Overheating issue

[texaswill]

I swapped out the thermostat and bled the Crap outta the cooling system. It's still trying to overheat. No fluid loss, no fluid in the oil. I noticed the radiator might possibly be a newer replacement from Nissan. I did take the huge plastic guard off from underneath the car and left it off because it makes oil changes way easier leaving it off. Has anybody experienced an fx35 overheating due to it missing that bulky plastic guard underneath the car.? Or, do you think it needs a new radiator? I mean I can't tel l how old the radiator is but my main question is about the plastic guard underneath..??

 

[Julian Antorelli]

I swapped out the thermostat and bled the Crap outta the cooling system. It's still trying to overheat. No fluid loss, no fluid in the oil. I noticed the radiator might possibly be a newer replacement from Nissan. I did take the huge plastic guard off from underneath the car and left it off because it makes oil changes way easier leaving it off. Has anybody experienced an fx35 overheating due to it missing that bulky plastic guard underneath the car.? Or, do you think it needs a new radiator? I mean I can't tel l how old the radiator is but my main question is about the plastic guard underneath..??

Hello,

This is a great question, and you've hit on a common point of discussion for a lot of cars with underbody panels—the Infiniti FX35 included.

The short answer is **yes, a missing plastic under-shield can contribute to overheating, but it's not the most likely primary cause.** It’s a factor, but there’s probably something else at play that’s more significant. Here's why the under-shield matters, and what to look at next:

The Purpose of the Under-shield
The large plastic panel isn't just for protecting the engine from road debris. A key function is to **direct airflow**. It creates a low-pressure zone underneath the vehicle, which helps to pull air down through the radiator, increasing its cooling efficiency, especially at speed. Without it, air can flow around the engine bay in ways it's not designed to, which can disrupt the intended cooling path.

Since you're noticing overheating, this disruption could be part of the problem, but it's usually not the main reason unless the car is already on the edge of overheating due to another issue.

More Likely Culprits
Given that you've replaced the thermostat and bled the system, here are the most probable causes of your continued overheating:

1. Air Pockets: You said you "bled the crap outta" the system, but this is a notoriously difficult process on many vehicles, including the Infiniti FX35. Even a small air pocket can block coolant flow and cause hot spots. The best way to bleed the system is with a "spill-free" funnel kit that attaches to the radiator neck, allowing the engine to run and purge the air. It's possible a small bubble remains.

2. Faulty Radiator Cap: The radiator cap is a pressure valve. If it's old or faulty, it can't hold the correct pressure in the cooling system. A properly pressurized system raises the boiling point of the coolant, allowing it to get hotter without boiling. If the cap is weak, the system can boil over at a much lower temperature, leading to overheating. A new cap is a cheap and easy part to replace and rule out.

3. Faulty Radiator Fans: The electric radiator fans are crucial for cooling, especially when the car is stopped or in slow-moving traffic. If one or both of your fans aren't kicking on, or aren't running at full speed, the car will overheat. With the A/C on, the fans should run. You can test this by turning on your A/C and seeing if both fans are spinning.

4. A Clogged or Old Radiator: You mentioned the radiator might be a replacement, but that doesn't mean it's functioning perfectly. Over time, radiators can get clogged with rust, sediment, or external debris (like leaves and bugs). A clogged radiator can't dissipate heat efficiently. If the fins are damaged or if the radiator itself is partially blocked, it won't be able to cool the coolant fast enough.

5. Water Pump Failure: The water pump circulates the coolant. While less common, a failing pump with a worn-out impeller can't move fluid effectively, even if it's not leaking. This would cause the coolant to just sit in the engine and not cycle to the radiator to cool down.

Your Next Steps:
- Re-Bleed the System:** This is a big one. Try the "spill-free" funnel method if you haven't already. It's a very effective way to make sure all the air is out.
- Check the Radiator Fans:** This is a quick and free test.
- Check the Radiator Cap:** It's a cheap part that can cause big problems. Replace it to be sure.
- Visually Inspect the Radiator:** Look between the fins for any blockages and see if the fins are bent or damaged, which can restrict airflow.

While the missing plastic guard isn't helping, it's very unlikely to be the sole cause of a severe overheating issue. Focus on these other possibilities first.