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You risk BOILING the water INSIDE the pump and also IN the Hx, therefore BAD application position for a pump. ---
Depending on the amount of suction head developed by the pump, it may cause the hot water to 'flash' or boil in the position youve located. Such pumps should always be placed on the 'cool' side and deliver PRESSURE to the hot side to prevent 'flashing' of the hot water (boiling at temperature below 212° when at less than atmospheric pressure).
Pulling a vacuum on hot water will depress the temperature at which it BOILS; so you need to be very careful so that you dont exceed the 'vapor pressure' of the hot water.
(I dont have my 'steam tables' with me but youre going to be close or exceed the vapor pressure (~6 psi @ 170°F) causing the water to boil with a single stage pump pulling up to 6" hg. or ~3+psi 'vacuum').
If the water 'flashes' or boils because of the vacuum, you will not have any water flow, just 'vapor' flow!!!!!! Thats why pumps always are used in 'pressure mode' in hot water applications ... the increased pressure RAISES the temp at which the water boils/flashes.
I would also surmise that youve omitted the cooling loop for the exhaust manifold as the Ex. Manifold will put as much heat into the cooling loop as does the engine block circulation. The exh. manifold (when not included in the FWC circuit) is always 'after' the Hx.
Other considerations - If this is a rubber vaned Oberdorfer type pump the rubber in the vanes probably will quickly deform as the 'softening point' will be around 170 deg. F.
With two such vulnerabilities ....... suggest you put the pump in 'normal position' in the circuit and 'suffer' the needed engineering to put it there.
Last edited by RichH; 03-19-2011 at 10:11 PM.