My girlfriend has just bought a second hand car. When I drive it around town for about half an hour the temp gauge goes up and hangs around the normal area. After leaving town and getting onto the motorway it then falls back into the cold region.
Should this be happening?
It’s a liquid cooled engine, not air. So surely the amount and speed of air shouldn’t make a difference, or should it?
Thanks.
The liquid is cooled by air blowing through the radiator, is it not? Said airflow will increase at high speeds.
In fact, at certain high speeds, the aiflow coming in the front of the car is more than enough to keep the radiator cool and, usually, the cooling fan will cut off.
That is standard behaviour. My electric fan only ever cuts in if I am in slow moving traffic, which is when cars most often overheat.
Engines are designed to run at a certain temperature where they can be most efficient. If you are getting large fluctuations after the car is warmed up there is most likely something wrong. In this case it sounds like the thermostat is stuck open. The thermostat is designed to stay closed until the coolant reaches a certain temperature, usually somewhere in the 170-190 degree range. When the thermostat opens up the coolant then circulates through the radiator and back into the engine. If it is stuck open the coolant will be circulating constantly and the engine may run cooler than is optimal. It’s not a major problem, but it would be a good idea to get the car looked at. It shouldn’t be very expensive to fix.
What you describe is not normal. I agree that it sounds like a faulty thermostat.
It should get into the normal range with about 5-10 minutes of driving – shouldn’t take anywhere near a half hour to reach that point. And while it wouldn’t be unusual for it to run somewhat cooler on the highway than in town, because of the constant significant airflow through the radiator, it shouldn’t get down to the cold range.
Water-cooled vs. air-cooled has to do with the medium that carries heat from the engine, but both designs depend on air to remove the heat. Water-cooled engines use liquid to relay the heat from the engine to where the air is (the radiator).
You guys may very well be right, but keep in mind we are talking about a dash gauge here. The OP never mentioned that the car was over-heating, or that there were wild fluctuations of any kind. I think this, as described, is completely normal behavior for many cars.
If this were my girlfriend I would verify that the electric fan (assuming a typical FWD transversely-mounted engine) was working, whenever the car got hot. And if the cooling system was otherwise OK, I’d tell her not to worry about it.
And none of our responses suggest he did. We’re surmising that the car is overcooling, which is caused by a thermostat stuck open. Overheating is caused by (among other things) a thermostat stuck closed.
Again, we didn’t say wild fluctuation. Jonathan D said huge fluctuation in reference to the OP description of the gauge going from the normal range to the cold range. That is a significant, if not huge, fluctuation.
It’s not. Some fluctuation, WITHIN the normal range, is normal once the engine is warmed up. Going down to the cold range is not normal. Taking a half hour to get to the normal range is not normal.
In the scenario described, which strongly suggests that the engine is not getting as hot as it should, it would probably never get hot enough to activate the fan.
Another thing to keep in mind is that most temp gauges are designed to be more like an “idiot light” than a gauge. The motion of the needle is heavily dampened so that it hardly ever moves once the engine is warmed up, even though the coolant temperature will always be slightly fluctuating. If it is moving, then there are some major temperature changes occuring.
This is exactly how my old car behaves (Seat Toledo)…it takes waaaaay too long to increase the temperature and I don’t think it ever reaches the normal range. Maybe I should look after it.
My other car though (Hyundai SantaFe) warms extremely fast (maybe 3 minutes, and thats while idling) and then the gauge stays right in the middle of the scale. No fluctuations at all. I wonder how it will behave when it reaches the age of my old car (12 years).
The op’s Q was answered very well already,
Sometimes the thermostat is removed for a lame attempt to remedy another problem, and the results can be somewhat confusing. One such situation was a higher than normal temp. apparently the fast movement of the coolant wasn’t dissipating the heat properly.