Abnormal Overheating

[andylaurel]

My 13T-U split a heater hose that runs between the water pump and just under the Carb. The engine hadn't overheated at all, because i had spotted the heater hose split and kept the radiator topped up. I replaced the heater hose and refilled the radiator with water. I took the car for a good thrashing and the car held its temperature beautifully. It was not leaking any water at all.

After only 15 mins of testing the temperature was still normal. However the next time i drove the car, the temperature climbed very slowly but never stabilized, nearly reaching the red mark on the factory gauge. The engine is still not leaking any water, its not boiling the coolant in the overflow either, but it slowly gets hotter and hotter.

Thoughts and diagnosis if you will?

My thoughts are that coincidentally, the thermostat has given up the ghost and the overheating has nothing to do with the replacing of aforementioned heater hose.

The car is a 1979 Toyota Sprinter 1.8 XL

[mumblezzz]

Has your car been hanging out with any 7M's? It might have got some ideas.

[IN 05 NT]

have you given the car a pressure test?

are you running the right radiator cap? ie is it a return type cap if its running an overflow bottle?

replace the thermostat, and jack the front of the car up as high as you can get it and BLEED the cooling syst of any air that may be in there,

running a thermo fan? or mechanical fan? if thermo, check that its operating as normal..

whats the condition of the rad? very dirty? might pay to get it cleaned out...

blake

[oldcorollas]

check thermostat first.... check all the above.. check there is still water in there.. etc
.

[EldarO]

my bets on the cooling system having air pockets like a marfucker.

bleed it like a fish.

[LeeRoy]

Temp sensors cant read air though and if there is no water then they display the engine as being cold.

[EldarO]

bubbles in the cooling track can do funny things, especially when the bubbles get to the pump and the pump cant push the water in front of it because all its spinning is air.

that said, your correct, but weirder things have happened :|

[LeeRoy]

Yeh 4a's and a low coolant level play havoc with the idle with the computer kicking in the cold start from the fake 'cold' reading.

[EldarO]

ive had 3 7M's, ive had every issue anyone, anywhere, anytime could ever have with a cooling system, and 98% of the time, whatever it was doing could only be justified by the fact that it was a 7M...

(cartman voice) ILL DO WHAT I WANT!

[thanhngo]

Here are few things you could try
* Recheck all other coolant hoses, clamps. (if one died, maybe few others maybe in bad condition), no kinks
* Thermostat is operational (boil it and see if the valve opens at specs)
* Pressure cap (ensure the rubber seal is in tact)
* clogged radiator? look down the filler to inspect the fins / channels
* faulty sensor? rare but possible.
* in the absolute worst case, warped head/gasket

[-GT-]

Temp sensors cant read air though and if there is no water then they display the engine as being cold.

Why can’t it measure the temperature of air? It reads temp as you said, how would it know whether it’s immersed in water or air? Given that air and water temp sensors are different styles it might not be the optimum way of measuring the temp of air, but it would still read? The sender doesn’t earth out through the water, so it’s resistance will still vary with temperature…

If anything, if it was surrounded by a bubble in the cooling system I would expect it to read higher, and probably rise gradually, as when there’s water flowing past it it would be ‘cooled’ like the rest of the block; without this water I would expect it to heatsoak from the block around it, conductivity increase, and hence read a higher temp??

As to the question, i agree with others, re-bleed system. If all else fails, is it possible the earth for the guage has been damaged or has become dodgy? I had a water temp guage behave exactly the same way, turns out the gauge 'damping' earth (3rd wire, 2nd earth off dash) was disconnected, guage would gradually rise to the top and hold, and would fall then hold when ignition was switched off then on again.

Something else to try if you run out of ideas.

[EldarO]

its just the way the sender works, water transfers heat energy a FUCKload better than air does...

i think thats the "technical" explanation, dont quote me lol

[-GT-]

Yeah i agree, that's what i was thinking, but figured the block would be hotter than the water..? ie without the water transfering so much energy out of the sender, it's temp would rise above the ~80-90C that the water is at?

The water has to be colder than the block, otherwise it doesn't work as coolant!

[EldarO]

water coming in fromt he radiator should be colder than the block, yeah, water going out should be the same temp theoretically, but is prob a few degrees lower.

remember, the temp senders are usually in the thermostat housing, the waters last port of call (aside from the top radiator hose) before being cooled by the radiator.

[-GT-]

remember, the temp senders are usually in the thermostat housing, the waters last port of call (aside from the top radiator hose) before being cooled by the radiator.

Exactly! What's normal max operating water temp from that sender? Cylinder temps get up to several hundred degrees, and that heat is transfered out through the block into the water. The water won't get close to the same temp as the block it's cooling, and that's a good thing, as the energy transfer is more the greater the difference in temps.

Massively OT though, sorry!