various problems with my MX

Problem #1 doesn't sound good. The 1st thing that comes to mind with air bubbles in the overflow might be a bad head gasket, but don't quote me on that since these radiators cane become plugged easy. A trip to a quality radiator shop should get you a correct answer.

Problem #2 with low gas mileage is no doubt due to the lack of an O2 sensor. When the sensor is bad the cars computer goes into a closed loop, just like before the coolant comes up to operating temp and the car will run in a rich state. It should only run rich when it's cold and above 4 or 5k rpm's. This condition will ruin the catalytic converter eventually.

Problem #3 is an easy one. The heat shield around your Cat and pipe ahead of is rotted and rattling. This can be fixed by hose clamps sometimes or by removing the heat shield. Midas put a new clamp around the shield on the forward pipe and removed the cat shield for free for me once. I understand that some cat replacements come without a shield.

Not sure about problem #4, but it can't be helping the emissions by missing. I don't even recall something like this on my 91A and would have thought that more stuff would have run off the same belt.

Good luck and keep us updated.

Here is a good thread on Miata.net. I hadn't thought about the cooling fans and the radiator cap either.

About a year ago I had an overheating problem and found the temp sensor at the front of the engine cracked. It was hard to find since it looked normal. I finally found it when I tried to take it out to replace it and it fell apart in my hands. As noted, without the temp reading the engine control computer thinks the engine is cold. The result is that the fans don't turn on leading to over heating at slow speeds and the engine runs rich leading to low gas mileage. I am real suprised that a dealer wouldn't find this, so may the problem is something else.

Gus (91 BRG)

#1 - It could also be a bad thermostat. This will show up if the car is run hard which may be the case due to the other problems.

#3 - Could be the cat failing which could also cause #2. I had similar noise form mine and it was shot.

Sounds like someone may have really messed with the emissions systems and caused a number of other problems.

glen '91 miata

elsewhere?

Just to let you all know. My car is now back on the road again. :-)

1. Overheating was down to a knackered thermostat. New one installed and no problems since. Although, it did start to overheat on my first journey for about 5 mins, and then setteled down again, and no problems since (about 300 miles later).

1. Oxygen sensor installed, and has now almost increased by MPG by

1. Metallic Buzzing Not fixed. Garage seem to think its the baffler in the rear of the exhaust, but I'm not so sure. If I do get a new rear exhaust, what's all this about Back-Cat's? and do they give more oomph? And how much? My car is just a lowly 1.6? Is it really worth it?

2. Second hand compressor costs about £300 so have left if for just now, until I'm a bit more flush.

However, just after getting this all fixed, my water pump in my car exploded and had to get a costly fix to it and the gaskets / seals. What a joyous month January has been.

Thanks for all your help and advice.

Alan

It's usually the heat shield on the downpipe, between the header and the catalytic conver. It cracks, or a spot weld breaks, and it buzzes around

OTOH, in my case it was the cat going bad.