[TR] water pump

[Randall]

Here’s a couple of questions you can ask your nephew:

1) On the high pressure side of a TR2 through early TR4 radiator sits a 4 psi pressure relief valve (aka radiator cap).  What happens when the dynamic head substantially exceeds 4 psi?
2) What happens when the water pump cavitates?
3) The TR2-4 water pump uses a spring-loaded face seal to keep coolant inside.  What happens if the dynamic coolant pressure at the seal goes substantially below the atmospheric pressure outside the seal?

(1) in particular, I believe, is the main origin for the old myth about the coolant moving too fast without a thermostat or restrictor plate.  It really can cause overheating, just not (directly) because the coolant is moving too fast.

Sent from Mail for Windows 10

From: dave
Sent: Sunday, July 28, 2019 6:35 PM
Subject: [TR] water pump

In the last few weeks there was some discussion about the new vs old water pumps.  Someone postulated that the newer water pumps move water faster through the radiator, which results in less cooling and a hotter engine.  I asked my nephew, a mechanical engineer who is also a car person, about this.  here is his reply:

I think the point of confusion is the notion that increasing flow rate is a bad thing. I get the basic thought of it spending less time in the radiator but it's one of those things that sounds correct without having any real science to back it up. One of the rules of thermodynamics is that flow rate and heat transfer are directly proportional. If you increase flow rate and all other things remain constant then you will reduce temperature.

For your specific use case, you're improving the efficiency of cooling because the fluid is moving more quickly through the engine. It's better to keep fluid at as low of a temperature as possible and moving it very quickly means that each molecule is exposed to the heat for less time. When it gets to the radiator there isn't as much heat to be removed so spending less time in the radiator becomes a moot point.

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