Project VIPER GTS: Part 11 – Understanding the Factory Temp Gauge

This isn’t usually a concern, but worth mentioning. The normal thermostat cycle closes the thermostat when water temps are too low, and the needle is left of the three center hash marks, until it warms up and the thermostat opens when the temp reaches the center of the gauge.

Now let’s look into this a bit more than simply accepting that anything to the left of the red is fine.


The normal fan cycle describes the needle behavior as rising slowly and then dropping fast, due to the fans effectively bringing down the temps.

The most eye-opening part of the cooling system service manual, is the programming of the factory radiator fans. The Low Speed fan comes on whenever the air conditioning is on, or when the coolant is above 207*F.  It does not shut off until the coolant drops to 201*F.  In weather above 70*F, the low speed fan rarely keeps the temperature in check when the car is stopped or moving very slowly.  As the temps creep up, the high-speed fan does not kick in until a fairly high 216*F! and then does not shut off until the coolant drops to 208*F.

With the knowledge of the fan’s factory programmed settings on hand, we verified that those temperatures were correct with an SCT tuner through the OBDII port, as well as with the AutoMeter gauge that we installed in Part 2: Maintenance that measures the temperature of the coolant post-thermostat.


  1. Amazing what you can find in owners manuals… Especially older ones. A 2002 CRV manual gave the recommended tire pressure for 160 mph runs. As well as instructions for how to change the spark plugs. You don’t see that anymore

  2. I keep coming back to re-read the articles from time to time.
    Any chances the car will go on sale at the end onf the project? That is one of the cleanest ’97s I’ve seen!

    Keep up the good reads!

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