Heat: cold when driving, hot when standing

[bstone]

Just did a round trip from Boston to Montreal and back. Heat was nice and hot when I was stationary but when I was moving fast on the highway it was barely lukewarm. I shivered on the way up when the temp was -22 F (no joke).

Friend said it sounds like the thermostat. I stood next to a mechanic 2 years ago who replaced the thermostat and the temp sending unit. I find it hard to believe it's dying again already.

So, if it does sound like the thermostat, please suggest one I should get which has a good reputation for living longer than 2 years.

Thanks!!!

 

[spdy0001]

Just my guess but I would check your coolant mixture. At -22F the windchill is really cold at the front of your truck but stopped it allows the coolant to warm up easier. I would say that if your thermostat was bad you would be overheating and not underheating.

 

[junglejet]

I would start with a coolant flush. When was the last time it was changed? are u loosing coolant?

 

[kb1cir]

Sounds like the thermostat is stuck open.

bat

 

[bstone]

I forgot to mention. The drive home was not nearly as cold and yet the air was only luke warm.

Does it make sense that the hot air is nice and hot when stationary but cooler when in motion?

I *am* losing coolant, but that is an old problem. I always make sure to keep premix in my car and add it in regularly. I also lose power steering fluid and a bit of engine oil. I'm a regular leak!

Being that the thermostat may be stuck open, which one should I replace it with?

 

[Anime]

It makes sense that the air is warmer with the engine at idle than at highway speed, but still with the climate controls on "HEAT" and "WARM", it should be pretty toasty either way. If the system wasn't flushed for the thermostat job 2+ years ago, and no maintenance has been done since, there might be buildup and deposits inthe heater core causing a slow flow of coolant, which would mean less heat. A new thermostat might help if the current one is stuck open. My suggestion is for a Motorcraft one, though a good brand name one will do well, just stay away from the cheap dinky ones. I'd say go ahead and do a coolant flush, possibly replace the hoses, and put a new thermostat in. If you could pinpoint the coolant leak and take care of that while you're at it, all the better.

 

[junglejet]

It's possible you have a small pinhole leak in the core that is causing loss of heat. if this is the case you woul loose small amonts of coolant. One way to detect if there is a coolant leak from the core is to stick a long cotton swab into the core drain hole.

 

[bstone]

Thanks, junglejet, for the advice.

Where do I find the core drain hole? How long of a cotton swab?

 

[Tony H]

Could also be that your 'X' is just leaky and with those temps you have cold air coming in along with the Hot from the Heater.
Ever sinse I bought mine ( very used) there is a cold air wind tunnel on teh passenger side. I've pulled away the Knee Bolster and everything appears sealed. I even put some additional fabric up in there around the open areas of teh Bolster. The wife still freezes her knees off during the winter.