Bleeding my cars cooling system?

Question

It's a '95 Mazda MX5 (Miata). At this point, I think there is some air caught in there. I had the thermostat replaced but no difference with my fluctuating temperatures (20-40 second overheats then back to normal operating temperature). They happen once a drive and sometimes re-occur on the same day if the car has been sitting for a while. I bled the system about 5 days ago and the problem vanished but it popped up again today. The system has been bled about 3 times now. This usually solves the problem for about 3-5 days tops. My mechanic thinks it may be a wiring issue with the actual temp gauge itself, but me bleeding the system shows that could be related to the cooling system. Could someone make a step by step guide for me? Preferably from taking off the radiator cap and starting the engine all the way to putting the cap back on for bleeding (just incase I'm doing it wrong). Thanks!!!! A few additional qs:

1. Could the thermo be stuck?
2. Could the thermo housing be beyond it's last leg? 
3. Should I try running the car with out the thermo and see if the problem continues?
4. Could the actual hoses from the cooling system be bad or need to be re-attached? 

PS: It's NOT a blown head gasket. I've had a few mechanics look at it just for that purpose. 

Thanks!!!!!

? · Accepted Answer

Attached to this post you will find three videos that go in to detail with regard to bleeding your cooling system and troubleshooting most causes of overheating.

I hope you find them useful and think they'll probably give you the information you need to isolate your cooling problems and fix your cooling problem.

Best of luck.

Old Man Dirt · Answer

I pull the heater hose at the back of the block where it returns from the heater. No, I can't give step by step instructions. There might be some at Miata.net.
A couple of things I have learned:
1. The thermal sensor for the ECM goes bad. This is close to where the heater hose returns.
2. The radiators do go bad too. These leak at the seams and I bought replacements off of e-bay on mine.
3. The fan relay fails.
4. Once the system is bleed, it should not need to ever be done again. So there is a leak some place. Radiator caps do go bad too and so does the water pump. Water pumps leaks are hard to detect, so most of us replace the water pump every other timing belt. If for no other reason then it is just cheaper to do when with a timing belt replacement then pay for the job separately. The timing belt as to come off to do the water pump any way and most timing belt makers do not recommend reinstalling them once they are taken off.

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Bleeding my cars cooling system?

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