I've got a question about temperature gauge operation. I've always owned Japanese cars and noticed that once the engine reaches operating temperature the temperature gauge never moves in the slightest. Yet I can feel hotter air blowing out of the heater when going up a hill and cooler air when going down so I'm sure the engine's actual temperature varies. I know the gauge works since the engine did over-heat once and the gauge slowly climbed into the red zone as I'd expect. My wife's car is a Saturn and other family members own Dodges and Fords all of which have temperature gauges that fluctuate constantly with varying operating conditions.
What is it about the gauges that is different and is there any reason why one manufacturer would choose one over the other?
It's not always the operation of the guage, but the efficincy of the cooling system and the heating system as well.
Ever live in a house with small pipes? You're taking a shower, and someone turns on the hot water in the kitchen, and you freeze your cookies until they turn the watre off, right?
Same thing in a car. When you open the valve to allow hot water into the heater core you're changing the dynamcis of the cooling system for a minute or two.
Now, I have owned Toyotas, many models, for a long time. I also have a Chrysler LHS and a Plymouth AWD Voyager. The Voyager has a heating problem, and acts like you describe: when I step on the gas, the heat gets better.
This is because engine RPMs are increasing and the water pump is circulating the water better. You didn't mention which car; make or model you're having this problem with. In my case, it is only the Voyager, and I suspect a weak water pump. My Camry, the LHS, my Supra and my old ('85) Celica don't exhibit this problem.
There are also a number of other factors which might come into play here. The most obvious is coolant level. If the car is running low on coolant, you'll get this kind of behavior. You have to remember that the heater core is basically another radiator, and that the cooling system may not have enough coolant in the system to keep the heater core "full" while going downhill, causing the reduced temperature coming through the air vents. When going uphill, the angle of the car probably causes the heater core to fill up again and heat up, increasing the heater temp again. If coolant levels are fine, you may want to check for blockages in the radiator passages, or perhaps check for air bubbles in the cooling system.
But generally, I've never owned a car that under normal operation, the engine temperature would vary SO much once the vehicle reached normal operating temperature that it would noticeably affect how hot the heater is. Yes, there are small variations in engine temp based on outside are temperature, how fast you're going and what accessories are running, etc, but it's usually not enough of a change to make the heater air temp noticeably cooler or warmer.
I wouldn't be so comfortable with a temp gauge that fluctuates TOO much, expecially on newer cars. A fuel injected engine works best within a specific temperature range, and the idea of a cooling system isn't to keep teh engine on ice, but to keep it not too hot, and not too cold.
Also, not all factory temp gauges are alike, nor are they the most accurate. Certain vehicle models might have temperature gaguges that report a wider range of temperatures, while others might just be calibrated to be more concerned about whether the car is going to overheat or not.
Well, yes: most major car manufacturers have preferred relationships with suppliers that used to be a subsidiary of the automaker itself. The "Big Three" as well as many foreign automakers chose long ago to make their own gauge clusters and other sensors and components in-house, and so separate divisions were made within those companies for that purpose. Ford eventually spun off their parts division (now known as Visteon, currently in financial trouble), and GM did the same (Delphi, now bankrupt but still manufacturing GM parts as well as XM and Sirius satellite radios). Chrysler's parts division (Mopar) is still a DaimlerChrysler subsidiary. And each company has their own ideas and philosophies on how such instruments should work.
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