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2001 Spyder GT
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Now I am troubleshooting a P0403 and P0442 code.I erased the codes but they came back the same thing so I may have to get a new EGR Valve .
Don't replace the EGR valve yet. The P0403 code is set by the EGR solenoid or it's wiring, not the valve. So start with the solenoid. You should measure 29 − 35Ω resistance across the solenoid's two electrical terminals. Check for signal to the solenoid by turning the ignition ON and measuring voltage between the disconnected harness pin 2 and ground. You should see battery voltage on your meter.
 

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You'll need to figure out whether it's overheating because its leaking; or, leaking because it's overheating. Also, assuming your coolant level is full, does it run hot all the time, or only when you're slow or stopped?
 

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Would this happen if my heater core is plugged?
A plugged heater core won't cause overheating and coolant overflow like you're describing.

Are the fans coming on late, once the engine is already too hot? That would point to a faulty coolant temp sensor. You could troubleshoot by pulling the electrical connector off of the coolant sensor. This will make both fans run constantly. Then see how the car behaves.

When I burp my system, I've noticed that higher rpms can sometimes bring up more air. I run the engine at ~1,500 rpm or so for a few minutes.
 

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I meant to add earlier that even when my radiator is a fair bit low on coolant, the engine temp stays at normal and doesn't overheat. I can tell it's low because the heater stops working.
 

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Boy oh boy... Do I feel like a dummy... The original rad has the fins running horizontally, whereas the Mishimoto has them vertically… My friend explained to me that the top part of the Mishimoto rad acts like an expansion tank. When I fill the rad to the top of the neck, it has no room to expand, so it pukes it onto the road. I took the car for a drive and the gauge goes to the three-quarter mark and then drops to the halfway point. I got the car out on the highway and all is okay. By the way...you don't have to agree with my comment about feeling like a dummy.
That still doesn't sound quite right. I also have a Mishimoto radiator and I keep it filled to the top of the fill neck. The temperature gauge stays at the middle of the range regardless of whether I'm at idle or full speed, cold days or hot days. Also, my overflow never spills onto the ground. Do you maybe have leak in your overflow tank?
 

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2001 Spyder GT
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I am wondering if it has anything to do with me having my intake powder coated.
No, the intake plenum doesn't impact the engine or coolant temp.

Check the engine temp seen by the ECM using your OBD reader, and compare it to the cockpit gauge. The radiator fans should come on when the ECM reads 230°F. What does the gauge show when the fans come on? I'd expect it to be at "medium" with the needle about horizontal. It's possible your coolant sensor isn't reading correctly and the fans aren't coming on until the coolant temperature is too high.

If the fans are working properly and the two temperature readings are about the same, I'd next remove the thermostat and run the car without it to see if the problem continues. Check that the thermostat was installed correctly, with the spring on the engine (hot) side, and the jiggle pin towards the top. Drive the car without the thermostat. If the problem goes away, replace the thermostat. Otherwise reinstall the thermostat and move forward.

Next I'd check for exhaust gas in your coolant. Free-rent an engine block tester from a chain auto parts store. It presses against your radiator neck and will detect a head or block leak. You'll have to spend $20 on a bottle of test fluid but it will last you many tests.

If all of this looks normal, I'd replace the water pump next.

I skipped flushing the cooling system because I can't imagine a plausible way that scale buildup would cause what you're seeing, where the engine overheats and then drops. But if you're going to replace the water pump and drain the system anyways, I'd run a radiator descaler first so it's all clean when you reassemble.
 
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