Keeping your GTO Cool
Ron Metz, Heart of Illinois GTOs, July
1999
Sometimes it seems that our GTOs are cursed when it comes to keeping the engine
temperatures somewhere below the melting point of cast iron. Well, maybe not quite
that hot but Pontiacs do seem to have chronic overheating problems. Proper operating temperature maintenance involves insuring the engine is fundamentally
sound, the cooling system is up to the task at hand, the motor is in a proper
state of tune and is operating efficiently. Here are several things you can look at
if you are having problems keeping your cool this summer:
1. Temperature Gauge
- No..., a gauge will not make the engine run any cooler but you need to
know if yours is accurate. There is no sense going through a lot of time and
expense
trying to fix a "problem" that isn't there and on the flip side, you'd hate to
waste your engine even though the temp gauge NEVER went past 180!
Mechanical gauges are typically more accurate, but in any case have your gauge
checked if you suspect an overheating problem.
2 Radiator - is it clean and flowing well? If you haven't had
it cored out in the last 5 years or so it may be a good idea to take it to a radiator shop
and have them clean and flow test it. Also, many of the standard 2 and 3 row
radiators won't handle a stock 389 very well let alone a warmed up 455.
Investing in a 4-row copper/brass radiator will make a big difference over a 2-3
row standard unit or a new aluminum radiator (BeCool and Griffin are good ones) would be even better.
3. Thermostat - At least every other year replace the
thermostat with a new one. I happen to like the Mr. Gasket 180 degree thermostats
because they are guaranteed to open +- 2 degrees from their rating point and they flow
better than the stock type thermostats.
4. Radiator hoses - Are the hoses dry rotted?
Is the spring
missing from inside the lower radiator hose? Maybe its time to replace them.
5. Water Pump - Is the divider plate installed behind the
water pump? If it isn't or if it is so corroded that it looks like Swiss cheese,
replace it. Places like Performance Years, Ames and Year One sell
replacements. The 1969 and later 11 bolt pumps are more efficient than the
earlier 8 bolt pumps. If originality and numbers-matching aren't as
important as cooling efficiency use this pump and front cover instead.
6. Fan - Especially clutch fans. Is
the clutch in good shape? Does it rotate real easy or wobble? If so it most likely
is bad. There should be noticeable drag when trying to turn the fan attached to a
good clutch. If replacing the clutch I recommend getting the heavy duty/RV
thermostatically controlled clutch.
7. Fan shroud - Do you have one? NO? Get one.
Using a fan shroud increases the efficiency of the fan by 50%. The
fan should be positioned so that half the thickness of the fan blade sits inside
the shroud.
8. Coolant - Ethylene
glycol antifreeze does not transfer heat energy as well (about 15% less)
as plain water. If you are running a coolant mix that is over
50/50% antifreeze you will run at least 10 degrees hotter than if you had less
anti freeze in your cooling system. The ideal mix
ratio for purposes of maximum heat transfer ability is no more than 30% antifreeze /
70%
water. If you choose to run water only in the summer months add two bottles of water pump
lube/corrosion inhibitor to the mix or use Red Line Water Wetter. As for the water to use its a good idea not to use tap water
(depending on the quality of your local water) but go out and get 5-6 gallons of distilled water. Your cooling
system does not need the minerals found in tap water collecting in the cooling
system. Also, don't forget that you will have to drain the
cooling system in winter if you live in an area where it gets below freezing and
you don't store your car in a climate controlled garage. If, for
convenience sake you wish to use anti-freeze I recommend no more than a 40/60
concentration and for the summer drop that to 30% anti-freeze 70% water if you
are a borderline hot runner.
9. Overflow container - For less than $10 you can add one of
these if you don't already have one. Besides catching coolant when the system heats up and
expands, you can fill the radiator to the top and purge air from the system.
Usually after a few hot/cold cycles all air will be replaced by coolant. With all
air removed from the cooling system it will operate more efficiently and you should see a
reduction in operating temperatures.
Engine Tune:
1. Ignition timing - Ignition timing is
critical to engine operating efficiency and therefore the temperature the motor will run
at over an extended period of time. Retarded timing from optimum invariably causes operating
temperatures to rise. Many factory advance curves are set so slow that total advance
doesn't come in until 4500 - 5000 RPM! I recommend total advance including initial
timing to be set from 32 to 38 degrees and have it all in by 2500 RPM. Depending on
your compression ratio, whether your engine is a 389-400 or a 428-455 and quality
of gas in your area will dictate the total advance and how fast it should come in.
Only testing your particular car will tell you how to fine tune it. Also, make sure
that your vacuum advance is functioning properly.
2. Carburetor jetting - Running too lean will also cause
engine temperatures to
rise, and could lead to detonation. This will cause you to back off timing to lessen
detonation which again leads to higher operating temperatures then leading to more detonation and on and on and on.
It used to be easy to diagnose your fuel mixture by taking a
look at your spark plugs after driving the car on the highway for a while (10 - 15
miles). Now with unleaded gas, even running a little rich will still show
as white porcelain. So reading the plugs is invalid now. But,
if you are running very rich, the plugs will show up very dark brown or black
and very lean will show as blued ground electrode (heat damage). It is better to be a little on the rich
side than too lean. Jets and/or metering rods are available from various
sources depending on the make of carburetor you have and are easily installed.
3. Camshaft duration - Big, long-duration cams sound way cool at
the cruise-ins but the use of these cams will shift your power band way up in the rpm
range, and decrease lower rpm power. The decreased operating efficiency at cruising
speeds (1800-2800 rpm) is akin to running retarded ignition timing or very low compression
- the motor WILL run hotter. Most street driven GTOs
will run very well with cams in the 205 - 215 @
.050 intake duration range like the '068' cam. 455's can get away with
about five degrees more intake duration than a comparably set up 400.
Select a cam on the mild side for the street. Not only will your GTO
run cooler but you will have gobs of low-end torque that can be used for smoke shows at
the local cruise-ins!
Engine Machining / Assembly
1. Overbore - The more a cylinder is bored out, the thinner
the walls get and if they get too thin and it doesn't take much, a hot running
motor will result. Generally, overbores in excess of .040 should be
avoided and especially on later 455's and other certain thin walled blocks for street driven Pontiacs.
2. Compression deck height - This is the distance between the
top of the piston and the block deck measured when the piston is at TDC. A large
dimension here can result in the "quench" (some call it squish) not being very efficient and over
heating the head and cylinders. When rebuilding your engines look out for pistons
with reduced compression height as this will lead to large deck heights. I would
recommend for most Pontiacs a deck height ranging from zero to .015".
Information on Dexcool Antifreeze
Engine compression test
Cruisin Paws, Tiger News, Vol. 5, iss. 6, Cruisin' Tigers GTO Club, Inc., October
1993
You need to do an engine compression test on your motor before every tune-up, or when a
miss or poor engine performance can't seem to be corrected with the obvious
checks/repairs.
You should test compression with a warm engine, all spark plugs removed and choke/throttle
wide open. Crank the motor through at least four compression strokes to obtain the
highest possible readings. NO cylinders should be less than 80% of the highest
cylinder (see examples below). Excessive variation between cylinders, along with low
speed engine miss of the cylinder or cylinders which are low, normally indicates an
improperly seating valve, a burned valve or even a broken piston ring. Low pressure
across the board even though uniform, may indicate worn rings. This condition is
also accompanied by excessive oil consumption.
Example #1
1
2
3
4
136 138 135
144
5
6
7
8
102 137 140
141
80% of 144 (highest) is 115. Thus, #5 cylinder is less than 80% of #4. This
would indicate a burned valve or broken ring.
Example #2 1
2
3
4
85 91
90
96
5
6
7
8
93 87
89
87
Safe-T-Track rear axle
David Meunch, Original Muscle, Western New York GTO Club, September 1993
Have you ever wondered what gear ratio you have in your car's rear axle? Have you
wondered if you have a Safe-T-Track ("posi") rear end? Here's a quick way
to check both other than pulling off the rear cover and looking.
First, safely support the rear of the car so that both tires are off the ground.
Next, place the car's transmission in neutral. Now, turn one of the rear wheels and
observe the rotation of the opposite side wheel. If the other side turns in the
opposite direction as the wheel you are turning, you most likely have an "open"
or non-posi rear end. If the opposite wheel turns in the same direction then you
have a "posi" or Safe-T-Track rear end.
To further determine this, have a helper hold the other wheel from rotating. If you
cannot rotate your wheel then you most likely have a Safe-T-Track rear axle.
To determine the gear ratio of a Safe-T-Track equipped car, simply turn either wheel one
complete revolution and count the number of turns the drive shaft makes. A chalk
mark or piece of tape will help. For example, if one turn of the wheel results
on about 3 1/2 turns of the drive shaft you most likely have a 3.55 ratio.
For open rear axles secure or lower to the ground one rear tire so that it cannot turn.
Next, turn the free wheel two revolutions and count the number of turns the
drive shaft makes. (The reason that you rotate the free wheel of an open rear end 2
turns is that when only one wheel is allowed to turn the spider gears inside the
differential case act as a 2:1 gear reduction). back to top
Misc. tech tips
Mikey, Tiger tales, Ohio Valley GTO Assn., June 1994
1. KINKY! Need to bend a kink-free fuel line? Simply use an
old v-belt pulley clamped in a vise. Different diameter pulleys will give you
various bends. Bend SMOOTHLY!
2. PENETRATING SOLUTION! Need to get penetrating oil on a frozen
bolt or nut in an inaccessible location? Bend some solid wire so that you can touch
the frozen fastener. Then let the penetrating oil drip down the wire to the nut or
bolt.
3. STICKY DRIVER! Trying to start a screw in a confined
space? Push the screw or bolt through the STICKY side of masking,
duct or electrical tape. Then stick the ends to your screwdriver or socket.
After it's started, pull the tape off and tighten down.
4. BAKED BOLTS! Ever paint bolts when you're detailing and
then have them get scratched just as soon as you put a wrench to them :(? An easy
fix is to bake 'em. Just as the enamel paint is dry to the touch, put the little
buggers on a cookie sheet and pop 'em in the oven at 325 degrees for 25 minutes. Let
them COOL for 25 minutes. Finally, install the little the rascals
with a six-point socket. Makes 2 dozen. YUM!
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Stay alive while working under your GTO
This important subject can be summarized in a few sentences. To preface, I
had a friend of mine have his car fall on him once which was supported by a bumper jack
alone. He was fortunate that someone else was there and that the little Rambler was
not all that heavy.
First, buy some GOOD quality jack stands, the best you can find.
Second, ALWAYS use them when working under a car, even if its for a very
short period of time. Hydraulic or bumper jacks just can't be trusted with your life
to hold a vehicle up as they are designed to raise and lower a vehicle, not hold it for
any extended period of time. Third, work on a level, hard surface. Finally,
try to have someone else around and let them know you will be under the car. In the
unlikely event (if you followed rules 1, 2 and 3) the vehicle falls on you, maybe
they will be able to save your life. That should do it, and safe wrenching!
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TH350 and TH400 transmission speedometer gear
charts & part numbers
Speedometer
gear chart for GM Manual and Automatic transmissions
Speedometer
gear chart for GM Manual and Automatic transmissions
TH400 driven gear PN#s: 36 white 1359270, 37 red 1359271, 38 blue 1359272, 39 brown 1359273, 40 black 1342048,
41 yellow 1362195,
42 green 1362049, 43 purple 1362196, 44 gray 9780470, 45 Lt Blue 9775187.
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