Ping Ray O re: temps for 4AC?

Seems to me on this engine, about 190-200 would be the max for coolant temps (that's Degrees F, BTW)

By any chance, are there any aftermarket accessories installed like fog lights, audio system, security system, remote start, etc.? If so, check the installation very carefully to make sure any power taps or screws are not causing the problem.

This is not easy, but you may want to check to make sure the connectors in the back of the instrument cluster are tight and ground connections are tight. I believe that there is a voltage regulator on the back of the instrument cluster, but they do not fail very often.

Without looking at the actual specifications, I can't say for sure, but I do not think the max temp is that high. My guess would be in the 115 to 200 Celsius range.

If you can get a hold of a factory repair manual, there are voltage or resistance specifications for temperature sender output. You can measure the voltage at the sender and then again at the instrument cluster to see if they are the same. The repair manual also shows how to diagnose whether the instrument cluster is working or not.

There are several and I am not convinced that they haven't caused the problem. The quickest (and hence most efficient) way to check the actual temp was to insert a thermocouple into the coolant stream at roughly the same point as the temp sender and compare. The only draw back of this method is that I do not know the maximum operating temp slated for the 4AC motor.

True, but things fail and considering I have experienced this problem before in other vehicles, I don't consider it outside the realms of probability. The thermocouple shows a temp of 110 and the gauge is _above_ red, which is just not possible (without the usual obvious signs of overheating).

That is the normal op temp, or do you mean max temp that should result in the engine being damaged?

I have replaced the sender unit and both unit where within a small amount of the other in terms of voltage. How this translates into temperature, I don't have that manual with me, nor do I have with me a device to increase the voltage to ensure I have the correct voltage is applied to the gauge.

Many thanks for your input.

Hammo

Coolant

Why so low? I have a pressurised system in the 4AC.

Cheers

Assuming that the thermocouple is correct, then the gauge must be incorrect.

Oops! That was a typo! I meant that my guess was 115 to 120 degrees Celsius. I've since checked the factory repair manual for a Previa, and the max temp is 110 to 120 degrees Celsius so my guess (at least the one I was thinking of and not what I typed) was in the right ballpark.

That max temp range is the temp at which the pressure relief in the radiator cap would open and let the coolant go into the overflow bottle.

I'm thinking that the problem is with the voltage regulator at the back of the instrument cluster. I suspect that replacing it involves replacement of the entire cluster. As a work around, you can install an aftermarket temperature sender and gauge.

Sorry I haven't been more help!

Yup, a pressurized cooling system with a proper mixture of antifreeze/coolant will raise the boiling temperature, much like a pressure cooker. This allows the engine to operate at a more efficient temperature range.

I agree with you here. I wasn't sure what the maximum operating temp would be and as the temp gauge was constantly in the red, I was getting uncomfortable about destroying the car!

I agree with that too. I take it boiling would occur and damage would be beyond that limit. The aftermarket gauge I got had a bulb on it that was and inch too long to fit into the temp sender "hole". It had an upper limit of 267 Farnheit!! The mid range was 116 celcius (~240 F).

------snippp-------

You were helpful indeed!

Cheers

Hammo

Let us know your final resolution. Good luck!