If you’re having a trouble with your coolant temperature and notice that your lower radiator hose is cold instead of hot, you may be having issues with your coolant system and you’ll need to get the issue taken care of.
To accurately diagnosis a lower radiator hose cold problem you’ll need to look at all the components that contribute to radiator temperature.
6 Causes of a Cold Lower Radiator Hose
The most common reasons for cold lower radiator hoses are:
- Faulty thermostat.
- Faulty water pump.
- Low level of coolant.
- Air locks.
- Clogging in the coolant system.
Here is a more detailed list of the six most common causes of a cold lower radiator hose:
#1. Faulty Thermostat.
Bad thermostat is the most common issue associated with a cold lower coolant hose. Engines have a valve-based thermostat that determines and regulates coolant inflow such that the engine operates at its proper temperature and does not overheat.
If your vehicle is overheating, and at the same time, does not heat the lower coolant hose, it is likely that you have a bad thermostat needing replacement.
When the engine is cold, and not operating, the thermostat should be closed. Thermostat regulation of water prevents engine hot spots. Once the optimum temperature is reached, the coolant water will be converted to the radiator to dissipate heat.
If the thermostat is not opening at this time, it will not permit water flow into the cooling system, resulting in the lower radiator hose to remain cold, while simultaneously overheating the engine.
#2. Faulty Water Pump.
So, the water pump has a job to pump the coolant from the engine block and send it to the radiator to cool it down.
If the water pump isn’t working right, there will be a pool of water in the engine, and no water will be sent to the radiator.
The lower coolant hose is most likely the coolant output side of your engine, which would explain why the hose is cold.
#3. Low Coolant Level.
A low level of coolant can create all kinds of issues in the coolant system. A low coolant level can create air pockets in the coolant system, and it can even leave the water pump in an air pocket.
Coolant level is easy to check. Pop your hood and consult your car manual to locate the coolant reservoir. Just remember, don’t ever open it when the engine is hot. If it’s hot, it’ll be boiling, and if you open it, the coolant will splash everywhere.
#4. Air in the Coolant system.
Air pockets in the cooling system is something you don’t really want. Air pockets lead to overheating and may affect the coolant circulation altogether.
If there is an air pocket around the water pump, it may not even pump water anywhere.
Air in the coolant system may be because of a leaky head gasket or either a poorly performed coolant fluid change. If you know that you recently changed coolant, then you are going to want to properly bleed the system.
Air in the coolant can also happen with too low of a coolant level.
#5. Clogged Coolant System.
Very rarely, the coolant system can get clogged. It is not common because the main coolant pipes are relatively large. Still, if someone ran your car without coolant and just water, it is possible to create a lot of rust in the engine.
This along with a leaking head gasket can cause a lot of mess in the coolant system. If you have done everything, try to flush the coolant system.
#6. No problem at all.
When you see a cold lower radiator hose, it doesn’t always mean there’s a problem! The engine has to be really hot and almost boiling before the thermostat opens and allows coolant to flow.
If your engine isn’t overheating, the cold lower coolant hose just means it isn’t hot enough and everything is fine with your engine.
Should both radiator hoses be hot
When the engine is at operating temperature, both upper and lower radiator hoses should be hot. This indicates that there is a sufficient flow of coolant through the radiator, so the internal combustion engine is not at risk of overheating.
Radiator hoses should be cold only while warming up the engine or sometimes if the engine is running cool while cruising outside when it’s cold out. In these scenarios, the thermostat will be closed prior to reaching a given temperature, preventing the flow of coolant.
Why is my car radiator hot at the top and cold at the bottom?
The reason for this is that the hot coolant from the engine will enter the radiator from the top.
As the coolant moves down, it will be cooled by the air coming through the radiator’s core. Therefore, if the radiator is functioning correctly, it will be cooler at the bottom than it is at its top end.
Do the upper and lower radiator hoses need to be the same temp?
If the cooling system is working as it should, the lower radiator hose should be cooler than the upper radiator hose.
The coolant enters the radiator from the upper end and flows through the core and will drop in temperature. But since both hoses are still very hot, you may not be able to feel much difference when touching them by hand, that is when an infrared thermometer or similar device can be used.
Should the lower radiator hose be soft?
When the engine gets up to operating temperature, the lower hose, like the upper hose, should feel firm to the squeeze.
The cooling system runs at a certain pressure, which, in most cars, is 10 psi or higher. That’s what raises the boiling point and allows for the more efficient operation of the engine.
Why is my radiator hot half and cold or cooler half?
A radiator will be hot on half and cold on the other half when there is a clog from dirt build up. If this is the case, the coolant will not flow through most of the core, and the cooling effect is severely diminished.
A car may drive fine with a radiator like that while under moderate loads, but the engine will quickly overheat if it is under heavier loads. This typically happens when a driver drives for an extended uphill period or while towing a load.
The main cooling systems are responsible for controlling temperature and preventing the engine from overheating. They consist of a pump (usually a coolant pump), a thermostat, and a radiator, among other things to help provide cooling, and several pipes and rubber hoses connecting it all together.
There are several common failure points in the cooling system, and a clogged radiator with dirt buildups is one of these.
Buckled radiators are commonly seen in higher-mileage cars that have been neglected. The coolant flow won’t be sufficient through radiators like this, causing overheating especially when putting a heavier load on it. If it is clogged from dirt buildup, it will be half hot and half cold.