cooling problems - collapsing raiator hose

[Disturbed1]

the other day after giving the car a bit of stick for prolonged period - i pulled up to a halt to notice a loud screetching/whistle noise. quickly turned the car off to notice that the the upper radiator pipe had collapsed due to some form of vaccum. now my cooling system comprises of a 3lt milk bottle as an overflow with holes punched in the top so that its not airtight.

now i believe i have filled up the coolant system properly with the car jacked up on crankign angle so that the rad filler is highest point etc etc hoping that i eliminated any air locks in system.

last night i drove 2 min on a cold engine so had barely heated up to 80 degrre colant temps (oil stuill stone cold). parked up - popped bonnet to fing that the upper rad pipe was throbbing away pulsating and pretty much sounded like it was boiling away.

now im pretty convinced that i dont have a bhg but im stumped as to what it could be

rather then having rad filled to very brim, i had about 500ml less in it so was just coverign the fins in the rad and went on a 2hr extensive road tune session without a drama

have tried a few diff rad caps and that made no diff at all

so im all ears for suggestions

cheers

[zombie]

blocked radiator?
thermostat stuck closed?
other blockage somewhere in cooling system?

[BrianRA23]

The system should not be under vacuum if the cap and overflow bottle are OK. It takes very little vacuum to open the return valve in the middle on the underside of the cap. I have seen these stuck closed with some sort of calcification so check the cap and (after washing with water) try blow and suck to see if it opens and then seals. If the cap is fine then see if the overflow bottle pipes are blocked, including the one that vents to atmosphere.

That said it should not be under vacuum if it hot as some of the water would have turned to steam and created pressure.

Maybe get the radiator backflushed if you don't know when it was last done, since I got one done once and it was apparently 60% blocked.

Which engine is it and where it is the thermostat located?

Suction from the water pump is through the bottom hose (or heater circuit when cold) and some vehicles have a metal spring there to stop it collapsing. If there is a blockage on the engine side of the top hose then the two hoses and radiator could be under vacuum.

[Disturbed1]

is a 7mgte with thermostat in factpry position. is runnign an almost new koyo 50mm aftermarket radiator.

another thing ive noticed aswell but not sure if its related... i got a pivot electronic water temp guage positioned right next to where the factory temp sensor is on the thermostat housing. now while the ecu tells me the water temp goes to 90 degrees then hovers around there (+/- 3 degrees when thermos come on and off etc... my pivot temp gauge flutuates between 110 and 80. if i go off th epivot gauge, when i first start the ca rup and let it warm up, it warms up really slowely to about 90 degrees, then shoots up to 110 in matter of 2nds, then drops back to 80 when thermos click on in matter of seconds and just repeats.

im stumpped

[BrianRA23]

I would say the pivot gauge is probably reading correctly as the factory sensor will be dampened by the epoxy between the outer housing and thermistor inside. Check it by putting in some boiling water. The fluctuation is going to be the opening and closing of the thermostat allowing precooled water from the radiator to surge into the engine whenever the thermostat gets hot enough to allow the water to flow. It sounds like your thermofans are just increasing the difference in the two temps rather than stabilising your engine temperature. In effect you are just bringing the average down by increasing the difference.

I am not familiar with the 7MGTE to where the sensors and thermostat are located, but I assume the thermostat is in the top radiator hose.

In the early 90s Toyota changed their thinking with cooling systems. The thermostat was taken and placed in the bottom hose to try stabilise the temperatures. When closed, water was drawn from the engine block (through the smaller hole in the pic below) and this enabled water to be circulating through the engine and keeping everything around the same temp. Since all the water was running over the thermostat it was sensitive to the temp of the whole engine and started to open, allowing water to be drawn through the radiator and closing off the feed from the engine. As the engine load changed and thermostat opens and closes maintaining the temperature.

This is a similar design I have seen for aftermarket where a T piece is installed in the top and bottom radiator hose with a pipe to run between them and bypass flow through the radiator. The thermostat is removed from the top hose thermostat housing and put in the bottom T piece. If two temp gauges were run (one on engine and one on the radiator) you would see the engine smoothly coming up to operating temp and staying steady, while the radiator one fluctuates with engine loading. My brother has this setup on his late 70s F100 and to get it the way he wants all water going through the radiator must go through a 9mm hole, which considering it weights over 2.5 tonnes, runs on LPG and he drives it through the wheatbelt mid summer is quite amazing.

This F100 and others have shown me that focus on a fancy radiator is often misdirected attention and just causes greater temp variation in the engine. If it were mixtures we would not drive the car but as long as the heavily dampened gauge is sitting steady it never gets a second thought.

Compare this to previous setups where the thermostat stays closed until water in that area gets hot, even if it has been boiling elsewhere. Cold water from the radiator enters the water pump and is pushed through the engine and you end up with a temperature differential between the two. As an example, apparently holden 308 V8s always blow the head gasket on the pot closest to the glove box and this is the last one to get water from the radiator so is potentially 30deg hotter (more in winter). When the cold water hits the themostat it shuts closed until the temp goes up again.

1HDT thermostat housing pic, which is in a similar location to the JZ engines and I assume to be the same. The shadowed area goes to the suction on the water pump. Water is always being drawn though the heater circuit through the top steel pipe and the thermostat moving changes the draw from around the cylinders to the bottom radiator hose as required.

[oldcorollas]

it warms up really slowely to about 90 degrees, then shoots up to 110 in matter of 2nds, then drops back to 80 when thermos click on in matter of seconds and just repeats.

sensor is after the thermostat?

the temp rises slowly as the hot water in the engine leaks past the thermostat.
then when thermostat opens, temp goes up for a bit, then thermostat closes as col water reaches it (since engine volume of water moves out of the engine, to be replaced by cold water from rad)

sound slike you may need to have a slightly larger hole in the thermostat, to keep the temp more stable.

as for hose..
waterpump pulls water from rad, into engine. if the thermostat is too closed (does it have a dongle thing in the hole?) then the water pump will try to suck too much.

[Disturbed1]

thermostat is in factopry position which is at the top of the motor and still contains the original jiggle thing.

ecu engine temp is on the motor side of the thermostat and i have moved the piviot gauge sensor on both sides of the thermostat and it made little difference

[oldcorollas]

same diff.. won't change much which side it is on..

can you cut out the stupid jiggle thing?

[Disturbed1]

can do anything

will cut the sucker out tonight and report back

[oldcorollas]

maybe get a second opinion first

[Disturbed1]

dont have faith in your own advice OC??

just aswell i got a spare thermostat hahah

[oldcorollas]

oh, remember that water doesn't expand or compress much.

if the pump is sucking enough to make the pipe suck in when engine running.... that water is going somewhere.. = air in engine...

[petergoudie]

1) The 'jiggle thing' is meant to vibrate with the engine and break the surface tension of any bubble that might form and will let the air through. If you cut it off there is a chance any air bubble will just stick on the hole with its own surface tension.

2) You said you had a new radiator. Some of these have plugs in the all the inlet/outlets. If there was one inside and you did not remove it, this could be the problem.

[oldcorollas]

even with the force of the water pump pushing against it?

[BrianRA23]

It might be a good thing to go for a drive without the thermostat and see what happens. If there is no difference you have saved a lot of time and can move on to look at something else. If you can't hurt anything then taking bigger steps is a more efficient use of time.

I doubt it is the headgasket, but to test it
Go for a drive and get everything hot, remove the spark plugs and put a cold/cool screwdriver in there. Remove them before they heat up and if there is communication between the cooling system and combustion chamber you will see condensation on the steel. Easy, unless you have individual coils for each sparkplug.