Corolla coolant temp?

Hammo,

To answer the question you ask, gauges are reasonably reliable in helping you spot any changes but not terribly accurate at registering emperical temperatures accurately. If a gauge always sits at a particular mark, a change off that mark indicates a potential problem even though a claimed absolute temperature e.g. 110C might be off by 10-15%. This is why most gauges simply read "cold" and "hot."

One possible source of your problem is that the lower coolant hose may be collapsing at higher engine RPMs once it's had a chance to warm and soften. Once you start seeing the symptoms at the gauge, open the hood and rev the engine while keeping a close eye on the lower hose. If you see it move, try to kink or "suck in" that may be your problem.

A scaled radiator may also be a cause, but your rapid onset of symptoms is unusual for this unless you've got actual rust flakes in the coolant or did some other work on the cooling system and used silicone rubber to aid in sealing (which can put solid beads of gasket goo into the coolant).

-- Mike Harris Austin, TX

Did you flush the radiator? I bet it's full of gunk.

____ That was my thought too, that the radiator may needing a good flushing or rodding out.

Hi Mike

No noticeable issues with the lower hose kinking, or collapsing.

TRemp gauge srops when heater is open up.

Thermocouple on on thermostat housing shows 85 (degrees centrigrade), then thermo fans kick on, drops temp to 80, then works up to 85, comes on etc.

Thermo couple at water pump top radiator house junction shows 80-85 C, gauge is showing 7/8 of full scale.

Both hoses are firm and hot to touch.

Car is now cold and squeezing top hoses is moving water in bottom hose and can hear the thermostat in the housing being moved.

My thoughts were to pull the temp sender and see what it reads vs a thermocouple. Also thought of removing the thermostat and seeing what difference that makes.

Any other ideas?

Cheers

Hammo

Mike Harris wrote:

Can't see any gunk in there (when drained and flushed), though, thats not to say it aint full of crap!

Cheers

Hammo

As Hachiroku suggested, check the radiator and coolant condition. The coolant should be translucent and the radiator should be free of scales and rust. Also, the fins should be free from any debris or restrictions to air flow.

Check the base ignition timing. Timing that is too advanced can cause higher temperatures.

Check EGR operation.

If you have an automatic transmission, check the condition of the ATF. It should be red and translucent.

You mentioned that you can squeeze the hoses when the engine is cold. The hoses should be pretty stiff and difficult to squeeze when cold. If you can squeeze the hose, consider replacing them.

You also mentioned that you can hear the coolant move when you squeeze the hose. You should not be able to hear the coolant move when you squeeze the hoses. With the engine cold, check the coolant level under the radiator cap. It should be up to the bottom of the radiator neck and the overflow bottle should be to the cold mark. If there is air in the radiator, set the heater to full hot, start the engine, and top off the coolant.

You mentioned that you can hear the thermostat moving when you squeeze the hose - you should not be able to hear the thermostat move in the housing. Hopefully, it is the correct thermostat and the spring is oriented down.

If the radiator cap is cool enough to touch when the gauge is reading normal or high then you most likely have a circulation problem.

This could be caused by a blockage or faulty pump.

Yes, this was flushed and replaced some 3000 kays ago in anticipation of freeway driving.

Where and what does this pollution control thing look like? How do you check it?

Maybe, though, I'd be surprised if most people couldn't squeeze radiator hoses when cold

Not on this engine! The thermostat housing is NOT orientated that way. The movement I refer to is a clicking or ticking sound of something that is restriciting flow, and, seeing as it coming from the thermostat housing, the thermostat is the most likely candidate.

Cheers

Hammo

By cool enough, I mean placing your finger on it and they don't get burn't straight away. The centre of the cap is cooler than the circumference. The radiator feels uniformly hot from top to bottom. Hoses feel hot and difficult to squeeze, indicating to me at least that they have pressure.

Heater on open drops the temperature guage by 1/5 - 1/7 of scale.

No obvious scale, debris or blockages.

Hammo

The Exhaust Gas Recirculation Valve is on the intake manifold and has a pipe leading to the exhaust manifold.

This link from Auto Zone, a parts store in the U.S., has procedures for checking the EGR as well as a drawing of the valve:

I don't remember how the thermostat housing is oriented in that engine, I'll assume that you installed it correctly.

The thermostat has what I call a jiggler valve, basically a small hole on the flange with a piece of sheet metal stuck in the hole. You may be hearing that piece of sheet metal moving in the hole, and if so, you must have really good hearing. I would open the housing and see if there is anything stuck in there. It is possible that something is keeping the thermostat from opening all the way.

leading to the exhaust manifold.

checking the EGR as well as a drawing of the valve:

port on the EGR valve, and if you apply vacuum while

assume that you installed it correctly.

flange with a piece of sheet metal stuck in the

so, you must have really good hearing. I would

that something is keeping the thermostat from

Check all the vacuum hose's for leaks while your at it.

GL Dan

Ah, thanks.

Ta. There is only one way the thermostat can go in, unless you like leaks, it can't be put in backwards.

Ah, OK, that makes perfect sense. Looking at the thermostat that i replaced the current one with, the "jigger valave" would be the obvious candidate to be making that noise. Listening for noises is all part of my job! I've yet to remove the housing to inspect for anything foreign matter in there. The original thermostat had a "pre -set" gap in the thermostat that made it slightly open at all times. Would you think it is likely that this was someones attempt to deal with the same problem?

Also, seeing as the tacho is jumping about like a mad bee, do you think that there maybe some sort of weird interferance that allows the gauge to increase as a function of time that would reflect the increased (albeit erronous to my view) temperature?

I am at a loss to why I get a thermocouple reading of 85 at the thermostat housing that coincides with the thermo fas going on and then ceasing when the reading is 80, whilst the gauge is showing a very steady 2 needle widths below the upper temp limit. The thermocouple on the water pump elbow (approx 4 inches) from the temp sender shows 85 degrees c. Where in your opinion should the gauge be sitting to reflect this measured temperature?

Cheers

Hammo

There has to be some kind of bypass to allow some coolant to circulate before the thermostat opens. The jiggler valve makes it easier to properly fill the cooling system after it has been drained.

BTW, when you replaced the thermostat, did you make sure that they open at the same temperature?

Possibly. Do you have any aftermarket accessories like a remote start, security system, audio system, cruise control, etc.? It is possible that the accessory installation has interfered with the gauge wire harness.

At those temps, my guess is that the temp gauge on the instrument panel should be between half and 3/4. The factory service manual can give you more exact specifications as well as procedures for checking sender resistance and gauge resistance. It is possible that the vehicle is not actually overheating and you are getting erroneous readings.

Dang, man, you've done your homework on this one! What is the physical condition of the radiator? Have you looked for kinked or damaged tubing? I am assuming you have electric fans on this, try wiring them temporarily to a switch inside the car, and keep an eye on the temp gauge. When it starts to climb, switch the fans on and watch the gauge. Even if they are turning on, they may be weak.

You seemed to have coverd all the bases, when you find out what it is, inform us!!! This is a weird one!

BTW, any guess as to the condition of the head gasket? Have you 'sniffed' the coolant for traces of exhaust? Even though things may seem normal, the gasket may be on it's way out.

Good Luck!!!

Oh, BTW, does this happen when the AC is on, or does it matter? There is an extra fan that comes on when the AC is on; I had a Nissan 240SX that this wasn't working on and it would overheat with the AC on. I'm guessing you already checked this, but it took me a 'minute' to figure it out... ;)