years I've seen hundreds of threads during the summer months. The responses
are always the same, I've done a search, and created this thread based on the
common answers from many CF members. I hope this helps out the typical nOOb
who comes here asking the same old questions.
Summer is here, this means it is hot outside 90°F~120°F
“My Corvette is running hot” is the number one thread of
all time in the forum since the day it was created. Forget about you been old
school, these cars do not have a carburetor, so be ready to change your
opinion about these cars. On the C4s the fans start around 235°F, this can be
changed by re-programming the car’s computer or chip.
Before you attempt to fix the issue with your keyboard asking the obvious
ensure you take these “quick-fix” recommended steps before starting an
1. Normal operating temperatures are between
190°F to 220°F and it stretches to 235°F.
2. Is the cooling system filled up with
antifreeze, and when was the last time you replace the cooling system cap?
GM used green antifreeze 1984-1995,
and orange Dexcool in 96 Vettes.
3. Are the fans working?
4. Is the water pump operational?
If you replace the thermostat an 1/8" hole in the
thermostat flange will help purge air during the burp/cooling cycle.
Performance thermostats like the famous 160°F 'stats already come with a
small orifice in them.
5. Is the radiator shroud area clean? This would
include the radiator, and condenser.
The radiator shroud collects all sort of road debris like;
newspapers, leaves, plastic bags, anything that it may fits, and make its way
in there. Those things and dead bugs will prevent proper air flow thru your
Ensure all components are clean.
6. Are the front spoilers in place?
The three-part front spoilers are part of the C4's cooling system. It's
imperative for them to be in place, not on top of that speed bump or
7. Have the cooling system been burped?
On the LT1 engines it is done by opening the screw on the
On the L98 few recommend to max-lift the front of the car. The majorities do
this, fill the system, start the engine and when the thermostat opens and the
level in the radiator drops, keep filling the radiator and then raise the
engine RPMs to around 2,500 RPMs and add more coolant. Then replace the
pressure cap before releasing the throttle!
CORVETTE THERMOSTAT - HYPERTECH POWERSTAT
This 160 degree Hi-Flow thermostat allows your engine to cool down to
lower temperatures than the factory thermostat. Lower operating temperaturesimprove performance in two ways. First, the mass flow rate of intake air is increased and second, the engine's
tendency to "ping" is reduced. This allows the engine to produce
8. Can the radiator be upgraded?
If you would like to run cooler than normal, visit Dewitt web
page, and buy their two row aluminum radiator. Your Corvette will run around
180°F on a hot weather day. There are other vendors, I have Dewitts on both
Vettes, and I'm very satisfied with their performance.
Reading Material to magnify your LT knowledge.
LT1 Reverse Flow Cooling System
By Scott Mueller.
One of the greatest features of the '92 and up Chevrolet LT1 engine is the
reverse flow cooling system. In fact it is reverse flow cooling that is truly
the key to theincredible
the modern LT1. Reverse flow cooling is vastly superior to the conventional
cooling systems used on virtually all other engines. This is because it cools
the cylinder heads first, preventing detonation and allowing for a much
higher compression ratio and more spark advance on a given grade of gasoline.
A fringe benefit is that cylinder bore temperatures are higher and more
uniform, which reduces piston ring friction. Because of this new cooling
system, the LT1 can easily meet ever increasing emissions standards with
significant gains in power, durability, and reliability.
Conventional Coolant Flow:
In a conventional engine design, coolant enters the front of the block and
circulates through the block's water jacket. The coolant is first heated by
the cylinder barrels, and then hot coolant is subsequently routed through the
cylinder heads and intake manifold before returning through the thermostat to
Because the coolant from the radiator is first directed to the cylinder
bores, they run at below optimum temperatures which increases piston ring
friction. The heads subsequently get coolant that has already been heated by
which causes the heads to run well above optimum temperatures. The hotter
cylinder heads promote detonation (spark knock) and head gasket failures. To
combat the increased tendency to detonate, compression ratios has to be
lowered and spark advance reduced, which significantly reduces engine power
output and efficiency.
Besides promoting detonation, causing gasket failures, forcing reduced
compression, spark advance, and significantly reduced power output, a
conventional cooling system causes several other problems. Since the
thermostat is on the exit side of the system, it does not have direct control
over the cold coolant entering from the radiator. This is especially true
when the thermostat first opens after reaching operating temperature. As the thermostat
first opens allowing hot coolant to exit the engine, a rush of very cold
coolant enters the block all at once, shocking the engine and causing sudden
dimensional changes in the metal components. The extremethermal shock experienced
by the engine causes head gaskets and other soft parts to fail much more
Conventional cooling system design also allows isolated engine hot spots to
occur, which lead to the generation of steam
pockets and coolant foaming. Coolant which is full of air and foam reduces
cooling system performance and can even lead to engine overheating.
LT1 Coolant Flow:
The LT1 is completely different since it uses reverse flow cooling. The
incoming coolant first encounters the thermostat, which now acts both on the
inlet and outlet sides of the system. Depending on the engine coolant temperature,
cold coolant from the radiator is carefully metered into the engine. This
allows a more controlled amount of cold coolant to enter, which immediately
mixes with the bypass coolant already flowing. This virtually eliminates the
thermal shock present in the old system.
After entering through one side of the 2-way thermostat (at the appropriate
temperature), the cold coolant is routed directly to the cylinder heads
first, where the combustion chambers, spark plugs and exhaust ports are
cooled. Then the heated coolant returns to the engine block and circulates
around the cylinder barrels. The hot coolant from the block re-enters the
water pump, and hits the other side of the 2-way thermostat, where it is
either re-circulated back through the engine or directed to the radiator,
depending on temperature.
The main concept behind reverse flow cooling is to cool the heads first,
which greatly reduces the tendency for detonation, and is the primary reason
that the LT1 can run 10.5 to 1 compression and fairly significant ignition
advance on modern lead-free gasoline. Reverse flow cooling is THE KEY to the
Generation II LT1s increased power, durability, and reliability over the
first generation smallblock engine.
All LT1 engines utilize a special 2-way acting full bypass thermostat. This
means that the thermostat regulates coolant flow both in to as well as out of
the engine, while the bypass portion of the thermostat circuit supplies the
water pump with a full flow of liquid coolant at all times. This is unlike a
conventional engine thermostat, which only regulates coolant flow at the
engine outlet, and which does not allow full flow through the water pump when
the engine is cold and the thermostat is in bypass mode.
Both sides of the 2-way thermostat used in the LT1 are linked together, and a
single wax pellet actuator operates the spring loaded mechanism at a pre-set
temperature. When the designated temperature is reached, the wax pellet
expands, opening the dual acting valve. All current LT1s come from the
factory with a relatively low 180 degree temperature thermostat. Most
conventional engines today use 195 degree thermostats in order to meet
emissions specifications at the expense of power, durability, and
It is important to note that the 2-way thermostat is unique to the Generation
II LT1 and is not interchangeable with older Chevrolet smallblock engines.
This is particularly important if you decide to change to a colder 160 degree
thermostat, make sure it is the proper dual acting type required by the
Additional LT1 Cooling System Improvements:
In addition to reverse coolant flow, there are several other improvements in
the LT1 cooling system over conventional engines.
Dry Intake Manifold:
The LT1 has absolutely NO water running through the intake manifold!
Conventional cooling systems have passages in the intake manifold which allow
coolant to crossover from one side of the engine to the other. In the LT1,
coolant crossover occurs in the water pump, which is also where the
thermostat is located. Since there are no coolant passages in the intake
manifold, a major source of leaks has been eliminated. Overall engine
reliability is improved since an intake manifold leak allows coolant to enter
the top of the engine which can quickly wipe out the camshaft, lifters, and
other major engine components. Designing a dry intake manifold without either
coolant passages or a thermostat housing also allows a much lower profile.
The LT1 engine is 87mm (nearly 3.5 inches) lower than the previous L98
Gear Driven Water Pump:
One big problem with conventional cooling systems is the water pump, which
simply cannot last a targeted minimum 100,000 mile reliability figure without
experiencing leaking gaskets or seal failures. This has traditionally been
caused by the excessive side loads placed on the bearings and seals of a
conventional water pump through the belt drive mechanism. In the LT1 this
problem is solved by driving the water pump directly via a spur gear driven
by the camshaft sprocket. This results in a dramatically more reliable water
pump that should easily last 100,000 miles or more.
Since the water pump is no longer belt driven, the vehicle will still be
drivable even if the serpentine belt fails. This
is a major safety factor as it allows one to drive the partially disabled
vehicle to the nearest service center.
The LT1 has strategically placed steam vents at the back of both cylinder
heads. Since the heads are the hottest part of the engine, pockets of steam
can be more easily generated there. The steam vents are connected together by
a crossover vent tube at the back of the heads, which directs any steam and a
small flow of coolant to the front of the engine where it flows through the
throttle body, warming it for improved cold weather performance. After
passing through the throttle body, most of the steam is condensed back into
liquid coolant and returned to the system.
In LT1 B/D-cars, coolant exiting the throttle body is passed directly into a
pressurized coolant reservoir where any air remaining in the coolant is
completely scavenged. In LT1 F-cars, coolant from the throttle body connects
to the heater outlet via a
vented "tee" connector, where any trapped air in the system can be
bled off manually. Eliminating steam pockets and foam in the coolant allows
for more uniform cooling system performance, preventing hot spots and
Reverse Flow Radiator:
Unlike a conventional cooling system, the thermostat coolant outlet is
connected to the bottom of the radiator. This forces the coolant entering the
radiator to push up through the radiator core and eventually emerge through
the top radiator coolant outlet. This
helps to eliminate air pockets in the radiator, and provides a more even
distribution of cooling through the core and improving radiator
Precision Machined Thermostat Housing:
The thermostat housing is a precision machined component that fits directly
onto the top of the water pump without a gasket. Instead, an O-ring is used
to seal the thermostat inside the housing. This precision design reduces the
tendency for leaks, plus it makes thermostat replacement a very simple job
since there is no old gasket material to scrape off. Servicing is further
simplified because the thermostat housing is situated directly on top of the
water pump, and access is unobstructed. I dare say that the LT1 thermostat is
the easiest to change I have ever experienced. Finally, an air bleeder valve
is located on the top of the thermostat housing, which allows one to quickly
and easily bleed out any trapped air after cooling system maintenance has
Low Operating Pressure:
The entire cooling system on the LT1 is designed to operate at lower
pressures than conventional cooling systems. The maximum operating pressure
in the LT1 cooling system is 15 psi for B/D-cars and 18 psi for F-cars,
limited by a pressure cap. These limits are similar to other cars, but in the
LT1, these maximum pressures are rarely reached. Running at a lower pressure
drastically decreases the number of leaks and significantly improves overall
reliability and durability.
Corvette and B/D-car LT1 applications use a pressurized coolant recovery
reservoir instead of a non-pressurized overflow tank used with conventional
cooling systems. All of the coolant flows continuously through the
pressurized reservoir, which is an integral part of the cooling system. The
pressurized reservoir in the LT1 B/D-cars is connected to the cooling system
in three places. One inlet hose connects to the top of the RH radiator tank,
a second inlet hose is attached through a "tee" connection on the
heater inlet hose, and a third outlet hose is connected to a "tee"
connection in the throttle body heater outlet.
The pressurized reservoir is mounted at the highest point in the system, and
provides a place where all air can be continuously scavenged from the
coolant. Any steam and bubbles are allowed to rise to the surface,
eliminating foam and providing pure liquid coolant back to the engine. Pure
liquid coolant is returned to the system via the heater outlet hose
connection. The pressure relief/vent cap in these systems is rated at 15 psi
and is located on the reservoir rather than the radiator.
LT1 F-cars use a conventional coolant recovery system which consists of a non-pressurized
coolant overflow tank connected to the radiator by a single hose. These cars
use an 18 psi rated pressure relief/vent cap on the radiator like most
conventional systems. Since these cars cannot scavenge air from the coolant
as well as the B/D-car or Corvette systems, they have two air bleeder valves
for manually bleeding trapped air from the system. One is in the thermostat
housing, which is the same as all other LT1 engine vehicles, and the second
one is located in a "tee" where the coolant from the throttle body
connects to the heater return hose.
B/D-car LT1 (Caprice/Impala/Roadmaster/Fleetwood) Cooling Systems:
Standard equipment for all LT1 equipped B/D-cars is a dual electric fan setup with a
150-watt primary (RH) fan and a 100-watt secondary (LH) fan. The electric
engine coolant fans are independently operated by the PCM (Powertrain Control
Module) based on the inputs from the Engine Coolant Temperature (ECT) sensor,
A/C Pressure Sensor, Vehicle Speed Sensor (VSS), and various other
The B/D-car coolant fans operate under PCM control at the following engine
temperatures and A/C system pressures:
Fan Mode Temperature A/C Pressure
Primary (RH)** Fan ON 107 C 225 F 189 psi
Primary (RH) **Fan OFF 103 C 217 F 150 psi
Secondary (LH) Fan ON 111 C 232 F 240 psi
Secondary (LH) Fan OFF 107 C 225 F 210
Additionally, the PCM will turn off the fans at higher vehicle speeds (above
48 MPH I believe) since running fans can actually impede airflow through the
radiator at high speed. Each fan also has a minimum running time.
Once activated, the primary fan will run for a minimum of 50 seconds, and the
secondary fan for a minimum of 26 seconds. Finally, certain Diagnostic
Trouble Codes (DTCs) may cause the PCM to turn on one or both fans.