Signs and Symptoms That Your Mid-Size Truck is Overheating

Overheating is one of the worst things that can happen to your commercial truck. If the cooling system in your medium-duty Isuzu NPR, Mitsubishi Fuso, Hino or UD Truck isn't working like it should, the engine could overheat and suffer extreme failure. We recommend you do some troubleshooting to know whether or not your engine is overheating, and what might be causing it.

Check the Engine: Start the engine on your truck and wait for it to heat up. When the needle on the temperature gauge sits at or near the middle mark, your engine is sufficiently warm. If it rises above the center mark on the gauge, your engine is starting to overheat.

Check the exhaust. If there is steam coming out of the tailpipe, then your head gasket has failed, and this is likely causing your engine to overheat due to engine coolant leaking into the combustion chambers instead of cooling the engine.

Related:  Isuzu NPR, NQR, NRR, GM, Mitsubishi FUSO, UD: Prevent Transmission Failure & Overheating Problems

Signs & Symptoms:
The coolant level is low. In hot weather, the coolant in your engine can get low by evaporating through the overflow reservoir. As hot coolant is pushed into the reservoir, a certain amount of steam is produced. Over a long time, this can lead to lowering coolant levels in the system. It may also be that the system was not filled properly after the last cooling system repair or maintenance. This is easy to diagnose. Remove the radiator cap when the car is cool and look at the fluid level. If the reservoir tank fluid level is at or below the lower mark on the reservoir tank, fill your reservoir tank with a mixture of 50/50 engine coolant and water.

You have a leak in the engine cooling system. Leaks can occur in a cooling system several ways. The radiator or heater cores can become old and develop pin holes that leak coolant under pressure. Likewise, radiator and heater hoses become weakened by the high pressure that they sustain until the hose ruptures and leaks coolant. Just before the water pump fails, it will often leak cooling fluid from the weep hole on the bottom of the pump. There are also a few places around the engine where gaskets can leak coolant. These leaks are usually either diagnosed immediately when the hood is raised while the car is hot, or antifreeze will be found on the ground under the car when it is parked.

The water pump is failing. If the water pump isn't circulating the coolant, your car will overheat. Most water pumps that are failing will give a high pitched squeeking sound that is hard to miss. When you start to hear the squeek, you will only have a few days to fix the problem or risk being stranded. Or the water pump may start to leak fluid from the weep hole at the bottom of the pump. This is a sign that the internal seal is failing. When this sign shows up, get the car fixed quickly because it will continue to get worse.

The thermostat is bad. Most of the time when thermostats fail, they fail to open. This means that the thermostat acts like a plug in the cooling system and keeps the antifreeze from circulating through the radiator to cool down. The result is that the vehicle overheats. When there are no system leaks and the water pump is not bad, the culprit is usually the thermostat.

Related:  Overheating in Isuzu Trucks

The radiator core has become clogged. This is a problem for older and high mileage vehicles. Oxidation, scale, and sludge can conspire to clog the radiator core. It can even be the result of adding too much stop leak to the system. Using a good quality radiator flush in the cooling system may help, but probably you are headed for a radiator replacement.

Your radiator cap needs to be replaced. Without a radiator cap pressure tester, it can be quite difficult to diagnose. If your radiator is spilling fluid around the cap as soon as you stop the vehicle when it is overheating, you have found the problem. Unfortunately, this is not the usual symptom of a bad cap. If you have a shop or parts store in town with a cap tester, take it in and have them check it for you.

You have a blown head gasket. Usually large amounts of white smoke billowing from your exhaust pipe will tell you that coolant is pouring into your car's cylinders. If it leaks to the outside, you will see puddles of coolant under your car that are not located near anything that should leak. In extreme cases, the car simply will not start after you have turned it off when it is hot.

If you or a co-worker is in an accident and you need replacement parts for your medium or heavy duty commercial truck, call us at (803) 564-3228 or (877) 564-6307. If you have any difficulties getting through our phone system, please use our Contact Form or Parts Request Form, or email sales@busbeetruckparts.com.

We have hundreds of Salvaged Medium Duty Trucks and Commercial Box Trucks for Parts including: Isuzu, Mitsubishi Fuso, UD, and GMC. With thousands of parts, including our most popular Isuzu NPR Truck Parts, we should have any part that you need in stock. Our sales professionals will be glad to assist you.  We are located at 4107 Festival Trail Rd, Wagener, SC 29164.


Be sure to Subscribe to the Busbee Blog for more helpful tips and tricks for safe and easy driving. Follow us on Facebook and Twitter, and sign up for our Free Monthly Newsletters.