Highlander Coolant temperature low

[MaximaGuy]

The vehicle has over 200K on original radiator, coolant temp sensor and thermostat. Over the past few months the temperature is lower than normal and the hot side hose is not hard enough when driven to pressurize the systm. It could be very well be non-pressurized to my liking and wondering if its the thermostat, radiator cap or just the coolant temperature sensor.

Any ideas on why the coolant hoses are not pressurized when pressed by hands.

 

[clinebarger]

I'd start with a thermostat, Toyota's are known for the rubber insert in the thermostat to deteriorate (arrow).

 

[HowAboutThis]

Originally Posted by MaximaGuy
The vehicle has over 200K on original radiator, coolant temp sensor and thermostat. Over the past few months the temperature is lower than normal and the hot side hose is not hard enough when driven to pressurize the systm. It could be very well be non-pressurized to my liking and wondering if its the thermostat, radiator cap or just the coolant temperature sensor.

Any ideas on why the coolant hoses are not pressurized when pressed by hands.



Have you kept up on maintenance? Flushes on time and such for coolant? How do you know the temp is low? Reading a dash gauge, OBDII readings, or??? Just curious how you've diagnosed it. Is fluid up in the overflow tank when cold? More often than not I've dealt with thermostats stuck open with things similar to what you're saying. But it can quickly turn into guessing and a lot of random parts and annoyance. Kind of depends on what your goals with the car are and if you do your in work or bring it to a mechanic, too.

 

[MaximaGuy]

The vehicle temperature is low on the instrument gauge although I could pull up the ODB numbers to be sure.
Other maintenance done thus far on the vehicle include a) replaced timing belt, water pump, coolant at 120K b) replaced coolant most of it at 180K by draining radiator and bolt under the B2 cat for the block drain (B1 is a PITA to get to). Always OEM coolant, the radiator cap looks new so it must have been replaced sometime cannot recollect.

As I said once the closed loop is in play the hot side is usually hard but that isn't the case and quite possibly its not a pressurized closed loop when the engine is hot leading me to believe its an open thermostat.

 

[mk378]

The only thing that causes "overcooling" is the thermostat stuck open. Replace it.

Pressure in the system results from the coolant expanding as it heats up. So no warm up, no pressure. When very hot, pressure is a good thing as it raises the boiling point. At lower temperatures it doesn't matter.

 

[Imp4]

Originally Posted by MaximaGuy
The vehicle temperature is low on the instrument gauge although I could pull up the ODB numbers to be sure.

I'd definitely start with the thermostat if the vehicle never comes up to temperature. Even more so if it is the original.
An OEM thermostat is about $25 on Amazon.
Spend the few dollars extra and you'll thank yourself later...

 

[wag123]

A situation like this will usually throw a CEL.

 

[MaximaGuy]

Originally Posted by wag123
A situation like this will usually throw a CEL.


Not in the case of a open thermostat and yes if the temperature is above 190F (highly doubt a code is thrown on low temperature)

 

[JMJNet]

Start with t-stat, make sure you get the Toyota Genuine on this one.
Stealership part is usually not much more expensive than the part store high end t-stat.

While doing it, you may want to replace the radiator hose and the radiator cap.
Hose does not need to be OE/Genuine but radiator cap need to be Genuine.

 

[Yah-Tah-Hey]

Originally Posted by JMJNet
Start with t-stat, make sure you get the Toyota Genuine on this one.
Stealership part is usually not much more expensive than the part store high end t-stat.

While doing it, you may want to replace the radiator hose and the radiator cap.
Hose does not need to be OE/Genuine but radiator cap need to be Genuine.

Right on JMJ. I would also use OEM hoses. Reuse the OEM constant tension clamps. Resist the urge to replace with screw clamps. You won't do any better that the OEM clamps not matter what some was may tell you. Those OEM clamps may look like a simple affair but they have a lot of engineering behind them. OEM all the way when it comes to cooling system. Regards

 

[wag123]

Originally Posted by MaximaGuy
Originally Posted by wag123
A situation like this will usually throw a CEL.


Not in the case of a open thermostat and yes if the temperature is above 190F (highly doubt a code is thrown on low temperature)
I beg to differ. I have seen this myself and the computer was storing a P0128 code.
The OBDII trouble code P0128 - Coolant Temperature Below Thermostat Regulating Temperature, means that the engine does not reach expected temperature after running for sufficient time, or in other words, takes too long to warm up. This code will typically cause the Check Engine light to come on. In addition to a faulty or sticky thermostat, a faulty engine coolant temperature sensor can cause this.

 

[MaximaGuy]

Originally Posted by wag123

The OBDII trouble code P0128 - Coolant Temperature Below Thermostat Regulating Temperature, means that the engine does not reach expected temperature after running for sufficient time, or in other words, takes too long to warm up. This code will typically cause the Check Engine light to come on. In addition to a faulty or sticky thermostat, a faulty engine coolant temperature sensor can cause this.


Good, I did go and hook up the OBB2 scanner and there were no codes registered in the vehicle. I may get this code in winter in all probability given a slow death of either the coolant temperature sensor or the in-deterministic thermostat

 

[wag123]

If the cooling system is not pressurizing the temperature will run low. First, I would replace the radiator cap. If that doesn't solve the problem you need to do a pressure test on the cooling system. Also, you can't discount the possibility that the temperature gauge is not reading correctly.

 

[Navi]

A car with 200k miles is due for a thermostat replacement and a coolant flush. The coolant cap and reservoir probably need to be replaced as well.

If you really want to figure it out take it to the dealer to diagnose and they will charge you 1 hour of labor for diagnosis. $130?? Seems expensive but better than guessing and replacing parts and waste time.

In any event the car is due for a flush, thermostat and coolant cap. Possibly a reservoir too if its brittle.

 

[GSCJR]

On my 2003 I always monitored warm up times from a cold start. When heat is selected the blower motor is not commanded until a target coolant temperature is met. No matter how frigid it got it would always turn on between 180 to 240 seconds until about two years ago. I also noticed within those two years the temperature gauge needle would sit about a millimetre lower but heat output was still strong as always with a 30 delay at most. Fast forward two years and I decide to replace some original parts in search of perfection. I replaced the radiator cap and thermostat with genuine Toyota parts with no change to the gauge reading or warm up times. I also tried replacing the coolant temperature sending unit (aftermarket) with no change as well. I drove the Highlander for another year and then sold it as the undercarriage was beginning to show it's age from living in the rust belt.

 

[MaximaGuy]

OK. I wanted to tackle this first thing on a Sunday when there is better weather to work on.. Bought OEM coolant, radiator cap, thermostat and gasket.

I also bought a radiator cap from the dealership and that was the first thing to remove and replace - lo behold there looked different and closer examination there is a small plunger in the center that was gone, it snapped and must have fallen into the radiator. For now the cap is replaced will tackle the replacement of the thermostat in winter!!

Hopefully the system gets pressurized now!!

 

[GSCJR]

It should help your situation. That happened to me once on a Prius I was working on, I was unable to get the genuine Toyota rad cap right away so I ordered an aftermarket one and it failed almost immediately. Thank goodness the factory one was still lying around because it worked better than the NEW leaking aftermarket one it replaced.