Temperature Reads Hot After Engine Start

If the temperature reads hot after the engine is started the possible reason is a lack of coolant, collapse radiator hose, bad water pump, or a bad thermostat.

Possible reasons why temperature reads hot after engine start

(1) Low-level engine coolant.
(2) Collapsed radiator hose.
(3) Bad water pump.
(4) Bad thermostat.

Low-Level Engine Coolant

First is to check the coolant level, open the hood of your car and remove the radiator cap. Only do this when the engine is cold... otherwise, you may burn yourself. Next, look down into the radiator fill hole and check the coolant level (use a flashlight if necessary). The coolant should sufficiently cover the little metal "fins" inside the radiator. If this is not the case, the coolant level is low. On most vehicles, you can also check the coolant level simply by inspecting the coolant recovery tank. Refer to your car's owner's manual regarding this approach.

How to Check Engine Coolant Level

Video Credit

If the coolant level is low, then this causes the temperature gauge to reads hot after the engine start. Obviously, an engine's cooling system must have the right amount of coolant to work efficiently. Since the coolant level is low (as you indicated), this is undoubtedly what is causing this problem. It might be that the coolant level is very, very low. Why? Because the temperature gauge "always reads hot SHORTLY after starting engine". This suggests that there can't be much of it (i.e. coolant) simply because it heats up too quickly (i.e. the less of something you have, the less time it takes to reach a certain temperature).

What to do?

Using a clean, empty container, make a 50/50 mix of water and anti-freeze (any auto parts store will carry anti-freeze). Then, when the engine is cold (say, in the morning), remove the radiator cap and pour ample fluid to cover the little "fins" inside the radiator. Replace the cap when done. Now, you might be wondering how the coolant level got to below. Has the radiator recently boiled over once or twice?

This would account for it. Alternatively, maybe there's a leak in the cooling system. Have you ever noticed a puddle of coolant underneath this vehicle? If no, maybe it's an internal leak... like that which results from a blown head gasket. If this is the case, white smoke will come out of the exhaust as you're driving. This is caused by coolant leaking into the engine's combustion chambers and burning off as steam. Whatever the case, have this vehicle checked out by a mechanic.

If the coolant level is not low

With the engine, both off and cold (say, in the morning), open the hood and locate the radiator hoses. If you need help in finding them, refer to a manual covering your car model. Next, while keeping your eye on the hoses, have a friend start the engine. Watch each hose closely until the engine gets hot. If you're having trouble seeing the hoses clearly (in particular, the lower radiator hose), use a flashlight. During the entire time that you're watching the hoses, try to determine if one of them is collapsing at all... sort of as though an invisible hand is pinching the hose. This can occur with an old hose or simply one which is defective (i.e. poorly molded).

How to Check Collapsing Radiator Hose

Video credit

If the radiator hose is collapsed, the collapsed hose is preventing the coolant from flowing through its cycle - from the engine to the radiator, and back to the engine. In other words, the collapsed hose is keeping the coolant trapped. This causes the coolant to heat up shortly after starting the engine and of course, the temperature gauge to read hot.

What to do?

Check the radiator cap if the radiator cap is bad, replace the radiator cap first hence, replace the hose which is collapsing. Any auto parts store will carry a new hose. If the radiator hose is not collapsed then the problem could be a bad water pump or a bad thermostat.

Let's explain what each of the above items does and from that, it should be clear how each can cause this problem. The job of a water pump is to circulate coolant through the engine, out to the radiator, and back to the engine. If the water pump is bad, the coolant won't be circulated through the radiator and thus it'll get too hot. Consequently, the temperature gauge will read hot within a short time after starting the engine.

As for the thermostat, its job is quite the opposite of the water pump. Specifically, when a cold engine is started, the thermostat (in its closed position) keeps the coolant from reaching the radiator. This continues until the engine warms up at which time the thermostat opens, allowing the coolant to reach the radiator. If the thermostat is bad (specifically, stuck in its closed position), the coolant surrounding the engine will get too hot and, as before, the temperature gauge will read hot within a short time after starting the engine.

What to do?

Take your car to a reputable car repair shop and ask the mechanic to determine if the problem lies with the water pump or the thermostat. Once the mechanic determines which is the culprit, ask him to replace it.

Related Topic:

Temperature Gauge Reads Hot During Traffic
v>