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Date:         Sun, 20 Sep 1998 17:06:48 -0500
Reply-To:     "John H. Rodgers" <inua@QUICKLINK.NET>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         "John H. Rodgers" <inua@QUICKLINK.NET>
Subject:      Re: expansion tank wierdness
Comments: To: Vanagon <Vanagon@VANAGON.COM>

-- [ From: John H. Rodgers * EMC.Ver #2.5.02 ] --

Been there, Done that!!

I went through this sort of thing last spring.

Sounds like you have a problem with the valve in the filler cap on the expansion tank. As you probably know, there are two coolant tanks ---- one expansion, the other for over-flow. The expansion tank has a level sensor and a pressure cap with an overflow line to the overflow tank. The overflow tank has three tiny little vent holes located on the upper side ot the tank towards the rear of the vehicle that vent to atmosphere.

Consider that the coolant(water and glycol) expands and contracts when heated and cooled. When a pot is completely to the rim with coolant and is heated, the coolant expands. The expansion will cause the coolant to run over and spill from the pot. It will expand to a maximum, then as more heat energy is applied, it will get hotter until it reaches the boiling point of 212 F at standard atmospheric pressure at sea level. At 10,000 ft above sea level......the boiling point is more near 200F or even less. At the BP the water will begin to evaporate. Antifreeze raises the boiling point. If a lid is put on the pot, the boiling point can can also be raised even higher without the water being boiled off into the atmosphere.

Combusiton engines are heat engines, and must be at a certain temperature to operate properly. To hot, and wear increases exponentially. To cool, and thermal efficiency is recuced dramatically.

So the trick is to allow the engine to make the heat where necessary , but to carry the heat away quickly so there is no damage. Water cooling works real well, but the limit of water is it's boiling point. So we put in additives to raise the BP and we pressurize it just a little to raise the BP . It is pumped to the hot spots of the engine to pick up heat, then sent to a radiator to discharge the heat. Those are real extremes. But it works really well if our systems are working properly.

In the van the operating pressure for the coolant cap is set at approximately 1 atmosphere( 15 psi - fixed) and the overflow tank is vented to atmospheric pressure(variable - depends on elevation and outside air temperature - but mostly 15 psi average).

Once the engine begins to warm up, the coolant begins to expand. With no where to go, pressure increases to over one atmosphere, and forces the valve open in the filler cap allowing the excess to overflow into the overflow tank.

When proper engine operating temperature is acheived, and temperature stabilized, expansion stops, and outside atmospheric pressure, acting through the vent holes pushes back against the coolant, the cooling system pressure is now balanced by the atmospheric pressure, and the valve shuts, leaving the excess in the overflow tank.A cooling system properly filled with coolant, when at operating temperature, will discharge sufficient coolant to bring the coolant level in the oveflow tank up to the "Maximum" line on the overflow tank.

When the engine is shut down and starts to cool off, the coolant begins to shrink, pressure in the coolant system begins to drop and a reverse suction or syphoning action is formed. AS the coolant continues to cool and shrink, the pressure continues to drop, and when the coolant system pressure drops BELOW 1 atmosphere(15 psi) , the force of the outside atmospheric pressure, operating on the surface of the overflow coolant stored in the overflow tank , pushes with sufficient force to push the coolant out of the overflow tank, throught the overflow line, and through the overflow cap, and back into the expansion tank, Now the coolant is back in the cooling system. As this happens, the coolant level in the overflow tank should be reduced to the "Minimum" mark on the overflow tank.

What you have described as happening with your vehicle, sounds like the expansion tank cap is faulty or the over flow line is stopped up or the three little vent holes in the overflow tank are stopped up. The pressure caps are inexpensive, as is new overflow hose. Since the sensor has blown out a couple of times, I would inspect it for damage as well. They have a real tendency to crack.

Good Luck.

John Rodgers '85 GL Driver with a new clutch assembly and tranny rebuild. Been There, Done That. -------- REPLY, Original message follows --------

Date: Saturday, 19-Sep-98 05:20 PM

From: Wes Johnson \ Internet: (wesj@callamer.com) To: Vanagon \ Internet: (vanagon@vanagon.com)

Subject: expansion tank wierdness

Installed a new expansion tank and coolant level sensor into our 89 Westy. Everything went fine, maybe too easy. Wife and I drove to another town about fifteen miles away for lunch. Came out of the restaurant to coolant under the car. Check it out and the coolant sensor switch is loose. OK. So the system gets hot and the sensor loosens up, tighten it down and head home. Park the van in the carport, step outside walk around the the back, whooooosh, steam, coolant everywhere. Look under hatch and coolant sensor is totally blown out of the hole. OK, look at sensor, no threads under the O ring, figure maybe this thing can be screwed down too far? Put the coolant sensor back in, refill coolant, test drive, park car, no leak, go into house . Ten minutes later go outside and check. Coolant under vanagon, coolant sensor laying on top of expansion tank.

Anyone ever experienced this wonderful scenario. Hard to believe that a few threads on the coolant sensor stand between driving this thing or not.

---------------------------- Wes Johnson wesj@callamer.com

89 Westy GL ----------------------------

-------- REPLY, End of original message --------

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