Coolant not circulating in '99 Sienna with 185K miles

toyota
coolant
sienna

#1

Our Sienna is overheating. The Toyota service center is looking at it.

  1. They said the top coolant hose was hot, bottom hose cold. They replaced the thermostat and both hoses now hot, but coolant is still not circulating.
  2. The fan not coming on, but when they disconnect the sensor fan comes on. Still no circulation.
  3. They want to try replacing water pump next, not sure this will fix it.

Note: the van was rear ended 1 week before this problem began. Hard enough to knock rear bumper loose on left side, and break parts holding bumper too van, but no major damage.

My questions:

  1. Does anyone know what is likely causing the circulation problem?
  2. Could the rear-end collision have anything to do with the circulation problem?
  3. Do you recommend I stop trying to fix this van (we need a vehicle, but I can’t afford a good van right now) or should I keep trying to fix the van?

#2

If both hoses are hot it would seem that some circulation is occuring, but if the fan’s not coming on it’ll still overheat. Have them fix the fan problem first, then see if there’s still a temperature problem.

If it still overheats it could be the water pump or a partially plugged radiator. Was the water pump replaced when the timing belt was replaced? When was that done?


#3

Has this ever had a water pump replaced? Does the electric fan turn on when you turn on the AC?


#4

I’d pull the radiator first and flow-test it. Just because the top and bottom hoses are now hot doesn’t mean the radiator is not blocked up and restricting flow. I had this problem with my Toyota truck, and the radiator shop couldn’t unblock the radiator with an ultrasonic bath. The new radiator fixed the problem.

Not saying the water pump is not at fault, but it just seems easier to check the radiator than to commit to replacing the water pump.


#5

Remove the thermostat. Replace the housing temporarily. Remove the upper hose from the radiator. Fill the system with water and start the engine. Water should shoot out of the open end of the upper hose with considerable force. If so, the water pump is fine. If it passes this test, pull the radiator and have it flow-tested by a radiator shop.


#6

Thanks for the comments. Some answers to your questions:

  • water pump and timing belt were replaced 6 years and 90K miles ago
  • they pulled the radiator and water flows through it (radiator replaced 2 months ago)
  • fan doesn’t turn once the car overheats, does turn on when it is cold
  • hose was removed from the radiator, water doesn’t shoot from end of hose

Based on your questions, it sounds like this is pointing to a bad water pump, and at bad switch on the fan, correct? …that is what they are going to try replacing next.


#7

It really just sounds like a fan problem to me. Don’t let them replace the water pump on a guess. In fact, this should not be all that complicated at all. Perhaps you need to find a different shop. In fact, why are you taking this senior citizen of a van to a dealer? In general, you will pay way too much and be sold things you don’t need and for no good reason since dealer’s have no special magic knowledge of the cars. Think about finding a good, locally owned, independent mechanic.


#8

Water won’t shoot from the hose when the engine is cold unless the thermostat is removed, it blocks the hole completely. It is supposed to do that.

Disconnecting the sensor does test the fan, so the sensor should be changed anyway, just to make sure you have a good one. The fan is supposed to work before the overheating happens. Just knowing where the right sensor is gives a great starting point. Sensors can fail too. It happened on a four year old car.

If the minivan doesn’t overheat when it’s constantly moving, the water pump is OK. If the engine overheats in stop and go driving, the fan switch (we called it the sensor) is dead and can’t open the circuit.

That is a very likely scenario. Then there’s the radiator. If about 6% of the cross fins are missing (check from the rear) there is no way the radiator can work properly.


#9

Martydew wrote:

water pump and timing belt were replaced 6 years and 90K miles ago

Since the recommended mileage interval for timing belt replacement on that vehicle is “every 90K”, why don’t you just go ahead and do it. While you’re in there for the belt, replacing the water pump is only incremental labor.


#10

Thanks again for the comments.

I took the van to a dealer for two reasons. First, I went to a local shop, they started by raplacing the thermostat, then did a bunch of “diagnostic tests”, then told me the coolant wasn’t flowing through the engine and the only fix was to replace the engine – a $3,000 fix. I figured a 2nd opinion was in order. Second, the dealer replaced the radiators 2 months ago.

I’m pretty sure they removed the thermostat when testing for water flow.

When I drove the van to the dealer, the temperature increase while I was on local street, and went over the max on the temp gauge when I got on the highway. As I mentioned above the radiator is new.

Based on the comment above, it’s sounding like the water pump and sensor/switch are the problem. Between the thermostat, water pump, fan sensor/switch, timing belt and all the of parts they should replace “while replacing the water pump and timing belt”, and labor, the dealer tells me the cost will be between $800 and $1,000. Does this sound right?


#11

I would NOT do this repair unless they guarantee it will cure the problem!! Do NOT pay for guesswork!!

It is quite rare, but I have seen engine blocks so badly corroded (from not changing the anti-freeze) that major cooling passages get blocked off and repair is no longer possible…

AGAIN, ask them to REMOVE THE THERMOSTAT and check for water-pump function…