I have noticed that after the thermostat opens and the temp dips down a little, the guage will sit right at 1/4 for a little bit before creeping up again. The 2nd time it creeps up it will usually get to 1/3 and then the add-coolant buzzer sounds.

Now, a month or more back i replaced my very poor condition radiator cap with one from AutoZone ($30 cap from dealer ), thermostat last week (RX7store), and flushed the cooling system the other day. This is the 3rd time in the past few days that i've had this happen, but the other two times i put it down to not properly filling the system (too much) since the overflow bottle had a little more coolant in it than before. This past time i only filled it up to the point where it comes out the air bleed on the radiator, but since it's dark out i can't check if it's still adding to the overflow or not.

This is an '87 GXL and i've already ordered a replacement radiator cap from Mazdatrix, but is there something else i should be checking?

 

I've an 87 base model and seem to have a similar problem. My best guess would be to keep an on on the levels (well, of course, you already are...) but you might want to take a look at some of the electronic components and see if something is indeed funky and causing the other stuff to go haywire. It may not help, but given the nature of the 87 and 88's electronic gremlins, I'd not discount the possibility.

If you get a proper solution, please let me know too.

 

The overflow bottle went from 1/2 full yesterday to top of the bottle when i checked it this morning, so the cap is either releasing too early or it's too cheaply made and it's letting coolant slip past. In any case it's not pulling coolant back in when it's cooled off, so it's probably not working right at all.

Unless the slow slow seapage from the coolant level sensor is somehow preventing that, but since the system is building pressure, i doubt it. Tomorrow I will see if i can fit an O-ring in there to help seal it, since i really don't want to attempt to use anything on the threads or fill it in with silicone.

 

I think you have the problem solved yourself by gettin another Rad Cap..You also may want to Look over the various threads on Filling and "burping the Cooling system"..since the Rotary has alot of places that pockets of air can settle into,and Give you problems like the ones you are having now..if you have a leak around the Threads of the coolant sensor use a bit of Teflon Tape to seal it.

 

Take your rad cap off and rev the engine a bit. If you see bubbles coming up in the coolant you may have a failed coolant seal in the engine. Just a thought.

 

I've been reluctant to drive my car except when i have to until i get the cap from Mazdatrix, but when my friends' Camaro nuked its water pump, i had to pick him up. Before the thermostat even opened, my add coolant light lit up. Pulled over and this is what greeted me...




Dealership can't get me a new one until Wednesday, so i used a universal oil drain plug to seal up the hole until i got the car home.