1999 Toyota Sienna Overheating

We purchased a 1999 Toyota Sienna last year. It had only 28,000 miles on it, and now has about 40,000.

Since November, we have experienced problems with the van presumably, overheating, and have had the thermostat replaced twice.

Other symptoms -

After the engine warms up, the heat starts working, and as long as we’re going down the highway it works, but if we’re in a stop-and-go situation, it will quit. Yesterday, we attempted to use the air conditioning for the first time and it did essentially the same thing. That’s when he noticed the temp gauge going up AGAIN.

We did not experience any significant problems on a several hour drive last night until we had a couple of small mountains to cross over. Thankfully the gauge never got into the red, but there was obviously something going on. Because it was night time and there were no weather issues, we didn’t need heat or air conditioning or the de-fogger.

Another (probably unrelated though strangely coincidental) symptom is that right before the temp gauge starts climbing, the emergency brake light comes on - this make me think the problem is electrical somehow.

I’d appreciate any thoughts or comments on similar experiences. We owned a 1998 Sienna for 10 years before we bought this one it was basically problem-free.

That sounds like one or more fans that cool the radiator are not functioning.  When you are driving on a nice level highway, enough air goes through the radiator to keep it cool, but with the A/C on or mountains or stop and go traffic it needs more air and the fans) should be coming on. 

This can be a sensor, wiring, relay or fan motor.

Funny you would suggest that - this problem was initially revealed when we discovered that the blades on both of the fans (in the front of the van open hood, right down inside) had been chewed up by a bolt that was left in the “cabinet” (whatever you call it) they sit in (no kidding, they showed us the bolt). Do you suppose there was more damage done than just the fan blades being damaged? The fans were replaced, naturally, back in November, when problem first presented itself.

With only 28,000 miles on the Sienna, it is possible the original owners never changed the coolant. It might have gone bad after two or three years of not being changed.

If you are driving around with old expired coolant, I would replace the radiator and flush the entire cooling system. Actually, I would:

  1. Perform a chemical flush on the entire cooling system. Make sure you follow the instructions on the bottle to the letter.
  2. Flush the entire cooling system with water to make sure you get all the chemical flush out.
  3. Replace the radiator with a new one. (This step might not actually be necessary, but if it is really clogged, the flush might not fix it.)
  4. Replace the thermostat. It probably isn’t the problem, but it is cheap to replace.
  5. Get the coolant drained and refilled every two years from now on, regardless of mileage.

Of course this advice assumes you are driving around with old coolant. I could be wrong about this.

I have a receipt from November 26 that reads “fill cooling system and bleed”.

Other people seem to be getting this but not me so I will paraphrase. Your engine overheats,your heater sometimes blows hot sometimes not, I must make a assumption when you say that you used your AC and it did the same thing (you must mean “the same thing” is a indicated overheat).

The no heat,indicated overheat makes me think of the old air in system condition but you say “system bleed”

Then you add that use of AC aggravates condition, makes me think radiator is not radiating.

A verification on radiator flow,fan operation,and water pump function would help. The possibility of plugged radiator is in the low end but possible due to coolant age (I do read it is new now) and a impeller failure is also in the low side of possibilities because of the low mileage. Verify fan operation.

I think the key here is to connect the loss of heat output and the indicated over heat

So someone added coolant to the system and bled it on November 26? What year was that? When was the last time the coolant was drained and replaced? Topping off the system and bleeding it doesn’t count if there was any old coolant left in.

Thanks for all of the “insights”. Yes, “same thing” meaning my temp gauge was indicating an overheat. I have an appointment at the dealer tomorrow and I’m going to be very persistent with them in getting this rectified. It sounds like they need to thoroughly check the radiator, along with the coolant and the fan(s). We have a trip planned in two weeks, with 4 kids in tow. Don’t plan to get stuck on the side of the road.

If the dealer changed the thermostat twice, and haven’t been successful in solving the problem, should you be going there, yet, once again?

They have only seen the van once in this problem, the problem actually started on a trip to Canada in November. It’s been 4 different places.

The symptoms are of coolant that has stopped circulating through the radiator and through the heater core. It has stopped circulating because of the steam produced at a hot spot in the engine, or from exhaust gases that are pushing into the coolant passages when the engine gets hot enough to cause an area to open (could be a crack, or could be where two components mate: head to engine block, head to intake manifold).
If you look at the dash area where you thought the emergency brake light came on, you may see the words “low coolant level”. Some Toyotas have that sensor attached to the radiator.
The shop will pressure check the cooling system. The check is usually done when the engine is cool, or lukewarm. Checks at that temperature may show nothing. The mechanic needs to run the engine until the coolant gets as close to boiling (212F degrees) as practical; then, do the pressure check.