Service Done Right #12: Correcting Engine Overheating Concerns

There are several factors that can result in an engine overheating. When faced with this customer concern, it’s best to start with a visual inspection – beginning at the coolant reservoir. 

Is the coolant level low or is it correct? 

If correct, has the customer been adding to the reservoir? 

These are a few questions you’ll need answers to in order to gain diagnostic direction. Coolant doesn’t just disappear. If the level is low, the coolant went somewhere. It could be an external leak or an internal one. Make a close inspection of the cooling system components, looking for any signs of coolant loss. 

Pay special attention to the weep hole area on the water pump. Some seepage is normal, but a stream of coolant is an indication of internal seal failure. If the pump has been replaced, it may be designed with a weep well and the weep hole you’re used to seeing may not be readily apparent. This design was introduced to avoid unnecessary pump replacement. Coolant loss due to normal seepage collects in the well and is allowed to evaporate. However, if the pump seal fails, the well will fill with coolant and when it does, it will seep out of a hole located near the top of the well. On these designs, the sign of liquid coolant on the exterior of the pump is a good indication of pump failure.

If you confirm a bad pump, then consider replacing it with a pump from our sponsor, Carter. Always new, never remanufactured, Carter water pumps will provide you, and your customer, the peace of mind that only comes with using a quality, performance-proven product. Visit CarterEngineered.com for more information and access to additional technical resources. 

If there is no sign of an external leak, suspect an internal one. You’ll be surprised at how many of your customers have leaking head gaskets! 

There are several ways to test for bad head gaskets but there are two I particularly like. One uses a 5-gas analyzer or a leak detector that detects the presence of carbon dioxide, like the one offered by Automotive Test Solutions. 

Use a fill funnel like this one and place a rag over the top. Allow the engine to reach normal operating temperature then insert the probe under the rag but do not put it directly into the coolant. If it alarms, that’s a good indication that there are exhaust gasses present in the coolant and a verification test should be performed to confirm the bad gasket.

Another way is a method I learned from the diesel guys. It’s called the bubble test. Connect a pressure tester cap to the cooling system and instead of running the hose to the pump, connect it to a clear line. Submerge the line into a clear container filled with water. Allow the engine to reach operating temperature while monitoring the jar.

Exhaust gases entering the cooling system will exit through the clear line, causing bubbles to form in the clear container. 

In both cases, make sure the coolant level is correct prior to making the test. 

Overheating can also be caused by improper coolant flow. That can be the result of cooling passage restrictions, radiator restrictions, improper thermostat operation or problems with the water pump itself. Often, you can see visual signs of this where the radiator hoses meet the engine block or thermostat housing.  

Thermostats can be tested by performing a “time to temperature” test. Engine temperature on late model designs is closely controlled because of the impact it has on vehicle emissions and fuel economy. The EScan scan tool allows me to perform this test through the DLC.

And don’t overlook the radiator cap! It should be changed with every coolant service but typically is not. Test it to see if it holds the pressure its rated for and replace if not, or if there is any damage to the seal. The coolant itself could be the cause of an overheating condition, either because the dilution ratio is incorrect or the wrong coolant has been used.  

You can test its overall condition using test strips designed for this purpose. Pay special attention to the pH level of the coolant. This is an indicator of the condition of the additive package added to prevent rust and corrosion in the system. Many things can cause the additive package to be depleted prematurely, so be sure to address these causes as part of your repair recommendations. And if your customer has been adding coolant or tap water to the system, recommend a flush and fill to restore the coolant condition, regardless of its pH level.