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 Water pump bypass

 Created by: croc7
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 Posted: Nov 21, 2019 04:01PM
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After looking at the design of the mini t'stat, I'm not convinced that it will fail in the open position.  Regardless, I installed a 194 degree stat without drilled holes and drove the car today in 50 degree weather.  Quickly warmed up and a steady 180-185 around town and at speed.  Go figure.  This engine has been a cold hearted beast since day one.  

 

"To catch one, you need one"....John Cooper

 Posted: Nov 8, 2019 02:12PM
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CA
With no bypass and the heater valve closed, there wouldn't be any flow until the t'stat opens. However, the coolant in the head wouldn't get to the boiling point before the t'stat does open. Even if it did begin to boil in a part of the head, the coolant would move around and re-absorb any steam bubbles until it all got yo the boiling point. (Put a pot of water on the stove boil. Set it partially on the burner to see the effect. You won't get a rolling boil until all the water is very hot.) You'd have to get the head temperature well above the boiling point before any damage to it might occur. By then it would have boiled dry and the t'stat would be wide open. Even if it stayed shut, the pressure on the cooling system would have the rad spilling its contents.

Thermostats are supposed to fail in the open position. I suppose the only way it would fail closed is if the cooling system is full of gunk and it corroded shut. A maintained motor wouldn't get to that point.

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"Hang on a minute lads....I've got a great idea."

 Posted: Nov 7, 2019 11:39AM
 Edited:  Nov 7, 2019 05:44PM
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Thanks, I remember reading your reply.  What started me thinking (or over thinking) is an answer given to a like question on another forum, relating to coolant circulation.  This guy stated that without the bypass feature, the pump was pumping to "a dead end-not good".  So, without a path for the water to take, either through a open heater valve or the bypass back to the pump, is the pump impeller is spinning without moving any water through the block or cylinder head?

 

"To catch one, you need one"....John Cooper

 Posted: Nov 7, 2019 06:17AM
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CA
As described in another thread, I have a 1275 high compression (internally stock MG Metro ) engine with no by-pass and have been using an un-drilled thermostat ( probably 185 or 190 deg.) successfully. The engine heats up to operating temperature a little quicker and the t'stat opens when the head coolant gets hot enough. Cavitation at the pump impeller would only occur at high revs with no flow - one should not be hammering an engine until it has warmed up. On a cold engine cavitation shouldn't matter anyway since it wouldn't require a full rate of flow. I like that my engine gets up to operating temperature quickly and actually provides heat for the heater. We tend to forget that a thermostat should close when the engine coolant temperature gets too low, which can happen in cold weather. Holes in the t'stat defeat this function and the engine can fail to maintain a good operating temperature.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Nov 6, 2019 08:31PM
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How many of you are running a 1275 without a water pump bypass and a ‘stat with no holes drilled in it?  I’ve always drilled holes in the ‘stat but am thinking about installing a 190 degree ‘stat without holes.  So, with an unmolested ‘stat and no water pump bypass, is pump cavitation a concern?

 

"To catch one, you need one"....John Cooper