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My car's heater waited until a string of Zero degree days to mess with my heat. Suggestions and insights appreciated.

Disclaimer: I have zero skillz
2003 Rav4
Barely any heat at idle, "kinda" warm while driving.

Possible causes gleaned from YouTube University
- I have checked the coolant level.
- I parked on a steep hill and let it run for 20 minutes with an occasional rev.

- I wanted to try to get possible air bubbles out using a spill-proof funnel. NAPA guy said that's not it but YouTubers are adamant about trying it. Should I?

If it's one of the following I'll take it to a mechanic:
- Replace Thermostat
- Partially blocked heater core
- Faulty heater valve

Thanks in advance for your input. Keep in mind my eyes will gloss over if you use terms like alternator misfires, pressurized hoses, tension alleviation, compression, etc.

What is this "heat" you talk about in automobiles???

Based on my experience before moving to Floriduh, Check coolant level & if ok, replace thermostat.
Everything else is of lesser likelyhood than those two.
A frequent failure of thermostats is hanging open, which will give those symptoms.

mickey wrote: ↑Wed Jan 12, 2022 2:54 pm What is this "heat" you talk about in automobiles???

Based on my experience before moving to Floriduh, Check coolant level & if ok, replace thermostat.
Everything else is of lesser likelyhood than those two.

It's what comes out of the vents if you ever turn the temperature control knob to the right (the red part)*.




*Except mine this week.

Probably a thermostat problem. Either stuck open or failed gasket allowing coolant to pass through and never warm up.

Check if you have a relay that controls the heater fan it may be bad or perhaps the fan itself has bit the bullet, if you get heat moving it is probably being force fed by air pressure into vents at speed. (My old truck does this and I haven't fixed it because I live where a warm sweatshirt is overkill most mornings.)

If your temp gauge never leaves the low side, then it is probably the thermostat. Aluminum engines take a lot of driving to get up to temp when the thermostat fails open.


Sent from my SM-G998U using Tapatalk

Maybe some wiseguy jacked with your heater hose/hoses. Check to see if they are connected well. It's a common thing.

Outside shot here, but our third vehicle is a 2004 Highlander and we had some HVAC issues with it last year. Turns out that there is a fairly thin ribbon cable that connects the HVAC controls ( the knobs ) back into the rest of the system, and the cable from the temp knob had worn through to the point of severing the physical connection. So it was basically stuck in the last known position - and it was only the temp knob - the rest of the controls worked fine.

Apparently this is a fairly common issue with that era of Toyotas and there are people on ebay who will send you a full refurbished control stack for about $200 if you send yours back as a core. I used the backyard mechanic method and just jumpered the connection with an old piece of thin wire.

Ok, do you get the same warm heat as when driving after you stop and idle? Or does the heat stop completely.

Turn off the radio et al....then turn up the fan to the max. Can you hear it? Is it blowing a lot of air through? If not, it's either a relay that turns the fan on, or the fan motor itself.

Does the flow come out of different vents when you redirect the flow via the knob? Does the air change to cold when you turn the heat off?

Thermostat is also possible, but I suspect that, given you get more heat when moving, the issue is with the fan.

I had a similar experience with one of my cars. It was the relay. I had to drive 20 mins to the dealer in -25C weather with the windows open to keep the windshield from fogging.

There are also problems with the blend doors not moving fully to the hot or cold position. You should be looking at the temp gauge on the dash, does it come up to heat? You want to find any common problems, go to a toyota forum.

@eicca

Probably a thermostat problem. Either stuck open or failed gasket allowing coolant to pass through and never warm up. I think that this is a correct diagnosis (confirmed by the replies below and a friend of mine.)


@Rollin Hand ..

Ok, do you get the same warm heat as when driving after you stop and idle? Or does the heat stop completely. Heat stops completely

Turn off the radio et al....then turn up the fan to the max. Can you hear it? Is it blowing a lot of air through? If not, it's either a relay that turns the fan on, or the fan motor itself. The fan's moving air well

Does the flow come out of different vents when you redirect the flow via the knob? Does the air change to cold when you turn the heat off? I have no reason to turn it to cold when it's Zero degrees but I'll try this tomorrow

Thermostat is also possible, but I suspect that, given you get more heat when moving, the issue is with the fan. Hm...

I had a similar experience with one of my cars. It was the relay. I had to drive 20 mins to the dealer in -25C weather with the windows open to keep the windshield from fogging. And I thought that I had it bad.

@uwmcscott ...

So it was basically stuck in the last known position - and it was only the temp knob - the rest of the controls worked fine. I think that mine works well but I'll check it out in the morning. Thanks.

@honyock ...


If your temp gauge never leaves the low side, then it is probably the thermostat. Aluminum engines take a lot of driving to get up to temp when the thermostat fails open. What you just described is what is happening. I spoke to a mechanically-minded friend and he voiced this same opinion.

@yesca ...

Maybe some wiseguy jacked with your heater hose/hoses. Check to see if they are connected well. It's a common thing. I did some pinching, pushing and fiddling. All seemed connected but, then again, I was probably pinching, pushing and fiddling with the wrong hose thingys.

@mozz

There are also problems with the blend doors not moving fully to the hot or cold position. You should be looking at the temp gauge on the dash, does it come up to heat? You want to find any common problems, go to a toyota forum. Temp gauge slowwwly climbs from cold to mid-way. This is a strong candidate for a fix (mechanic).

Gauge should climb up to half normally. If it's slow or wavers could be stuck open/ not fully closing. That is the normal mode of their failure. I mentioned the blend door because I have seen where all the way on hot did not work properly, if turned it down a little bit you got full heat. There are calibration end points on the dial that get messed up in software. Also, some years of Toyotas used soy in the wiring insulation and mice chew through that and cause wiring problems.

tlarson58 wrote: ↑Wed Jan 12, 2022 2:50 pm - I have checked the coolant level.
- I parked on a steep hill and let it run for 20 minutes with an occasional rev.

Did you get this working? Sorry for the Kate response. You have to check the level in the radiator with the cap off. Remove the radiator cap, start the car, let it run. Add coolant at the cap inlet. Squeeze the upper and lower radiator hoses to purge air. Keep adding fluid. Be persistent.

I had a 1997 Rav4. The heater only blows warmish air because it's partially filled with air, not completely filled with hot coolant.

Hope this helps.

jam wrote: ↑Wed Jan 26, 2022 3:04 pm

tlarson58 wrote: ↑Wed Jan 12, 2022 2:50 pm - I have checked the coolant level.
- I parked on a steep hill and let it run for 20 minutes with an occasional rev.

Did you get this working? Sorry for the Kate response. You have to check the level in the radiator with the cap off. Remove the radiator cap, start the car, let it run. Add coolant at the cap inlet. Squeeze the upper and lower radiator hoses to purge air. Keep adding fluid. Be persistent.

I had a 1997 Rav4. The heater only blows warmish air because it's partially filled with air, not completely filled with hot coolant.

Hope this helps.

I'm on it. How do I know when I've added enough coolant?

Will it overflow from the cap? Do I need to purchase the no-spill funnel?

I was starting to look up mechanics.

this guy just used a water bottle and duct tape

The usual way to check coolant level is using the overflow tank. It should have a line for cold level and hot level.

That said, given that you started on this weeks ago, time to take it to a shop. Check with your local BBB for a good one.

@jam
@adad

No coolant in radiator. Filled it, then used the video and your advice.

Fill..burp...Fill...burp until the coolant reached the top.

Cabin warmed immediately. Fingers crossed.

Thanks guys!

tlarson58 wrote: ↑Sat Feb 05, 2022 2:42 pm @jam
@adad

No coolant in radiator. Filled it, then used the video and your advice.

Fill..burp...Fill...burp until the coolant reached the top.

Cabin warmed immediately. Fingers crossed.

Thanks guys!

You kidding?
Around here, no coolant means your engine would overheat & blow up before you made it to the dealer's!

No coolant either means it's leaking out or burning it. Once you fill it, better keep checking it. If it gets low again, you need to fix that problem, which could mean head gasket.

@mozz @jam @adad

I have a strong suspicion that I may be burning it in the head gasket. I saw some of this stuff. Will it work?

No, I wouldn't use that, seems like snake oil. You should be able to smell burning antifreeze in the exhaust. It will get to the point of heavy white smoke and you might start getting misfires. I'd really look up a Toyota forum and see if them motors and years are known to blow head gaskets.

How many miles? Does the coolant look like something else is getting into it? Does the oils have anything that looks funny or milky in it?

My minimal research indicates that there are some head bolts that can work their way out on the back of the engine. Look at the back of the engine to see if there is any obvious spray. Also take the rad cap off and listen for gurgling on a cold start.

If the price to fix is very high, it wouldn't be worth it.....except the US used car market is bonkers now, making fixing more palatable.

@Rollin Hand @mozz @adad @jam

Not a head gasket.

Wicked-good mechanic friend of mine is replacing out water pump and thermostat next week. I didn't want to go this route because he's helped me out before and I don't want to be a pain.

Replacing both because the alternator blocks them (I've never replaced the water pump and I guess, with $150,000 miles, it's time to do so).

I'll be continuing this thread as a PM so the rest of the forum doesn't have to follow the conversation. Let me know via PM if you'd like to join the PM party.

Just got back to this. The overflow tank often shows being full when the rad is not. You did it just right: fill rad, burp, repeat. I burned/boiled off fluid to ghe point that I just carried a few 1 gallon jugs of water at all times. Less effective at -30...

Never used gasket in a can. Not likely to work on a truly blown head gasket.

The car isn't over heating but may a have a slow leak at higher speeds (fluid warms up), drip out and evaporate.

Replacing thermostat soon.

tlarson58 wrote: ↑Sun Feb 06, 2022 2:11 am @mozz @jam @adad

I have a strong suspicion that I may be burning it in the head gasket. I saw some of this stuff. Will it work?




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Hell no. If you are at that juncture - take it to a mechanic. That bottled stuff gets in your oil if you have a gasket leak and clogs the waterways inside your engine.

If your thermostat is stuck open, your engine has a tough time staying warm on really cold days. Ease of replacing is different on each motor. If it is up front in a reachable place, it is very easy. Trans-mounted engines like the Rav - not so easy.

My wife had a 2004 Rav4 - great car, but the original water pump went at 60K miles and the tubines were non existent. However, symptoms of that would be overheating in the engine and hot water not getting to your heater core.

Feel the rug on the passenger side under the dash. If it is damp or wet - you have a heater core clog or leak. Also, replace the abin air filter and make sure that area is clean - sometimes the heater air baffle gets stuck closed .