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Fresh thermostats Posted by Ari [Email] ![]() ![]() In Reply to: Bill, 82 deg thermo about 6 weeks ago..., Patrick in Abq, Thu, 18 Sep 2003 08:47:48 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I find that when the thermostat is fresh (new), sometimes they act a little 'jerky'. That goes away with time.
Also, it's not uncommon to see that big rise, then big drop. Here's why-
The thermostat opens at a temperature. When the engine is first warming up, the coolant on the engine side is getting hotter, but the coolant on the radiator side of the thermostat is pretty cold. The thermostat is stuck in the middle. Yes, the bi-metallic bits are on the engine side, but all that cool coolant acts as a heat sink. So by the time the thermostat gets hot enough to open, it's a bit hotter on the engine side, where the temperature sensor is, so the temp is a bit high.
When the thermostat opens the first few times as the engine warms up, a big slug of cold coolant comes rushing in. This quickly drops the coolant temp in the engine, and the thermostat closes. But you see a big drop in temperature quickly. Very noticeable. As the engine warms up and the coolant in the radiator gets warmer, there is less of a 'shock' as the coolant comes in when the thermostat opens, so the drop on the temp gauge is less noticeable.
Yes, a cooler thermostat will theoretically result in lower gas mileage, but I don't think it's significant. It's combustion chamber temperatures that set the thermal efficiencies, not the temperature of the block.
And, quite frankly, those mileage figures sound pretty reasonable. That's what I get with my 9000's, and at sea level. The biggest factor in gas mileage is driving habits.
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