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Overheating?


peterd

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So I took the ke35 for a longer drive than usual the other night. On the way home, I sat on 90kmh for about 40 minutes in the pouring rain. Everything seemed fine until I got home and noticed the steam pouring out from the side of the bonnet. The overflow tank was full and bubbling away. The temp gauge was on about 10%, which is where it normally sits. 

The next morning I checked the coolant level in the radiator and of course it was low. I checked the plugs looking for a clean one, wondering if I'd blown the head gasket. All ok here. 

I flushed the radiator, changed the thermostat and put a new cap on the radiator. The old cap was really loose when compared to the new one, so I assumed this was the problem. 

Driving around again, it seems fine, but I haven't had it on the freeeway. The temp gauge was still on 10%. I wondered why the temp gauge never went up when it was bubbling away. So now I've replaced the temp sensor and instead of sitting on 10%, it's now sitting on 90%.

Now I don't know if it's actually running hot all the time or if there's nothing to worry about. 

How can I tell where the temperature is really at? 

Sorry for the novel. 

Thanks. 

4k/5k head. Trimatic. 

 

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Nearly the same thing happened to the Princess' ke55 in as much as the temp said normal but she had blown a heater hose and dumped most of the water out. My theory was there was no water around the temp sensor so the gauge couldn't read the true water temp. I have found in the past that all temp sensors are not calibrated the same. I have changed same for same and the gauge reads differently. The best way is to install a proper temp gauge and use a thermometer to check its accuracy.

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I found this on an old thread about the difference between 4k and 5k temp senders. With my motor being a 4k/5k hybrid, maybe my temp is fine and I just  have the wrong sender. 

"When I chucked my 5K into my KE30 I had to swap the senders over. The temp kept reading really high as if it was overheating but it wasn't. There must be a real reason, not cosmetic, as to why Toyota did this." 

 
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"The best way is to install a proper temp gauge and use a thermometer to check its accuracy. "

Yep- buy a 110deg thermometer for $10. Then idle the motor from dead cold to the maximum it gets to with the rad cap off and the thermometer in the top of the radiator. You can slip a sheet of newspaper down in front of the rad to help it as the motor isn't under load.

Note down the temp and time it takes, and you will get a  curve.  If the temp gets to 100deg you have a problem, the cooling system just isn't up to it anymore.  It should show cold, then quite quickly go to 75deg or so, and slowly climb to maybe 80 odd. Then you will know what temperature the marks on the gauge really mean.

In pouring rain it shouldn't get hot at all.

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Hi Peter,

              There are two (2) guages in the car that are critical, being the coolant water temperature, & the fuel tank level.

Both guage needles work by a bi-metal strip, with a tiny heater winding around it. The current through the heater winding heats the bi-metal strip & the needle bends. Simple ! The current in these guages are controlled by the wire wound variable resistance sender in the fuel tank, & the variable resistance temperature sensor screwed into the thermostat housing.

However, there is another variable. If the battery voltage is high, the guages will read higher. If the battery voltage is low, the guages will read lower.  To overcome this issue, Toyota designed both guages to not operate on 12 volts, like everything else in your car.  The guages run off 7 or 8 volts, supplied by a little electronic regulator, on the back of your dash panel, or as I found once, a mechanical regulator built into a guage itself.

https://www.rollaclub.com/board/topic/73224-that-pesky-little-guage-voltage-regulator/?tab=comments#comment-708505

As the battery voltage should never get below 7-8 volts, then the guages should always read repeatably & accurately, irrespectively, of what the alternator output voltage is.  Unfortunately, these regulators do fail, or sag usually, resulting in low readings.  OK, if it's the fuel guage, you just fill up a bit earlier, & don't run out of petrol.  However, with coolant temp, it results in a reading lower than what it actually is. I say reading; but there are no definitive readings on either guages, just coloured bands.

Personally I would fit new hi quality coolant gauge & sensor for both, as others above have suggested.

If you buy a good quality coolant temp guage, it will invariably come with a matching sensor.

Cheers Banjo  

 

 

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Hi Peter,

               If you can't afford a $50 temp guage, you might like to try one of these 52mm type, selling on ebay for around $ 10.00 complete with sensor & mounting bracket, & free postage.

https://www.ebay.com.au/itm/2-52mm-Car-Auto-Digital-LED-Water-Temp-Temperature-Gauge-Kit-40-120-Black-12V/222900115049?epid=503179273&hash=item33e5e1d669%3Ag%3AQoMAAOSwVqlaOjpE&_sacat=0&_nkw=2"+DC12V+Car+Auto+Tint+Pointer+Water+Temperature+LED+Temp+&_from=R40&rt=nc&_trksid=m570.l1313

I bought one a couple of months ago, thinking, if its's a dud, then I've only done $ 10.  It is still going perfectly, & surprisingly is very accurate.

However, if you can afford a good VDO unit, as Dave has suggested, you will have a temp guage that will probably outlast the car. 

Cheers Banjo

 

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1 hour ago, Banjo said:

 If you can't afford a $50 temp guage, you might like to try one of these 52mm type, selling on ebay for around $ 10.00 complete with sensor & mounting bracket, & free postage.

Quick question--is the sensor the right size for the hole in the thermostat? I found it hard to find adaptors when I looked for a friends cars, and when we finally did it cost twice as much as that gauge!

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Hi Jasper,

                  Just saw your question, & had to nip outside in the dark, & take a look under the bonnet, as I couldn't remember whether it required an adaptor or not.  It did, require an adaptor, as the original Toyota one was M16 thread, & i think the one that came with the temp guage was M10, or something small.  Luckily I had a box full of adaptors I've collected over the years, which include what I needed.  However, I think you are right, that the brass adaptors are a bit exxy, as the ones available all seem to be VDO brand.

Cheers Banjo

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I put one a vdo one on a 4k. I don't recall having any issues. The threads are all standard sizes. Worst case you'll just have to get a threaded reducing bush. M12 to m10 or something. 

I only said vdo cause they are a known brand and are dirty cheap. And the gauges look fairly OEM. On my old ke70 I put the vdo temp gauge inside the cluster where the old temp gauge was. Just hacked it up and stuck it in. Looked factory. Any gauge with numbers is the go. Like banjo  suggests even a $10 jobby will do!

I'm a sucker for data so I always put a proper temp gauge in my old cars. Gives me something to stare at in stop start traffic.

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Quote

I'm a sucker for data so I always put a proper temp gauge in my old cars. Gives me something to stare at in stop start traffic.

 

Love it !  I'm a sucker for data also.   I log it, as well as watch it real-time.  Then I can look at it, at home, even when I'm not driving.

There is a couple of sayings within the "measurement industry".

"What gets measured, gets managed !"

&

Without data, it's only a matter of opinion !"

Cheers Banjo

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