Date: Sat, 4 Apr 1998 06:04:36 -0500
Reply-To: Mark Hudgik <mhudgik@THE-SPA.COM>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Mark Hudgik <mhudgik@THE-SPA.COM>
Subject: Re: Head (gasket) fix
In-Reply-To: <35257AB2.151069D4@uakron.edu>
Content-Type: text/plain; charset="us-ascii"
All this gasket talk has me ponderin' and...
New theory:
It's not output pressure from the pump forcing the coolant under the gaskets. In most cooling systems, the pump is used to circulate the coolant, not pressurize the system. Due to the action of the coolant pump, there will be a small positive pressure increase where the coolant enters the heads and conversely, a small negative pressure where the coolant exits the heads. Not sure exactly what these pressures are, but the main purpose of the pump is to overcome system friction loses and establish a certain flow rate, not build pressure. If pump pressure was an issue, you would see more corrosion in the area where the coolant first enters the heads and less in the areas where the coolant returns to the pump suction. This was not the case with my heads. They were evenly pitted across the head surface.
The thermostat does not really add anything to the mix. It is simply a diverter valve of sorts, directing most flow within the engine when cold and gradually diverting more of the engine coolant outlet to the radiator as the engine warms.
There is a "pump" problem here though! The flexible gaskets and heads/cylinders are the pump mechanicals and the energy input for this "pump" is the expansion and contraction of those parts as they are heated and cooled. This expansion/contraction action can suck minute amounts of coolant in (during cooling) and out (as heat is applied) of the area under the gasket. The trapped coolant becomes "old" coolant and this may be why other parts exposed to the coolant are not similarly affected.
Ok, but "What about the diffence in mileage (or kilomeage? <g>) that different owners are experiencing before failure or non-failure?" you ask. How about the following:
1. Head Torque - Different torques for different folks? How close a tolerance to spec has been followed by different factory guys, mechanics and backyard types. What happens to torque settings on a flexible gasketed head over time?, anyone re-torqued their heads lately? If not, it may be too late anyway. Coolant trapped under the heads becomes "old" coolant and then...?
2. Sealant and Gaskets - How well were they sealed at the factory or during a rebuild? Has the sealant and/or gasket become brittle over time? Shrinkage?
3. Driving Habits - A heavy foot before the engine thoroughly warms up can cause uneven heating of disimilar metals increasing the "pumping" action at the heads. Same for warm-ups by idling. Best to idle for 30 seconds and then moderate driving until the engine is up to temperature. Leave heater valve closed to shorten warm up time period.
In summary, I think the problem is with the head/gasket arrangement. It seems that properly sealed, torqued and driven engines may not experience problems long into the future, if ever. Proper coolant changes probably don't hurt either.
- Mark *** 91 Carat ***
