp. Heat from the vents was never warm enough. $8 and 20 min later it was fixed.

Other cheap fix could be a radiator cap. Again under $10 and sometimes fixes cooling issues, depending on the type of system in your vehicle.

Obviously check for leaks in the coolant system, hoses, radiator, overflow resevoir, etc. If none are found, but you have to add coolant again, check your oil. If you find antifreeze (or smell it) in the oil you could be losing coolant due to a bad head gasket. (Big money and PITA).

IMO, if the water pump was bad you'd know it. Usually they fail catostrophically; as in they bite into the block and the pully snaps off due to pressure from the belt. I've had this happen twice. Once each on two different cars once they got around 160K miles. They also tend to make noise before they fail.

Heater cores don't fail often. When they due, it is usually because they spring a leak and fill your floorboards with coolant. I've only had to replace one once; it failed to get hot and yet was not leaking. I believe it was plugged.