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Discussion Starter #1 (Edited)
Shouldn't I see some coolant flow into the radiator even with the thermostat closed?

The heater piping comes off the lower intake manifold and runs to the heater core which returns to the thermostat housing. [Edit: it returns to the water pump] So it looks like I should be able to see at least some coolant flowing even with the t-stat closed. Is that correct?
 

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Are you still using the egr valve? Either way the heater flow should originate from the manifold and return to the water pump. Egr valve coolant is in between if used. And no flow visual at the radiator cap assuming that is where your looking. With the t-stat closed, heater flow is from engine so it warms up quickly.
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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Old school way of finding out when the thermostat opens is to idle the engine until movement of the coolant is seen (finally). IE, it does NOT move with the thermostat closed. Also that procedure is to "burp" the the cooling system. When the thermostat opens often you can add some more coolant. If you have replaced the water pump or done some other work to the cooling system so that you are refilling it.
 

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Discussion Starter #4
Thank you both.

I had the engine idling for a while today. The stock temp gauge wasn't much more than half way but I felt that it was running long enough and should have been hot enough for the thermostat to open up. It's a 197* t-stat and I tested it before installing. I had the radiator cap on and thought it wasn't a good idea to open it at this point.

I let it run a bit more feeling the radiator hoses and I did feel the upper radiator hose start to warm up, the top tank of the radiator starting warming up too. But the radiator core was still cool and the lower hose was cool as well (no fan). To me, this seems like the t-stat was open but the pump was not moving coolant. I shut it down and the warm parts continued to get hotter. After a few minutes I heard some leaking under the car and saw coolant dripping, and it was steaming hot. It looks like it just came from the heater hose connection.

Is there any risk that any damage was caused? Radiator cap is 16 PSI and new. It didn't release.

Should I install a new water pump. Or run it again with the cap off?
 

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You might have to drive the car a little to get it up to temp, or rev the engine until it gets warm, but when the t-stat opens you will see an obvious coolant flowing looking in the top of the radiator. Rev the engine up with the cap off and you will see a flow increase as well. Normal for the upper tank and hose to get warm from engine heat migrating towards the radiator, even with the t-stat closed. Sounds like you need to run a little longer as it was probably not up to temp. You can grab a cheep harbor freight infrared thermometer and shoot the t-stat housing to verify your temps.
 

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Discussion Starter #6
My original post was wrong. The heater piping comes off the lower intake manifold, runs through the heater core and returns to water pump. So I should have observed heat in both the supply and return. Only the pipe coming off the lower intake was hot. I'll be replacing the water pump.
 
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