Still Overheating After Replacing the Thermostat? Here’s What’s Really Going On

At Tim’s Automotive in Clackamas, We Fix the Real Problem — Not Just the Obvious One

You replaced the thermostat, expecting your truck to run cooler. But now it’s still overheating — or maybe it’s even worse than before. So, what gives?

At Tim’s Automotive Repair and Sales, we’ve seen this story play out time and time again. A customer replaces the thermostat thinking it will solve the overheating issue, only to find that nothing has changed. That’s because your cooling system isn’t just a thermostat — it’s an entire network of components that must work in perfect balance.

We don’t guess. We diagnose. And we solve what others overlook. If you’re driving through Clackamas, Happy Valley, Oregon City, or Damascus, here’s why your truck may still be overheating — and what we do differently to fix it for good.

1. Air Trapped in the Cooling System

When a thermostat is replaced, air can easily get trapped inside the system — especially if it’s not bled properly. These air pockets can block coolant flow and prevent the thermostat from opening as designed.

Common signs:

• Heater blowing cold air
   

• Gurgling sounds in reservoir
   

• Temperature spikes that come and go
   

Tim’s Fix:
We vacuum-fill and pressure-bleed the cooling system to ensure all air is removed, restoring smooth and consistent coolant flow through the engine and radiator.

2. Radiator Blockage or Flow Restriction

Even with a brand-new thermostat, if your radiator is partially clogged with rust, debris, or buildup from old coolant, it won’t transfer heat properly — especially when idling or towing.

Watch for:

• Engine runs hot in traffic
   

• Sludgy coolant
   

• Cold lower radiator hose
   

Tim’s Fix:
We inspect radiator flow using temperature differential testing and flow diagnostics to ensure coolant is traveling through the system at the correct rate.

3. Water Pump Malfunction — Even Without a Leak

Water pumps don’t always fail loudly. A worn or corroded impeller might still spin but move very little coolant. This is especially common in high-mileage trucks.

Clues:

• Truck overheats while driving
   

• No coolant movement visible in radiator
   

• Coolant surges or returns too slowly
   

Tim’s Fix:
We test water pump performance under real engine load — checking for circulation volume, impeller integrity, and pulley operation.

4. Head Gasket Leak or Combustion Gas in the Coolant

This is the one most drivers — and many shops — miss. A head gasket failure can allow combustion gases to enter the cooling system, superheating the coolant and forcing air into the radiator.

Symptoms:

• White smoke from exhaust
   

• Coolant bubbling in the reservoir
   

• Coolant disappearing with no visible leaks
   

• Milky oil or strong exhaust odor
   

Tim’s Fix:
We perform a chemical block test, pressure testing, and combustion leak detection to determine whether your head gasket is compromised before further damage occurs.

5. Faulty Radiator Cap or Overflow System

Your radiator cap keeps pressure in the system. If it’s weak, your coolant will boil at a lower temperature — and steam pockets will form, causing erratic overheating even if everything else is working.

Look for:

• Coolant overflowing or steaming
   

• Radiator hose collapse
   

• Sudden temperature spikes at low speeds
   

Tim’s Fix:
We test your cap’s pressure rating and inspect the full overflow return circuit to confirm the system is sealed and functioning properly.

6. Cooling Fan Isn’t Engaging Properly

Whether your truck uses electric fans or a clutch-driven setup, if the fan doesn’t turn on or ramp up when needed, your engine will overheat in traffic or at idle — even with a perfect thermostat.

Signs:

• A/C cuts out at stoplights
   

• Truck runs hot when stopped
   

• Fan doesn’t activate when engine is hot
   

Tim’s Fix:
We test fan motors, relays, switches, clutch operation, and temperature sensors to ensure fans kick in when they’re supposed to.

7. Incorrect Thermostat or Installation Error

Believe it or not, some thermostats are installed backward, rated incorrectly, or simply fail right out of the box — especially cheap aftermarket parts.

Symptoms:

• Immediate return of overheating symptoms
   

• Temperature gauge behaves erratically
   

• No hot coolant in upper radiator hose
   

Tim’s Fix:
We only install high-quality, OE-grade thermostats, confirm proper orientation, and run a full warm-up cycle to verify system operation before the job is considered done.

Tim’s Automotive — Trusted Cooling System Diagnostics in Clackamas

When it comes to overheating, we don’t take chances — because engine damage is too expensive to risk. At Tim’s Automotive, we use professional diagnostic equipment and real-time testing to find the true cause of your truck’s overheating — and we show you everything we find, step by step.

Whether you're hauling, commuting, or working locally in Clackamas, we protect your truck, your engine, and your bottom line with integrity-driven repair and no guesswork.

What to Do Next

Still overheating after a thermostat replacement? Let’s get your truck properly diagnosed and back to full strength with:

✅ Cooling system pressure testing
✅ Radiator and hose flow inspection
✅ Water pump diagnostics under load
✅ Radiator cap and overflow testing
✅ Combustion leak and block test
✅ Fan operation and electrical testing
✅ Full coolant system bleed (vacuum fill)

📍 Visit us at 15688 SE 135th Ave, Clackamas, OR 97015
📞 Call now: (503) 656-0600
🌐 Schedule online:http://tims-automotive.com

Summary Table: Why Your Truck Still Overheats After a Thermostat Replacement

Tim’s Automotive — Because Guessing Costs More Than Diagnosing

At Tim’s Automotive, we fix it right the first time — because your time, truck, and money deserve more than a random guess.

For more information you can watch the video.

https://youtu.be/YC5E9wk1XyQ