GM F-Body Electric Coolant Fan Specifications and Modifications (Dual Fan)

General Information

General Motors engineered these cars to run HOT!! The primary coolant fan does not engage
until 222° F or higher (depending on year and engine) and the secondary fan until 243° F! It’s
been shown that at these high temperatures, air and fuel burn more completely and therefore
producing less hydrocarbons. However, these temperatures severely reduce engine life and kill
performance. So why not just install a lower temperature thermostat and call it done? Simply
because a lower temperature thermostat only allows coolant to flow through the engine sooner.
In stop-and-go traffic, the engine’s temperature will continue to rise unless there is sufficient
airflow to the radiator. Assuming the A/C is turned off, have you noticed that on the open road,
the temperature is acceptable, but when you hit city traffic, it climbs to astronomical levels?

Factory Coolant Fan Circuit Operation

The primary fan is controlled electronically through the ECM (Electronic Control Module). The
EPROM (or “chip”) is programmed with a fan turn-on temperature of 222° F or higher, depending
on year, or when the A/C head pressure exceeds 232-psig as long as vehicle speed is below 35-
40 mph.

The secondary fan is controlled two ways, depending on year. In 1987, an in-cylinder head
thermal switch is used. This switch engages the fan when coolant temperature reaches 243° F!
An A/C head pressure sensor is used in addition to the thermal switch in 1988 through 1992
which turns the fan on with the A/C.

Objective

Engine operating temperature must be lowered. This involves installing a lower temperature
thermostat and modifying the coolant fan turn-on temperature. The ideal system would
incorporate a simple, straightforward design without disabling GM’s system. I will explain this
later.

So let’s say that you install a 160° F thermostat and a switch that engages the fan at 176° F (or
so). It seems like the ideal situation — until the first cold day. Then, the engine will never reach
full operating temperature because the fan is running — when you don’t want it to. The heater will
only work marginally, at best. Of course, you can change your thermostat and fan switch twice
per year, but do you really want to do that? How about a typical fall or spring day when it’s cold in
the morning and warm in the afternoon. What do you do then? Or how about on a beautiful day
when suddenly, a weather front moves in, drastically dropping the temperature within hours. Is
there a practical solution?

Overview

We know that heat shortens the life expectancy of engines. The temperature that GM operates
their engines is acceptable for lower emissions, but a killer for performance and longevity. I found
it imperative to lower the operating temperature.

Through five years of research, primarily trial and error, I believe that I have designed a system
with the most versatility. I call this my “Total Fan Control” system.

For most performance enthusiasts, the approach is to lower the operating temperature by using a
160°F thermostat and either running the fan constantly or using a manual fan turn-on switch,
while monitoring the engine temp gauge. This is acceptable and fully functional but what if you’re
distracted and “forget” to keep a constant eye on the temp gauge? Not good. So is there a
foolproof method to prevent this from happening? Also, running the fan during the winter months
or emissions testing is neither necessary nor desirable. If we follow this approach, the engine
never reaches full operating temperature in the winter months and the heater works marginally at
best. I suppose you could change to a 180°F or higher thermostat and change the fan operation
back to stock, if you’re willing to do this twice per year. I do not find this solution acceptable.
Also, think about the ambient temperature on a typical spring or fall day. In the morning and
night, it’s cold. In the afternoon, it’s rather warm. On these days, it would be ideal to use the
160°F thermostat and modified fan control in the afternoon and a 180°F with factory fan control
on those cold mornings and nights. If there were a way to run “Summer Mode” and be able to
change to “Winter Mode” at the flip of a switch — that would be ideal. This was my goal — and I’ve
accomplished it.

In analyzing all the products on the market, I came to the conclusion that none of them would
meet all my criteria. It would take a combination of products and a little ingenuity on my part. In
analyzing the factory coolant fan wiring diagrams, I decided that I would not disable GM’s wiring
scheme in any way for two reasons:

1) For those who live in states with a yearly emissions check, wouldn’t it be nice to revert back
to the factory settings at the flip of a switch?
2) By supplementing the factory system, there are actually two systems working independently
of each other, the factory system and the Total Fan Control system. If the Total Fan Control
system were to fail (in twelve years, it never has failed me), the factory settings, which have
not been disabled, will engage the fan(s).

The information I share with you is a culmination of my research. I think you will agree that this is
the best and most versatile system available today.

Low Temperature Thermostats and Closed Loop Operation

Contrary to popular belief, closed loop operation is attained when engine coolant temperature
reaches 104°F and exhaust gas temperature reaches 600°F. On a cold engine, this occurs
within five minutes of normal driving. Therefore, there is no concern about attaining closed
loop operation, even with a 160°F thermostat.

Thermostat
Of the numerous experts on tuned port injection engines, Greg Carroll of Carroll Supercharging
Company and Myron Cottrell of TPI Specialties are the forerunners. Greg Carroll states that
160°F is too cold for these engines. He suggests a 170°F thermostat. Myron Cottrell says, “We
have found that 170°F is a better temperature for all-around driving. The computer in your car is
designed to provide a correct fuel mixture at whatever temperature the motor is controlled. The
170°F thermostat provides the best compromise between power, economy and wear.” I have
found that with a 170°F thermostat, I do not need to change between a 160°F for summer and a
180°F for winter, but that I can use it year-round.

I used to use the 160°/180°F thermostats in combination with my coolant fan system and a stock
EPROM for about ten years with no problems. I did grow tired of having to change it twice per
year, though. I knew of the 170°F thermostat, but who makes one? There are no listings in any
of my local auto parts stores?? A little known fact is that GM does produce this thermostat but
the parts advisors cannot look up this part without an application or a part number. I have taken
the liberty to find this part number. It is 10220957, made by AC Delco.

With the 170°F, the heater functions very well on those cold mornings, It never really worked
effectively with the 160°F thermostat (luke warm at best). And as for those hot days, think of this;
with a 160°F thermostat, what do you think your normal operating temperature is with the A/C off?
I’m willing to bet that it’s not between 160°F and 170°F. It’s probably around 170°F to 185°F.
Even with a 160°F thermostat and both fans running, the engine will only cool to around 170°F to
185°F. Therefore in the summer, it’s irrelevant whether the thermostat is a 160°F or a 170°F.

Before installing the thermostat, modify it by drilling four 0.150-inch diameter holes around the
perimeter of the thermostat. The holes allow a constant restricted flow of coolant through the
engine, which prevents hot pockets of coolant from forming.

Now that I’ve decided to use the 170°F thermostat, how do I turn the fan on sooner?

Fan System

“Fan On” Indicator LEDs

Not only is this information important, especially in the summer, but it is an excellent
diagnostic tool. Have you ever wondered while cruising down the speedway whether your fan
is running or not? With these LEDs, you can actually tell when your fans are on!

_____________________________________________________________________________
If you would like wiring instructions for your specific application, please e-mail the following
information:

Year, Make and Model
Engine Size, TPI, TBI or Carbureted, &
Factory Single or Dual Fans.

To:

Willie
Moderator
History/Restoration Board
tplsz87@cox.net