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weatherstripping that’s perhaps twice the width of the gap, it’ll stay in place just by friction; there’s no need for the
adhesive on the weatherstripping to stick to anything.
If the upper radiator support rail is off, make sure to seal it against the top of the radiator, against the top of the A/C
condenser, and against the top of the fan shroud before reinstalling it. The top of the A/C condenser in particular may
have such a huge opening that it doesn’t even appear sealable; you may need to stack 1/2” foam tape two or three layers
high to fill the hole.
FRONT SPOILER: It’s important to have the front spoiler in place. Engine cooling relies on air coming in through the
radiator, and it must have a place to go. The XJ-S does not have vents through the hood or out the sides, so all this air
must go out the bottom. The front spoiler is designed to direct air either into the radiator or around the sides of the car,
and to restrict air from going under the nose of the car as much as possible. This results in low pressure under the car,
so the air going through the engine compartment can easily flow out that way.
However, if the spoiler is missing, air can flow right under the nose of the car unimpeded. This increases the pressure
under the front of the car, which in turn resists the outflow from the engine compartment. The air coming in through
the radiator cannot escape as easily, and builds up pressure in the engine compartment. The resulting backpressure
prevents as much air flowing through the radiator. It also tends to cause significant lift on the front end (try multiplying
a very small pressure over the entire area of the front half of the car; the total lift can be very large indeed) and can
cause the car to “wander” at high speed.
HEATER CONTROL VALVE: See page 493.
Post-Shutdown Cooling
It it commonly acknowledged that the worst cooling problem the XJ-S has is not when running but after shutdown.
The small electric fan runs after shutdown if the thermal switch has it running when the engine is shut off, but once the
switch cuts out -- which it does all too soon, since it is reading coolant temperature at radiator outlet -- it will not come
on again. 700 pounds of hot engine plus hot exhaust manifolds and hot catalytic convertors tend to raise the underhood
temperatures after shutdown considerably higher than they ever were while running, and there are indications that parts
of the engine itself get hotter after shutdown as well.
There are three problems generally associated with post-shutdown heating: Dropped valve seats, hot start difficulties,
and heat-stressed engine compartment components. The exact mechanism of dropped valve seats is unclear, but several
owners have suffered dropped seats after a hot shutdown rather than while running. The other two problems are
clearer, and result from the high temperature of the air surrounding the engine -- and all the extraneous components that
are heated by the air. Since there is no longer fuel flow in the rail, the fuel sitting in it gets hotter and hotter, causing
serious hot start problems that Jaguar has addressed with a coupla different types of fuel rail temp sensor providing fuel
enrichment. The post-shutdown underhood temperatures are clearly a key cause of deteriorated hoses, brittle wiring,
short-lived electrical components, and a host of other traditional Jaguar afflictions.
This section includes several ideas for dealing with the post-shutdown temperatures. Most address primarily the
temperature of the air within the engine compartment, which may or may not have a significant effect on the
temperature of the heads themselves in the vicinity of the valve seats.
HOOD VENTS: Just the ticket for letting the heat rise naturally out of the hood after shutdown. It’s a body
modification, so it’s discussed further on page 470.