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MG MGA - Can a thermostat get stuck in the closed position?

Strange goin's on....
Drove the car 250 miles, to a British car event , a week ago, and it ran and cooled perfectly....
Since next week, I am planning on replacing the clutch, I decided to back the car onto my lift.....
In the process of turning and backing, I noticed that the temperature began to climb much higher than the normal 85-90 degrees.....
I turned the heater on to see if the temp would come down, and no hot air came out....The upper heater hose (the one connected to the copper tube), stayed cold, but the lower one (attached to the heater valve), was hot....The radiator felt much cooler than normal......
Now...Should I expect to find a stuck thermostat, or did my water pump just suddenly quit altogether?.
I will know soon enough, when I get the engine out (I'll test the thermostat)...But I thought I would put this out there to see what the forum thinks.
Thank you for your input.
Edward Wesson 60MGA

Edward. Yes, I once had a thermostat stick in the closed position on, of all things, and MGA. So, test yours out and see what is happening with it.

Les Bengtson

Can we assume you checked there was plenty of water in the system...?
P N Tipping

The thermostat relies on a waxstat to operate. Failure closed is the usual way a waxstat fails. It is probably because the rubber inside the capsule has perished.

Here is a useful writeup on the thermostsat's operation

If your water pump had failed you would still see a normal water flow through the radiator, albeit at a slower rate.

Paddy Reardon

Thank you all for the input....
I will be checking it today and let you know....
And yes, plenty of coolant in the radiator (which I drained yesterday).
Edward Wesson 60MGA

Waterpumps don't just suddenly fail, at least I've never heard of that happening. If the fan is turning, the pump is likely working. Normally, the bearing starts to go bad, which damages the seal and the pump begins to leak. A failed thermosat seems much more likely. It is also possible that a hose delaminated causing a blockage.
G T Foster

Getting wierder....
Pulled the thermostat, and placed it in a pan of water on the stove, with a thermometer.....As soon as temp got up to 160, (the preset), it opened....Down to 130, it closed...
This is a high-quality thermostat...not a Chinese or 3rd-world type....
Now, do I trust it to work, or just go ahead and replace it?
Edward Wesson 60MGA

Stuck thermostat won't affect the heater since it bypasses the stat.

No heat from heater and one pipe hot & the other cold either means that the valve is clogged or the water level is low.

Taken with the higher than normal engine temp reading my guess is that you had a low water level - even if there seemed to be plenty when you drained it.
Chris at Octarine Services

I have had a water pump fail when the impeller came loose from the shaft - water boiled at the top and cold at the bottom.
Cam Cunningham

I wonder if there is a way to know if it's the water pump, without removing the pump?...Seems tight, and no leaks.
I'm suspecting a low water level, as Chris mentions...
When I drained the radiator, there seemed to be plenty of water, but the drain cock on the block had little water draining from it, after the radiator was drained....
I wonder if the cap has lost its ability to hold pressure (7 lbs)? I will replace that as well.
I did notice that the radiator drain cock had a small drip, and it's possible that enough coolant drained out of the system to cause the high temp...
Replacing that valve....and possibly having the radiator serviced, as well. (although I have never seen a leak in the radiator)....
Edward Wesson 60MGA

This thread was discussed between 10/11/2013 and 12/11/2013

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