Diagnosis makes no sense

bobuk said:
Thermostat ?
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Yes, check this. They can sometimes stick.

When the engine is cold, the thermostat is closed to force the coolant to stay within the engine loop and heat up the engine quicker from cold. As it rises, the thermostat will open, allowing the coolant to enter the "cooling loop" (pass through the radiator) and be cooled down prior to entering the engine loop again.

This "cooling loop" is also where your hot air from the blowers comes from so, if you the hot air stops, it could be the thermostat jamming shut.
 
Richie said:
Yes, check this. They can sometimes stick.

When the engine is cold, the thermostat is closed to force the coolant to stay within the engine loop and heat up the engine quicker from cold. As it rises, the thermostat will open, allowing the coolant to enter the "cooling loop" (pass through the radiator) and be cooled down prior to entering the engine loop again.

This "cooling loop" is also where your hot air from the blowers comes from so, if you the hot air stops, it could be the thermostat jamming shut.
Click to expand...
Nope, generally the heater core is not on the "cooling" side - it runs straight to/from the block without going through the t'stat. Otherwise you'd get zero hot air in the car before the engine was fully up to temperature (they generally start opening around 90 degrees). They're also designed to fail open - so with a failed thermostat the engine won't get up to temperature, rather than overheat.
 
Sinbad2000 said:
Nope, generally the heater core is not on the "cooling" side - it runs straight to/from the block without going through the t'stat. Otherwise you'd get zero hot air in the car before the engine was fully up to temperature (they generally start opening around 90 degrees).
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Generally? So not every time?

Sinbad2000 said:
They're also designed to fail open - so with a failed thermostat the engine won't get up to temperature, rather than overheat.
Click to expand...

That's all well and good unless they stick...How does a sticking thermostat fail open if its stuck :confused:... I had it happen on one of the Astras I had. Give it a few tap and it opens. I then removed it and freed it up before refitting.

Depending on where the thermostat is located, it can be a simple thing to check before starting more involved repairs
 
Richie said:
Generally? So not every time?



That's all well and good unless they stick...How does a sticking thermostat fail open if its stuck :confused:... I had it happen on one of the Astras I had. Give it a few tap and it opens. I then removed it and freed it up before refitting.

Depending on where the thermostat is located, it can be a simple thing to check before starting more involved repairs
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I say generally because I don't know every car out there :D But it would not make sense to have the heater core outside the thermostat.
Sticking closed? That's a major design flaw, reminds me why I don't buy GM :D
 
Sinbad2000 said:
They're also designed to fail open - so with a failed thermostat the engine won't get up to temperature, rather than overheat.

I didn't know they had changed the design, normally they fail closed (spring pressure forcing the wax sat closed.)
 
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glenman1966 said:
Recently car is overheating after about 15mins,if driving fast,ie motorway,heating sometimes works,then dosent,then needle starts climbing,additionally alternator pulley is faulty,metal shearings can be felt,when putting hand in,on leaving it into garage,was told need a new alternator,fair enough,but when i asked about car overheating,he said replacing it would cure heating problem, surely given that my water pump is driven off the timing belt(vectra ctdi )this wont be the case
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Could be, blocked radiator, coolant hose collapsing, water pump impeller faulty, cooling fan not working, head gasket leaking, blocked air flow, is it only on the motorway ?
 
bobuk said:
Sinbad2000 said:
They're also designed to fail open - so with a failed thermostat the engine won't get up to temperature, rather than overheat.

I didn't know they had changed the design, normally they fail closed (spring pressure forcing the wax sat closed.)
Click to expand...
crossroadsfw.com

Understanding Thermostat Failure Modes - Learning About Auto Service Tasks

Performing routine auto service on your vehicle can keep it in excellent condition for years to come. Check out how auto service will benefit you.
crossroadsfw.com crossroadsfw.com

One Component, Two Failure Modes

Your thermostat's job isn't complicated: spring open when the engine is hot, and stay closed when it's cold. These two states also reveal the two common ways that a thermostat may fail. Thermostats typically stop working when they become stuck, which can happen while open, closed, or anywhere in between.

Manufacturers design their thermostats to fail in a safe or open position. Thermostats that fail open allow a steady stream of coolant into the engine from the moment you turn the car on, which prevents your motor from reaching its optimal temperature. Cold temperatures can cause your car to run poorly, burn more gas, and even accelerate wear on internal engine components.

While there are severe consequences to your thermostat sticking open, they pale in comparison to a thermostat that's stuck closed. In this case, the coolant won't flow through your engine at all, causing it to overheat rapidly. This situation can result in rapid engine damage, especially in warm temperatures or if you attempt to drive the car while your thermostat is stuck.

Thermostats rarely fail in the closed position, but it can happen, and it's critical to recognize the signs of overheating and act quickly.

This matches my understanding of the device :) (and my experience)
 
Sinbad2000 said:
crossroadsfw.com

Understanding Thermostat Failure Modes - Learning About Auto Service Tasks

Performing routine auto service on your vehicle can keep it in excellent condition for years to come. Check out how auto service will benefit you.
crossroadsfw.com crossroadsfw.com

One Component, Two Failure Modes

Your thermostat's job isn't complicated: spring open when the engine is hot, and stay closed when it's cold. These two states also reveal the two common ways that a thermostat may fail. Thermostats typically stop working when they become stuck, which can happen while open, closed, or anywhere in between.

Manufacturers design their thermostats to fail in a safe or open position. Thermostats that fail open allow a steady stream of coolant into the engine from the moment you turn the car on, which prevents your motor from reaching its optimal temperature. Cold temperatures can cause your car to run poorly, burn more gas, and even accelerate wear on internal engine components.

While there are severe consequences to your thermostat sticking open, they pale in comparison to a thermostat that's stuck closed. In this case, the coolant won't flow through your engine at all, causing it to overheat rapidly. This situation can result in rapid engine damage, especially in warm temperatures or if you attempt to drive the car while your thermostat is stuck.

Thermostats rarely fail in the closed position, but it can happen, and it's critical to recognize the signs of overheating and act quickly.

This matches my understanding of the device :) (and my experience)
Click to expand...
For me personally,its best case impeller,worst pump failure
 
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