<HTML>
<!--This file created 4/23/00 6:38 PM by Claris Home Page version 3.0-->
<HEAD>
<META NAME="GENERATOR" CONTENT="Claris Home Page 3.0">
<meta name="robots" content="index, follow">
<meta name="keywords" content="Saab, Repair, Best, Townsend, Ywan Mason, Tom Townsend, Townsend Imports, SaabMaster, high temperature, degree thermostats, electrolytic action, common coolants, engine temperature, big temperature, engine rpm, Gasket Latest, Gasket Procedure Engine, 2.1L Gasket Latest, GASKET REPLACEMENT 16V, Special maintenance procedures, flat cadmium colored">
<meta name="description" content="Best Saab Repair The pictures of the blown gaskets are typical of what we see in cars suffering from a high temperature fan switches, neglected thermo">
<TITLE>headgasindex</TITLE>
<X-CLARIS-WINDOW TOP=162 BOTTOM=870 LEFT=24 RIGHT=936>
<X-CLARIS-TAGVIEW MODE=minimal>
</HEAD>
<BODY TEXT="" BGCOLOR="" LINK="" ALINK="" VLINK="">
<P><FONT SIZE="+2" COLOR=""><B><I>The pictures of the blown
gaskets are typical of what we see in cars suffering from a high
temperature fan switches, neglected thermostats or 89 degree
thermostats, and common "green" coolants. They did not fail from a
single overheat episode, but from both the repeated temperature
overshoots the higher rated thermostats and fan switches cause and
from the deposits from the electrolytic action of common coolants and
the metals in the head and block. The movement of the expansion and
contraction during temperature changes and the action of the deposits
and the coolant got the gaskets over a long period of
time.</I></B></FONT></P>
<P><FONT SIZE="+1" COLOR=""> </FONT></P>
<P><FONT COLOR=""><B>Keeping the engine temperature from big
temperature changes, i.e. installing a matched cooler thermostat and
fan switch minimizes frequent temperature changes during operation.
This minimizes the movement of the head and gasket. The interface
between the gasket the head and the block is not a static one. The
head is made of aluminum, the block is steel. They have differing
expansion and contraction rates as they heat up and cool down. The
head ,in effect, "floats" on top of the block and the gasket is the
one caught in the middle. With a fan switch that is hotter than the
thermostat, the head actually gets much hotter than the coolant at
the switch that turns the fans on. By the time the fan switch does
get hot enough to turn the fans on, the radiator and fans have a lot
of catching up to do. The head gets even hotter before it starts to
see the cooler coolant from the radiator. This is a temperature
overshoot. The best example is to watch your temperature gauge after
you pull off the highway and get stuck in traffic. You'll see it go
way high before the fans come on. The head and block are expanding
with the heat. You're moving less coolant (low engine rpm), and
flowing next to no air through the radiator (low vehicle speed). By
the time the fans do come on, they are way behind and getting farther
behind. When they do come on and start to cool the coolant in the
radiator, the head and block then get the deluge of the cooler
coolant and start to contract. During these expansion/contraction
cycles, the head gasket just as well be in a grinding
mill.</B></FONT></P>
<P> </P>
<P><A HREF="blown2lgas.htm">Blown 2.0L Head Gasket</A></P>
<P><A HREF="blown21gas.htm">Blown 2.1L head Gasket</A></P>
<P><A HREF="newheadgas.htm">Latest Design Head Gasket</A></P>
<P> </P>
<CENTER><A HREF="headgasket90016v.htm">Head Gasket Procedure</A>
<P><A HREF="engine_systems_docs.htm">Engine Index</A></P>
<P><A HREF="../cooling_system_folder/coolingsys.htm">Cooling System
Service</A></P>
<P><A HREF="../cooling_system_folder/cooling_system_docs.htm">Cooling
System Index</A></P></CENTER>
</BODY>
</HTML>