Overheating problems on trucks can sometimes seem straightforward.
Blocked radiator.
Faulty thermostat.
Water pump failure.
Most of the time, one of those is the culprit.
But sometimes the real cause is harder to track down.
Recently we had a Volvo come into the workshop that had been dealing with an overheating issue. The truck had previously had a radiator clean, and the engine had been rebuilt by another workshop over east around 100,000 kilometres ago.
The customer’s complaint was simple:
the truck kept overheating.
First Suspect: Airflow
When the truck arrived, the first thing we looked at was the radiator.
It was quite dirty and clogged, which meant airflow through the cooling system was restricted. Poor airflow is one of the most common reasons trucks overheat, so cleaning the radiator made perfect sense.
After the clean, the truck left the workshop and everything looked good.
But about a week later, the customer was back.
The overheating problem hadn’t gone away.
Time to Dig Deeper
At this point we started going through the cooling system step by step.
We tested the thermostats.
They were opening correctly.
We removed the fan belts and checked all the rotating components and bearings.
Everything felt smooth.
The water pump was inspected and functioning correctly.
We checked the air cleaner, inspected the turbocharger, and pressure-tested the cooling system to ensure there were no combustion gases or abnormal pressure entering the coolant system.
We even isolated the air compressor to confirm it wasn’t pressurising the cooling system — something that can occasionally cause overheating symptoms.
Still nothing.
Road Testing
Next step was a proper road test.
We took the truck for a long drive to try and recreate the overheating issue.
The hottest temperature we could get the truck to reach was 92°C, with the thermostats opening exactly where they should — around 82°C.
In other words, everything was operating normally.
Sometimes the Workshop Isn’t Enough
After explaining the situation to the customer, we agreed to replace the fan and fan belts as a precaution.
But the key detail was this:
The overheating seemed to occur only when the truck was working hard with trailers attached.
That means the next step may be riding along with the driver while he does his normal work.
Because some overheating problems only appear when the truck is under full load — climbing hills, pulling weight, and working the way it was designed to.
And those conditions are very difficult to fully replicate inside a workshop.
The Takeaway
Cooling system faults aren’t always obvious.
Sometimes solving the problem means eliminating every possible cause until the real trigger shows itself.
That’s why proper diagnostics take time — and why guessing at parts can become expensive very quickly.
At Webbie’s Mechanical, we prefer to prove the problem before replacing parts, so when a repair is done, it actually fixes the issue.
📍 Webbie’s Mechanical
Diagnosing problems properly — even when the answer isn’t obvious.
https://www.tiktok.com/@webbiesmechanical/video/7615497706525543688