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Date:         Sat, 29 Apr 2000 23:52:33 EDT
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: Cooling System Comments
Comments: To: mike_l_f@hotmail.com
Content-Type: text/plain; charset="US-ASCII"

Mike,

Sorry I didn't get back to you before now. I connected the pressure gauge to the coolant level sensing plug which inserts into the coolant expansion tank. Details in the archives. Added a swage standoff to the plug, filled with radiator seal epoxy. Added a needle valve between the line to the gauge and the coolant tank, and also plumbed in a valve and nipple between the gauge valve and the coolant tank so I could independently evacuate the system or pressurize it. Bought 1/8 inch OD nylon pressure tubing at FLAPS to run to spare tire area. Spliced the line from the gauge to this line and cable tied both to the radiator hose.

The details of the gauge I used and other possible mounting points are all in the archives.

It is rather easy to see air in the coolant tank because:

1) The system pressure doesn't rise sharply as the engine heats up in the morning.

2) Minimum cold overnight pressure doesn't go below about negative 0.2 to 0.4 psi.

3) System pressure decrease upon hard acceleration is about 5 to 7 psi instead of 1 to 3 psi. (note: the engine compartment cooling system (I-4 valid comment only) are very soft and expand and contract with both positive and negative pressure. A fully evacuated system has harder sidewall containment (less air). When the water pump is accelerated, a pressure differential across the inlet to outlet of the pump can develop depending on the rigidity and the flow rate. The higher the pressure differential, the lower the volume of water that the pump will move at any given impeller velocity. In other words, overcoming a pressure differential takes work away from that which can be exerted to push the water through.) This is the phenomena that leads to reduced system cooling capacity when air is present. This is further exaggerated when air is mixed with the coolant, leading to bubble formation (significantly reduced heat capacity) and hot spot cavitation (rapid onset of local boiling in the head for example). The heterogeneous phase equilibria (air and coolant mixing) are strongly mitigated by surfactants such as Redline's Water Wetter.

4) For major amounts of air in the tank (air gap of 1.5 inches or so - water level electrodes just covered) the maximum pressure in the system will only get up to 5 to 8 psi, instead of the cap limit of about 12.5 psi. Sure, sure the cap says 14 psi but they lie!

Finally, I would suggest that the coolant pressure gauge (and an exhaust temperature gauge) quickly show a fingerprint of characteristics that you will recognize as nominal performance. You will learn to recognize signs of failure or system degradation quickly.

I'll post this response to the list in case others may be interested.

Good luck,

Frank Grunthaner


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