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Temp Sensor(s) gone whacko

Posted by Kelly 
March 31, 2011 09:13PM
Hi Kids,

Well, about a week after resolving the disappearing coolant mystery (slow leak in water pump), another mystery appears. So Beemie and I driving to work, and usually it is fully warmed up after about 2 miles when we reach the bridge. HaHa, not today. No, the engine starts cooling down according to the temp gauge. I make a safe u-turn, and we roll back to the mechs before crossing the bridge.

The mechs check the coolant level which I'm pretty sure was fine. I know the coolant level sensor works. They want me to return next week.

Up until today, the temp gauge almost always landed on the white mark which is half way between the blue zone and the upper vertical white mark. Now it barely moves out of the blue.

Thoughts?

Kelly
March 31, 2011 09:27PM
Kelly,

Was the thermostat also replaced along with the water pump? I experience this same type of phenomenon when my t-betl, water pump and thermostat were replaced. In the end the thermostat(brand new) failed within a couple of months. The new one; that I personally put in; always read a little lower than the original one did but since the actual coolant temperature(measured twice) was within normal operating spec; I simply learned to live with the lower gauge readings.

It is highly unlikely that your gauge or the sensor suddenly changed...the more obvious culprit would be the thermostat; new or not.
March 31, 2011 11:48PM
I have had a thermostat fail like that. It was pretty annoying too as it happened in January. The gas mileage went south too. The thermostat failed structurally on the bridge that supports the thermal pill. It consequently would not close completely. I was never able to find another that went to the 85C temp and my mileage has not been the same since.

Bob in Everett
April 01, 2011 01:05PM
Agreed, most new thermostats today fail in the open position, unlike the old ones that would fail closed, and end up cooking your motor.
I am sure you will find that to be the problem.

----------------------------------------------------------------------------------------------------------------------------------
E30'S AREN'T BUILT, THEY'RE CAUGHT IN THE WILD!!!



When in doubt, use full throttle,
it may not improve the situation, but it will end the suspence.
April 05, 2011 09:28PM
Quote
Archeo-peteriX
Kelly,

Was the thermostat also replaced along with the water pump? I experience this same type of phenomenon when my t-betl, water pump and thermostat were replaced. In the end the thermostat(brand new) failed within a couple of months. The new one; that I personally put in; always read a little lower than the original one did but since the actual coolant temperature(measured twice) was within normal operating spec; I simply learned to live with the lower gauge readings.

It is highly unlikely that your gauge or the sensor suddenly changed...the more obvious culprit would be the thermostat; new or not.

Hi All,

I do not think that the thermostat was replaced with the water pump almost 4 years ago. I could be wrong. I'll need to check the mech's bill.

A thermostat failure would make sense. The engine will eventually heat up: it just takes a heck of a long time.

Humm. Am I sensing a failure trend? Should I just call the mechs and sch the timing belt, water pump, and thermostat replacement for next week rather than next month?

Is the problem decreasing my MPG? Even more motivation not to wait.

Thanks a ton, Kelly :-)
rkj
April 05, 2011 09:51PM
Quote
Kelly
Quote
Archeo-peteriX
Kelly,

Was the thermostat also replaced along with the water pump? I experience this same type of phenomenon when my t-betl, water pump and thermostat were replaced. In the end the thermostat(brand new) failed within a couple of months. The new one; that I personally put in; always read a little lower than the original one did but since the actual coolant temperature(measured twice) was within normal operating spec; I simply learned to live with the lower gauge readings.

It is highly unlikely that your gauge or the sensor suddenly changed...the more obvious culprit would be the thermostat; new or not.

Hi All,

I do not think that the thermostat was replaced with the water pump almost 4 years ago. I could be wrong. I'll need to check the mech's bill.

A thermostat failure would make sense. The engine will eventually heat up: it just takes a heck of a long time.

Humm. Am I sensing a failure trend? Should I just call the mechs and sch the timing belt, water pump, and thermostat replacement for next week rather than next month?

Is the problem decreasing my MPG? Even more motivation not to wait.

Thanks a ton, Kelly :-)

How long since your last belt, mileage/time?
April 06, 2011 07:02PM
Quote
rkj
Quote
Kelly
Quote
Archeo-peteriX
Kelly,

Was the thermostat also replaced along with the water pump? I experience this same type of phenomenon when my t-betl, water pump and thermostat were replaced. In the end the thermostat(brand new) failed within a couple of months. The new one; that I personally put in; always read a little lower than the original one did but since the actual coolant temperature(measured twice) was within normal operating spec; I simply learned to live with the lower gauge readings.

It is highly unlikely that your gauge or the sensor suddenly changed...the more obvious culprit would be the thermostat; new or not.

Hi All,

I do not think that the thermostat was replaced with the water pump almost 4 years ago. I could be wrong. I'll need to check the mech's bill.

A thermostat failure would make sense. The engine will eventually heat up: it just takes a heck of a long time.

Humm. Am I sensing a failure trend? Should I just call the mechs and sch the timing belt, water pump, and thermostat replacement for next week rather than next month?

Is the problem decreasing my MPG? Even more motivation not to wait.

Thanks a ton, Kelly :-)

How long since your last belt, mileage/time?

The timing belt and water pump were changed almost 4 years ago. I think the mileage was 116,000 then. Now it is 139,000.
April 06, 2011 07:40PM
Quote
Kelly
Quote
rkj
Quote
Kelly
Quote
Archeo-peteriX
Kelly,

Was the thermostat also replaced along with the water pump? I experience this same type of phenomenon when my t-betl, water pump and thermostat were replaced. In the end the thermostat(brand new) failed within a couple of months. The new one; that I personally put in; always read a little lower than the original one did but since the actual coolant temperature(measured twice) was within normal operating spec; I simply learned to live with the lower gauge readings.

It is highly unlikely that your gauge or the sensor suddenly changed...the more obvious culprit would be the thermostat; new or not.

Hi All,

I do not think that the thermostat was replaced with the water pump almost 4 years ago. I could be wrong. I'll need to check the mech's bill.

A thermostat failure would make sense. The engine will eventually heat up: it just takes a heck of a long time.

Humm. Am I sensing a failure trend? Should I just call the mechs and sch the timing belt, water pump, and thermostat replacement for next week rather than next month?

Is the problem decreasing my MPG? Even more motivation not to wait.

Thanks a ton, Kelly :-)

How long since your last belt, mileage/time?

The timing belt and water pump were changed almost 4 years ago. I think the mileage was 116,000 then. Now it is 139,000.

The length of time between changes is just as important as the mileage. Four years is the limit recommended by BMW...so it behooves you to get that belt changed...might as well do the rest while you're at it; no more labour; just extra parts smiling smiley
rkj
April 06, 2011 09:41PM
Quote
Archeo-peteriX
Quote
Kelly
Quote
rkj
Quote
Kelly
Quote
Archeo-peteriX
Kelly,

Was the thermostat also replaced along with the water pump? I experience this same type of phenomenon when my t-betl, water pump and thermostat were replaced. In the end the thermostat(brand new) failed within a couple of months. The new one; that I personally put in; always read a little lower than the original one did but since the actual coolant temperature(measured twice) was within normal operating spec; I simply learned to live with the lower gauge readings.

It is highly unlikely that your gauge or the sensor suddenly changed...the more obvious culprit would be the thermostat; new or not.

Hi All,

I do not think that the thermostat was replaced with the water pump almost 4 years ago. I could be wrong. I'll need to check the mech's bill.

A thermostat failure would make sense. The engine will eventually heat up: it just takes a heck of a long time.

Humm. Am I sensing a failure trend? Should I just call the mechs and sch the timing belt, water pump, and thermostat replacement for next week rather than next month?

Is the problem decreasing my MPG? Even more motivation not to wait.

Thanks a ton, Kelly :-)

How long since your last belt, mileage/time?

The timing belt and water pump were changed almost 4 years ago. I think the mileage was 116,000 then. Now it is 139,000.

The length of time between changes is just as important as the mileage. Four years is the limit recommended by BMW...so it behooves you to get that belt changed...might as well do the rest while you're at it; no more labour; just extra parts smiling smiley

Absolutely, the 2.5 motor cars go through timing belts more often than the Eta's
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