Ok, here's what I did.

1. drained coolant, changed thermostat, installed temp gauge at the coolant housing. (drained only from radiator, not from the block)

2. put things back together, filled with water for flushing the system. AST full.

3. Starts car for 5 to 7 mins, the new temp gauge shows 0 but the instrument panel temp gauge shows 9 o'clock. Heater blowing cold

4. waited, stock gauge raised to 10 o'clock, new gauge reads 0. No heat.

5. shuts car off, fan runs for like 10 mins

I tried opening the filler cap, but steam came out. I'm guessing there isn't enough coolant in the whole system. Do I just repeat filling up the system and start the car again? Does this happen to anyone? help...

I did put in as much water as I can so why is system still low? if i guessed correctly...

thanks
Kevin

 

That's one of the reasons I strongly recommend against drilling/tapping the filler neck for a temp sender install. If the thermostat is stuck closed, you will get NO reading. That's exactly what's happening to you.

Too late now, but you get a MUCH better reading, and MUCH less installation work, by installing a T into the rubber coolant hose going to the throttle body.

Anyhow, something is WAY wrong with that thermostat. If it's not a Mazda OEM thermostat, throw it in the trash and get the OEM part. Also, make sure it's not installed backwards or something really crazy. The jiggle pin on the thermostat needs to be at the top (12 o'clock) position to let air behind the thermostat out as well.

Dale

 

Sorta related.... Oddly, I installed my temp gauge into the TB hose location, and I only get a nonzero temp reading when the car begins to get very hot (as in the OE temp gauge sits either at or above 9 o'clock). When this happened, I got a reading of 180 deg F...

 

the thermostat from pepboys has no little pin/hole in it. So that's the problem?


damn, i searched around for a while and on one had discussed it. can someone elaborate on this pin's purpose?

 

dale don't' u have a writeup on this topic? (aftermarket water temp sensor positions)

wow a pepboys thermostat

 

The jiggle pin lets trapped air from behind the thermostat get out to the top of the system. Trapped air is a Bad Thing.

Seriously, get a Mazda thermostat. On the various 2nd gens I've worked on, I've seen parts store thermostats fail in only a month. They're JUNK. They may be fine for Grandma's Buick, but not for the RX-7. Even if you have to get it from a dealer, they are typically in stock - you'll pay a bit more (typically less than $20, though). As of now, the car is not in driving condition - keep it off the road until this is fixed!

Dale

 

Not to go against the thermostat crowd, but it may have been just trapped air. Did you burp the system with the throttle body hose off? This is a very common problem when people flush the system. The way the coolant passages are designed it is very easy for air to get trapped around your water pump and not allow it to push water through the engine.

What I do is take the top hose off the throttle body and fill the system. Put the cap back on and squeeze the upper radiator hose. You will hear water squishing. Repeat this until you start pushing water out the throttle body coolant hose and no longer here the gurgling sound. Start the engine with the heater on and let it start to warm up. If the gauge goes past the normal mark, repeat the steps.

Hope this helps,
Dan

 

ok, replaced the old oem thermostat and everything is running like before. I guess without the little hole, coolant isn't circulating. The dp was glowing while engine was idling!

Just wonder how other cars' cooling system work without the hole? is the engine block air tight?

I've also read that when warming up the system, I should uncap the filler to help air escape. is this correct?

thanks for the comment on the throttle body line. I was gonna do that after flushin is done.

 

^^to expand on what Chadwick said, it's very likely that you've got air trapped in the system. The Mazda service manual recommends that you refill the cooling system at a rate of 1 litre/ minute, to avoid the formation of air pockets. That is VERY slow, and most people pour at a faster rate.

Even if you pour slowly with the throttle body hose unhooked, and 'burp' the system by squeezing the radiator hoses, you will STILL get a lot of air out of your system by using this tool:

Coolant Burping Tool/ Radiator Cap Funnel
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/radiator-cap-funnel-eliminate-air-bubbles-342309/


-s-

 

Sounds to me like he didn't get all the air out. Depending on where he drilled and tapped the thermostat housing for his sending unit, it should work just fine there if mounted in the same location Mazda puts there temperature sensor for the automatic transmission. It should work just fine as long as the colling system is refilled and burped of as much air as possible. Hevwery well have just created an air pocket in the water pump area and it wouldn't have pumped or circulated any coolant.

 

I am a HUGE believer in the OEM mazda thermostats. I have had overheating in the following cars, all solved by going to a stock Mazda stat:
Ford Probe
Mazda Millenia
Second gen base