Hi all,

Ive been rebuilding my 1980 RX7 I picked up in March and finally got the temperature gauge working. I had some issues previously where it died on me while driving and wasn’t sure what caused them so I prioritized fixing all the remaining issues I knew of so I would have all gauges working if it happened again. I am wondering where the temp gauge usually floats after the car is warmed up and running. Mine was hovering just below the word temp on the gauge and I replaced the coolant in it yesterday so unsure if this is abnormal or just what how it is.

Thanks for the help!

 

Mine have always been below 1/2 on the temp gauge. I have never really trusted the factory gauges so have added aftermarket ones.

 

Mine all run about 1/4to 3/8 up from the Cold mark. Thats even in the summer. For me, even 1/2 up the scale would be abnormally high in my experience.

 

So ive replaced the thermostat, most of the cooling hoses and the radiator was repaired after the top was leaking a bit. I think tomorrow ill get it warmed up and see if I can see if the radiator has any parts that are colder that maybe aren't getting enough flow with an infrared thermometer. If I dont see anything there anything else you would suggest? Maybe I have a worse aftermarket thermometer? Im not great with approaching cooling solutions and the radiator in the car doesn't have a convenient drain plug so its detaching a hose every time I drain it.

 

For reference I am out on the coast in CA and today was a high of 77 degrees so its not overly hot right now and im just using the zerex red in it

 

There's a 10mm bolt in the lower part of the center housing that's a block drain, which might help you get as much of the old out and the new coolant in. Also, be aware that the temp gauge is on the rear housing (*IIRC) and is prone to getting air bubbles around it when you drain the coolant. This air bubble or cavitation in the area can cause false high readings on the interior temp gauge. If you raise the front of the vehicle about 6" using jacks or ramps, and fill the radiator from the cap, it will help the system to burp and get all of the Air out of the system. Regardless, just driving it will also eventually get all of the air out, as the radiator cap and overflow system accomplish their design purpose.

If everything else is in good shape cooling-wise, I'd just drive it and let it burp on its own. Keep an eye on the overflow bottle and make sure there's coolant in it above the feeder tube or you'll constantly be sucking air back into the system when it cools.

As shown in your pic, that temp reading is high. It should be about 1/3 of the way up, and no more - esp. given your cool daytime temps.

 

Drained the coolant from the engine block now that I found the drainage plug and my 1 day old coolant was quite brown. I’m going to proceed with a chemical flush and see where that gets me as using an infrared temperature gun on the engine has temperatures that are way too high for the car. Will proceed with that and maybe replace the thermostat again as well while I’m at it to be sure.

 

The gauge can be fairly reliable but also fairly useless if you like numbers. I have a mechanical gauge mounted on my '84, threaded in to the top of the engine where the coolant port for the throttle body heat used to be. (There is juuust enough room to be able to pull the nipple, drill it to 7/16", then tap it 1/4NPT to take the coolant bulb.)

For my '81, I don't want a bunch of non stock looking crap in the interior, so I bought a radiator cap with a thermometer in it. Cost about $40 from Summit. On my car, that needle position is about 210F.

 

So I completed the coolant flush, replaced the thermostat with a Mazda one, and replaced the fuel pump that went out with a Mazda one and it’s better but still reading higher than normal. Debating wether it would be a synthetic oil vs conventional that could be causing it and I’m thinking I may try that next to see if it makes a difference at all.

im pretty much out of ideas, the only time it was running cold was when I had the water and coolant flush chemicals in the system. I have replaced the thermostat, temperature sender, all belts, coolant hoses, radiator cap, had the radiator repaired and cleaned, it has a fresh oil change

I don’t know what else i could do that would bring this back to what I would think normal is, I guess I could have a shop do a coolant flush.

 

Is your fan working properly?

 

It's not the oil.

Does the temp stay at that range when driving on the highway?

Have you tried an aftermarket temp gauge?

 

Fan is working properly, it seems very strong with the hood open when it’s hitting me with air.

temp guage is steady when driving at highway speeds but it seems too high, I have not tried an aftermarket temperature guage yet.

 

It's a little hard to see in this image, but some t-stat necks from early 2A engines have a flat area where you can drill and tap for a 1/8NPT gauge sending unit. This is the engine from my 1979 I did this to. It allows me to run an aftermarket temp gauge.

My water pump housing looks a little different because it's from an S4. I recently swapped it out for the factory one. I didn't like the belt alignment with the air pump.

 

Is it a stock or aftermarket fan? If it's an aftermarket fan that someone else installed is it rotating in the correct direction? Drawing air through the radiator and not blowing air towards the radiator, they can be wired backwards, just a thought.

 

If you are missing the grille under the bumper, that can cause hot running on the highway, especially with the short radiator. Its purpose isn't just to look cool, it directs air up towards the radiator.