The temperature has dropped quite a bit around here this past week so the heater has been on a lot, but I've noticed it only seems to get warm, not at all hot like it used to.

The valve is working, I can switch it from warm to icy with no problems. I don't think there is any problem with the core, no leaks and both hoses heat up just fine (in and out of the core). I noticed today on the highway that it seems to be a little cooler at highway speeds, but not a large change. This makes me suspect the thermostat, however the temp gauge never wavers (which I realize doesn't say much) but also I checked it the other day, started the truck cold, let it warm up. The top radiator hose stayed cold until the engine hit operating temp then heated up quickly. There are no bubbling sounds, coolant is full.

I'll probably put in a new OEM double hole thermostat anyway, no idea how old the current on is anyway. Any other ideas though? Preferably an ingeniously simple solution I've overlooked that doesn't involve me being mechanic outside in below zero weather. <img src="/forums/images/graemlins/smile.gif" alt="" />

Wow, I guess you guys are cold after that freekin' Hades of a summer (was down in Aug in Lewiston/Grangeville). I just looked at wunderground.com for Cd'A.

Couple things-
**Get your coolant tested and make sure you're good for at least -20F.
**Put some cardboard in front of your radiator- I know in the Palouse country you know what wind chill factor is about. I just draw some shark teeth on mine and ziptie it to the grille. <img src="/forums/images/graemlins/notooth.gif" alt="" /> These little 22Rx's have a bit of a time keeping up the temp exchange when the mercury seriously goes south.
**Keep a t'stat handy in case things come to an abrupt and unacceptable stop.
**That being said, make sure you keep some extra cold weather gear in the rig with you during this cold snap in case you do get stranded, or need to work on your rig next to the road.

You could try back-flushing the heater core, but first feel the two hoses that go to it, the inflow and the outflow, the in should be as warm as the top radiator hose and the out not as warm but not too cool which could mean a flow problem

probably similar problem just about a week ago from GaryMC.

"-2003 Tacoma 4x4 TRD, V6 and manual tranny

Symtoms:

-The heater stopped working for about ten minutes this morning when it was 5 degrees out and snowing. It came back on after I futzed with the controls a bit.

-About twenty miles of in town driving with no ill effects

-After three'ish miles of snow/ice covered I-70 driving the Taco started to lose power, I looked down at the gauges and the temp. guage ws pegged. I was unable to pull over due to the wall of snow on the shoulder and limped it a 1/2 mile to the next exit and then two miles of very slow driving to a gas station.

-The engine made an unusually loud clattering noise the last few hundred yards and died as I pulled into the parking lot. It refused to start again and sound very labored when I cranked it. Ugh....

-There were no obivios blown/ruptured hoses and ther appeared to be no water in the oil."

& turns out:

"6 hours at Safari Ltd, a new all metal radiator, a new thermostat and the Taco is back on the road! There seems to be no engine damage and things are good to go. Hugh seems to think that the thermostat stuck closed and caused the radiator to blow it's seal. At least I think that's how he explained it..."


http://expeditionportal.com/forum/showthread.php?t=21536

my dads 99 auto 4runner did the same thing, but the radiator cracked internally and the ATF mixed with the coolant and buggered everything up. a new rad and $1300 later, its like new again.... (lots and lots of labour to get all the oil/coolant out)

Well the hoses going in and out of the core are both the same temp, and also the same temp as the rad hose, So I would suspect the heater core is working fine. I'm going to go pick up a new thermostat today anyway, cheap and easy to check. Luckily its almost 10 degrees and only lightly snowing so won't be too bad to work on...

Hoses in and out the same temp? Not the thermostat. You have a buggered up heater core. No heat transfer going on. You back flush it and it may clear up. Probably not. If it does actually get cleaned out, it will leak. Bite the bullet and get a new core. My son just went through the same thing with a 93 corolla. Sorry.

Well I changed the thermostat this afternoon anyway, probably the original one. I had an identical problem on my last truck and it turned out to be a bubble in the heater core, tomorrow I'll try burping the system again, I did it yesterday but didn't have much of an incline to work with. If that isn't it have to start messing with the heater core. Out of curiosity anyone know exactly what causes the heater cores to fail, just fouling from gunk or is it the material of the exchanger itself that degrades?

Material usually degrades from us using tap water to mix 'freeze- and not descaling the system periodically. I reservice my system every 2-3 years. It's a little of both, esp if someone has tried doctoring the system with stuff like Stop Leak. <img src="/forums/images/graemlins/shame.gif" alt="" />

Usually works well to back flush the heater core every few years. How? Take a garden hose and shove it into the heater core return line (with the inlet line disconnected and the valve open). I find a tapered hose nozzle will shove up inside the end of the rubber hose and seal up well. Gradually open the nozzle to let the water flow through the core until it runs clear, and watch the pressure, if water does not flow you may build up too much pressure and blow out a rubber hose. The repeat with a forward flush and alternate back and forth until you get clear water flowing both directions.