Here on some tips to keep your cool:



1)  Flush your cooling system annually.  A clean system has better heat

transfer, both from the engine, and to the radiator.  While you're are

flushing, take a look in the radiator for tube blockage.



2)  Flush bugs and other debris off of your A/C condensor with a garden hose.



3)  Make sure your spoiler is in good shape.  Corvettes are "bottom

breathers", and the front spoiler is an integral part of the cooling system.



4) Turn your A/C on and open the hood.  After 1 to 10 seconds or so, your

electric fan should be spinning (once the A/C head pressure reaches about

190 psi), and a good volume of air should be ejected by the fan.  Also

check the fan shroud it is not cracked or broken (if it is, air will just

recycle itself, rather than being pulled through the radiator.



5)  Make sure your radiator baffles are in place.  The radiator cannot do

its job if air just travels around it.



6)  Test the cooling system with a pressure checker for leaks.  Also

check the cap to be sure it does not relieve pressure below 15 psi.



7)  Check your ignition timing.  Retarded ignition timing will cause the

engine to reject more heat.



8) Use premium fuel.  Hot weather is not the time to economize on gasoline

costs.  Low octane will cause detonation, which increases engine heat

rejection, and will cause knock sensors to retard ignition timing also

increasing heat rejection.  Low octane fuel can also result in preignition

in a extreme situations (if that happens, you no longer have to worry about

overheating, because you will have a hole in your piston-ouch!).



9) Check your belts to make sure they are in good shape.  Water pump loads

are low, so slippage is not usually a problem (the L98 even runs the pump

on the back side of the poly-V belt, so that should give you an idea of

how low it is), but belts are also more prone to failure in hot weather,

thus leaving you stranded.  Check the entire circumference of the belt,

both inside and out.  I recently has some delamination on my '89 on the

top surface of the belt.



10)  If you have a booster fan (Z51 models), and your coolant temperature

is above 228 degrees, check and be sure the fan turns on.  This fan does

not automatically turn on with the air conditioning.  It only comes on

when it reaches the prescribed coolant temperature.  I had a defective

switch on my '89.



11)  With the engine up to operating temperature, carefully run your hand

over the radiator.  The temperature of the core should be relatively

even.  If not, you probably have plugged tubes.



12) Use high gear!  Contrary to all of the myths out there, the engine

rejects the least amount of heat at a given load, if the engine is

operated SLOWER, not faster.  So if your engine is getting hot, DO NOT

do what many people will tell you to do, which is run the engine faster

(for which they have all sorts of arm chair "theories", ie. coolant

circulating faster, fan running faster, etc.) Do the opposite!  Get that

car in the highest gear possible.  This applies to cars with either

electric or engine driven fans.





Other things to watch for...



a) Parking next to a building and idling the engine can cause your car to

overheat in hot weather.  The radiator air will recirculate from the exit

of the radiator, and back into the inlet.  In fact, this is how G.M. tests

the "idling in traffic" condition.  The car is parked up to a wall, and

left idling.



b)  If you are driving down wind, especially in traffic, expect your car

to run hotter.  Again, you get radiator air recirculation.



c)  If you are towing a trailer in temperatures over 100 degrees, be

prepared for overheating.  G.M. does not certify cars for trailer towing

over 100 degrees, even with a heavy duty radiator (which is not an option

on Corvettes, except perhaps the earlier models).  If you do not have the

heavy duty radiator option, your maximum trailer towing temperature is

even lower.



d) Monitor your thermostat from time to time during cool weather.  On a

cool day, going down a gentle slope, after the engine has warmed up,

operate the car at low engine load (but do not coast).  The coolant

temperature should fall to the thermostat opening temperature, or slightly

below (188-195 F).  Note:  if you *coast* down a long hill, your coolant

temperature can go quite a bit below thermostat opening temperature, and

you really will not have a test.



e) With electric fans, stop and go driving is not the problem it was with

engine driven fans.  If you have an engine driven fan, your best cooling

speed is about 40 to 50 miles per hour (good air flow through the

radiator, but not much heat rejection due to engine load).  With electric

fans, this is also usually the best speed, although some electric fan

cars do just as well stopped completely, as they do moving.



f)  If your car starts getting hot, and you are driving fast, slow down

to about 40 to 55 (speed limits permitting).  You should see an almost

immediate reduction in temperature.  If not, there is an engine or

cooling system malfunction.



g)  Turning off the A/C and turning on the heater is good advice if your

engine is overheating.  If you get to this point, though, there is

something wrong with either the cooling system, or engine, and some sort

of repair is in order.



h)  Check your coolant recovery tank to be sure it is topped off at the

appropriate markings.



i)  If your engine overheats at over 60 miles per hour, your problem is

not likely to be fan related.  Most fans are free wheeling, like a wind

mill at 60 miles per hour.  There were only a few cars built with engine

driven fans using VERY heavy duty clutches (the Turbo Trans Am being one

of them) that would actually get cooling help from the fan over 60 miles

per hour (and it sounded like an aircraft when it engaged!).



j) One of the worst conditions for overheating on electric fan cars is

brisk hill climbing up winding roads.  The engine load is high, with

frequent accelerating and braking, and speeds are too low to get good air

flow through the radiator.  Do not be surprised if you get high cooling

system temperatures, even with fairly low ambients (80 F).  The booster

fan (Z51) was added to help compensate for this.  Cars with engine driven

fans can move much more air through the radiator, and generally do not

experience this problem.



k) Do not panic if your coolant temperature reaches 240 degrees.  We

didn't, while testing the cooling systems.  We just kept driving with the

A/C blowing full blast.  This is the reason idiot lights are better for

many drivers, so they will not panic while the system in still within

normal operating ranges.  Your overheat light does not even come on until

255, and boilover is about 262.  The nice thing about a guage, is that you

can monitor *changes* in coolant temperature.  If the temperature is high

(below 245) on a very hot day, but relatively stable, keep an eye on it,

but enjoy the drive. (Between 245 and 255, take measures to lower the

temperature, such as slowing down.) On the other hand, if it looks like

the temperature is quickly soaring to the moon, you better pull over and

shut the engine down.  Stuck thermostats will give you this behavior.



Hope this information helps a few of you during this hot season we are

having.



Michel Adams

'89 Coupe 6-speed Z51



                                             msadams@netcom.com