I’ve been a Pontiac fan for 39 years and a subscriber to High Performance Pontiac for many of them. I’m also the original owner of a ’75 Formula Firebird.
For the 400 engine’s new rebuild, the block was bored to 4.1812 inches and stroked to 4.250 inches using an Eagle crank and rods, Ross pistons, and a roller cam (0.520/0.540 lift). The heads are ported Edelbrock 87cc Round-Ports with 1.52:1 roller rockers. The intake is an Edelbrock Torker II. The compression ratio is 10.2:1; total timing was set to 34 degrees. The combo was balanced and blueprinted, and dyno’d at 530 hp/551 lb-ft.
The new cooling system was upgraded to a Be Cool aluminum radiator, stock clutch fan and fan shroud, high-volume water pump, 160-degree thermostat with 1⁄8-inch hole drilled on the side, and a new temperature gauge and sender.
The water temperature reads steady at 195 degrees on city and freeway driving. Is this normal or too high? I’m hesitant to take the Firebird for a long drive because I don’t want to ruin the new motor. I’m open for some good ideas or advice.
A.J. from California
Rocky Rotella responds:
Thanks for being a loyal subscriber to HPP, and congratulations on owning your Firebird Formula since new! It sounds like you’ve assembled a very potent combination, and with the amount of power it generates, I’m sure it’s a blast to drive.
I’d be glad to help you with your concerns. Let’s begin by briefly outlining some coolant-system-related basics.
An engine’s water pump circulates coolant throughout the entire cooling system. Its thermostat restricts coolant flow through the radiator, allowing it to circulate through the engine only during cold operation to force quicker warming. The thermostat has an internal plunger (or valve) that reacts to coolant temperature and opens at a predetermined temperature to allow a normal coolant circulation path. If at any point coolant temperature falls below that point, the thermostat partially or fully closes, restricting flow through the radiator until the coolant again reaches its intended temperature.
Generally speaking, a thermostat doesn’t reach maximum flow capacity until some 15-20 degrees above its rated point
The thermostat’s temperature rating is misleading to many consumers. Most believe the stated number is the coolant temperature a given engine will operate at during normal use. In reality, it’s little more than the temperature the thermostat plunger begins to open. Generally speaking, a thermostat doesn’t reach maximum flow capacity until some 15-20 degrees above its rated point. Then it is the coolant system’s responsibility to regulate and maintain that temperature during normal operation.
With that said, there’s a specific temperature range in which an internal- combustion engine operates most efficiently. Pontiac used a 195-degree thermostat in practically all its production V-8s, and its target normal operating temperature was about 210 degrees. While we hobbyists often think that’s excessive today, the temperature-sending unit, which Pontiac installed on its vehicles equipped with a warning light (as opposed to an actual gauge), didn’t force illumination until approximately 240 degrees!
While I don’t recommend operating your engine for any length of time at or above that temperature, if it’s in otherwise excellent condition, I don’t think momentary operation would inflict any serious damage. However, consistent operation at that temperature can cause any number of concerns, including engine-damaging detonation and/or poor bearing lubrication. You’re obviously nowhere near that point with your engine.
Aluminum dissipates heat quicker than cast iron. That’s what allows an engine with cast-aluminum cylinder heads to tolerate a compression ratio that’s typically 0.5:1-0.75:1 greater than iron castings. While one might assume the additional compression equates to additional power output, an engine with cast-aluminum heads actually requires additional compression to produce an equal amount of power of iron castings. That’s why you’re able to run a compression ratio of 10.2:1 on pump gas without detonation issues.
Whatever thermostat you choose, get out and enjoy your Pontiac
When selecting a thermostat for my Pontiac V-8s, I think of the thermostat’s rating as the minimum temperature the engine will operate. While a 160-degree thermostat is the choice for most, I think it keeps the engine a bit too cool for optimum performance. I prefer a 180- degree thermostat when running cast-iron cylinder heads on our performance engines as it provides regular operation at 190-195 degrees. Since the thermal efficiency of aluminum is greater than iron, a 195-degree thermostat could be a better option to retain a sufficient amount of heat in the chambers for maximum power output.
This all assumes that the coolant system is adequate for the application. It sounds as if you have a very efficient coolant system on your Firebird. That makes me wonder, are you absolutely certain the coolant temperature is 195 degrees? A 160-degree thermostat should run closer to 175 degrees with the stated components.
The only potential issue I see is that the high-flow water pump circulates coolant too quickly, which prevents it from staying in the radiator long enough to sufficiently exchange heat. I wouldn’t expect to see that with an aluminum radiator, however.
I suggest verifying the accuracy of your new temperature gauge and sender. Check it with another gauge, or by using an infrared thermometer aimed at the thermostat housing or near the temperature sender. If the gauge is accurate and coolant temperature doesn’t waiver far from 195 degrees, I would have no qualms running your engine at that temperature, or even slightly higher, for any length of time. In fact, I would most likely install a 180-degree thermostat to be sure the engine doesn’t fall below that operating range. As opposed to running worse with a slightly higher temperature, I bet your aluminum-headed Pontiac will run a bit more efficiently.
Whatever thermostat you choose, get out and enjoy your Pontiac. I’m confident you have nothing to fear running in that temperature range!
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