Help Needed Please!?

[antony140487]

hello i have a 98 2.0td toyota avensis, coolant started boiling recently i have since put a new thermostat, waterpump, and radiator in it and it is still boiling. the temperature hand sits at half ways on the normal working temperature never rises.i also checked the dipstick for a milky substance but it seems ok so the water isnt mixing with the oil so wat could the problem be it is really puzzeling i really like this car and never had bother with it before i hope it is something simple??

[alan333]

You say it's boiling but the temperature guage stays at normal. These two things don't stack up. As you've changed the major components of the cooling system (and bled it properly I assume,) then it could be cylinder head problems and the boiling you can see is actually bubbling ie combustion gases escaping to the water channel and showing in the radiator or header tank.

[antony140487]

You say it's boiling but the temperature guage stays at normal. These two things don't stack up. As you've changed the major components of the cooling system (and bled it properly I assume,) then it could be cylinder head problems and the boiling you can see is actually bubbling ie combustion gases escaping to the water channel and showing in the radiator or header tank.

how do you bleed it? i just filled the radiator with water and top it up when engine was running.this car is owned by my mother and it never gets any abuse i can't see why the gasket would be gone there is 250 000 miles on it but these toyotas should do twice that with no problems?

[antony140487]

hello i have a 98 2.0td toyota avensis, coolant started boiling recently i have since put a new thermostat, waterpump, and radiator in it and it is still boiling. the temperature hand sits at half ways on the normal working temperature never rises.i also checked the dipstick for a milky substance but it seems ok so the water isnt mixing with the oil and she isnt using any water there is no smoke coming from her and she never gets any abuse it is always looked after could it be that the water isnt properly bleed in the system we also took out the thermostat now and the temperature hand doesn't rise at all so wat could the problem be it is really puzzeling i really like this car and never had bother with it before i hope it is something simple??

[alan333]

Often there are bleed points around the system. Look for dust caps or bleed nipples etc on all of the coolant system, slacken these until coolant comes out and tighten. If there are a few then start at the bottom. Feel all the hoses and see if they are hot or cold. Same with the radiator. Mind not chop your hands off with the fan tho.

A cylinder head or cylinder head gasket doesn't necessarily go because an engine is thrashed etc - sometimes they just go. At 250k miles I would certainly consider it possible.

I still don't understand your problem tho. On the one hand you say the coolant is boiling, but on the other you say the temp guage is normal and it's not using water. Surely if it's boiling then coolant is being thrown out the expansion tank or the radiator cap.

Coolant flows throughout the engine and cylinder head, and if there's a fault somewhere then any of the three things can mix. Ie coolant, oil and combustion gas. Therefore you could have combustion gas in your coolant - which could explain the bubbling, or your coolant could be mixing with oil, which would show as the milky substance you looked for earlier, but only if there's enough of it.

The cooling system is basically a water circuit pushed by a pump. The coolant absorbs heat as it is pumped around the engine, then it cools again when it's in the radiator, assisted by fans if it's too hot. The thermostat controls whether all of the system, or only part of it, receives the flow. If the pump is faulty it won't flow and will get too hot. If the radiator is faulty it won't cool it. If the thermostat is faulty it will cut out the radiator and get too hot.

If you're confident your new parts aren't faulty and there's no air in the system then it's fair to say your coolant system is overhauled and you're back to my original diagnosis of cylinder head troubles.

[antony140487]

ok thanks for your speedy and helpful reply. im confident the new parts are working ok i tested the thermostat in a saucepan of boiling water before i put it in the car and it opened. i felt all the pipes and they are warm also the radiator and it is warm so the coolant is flowing around.i think you may be right about the gases in the coolant that would explain bubbling it may not be boiling but just bubbling from the gases but i have since taken out the thermostat and there is no bubbling now and the temperature barely moves from cold position??should it not still be bubbling from the gases?

[alan333]

Yes I'd think it would still bubble without the thermostat fitted, however when the thermostat is closed only part of the cooling system is open to the flow. Ie the engine and the heater. When the thermostat is open the complete system is open, therefore the car won't really heat up unless it's been running for hours, if at all. Perhaps the exhaust gases can seem to disperse better within the longer cycle. Ie with thermostat closed.

Try bleeding the system to make sure it's not trapped air. Other than that I'm pretty stumped and you'll maybe need to do compression tests etc to confirm cylinder head integrity.

[antony140487]

Yes I'd think it would still bubble without the thermostat fitted, however when the thermostat is closed only part of the cooling system is open to the flow. Ie the engine and the heater. When the thermostat is open the complete system is open, therefore the car won't really heat up unless it's been running for hours, if at all. Perhaps the exhaust gases can seem to disperse better within the longer cycle. Ie with thermostat closed.

Try bleeding the system to make sure it's not trapped air. Other than that I'm pretty stumped and you'll maybe need to do compression tests etc to confirm cylinder head integrity.

ok i wil try bleeding her. would the compression test be the wisest thing to do first instead of !Removed! off the head to see if theres a problem and how much roughly does that cost?can you buy a compression tester and how much would one cost?

[alan333]

Any time I've done compression tests I've done them via the injector holes with a simple tester. It's probably not the most accurate one in the world but it gives you an idea. They seem to start around £20 odd quid at machine mart.

[antony140487]

Any time I've done compression tests I've done them via the injector holes with a simple tester. It's probably not the most accurate one in the world but it gives you an idea. They seem to start around £20 odd quid at machine mart.

ok thanks you have been very helpful would you be intereted in buying it ha?