u/TheWhiteWulff

Hey everyone,

I need a sanity check on my cooling system issue. I’m driving a 2003 FX35 (AWD VQ35DE) with 191,000 miles on the clock. It’s basically the heavy cousin of the 350z/G35, so I’m hoping the VQ experts here can weigh in.

The Symptoms:

• Highway driving is perfect: I can drive for an hour at 75-100 mph (120-160 km/h) and the temps stay perfectly stable around 185-195°F (85-90°C).
• The problem: The moment I exit the highway, slow down to city speeds, or stop at a drive-thru/traffic light, the temp gauge spikes rapidly. According to my OBD2 logs, it hit 268°F (131°C) at its worst.
• Coolant boils over into the overflow reservoir and spits out.
• The temporary fix: If I rev the engine while idling, the temperature drops down to normal almost instantly. Also, if I bleed it and top the coolant off to the absolute brim in the morning, I can drive around the city all day with zero overheating issues.

What I have already replaced/tested:

• New Radiator (old one got damaged, replaced with a new aftermarket one).
• New Thermostat (OEM Nissan).
• New Radiator Cap.
• Cooling Fans: They work perfectly. Both fans kick into high gear immediately when the A/C is turned on or when it gets hot.
• Head Gasket Test: I’ve done the chemical block test (blue fluid) literally 10 times. Even right after a hard pull. It stays blue every single time. Oil is super clean, no milky residue. No white smoke.

My Hypothesis: Since the head gasket seems fine, I'm leaning heavily towards the Original Water Pump. With 191k miles on it, my theory is that the impeller is either heavily worn down by cavitation or slipping on the shaft. At 3000 RPM on the highway, it spins fast enough to keep the flow going. But at 650 RPM idle, it lacks the mechanical efficiency to push the coolant through the block, causing a massive heat soak, boiling the coolant into a steam pocket, and pushing it out to the reservoir. Revving it manually forces the pump to clear the steam pocket.

Before I open up the timing chain access covers to swap the pump for a new Aisin one, does this sound like a textbook VQ35DE failing water pump scenario to you guys? Has anyone experienced this exact "only overheats at low RPM" issue?

Thanks in advance!

Hey everyone,

I need a sanity check on my cooling system issue. I’m driving a 2003 FX35 (AMD VQ35DE) with 191,000 miles on the clock. It’s basically the heavy cousin of the 350z/G35, so I’m hoping the VQ experts here can weigh in.

The Symptoms:

• Highway driving is perfect: I can drive for an hour at 75-100 mph (120-160 km/h) and the temps stay perfectly stable around 185-195°F (85-90°C).
• The problem: The moment I exit the highway, slow down to city speeds, or stop at a drive-thru/traffic light, the temp gauge spikes rapidly. According to my OBD2 logs, it hit 268°F (131°C) at its worst.
• Coolant boils over into the overflow reservoir and spits out.
• The temporary fix: If I rev the engine while idling, the temperature drops down to normal almost instantly. Also, if I bleed it and top the coolant off to the absolute brim in the morning, I can drive around the city all day with zero overheating issues.

What I have already replaced/tested:

• New Radiator (old one got damaged, replaced with a new aftermarket one).
• New Thermostat (OEM Nissan).
• New Radiator Cap.
• Cooling Fans: They work perfectly. Both fans kick into high gear immediately when the A/C is turned on or when it gets hot.
• Head Gasket Test: I’ve done the chemical block test (blue fluid) literally 10 times. Even right after a hard pull. It stays blue every single time. Oil is super clean, no milky residue. No white smoke.

My Hypothesis: Since the head gasket seems fine, I'm leaning heavily towards the Original Water Pump. With 191k miles on it, my theory is that the impeller is either heavily worn down by cavitation or slipping on the shaft. At 3000 RPM on the highway, it spins fast enough to keep the flow going. But at 650 RPM idle, it lacks the mechanical efficiency to push the coolant through the block, causing a massive heat soak, boiling the coolant into a steam pocket, and pushing it out to the reservoir. Revving it manually forces the pump to clear the steam pocket.

Before I open up the timing chain access covers to swap the pump for a new Aisin one, does this sound like a textbook VQ35DE failing water pump scenario to you guys? Has anyone experienced this exact "only overheats at low RPM" issue?

Thanks in advance!