Texas Classic Chevy Experience: Engine Water Temperature You gotta know what is going on

Engine Water Temperature

You Gotta Know What's Going On

-Alan Arnell

In Texas it gets hot, damn hot, as a matter of fact. As the Texas old saying goes, “Hotter than a firecracker lit on both ends!” In those blistering hot summer months every car guy wants to insure that the engine of his or her beloved classic car does not overheat destroying the engine.

The factory Tri-Five temperature gauge is very vague and has no temperature numbers on the gauge. The so called numberless panel just has a needle that swings from C to H. It’s a mistake, however, to think that this type of gauge is giving you an accurate readout of your car’s motor temperature. In fact, that middle section of the gauge, between the cold and the hot readings, can represent a wide range of temperatures for the car’s engine. I question the reliability of the 50’s technology. This layman believes the Tri-Five dash gauges are not a good as today's newer model aftermarket temperature gauge.

1955 Bel Air Dash Instrument Cluster

1956 Bel Air Dash Instrument Cluster

1957 Bel Air Dash Instrument Cluster

Try towing something, or even fully loading your vehicle with your large friends, and driving up a long incline. Sure your numberless gauge might show the needle closer to H but what does that really mean? Is the H on the gauge 210 or 250 degrees. The boiling point of water is 212 degrees, however the radiator is a pressurized system and should be filled with coolant that raises the boiling point.

The pressure cap on a cooling system is the key to raising the boiling point of the 50/50 mix of antifreeze and water. For every pound of pressure the cap provides increases the boiling of point of the coolant mixture 3 degrees. If you had plain water in your cooling system with a 15 pound pressure cap the water would boil @ 257 degrees. If you had a 50/50 mix of antifreeze and water the coolant would boil @ 265 degrees with a 15 pound cap. The boiling point would raise to 270 degrees if you had a 60% antifreeze mixture with a 15 pound cap. If you had a 70% mixture the boiling point would raise to 276 degrees.

FYI: A good temperature for a classic Chevy engine is usually 160 to 180 degrees. If you reach 200 when siting, but the temperature reduces when driving that is O.K.

Any car can be damaged by overheating. Overheat the engine enough and you will blow a head gasket and be in for an expensive repair. A car’s temperature gauge should accurately inform you of the coolant temperature so you may know when to make adjustments to stop the engine’s overheating. If your engine overheats but the head gasket do not blow the high temp heat soak into the cylinder head may cool too quickly after the engine is shut down. This rapid cooling of the heads will produce cracks between the cylinder and water jackets of the engine.

After an engine warms up and little bubbles appear in the coolant like this that indicate a blown head gasket.

Coolant in the oil that causes your engine oil to become a milky chocolate milk which is a sure sign that there is a blown head gasket. Other signs are if the engine is running poorly (skipping, hesitating, or lack of power). Another symptom may be excessive pressure in the crankcase causing extreme blow by out the oil cap or engine oil seals.

White exhaust smoke is one sure sign of a blown head gasket

I prefer to have a metered gauge for the coolant temperature on the dash, rather than a stock Tri-Five gauge or warning light. I regularly look at the coolant temperature gauge and the voltage and oil pressure gauges while I drive. I know where the gauges’ needles should sit while driving. If I see something abnormal I can jump on the problem straight away.

1969 Chevrolet Chevelle Malibu fuel gauge warning lights

A better coolant gauge can also indicate problems well before anything mechanically needs to be fixed. For example, in an engine where the temperature rises while travelling at highway speeds is a concern. The gauge at speed should be reading close to temperatures shown at idle. When is was 16 years old my 1969 Chevy Chevelle had this problem. I found after inspection of the engine fan by wiggling it up and down that the water pump shaft could be move up and down and had worn out bearings. The pump’s impeller was not allowed to pump enough coolant at speed to adequately cool the engine.

Chevelle SS 396

Later in life I owned a 1978 Chevy Corvette Pace Car. I discovered from the metered gauge that the car was running cold. This fact told me that the thermostat was stuck open. This is something that I would never have known about without a proper gauge.

1978 Corvette Indy Pace Car

There was also the problem back in the good old days in cars with only the warning light. If you lost the coolant out of the engine’s cooling system the light wouldn't come on, because there was no hot coolant to tell the warning light switch that it was hot. A temperature sender just sitting inside a hot manifold with no fluid will not trigger some warning lights and older gauges may not be sensitive enough to show the problem.

Installing a Water Temperature Gauge

Water temperature gauges come two different in metering methods. You may buy a gauge that either gauges the engine temperature by electrical or mechanical means.

Electrical Gauge

When installing an electrical water gauge, a special sending unit must be installed to the engine. Small-block Chevys have pipe plug fittings in each cylinder head and most intake manifolds.
Before starting the installation drain the the coolant before removing the plug.
A 18-gauge wire is used to create a suitable ground for the electrical gauge.
Connect the sending unit to the terminal marked “S” for sender on the gauge.
Connect a switched 12-volt source to the terminal marked “I” for ignition.
The wire to the engine will be routed through the fire wall. A rubber grommet must be used to prevent chaffing.

AutoMeter Water Temp Gauge Wiring Diagram

Engine Coolant Temperature Sending Unit Sender

Mechanical Gauge

When installing a mechanical water gauge a special sealed tube relays engine temperature information to the gauge.
The fitting will require a larger hole in the firewall to route the tube.
With mechanical temperature gauges pass the tube through the gauge panel first. a rubber grommet must be used. If you don’t you might have hot water spraying on your feet.

Mechanical Water Temperature Gauge - Stewart Warner Deluxe

Find a good location for the gauge so that the engine water temperature is only a glance away and out of sight and out of mind.

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