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Discussion Starter · #1 ·
2006 Sienna LE
Acquired the Sienna at 97K, not at 147K, that is some six winters.

In the winter, especially the foot well heat is not hot enough, which makes the whole cabin not at the top expected heat temperature. Since it's been that long, I feel I need to flush the system, just for the sake of maintenance. The coolant (from the radiator) looks pretty clean to me. The seen coolant at the radiator cap should be the same in the whole system; right? In my other vehicles, the coolant kinda changes color after some years.

Should I drain, flush and use a radiator chemical flush to clean up the system, or just leave it alone? Also, how about he thermostat and coolant temperature sensor?

Cheers
Liquid Dishware Tableware Fluid Serveware
 

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That looks clean to me. I wouldn’t bother with a chemical flush. You can try a plain water flush but I don’t know how you get it all replaced with premixed coolant.

The block drains are easy to get to and should open easily if the underside isn’t rusted. At least with FWD.

I’ve had two thermostat failures - one stuck closed identified by the AC compressor cutting out and so slight as to be imperceptible increase in temp gauge reading, the other stuck open identified by check engine light indicating temperature too low and so slight as to be imperceptible decrease in temp gauge reading. Pardon the language but the gauge is [email protected]

I don’t read much here of temp sensor failures. It’s by the pressure cap and easy to replace. You have to lower the coolant level to avoid coolant loss.

Use an OBD scanner with live data feature to read actual engine operating temp after a 20 minute drive (not just idling). It should be around 180*F which is the thermostat rating. If it’s cooler, that could be why cabin heat is inadequate (but why no CEL like me?). Otherwise the heater core might be clogged internally (which a chemical flush might clear) or externally (which an evaporator treatment might clear).

Sixto
‘04 LE FWD 200K miles
 

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Discussion Starter · #3 ·
That looks clean to me. I wouldn’t bother with a chemical flush. You can try a plain water flush but I don’t know how you get it all replaced with premixed coolant.

The block drains are easy to get to and should open easily if the underside isn’t rusted. At least with FWD.

I’ve had two thermostat failures - one stuck closed identified by the AC compressor cutting out and so slight as to be imperceptible increase in temp gauge reading, the other stuck open identified by check engine light indicating temperature too low and so slight as to be imperceptible decrease in temp gauge reading. Pardon the language but the gauge is [email protected]

I don’t read much here of temp sensor failures. It’s by the pressure cap and easy to replace. You have to lower the coolant level to avoid coolant loss.

Use an OBD scanner with live data feature to read actual engine operating temp after a 20 minute drive (not just idling). It should be around 180*F which is the thermostat rating. If it’s cooler, that could be why cabin heat is inadequate (but why no CEL like me?). Otherwise the heater core might be clogged internally (which a chemical flush might clear) or externally (which an evaporator treatment might clear).

Sixto
‘04 LE FWD 200K miles
Ok, thanks a bunch for your reply.
I'll do the drive with life data, and go from there. I'll report back as soon as I get the result.
 

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Discussion Starter · #4 ·
That looks clean to me. I wouldn’t bother with a chemical flush. You can try a plain water flush but I don’t know how you get it all replaced with premixed coolant.

The block drains are easy to get to and should open easily if the underside isn’t rusted. At least with FWD.

I’ve had two thermostat failures - one stuck closed identified by the AC compressor cutting out and so slight as to be imperceptible increase in temp gauge reading, the other stuck open identified by check engine light indicating temperature too low and so slight as to be imperceptible decrease in temp gauge reading. Pardon the language but the gauge is [email protected]

I don’t read much here of temp sensor failures. It’s by the pressure cap and easy to replace. You have to lower the coolant level to avoid coolant loss.

Use an OBD scanner with live data feature to read actual engine operating temp after a 20 minute drive (not just idling). It should be around 180*F which is the thermostat rating. If it’s cooler, that could be why cabin heat is inadequate (but why no CEL like me?). Otherwise the heater core might be clogged internally (which a chemical flush might clear) or externally (which an evaporator treatment might clear).

Sixto
‘04 LE FWD 200K miles
If you won't mind, what would be your input on this post.
Need To Start Using Synthetic Blend Engine Oil
 

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The heater in my 2005 has never worked well IMO. If the van has been using the correct Toyota Super Long Life pink coolant all along (it appears that this is what is in yours), I would not flush the cooling system, just a drain and fill. Make sure you get most of the old coolant out by opening the two engine block drains.
 

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Discussion Starter · #7 ·
The heater in my 2005 has never worked well IMO. If the van has been using the correct Toyota Super Long Life pink coolant all along (it appears that this is what is in yours), I would not flush the cooling system, just a drain and fill. Make sure you get most of the old coolant out by opening the two engine block drains.
I am really shocked how clean the coolant looks like, after over six years.
Interesting. Just curious, did the drain and refill give you a much better heat?
 

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Discussion Starter · #8 ·
Food for thought -


Sixto
‘04 LE FWD 200K miles
Wow, that's an extreme. Wifey's Sienna will not have all that in it. Alaska does not favor such inhabitants. Like snakes, wild ones are not in existence; I have the highest level of phobia of that in the whole world.

I just ordered a cabin air filter. That might be dirty, since we have very dusty air from our geography. It could just stop raining, and in the next hour, it's dusty. Will go through the video again.
 

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I am really shocked how clean the coolant looks like, after over six years.
Interesting. Just curious, did the drain and refill give you a much better heat?
I have done 3 coolant drain and fills on my 2005. It always comes out clean. No difference on the heater.
I purchased my 05 new and the heater was never strong. I had it back to the dealer once to have a couple of TSBs done and I fussed at them about the heater. After checking it out their answer was that it was working normally. Other people that I have talked to have said the same about their 04-06 Siennas. For me, the A/C works really good which is far more important in Texas.
 

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2014 Sienna LE
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I second the ODB temp check of coolant. If that's all good, you could check that the air mixing damper is working properly. If that doesn't move all the way over to the hot air side, then even if the coolant is at the right temp and circulating properly you won't get full heat out of the system.

I'm not sure how the Sienna works in this regard, but most vehicles always circulate hot coolant through the heater cores, regardless of the cabin heat setting. Heat in the cabin is controlled in these cases simply by an air damper. If the controls call for heat, the air damper moves to one side and air in the ducts flows through the heater core. If no heat is called for, it moves to the opposite side and no air is drawn through the heater core. Partial heat is controlled by moving the damper proportionally to the amount of heat requested, mixing various amounts of air drawn through the heater core and air not drawn through the heater core.

I’ve had two thermostat failures - one stuck closed identified by the AC compressor cutting out and so slight as to be imperceptible increase in temp gauge reading, the other stuck open identified by check engine light indicating temperature too low and so slight as to be imperceptible decrease in temp gauge reading. Pardon the language but the gauge is [email protected]
Coolant gauges lie to you, on purpose. The reason they do makes sense, they are trying to avoid people who don't understand normal engine coolant temp fluctuations from complaining that something is wrong. But then you can have thermostats that aren't functioning quite correctly, but not misbehaving enough that they actually cause the gauge to swing much, if at all, but can lead to issues like lack of heat.

From reading, most gauges are programed that once the engine is warm, the gauge goes to a specific pre-defined location within the "normal" section of the gauge and doesn't move unless something gets really out of wack. Once I knew this, and started looking at live temp data with an OBD reader on my 2013 Honda Pilot, I noticed something I had not noticed before. Normal coolant temp was around 175 °F on that SUV. As I watched the live temp increase on a cold start, around 160 or so I saw the gauge on the dashboard smoothly, but suddenly, move from where it was indicating up to the one pre-determined "normal" spot on the gauge, even though it hadn't yet gotten to the normal 175 yet. And when towing, even though my coolant temps often got up to 225, the gauge never budged any higher. These ranges therefore, had been determined by the engineers to be "normal" so they programmed the gauge to just read the same regardless of if the coolant temp was 160 or 225. Somewhere above that of course the gauge would start moving to hot, and below 160-ish the gauge would start reading colder again. But if you were doing normal driving (not towing) and the coolant was 225 cause the thermostat wasn't open? You'd get no indication of that. Same if it was sticking slightly open and the temp was 160 the whole time and not the normal 175.

Basically, it indicates something majorly wrong, but nothing else. If you suspect a partial cooling system defect, 100% you need an OBD reader and monitor the actual coolant temps to know for sure.

That looks clean to me. I wouldn’t bother with a chemical flush. You can try a plain water flush but I don’t know how you get it all replaced with premixed coolant.
Yup, you don't flush. The 3rd gen FSM doesn't talk about flushes at all. It says for coolant changes to open all the drains, drain, then refill. The jug of SLLC I have says that if flushing is needed, you drain, refill with SLLC, get up to normal operating temp and run all heaters for a bit, then drain and refill with SLLC a second time. So they never intend that the system is flushed with water or a chemical flush, just drain and fill only.
 

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I've seen videos on YouTube where they remove the coolant lines to the heater block in the engine compartment and then run water in the reverse direction, and tons of crap comes out, then the heater blows a lot hotter.
 

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I would change the thermostat if it's never been changed. Drain and fill with new coolant.

I noticed my heat/AC output was way better after I fixed the blend door actuator that was clicking in the dash. It must of been misaligned slightly.
 

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Discussion Starter · #13 ·
I have done 3 coolant drain and fills on my 2005. It always comes out clean. No difference on the heater.
Am asking this since I'm still learning a lot.
What was/were the reasons for the 3 drain and fills?
 

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Am asking this since I'm still learning a lot.
What was/were the reasons for the 3 drain and fills?
Time and miles. The protective additives in the coolant eventually get depleted and the coolant needs to be replaced. Doing timely maintenance is one of the keys to getting a Toyota product to last over 300k miles. Unlike most other brands, Toyota products don't tend to self-destruct for no particular reason, just take good care of it and don't abuse it.
 
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