1985 Volvo 745 Coolant Temperature Sensor: A Mechanic's Guide
Is your Volvo 745 running rough or getting bad gas mileage? Your coolant temperature sensor might be the problem.
- A bad coolant sensor on a 1985 745 typically causes poor fuel economy, rough idling, and black exhaust smoke.
- This car has two temp sensors; be sure you are replacing the one for the ECU under the intake manifold, not the one for the gauge.
- Accessing the sensor is difficult; removing the intake manifold is often the easiest approach for DIY replacement.
- Using a quality OEM-style brand like Bosch is highly recommended over budget parts to ensure proper performance and avoid re-doing the job.
Understanding the Coolant Temperature Sensor in Your 1985 745
The Engine Coolant Temperature (ECT) sensor is a key player in your Volvo's engine management system. It acts like a thermometer, telling the engine's computer how hot or cold the engine is. This signal is critical for calculating the right air-to-fuel mixture. A bad sensor can feed the computer false information, leading to a host of engine performance problems. If the sensor wrongly tells the computer the engine is always cold, the computer will keep sending extra fuel, causing a rich condition.
Symptoms of a Failing Coolant Temperature Sensor
When this sensor starts to fail, your car will give you clues. Paying attention to them can save you from bigger headaches down the road.
- Poor Gas Mileage: One of the most common signs is a sudden drop in fuel economy. The engine uses more gas than it needs because it thinks it's constantly in warm-up mode.
- Rough Idle: Your 745 may shake, vibrate, or run unevenly when stopped. This is due to the incorrect fuel mixture upsetting the engine's balance.
- Black Smoke from Exhaust: If you see black or sooty smoke coming from the tailpipe, it's a sign of unburned fuel. This happens when the engine runs too rich.
- Hard Starting: A faulty sensor can make it difficult to start the engine, especially when it's cold, because the computer isn't providing the right fuel mix for a cold start.
- Engine Overheating: On some models, this sensor also helps control the electric cooling fans. A bad sensor might fail to turn the fans on, causing the engine to overheat.
Don't Confuse the Sensors
Your 1985 Volvo 745 has two separate sensors. One sends information to the engine computer (this is the one that causes running issues), and the other operates the temperature gauge on your dashboard. The computer's sensor is located under the intake manifold, near the third cylinder. Make sure you are replacing the correct one.
Choosing the Right Aftermarket Sensor
For an older car like the 1985 745, you have a choice between Original Equipment (OEM) parts and aftermarket ones. While aftermarket parts are often cheaper, this is one sensor where quality matters a lot.
- OEM/OEM-Quality: Brands like Bosch or VDO were the original suppliers for Volvo. Choosing one of these ensures the sensor is calibrated exactly to your car's needs.
- Aftermarket: Some budget aftermarket sensors can have poor quality control. Forum users have reported aftermarket sensors that caused rough cold starts or didn't trigger the cooling fan correctly. An incorrectly calibrated sensor can send the wrong voltage signals, creating the same problems as a failed sensor.
Pro Tip: Given the difficult location of this sensor, it is worth spending a little more on a quality part to avoid doing the job twice. The small price difference is much less than the frustration of continued engine problems.
Cost to Replace a Volvo 745 Coolant Temperature Sensor
| Part or Service | Estimated Cost |
|---|---|
| New Aftermarket Sensor | $17 - $30 |
| New OEM Sensor (e.g., Bosch) | $25 - $50 |
| Shop Labor | $100 - $250 |
Costs are estimates and can vary by location and repair shop. The labor cost can change depending on whether the mechanic needs to remove the intake manifold for access.
Frequently Asked Questions
Where is the coolant temperature sensor located on a 1985 Volvo 745?
The sensor for the engine computer is located on the driver's side of the engine, screwed into the cylinder head underneath the intake manifold, usually near the #3 cylinder runner. It is difficult to see and reach.
Can I replace this sensor myself?
Yes, this is possible for a DIY mechanic. However, access is tight. Some people manage to do it without removing the intake manifold, but it is frustrating. The more common method is to remove the intake manifold, which requires a new gasket upon reinstallation. The job can take 1-2 hours.
Are there any recalls for this part?
No, there are no specific recalls for the coolant temperature sensor on the 1985 Volvo 745. There was a recall for the engine wiring harness on 1985-87 models, which could cause similar electrical issues, but it is not related to the sensor itself.
What happens if I don't replace a bad coolant sensor?
Driving with a bad sensor can lead to long-term problems. Persistently running rich can foul your spark plugs and damage your catalytic converter. It also wastes a lot of fuel. In a worst-case scenario, if the sensor fails to trigger the cooling fans, your engine could overheat, leading to severe damage.
Technical Specifications
OEM Part Numbers: 1346030 1362645
The sensor for the fuel injection computer (ECU) is typically located under the #3 intake runner and has a two-pin connector.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Volvo 745: