2000 Sienna Overheating..help! I'm at a Loss!

[Depechelkin]

Ok, a year and a half ago I bought a 2000 Sienna, I love my van! I want to keep it as long as I can since I don't have the money to buy another one, but I'm having the strangest problem and I'm at a loss:

My van overheats..but seems to only do so after I have driven for a while and then get stuck in traffic congestion... on hot days..the problem only happens on hot days, I live in Texas, so most of our days are hot!

The sign is always the same, the temp gage slowly climbs up then the ac stops blowing cold air, I then have to pray I find a spot to pull over, and in the meantime I put the heater on and rev it in neutral while at a standstill:

I have had the sensors, fuse, thermostat, radiator all changed. the Fans blow when they are supposed to. There are no visible signs of leaks, and the coolant level is fine. Also, when I bought the van, I had the timing belt, water pump, spark plugs, wires and head gaskets replaced for preventive measures. I have brought it to the shop four times last summer regarding this problem, and both me and the shop are at a total loss at to what the hell it could be. The very last time they said they couldn't re-create the problem, so I had them replace the radiator and thermostat...that was less than a year ago. I just got a flush from jiffy lube 2 weeks ago. I tried to recreate the problem today by deliberately driving around for a bit then sitting in my carport with it in drive for almost an hour with the a/c on full blast.... it didn't overheat at all..even took it out in traffic for a bit..today was mild and pleasant..it seems this only happens on hot days.. does anyone know what this could be? I live in Austin, Texas, it is ridiculously hot here in the summer and traffic is atrocious so I really can't have this problem happening over and over. what would cause the vehicle to do this when I have replaced so much already?

ANY help would be appreciated!

[chuck's sienna]

I need to think about this for a while, but first.....Do Not sit somewhere for an hour in drive with the AC on full blast. Why would you do that? You just cooked your transmission, stressed your alternator and ran down your battery most likely. Your van is NOT made to do that. It is made to drive, and needs to have air blowing through the radiator. If a shop failed four times to fix a problem, then why keep going back? After the second time, find a better shop. With new anti freeze in there, why did you have an oil change specialist flush it out? Antifreeze lasts for years! Regardless, if it sat for an hour and did not overheat, I don't see how you have a problem. We are going from winter now to summer. My bet is that the van is fine now, but as ninety degree and hotter days arrive, this summer will prove if there is a problem or not remaining. I think now as well you need to have the trans fluid changed, and NOT at a jiffy lube.

[FinalCoda]

Originally Posted by chuck's sienna

I need to think about this for a while, but first.....Do Not sit somewhere for an hour in drive with the AC on full blast. Why would you do that? You just cooked your transmission, stressed your alternator and ran down your battery most likely. Your van is NOT made to do that. It is made to drive, and needs to have air blowing through the radiator. If a shop failed four times to fix a problem, then why keep going back? After the second time, find a better shop. With new anti freeze in there, why did you have an oil change specialist flush it out? Antifreeze lasts for years! Regardless, if it sat for an hour and did not overheat, I don't see how you have a problem. We are going from winter now to summer. My bet is that the van is fine now, but as ninety degree and hotter days arrive, this summer will prove if there is a problem or not remaining. I think now as well you need to have the trans fluid changed, and NOT at a jiffy lube.

..this silly forum won't let me log in with my previous user name, so I had to create a new one:

Thanks for your reply. I appreciate your feedback on not letting the van sit there for a bit, I didn't know it would strain anything, as most of the time, in Austin, you can do the same exact thing that I did, sit in trafifc for an hour, I did simulate this by staying in "drive" and doing a stop-n-go thing in my driveway. Next time I'll know better.

As far as the shop, I am frustrated with them as well, the reason I kept going back is because they were not charging me labor after the 2nd time, since the problem kept occuring. I haven't had this problem all winter. I am through with them and I'm not going back. I had the radiator flushed because jiffy lube told me it was necessary, and I don't like to take chances so my naivety got the best of me I presume , even though I told them it was a less-than a year old radiator, again..thanks for the info!

With all due respect, the van is not fine, I wouldn't be sitting here writing this and searching forums and googling like crazy if it were so. I took it to another shop today and they couldn't re-create the problem. The problem seems intermittent, and only after the vehicle has been running a while, the A/C is on, it's hot outside, and I enter stop-n-go traffic. This is an unavoidable situation since I live in a very hot, traffic-ridden region with lots of highways to get nice and gridlocked during peak hours.

I am like you, I don't see how I am having this problem, but I am! This very situation I am speaking of happened last Friday when it was quite warm outside for the first time this year, so it is not a figment of my imagination. I, much like everyone else, assumed that since it didn't give me any problems all winter and fall that everything was ok. I am, apparently wrong.

Anyone with any information as to what might be the culprit , please let me know! Thanks!

[wiswind]

I am afraid I do not have any great ideas.
I'll mention a couple things that come to mind.....
Air in the system.......do you EVER need to add more coolant?
A small pinhole.....or slight leak someplace can give you an air pocket......which WILL cause overheating.
My thinking is this.......your cooling system runs with a pressure in it when hot......but when it cools, it actually can have a slight vaccum......this is when it pulls coolant IN from the overflow bottle.
If there is a slight leak.......I'm thinking a loose hose clamp, etc that lets a little air into the system......then THIS could cause the intermittent overheating.
Since this problem does not happen all the time, it could be very difficult to track this down.
There are a LOT of possibilities for a leak.......all the heater hoses, radiator hoses, the hoses that go to and from the throttle body (yes.....even there).
Of course, a leak at the thermostat housing, or a engine part is possible......if you cannot track something down....(the FIRST thing I would check is hose clamps), maybe some Bar's Stop Leak in the coolant.

As far as the thermostat......I noticed that for my 2003, MOST of the aftermarket thermostats physically looked different.........so I bought a Genuine TOYOTA thermostat.

Normally, the radiator fans will STAY on when you have the A/C on........and the vehicle is not moving more than some given speed.
This is to keep air moving over the condensor coils, which are located in front of the radiator.
This (the radiator fans staying on) will also keep the radiator cooler, which also keeps the temperature gauge lower.
I'm wondering if there is an intermitten loss of radiator fan operation.
There are 3 different relays that control your radiator fans......I just read a post this week on one of the forums that I visit about a person having intermittent NO radiator fan operation.

When you pull over to cool the motor.......just turning the heat on will INCREASE the cooling capacity of your system.
Reving the engine normally will cause MORE heat.......as the radiator fans are electric.
Next time you pull over.......LEAVE the A/C on.......and if you can get out of the vehicle safely.......raise the hood and CAREFULLY check to see if your radiator fans are running.
AGAIN.....I'm thinking of them sometimes not running (an intermittent issue).

You have several temperature sensors......
The temp gauge usually has its own sensor......it does nothing but control the temperature gauge.
This sensor is located on the top of the motor, at the passenger side.....right next to the sensor for the computer.....but slightly more to the passenger side of the computer sensor.
I think that THIS is the sensor.....green wire to it below the radiator overflow hose that you can see connecting at the radiator cap. (the arrow is pointing to the PCV valve, which is metal on my 2003)


There is a sensor for the computer.
At room temperature, it should be roughly 2K (2000) ohms.
As the temperature increases, the resistance goes down.......gets less.
As the temperature decreases, the resistance goes up.....
This sensor is located on the passenger side of the motor.....next to the temperature gauge sensor.....but very slightly toward the center of the motor.
I think I have a view of it in this picture, where I have the upper intake manifold off....
I think it is the connector that is right behind the radiator cap location.




The AC compressor switch, that OPENS when the AC pressure is above 224psi, is in SERIES with water temperature switch #1 which OPENS when the coolant is above roughly 203 degrees F.......which turns the radiator fans ON......either one of these 2 switches opening should turn the radiator fans on at high speed.
This temperature switch is located more up front.....I cannot find a picture of it right now...but it might even be on the radiator.....passenger side.

Water temperature switch #2 CLOSES when the water temperature gets to around 194 degrees F.
The thermostat is a 180 degree F thermostat.....so the radiator fans will come on when the temperature at this location gets a little warmer.
This switch is mounted into the thermostat housing as shown in this picture, you can see the grey electrical connection on it.

[Black Sunshine]

Sienna's act funky if there is air in the cooling system but if your reservoir bottle is full then the air should have worked itself out.

I live in Phoenix, AZ although I've never had a cooling system problem in our van I understand the problems with heat. The desert heat here kills my alternators and batteries nonstop.

[wiswind]

OK.....I went out and looked on my 2003 Sienna.....technical difficulties (low batteries in camera).......the water temperature switch #1 IS mounted on the radiator.....passenger side bottom, right next to where the bottom radiator hose goes into it.
This is the switch that I mention above that opens up if the temperature at that location gets above roughly 203 to 208 degrees F.
If you unplug this temperature switch, the radiator fans should come on.
(Be careful).

I know my previous post is kind of long, but there are so many things to check.
I am sitting here thinking that it might be more of a radiator cooling fan issue since the AC was not cooling......which it would have a problem doing if the radiator fans are not moving air across the condensor coils.
But that is just a theory........and intermittent problems can be really tough to track down.
These temperature switches will cause the fan relays to activate.....the fan relays are all 3 located in the long relay and fuse box in the engine compartment.
The "main engine relay" is also involved in the radiator fan control (as is the computer) and this relay is located in the same box.

[FinalCoda]

thanks, guys! Thanks for the detailed pics and all the good info, I will give my guy all the info..anyone can think of anything else, just let me know!

[yotatoter]

There is one more thing to check,and that is the condensor itself. The condensor is basically the radiator in front of the actual radiator. If that gets its fins plugged there is not much air movement thru the radiator causing it to over heat the van and also the condensor gets too hot to cool. You can check this by checking your 2 condensor coil lines that go to your condensor,BE CAREFUL/ the line going in is very hot and if you have enough air movement the one coming out should be lukewarm, not hot. I had the same thing happen to my 1997 t100. If you check that forum you might find more info...

[lfootmatt]

There is a commonly known probelm with the fan relay(s) going bad. this will greatly contribute to overheating especially whne running the AC.

Later,

Matt