I have a 2001 Hyundai Elantra, 95K miles. I’ve had it a year and it’s been great and now it’s having its first problem. Well, maybe second, the clutch is leaking fluid somewhere. Anyway, the temp guage shows normal, maybe even a bit high, and the heat blows hot, but only when I’m moving. If I’m not moving, the air blows cold. As soon as I start moving again it heats back up quickly. The temp guage doesn’t change, just the temp of the air blowing out the vents.
I’m going to take it to the mechanic next week, I’m just curious really. And I want to find out about the clutch.
Yes, the coolant level is significantly low. And while it may not be overheating right now, it’s on the verge of it and could badly overheat at any time. You do not want this to happen, as it could do some major engine damage. Top it up before you drive it again.
With the engine COLD, remove the radiator cap and fill the radiator to the top. Also fill the overflow jar about halfway, but do NOT depend on filling the overflow jar to fill the system, nor on the level in the overflow jar to tell you that the system is full. Go straight to the radiator. Check (and fill) it at least once a day until you get the car to the shop.
The coolant is the liquid in the cooling system. Normally, it’s a 50/50 mix of antifreeze and water.
Topping up with plain water will do the job, but will affect the antifreeze/water ratio and thus the freezing point of the mixture. As long as the ambient temperature is above freezing, it’s not a concern (for the short term - having antifreeze in there also retards corrosion). If it is going to get below freezing, get some antifreeze to add later.