Here's the deal. For awhile, the water temp on the pfc read 87-88 C. Now, if I drive on the highway, the temp will rise to around 98 or 99C and keeps on going. However, if I drive in the city, the temp is around 86-90 C. What do you think could be the problem?

Also, before it starting this little ordeal, the coolant buzzer when off. I put more coolant in and it seemed to full already. Could it be the thermostat? I hope it's not another coolant seal issue. Help is always appreciated.

 

Always a good idea to swap the thermostat if you haven't done it in recent memory - get a new Mazda thermostat and put it in there. The thermostat could be getting lazy.

Next, make sure your coolant is topped off, no leaks, and the fans are kicking on like they should.

Dale

 

i have the same thing.. are you running an under tray? I think that's the problem for me. I recently change my thermostat. Your thermostat should be good if you're only reading 180 and above..meanin it's working properly....

 

Under tray is in route. Broke the last one somehow.

 

I agree on the thermostat. I recently had a thermostat go on my car (it eventually physically broke), and it started out with very similar symptoms, which I didn't even connect to the thermostat at first. I was thinking air in the system at the time. And it got hotter at higher speeds like you're describing.

Then, sitting in traffic on the way home from work one evening, temps suddenly shot up to about 250F in a matter of a minute or so - the thermostat wasn't opening because the retaining ring which holds the shaft had broken in two pieces! In the couple minutes it took me to get off the road (bumper-to-bumper traffic around here), it had boiled off more than half of the coolant in the engine. Good thing I already had a flat apex seal spring and needed a rebuild, because it definitely needed a rebuild after that!

Bottom line, **** can happen very quickly. I could probably have gotten another 6 months out of that motor if it weren't for that damn thermostat.

Of course, I doubt thermostats fail catastrophically like that very often...

 

Couldn't we just run without a thermostat. It'll run cooler, but it'll take a little bit longer to warm up. I'm pretty sure that's safe. Anybody run without a thermostat?

 

You're not running an undertray?

 

It's not the t-stat, it's because you aren't running an undertray. That's why your temps around town are fine and your high speed temps aren't.

And NO, it is a BAD idea to run without a t-stat, period.

 

I had the exact same problem and changing the thermostat sloved the problem. High temps on freeway, low temps in city. Now I'm back at 86-90 temps all condition driving so far.

 

No, it's on it's way. For now, I'm waiting on some parts from ray crowe.

 

The reason no undertray causes higher temps at speed is because the undertray helps to force air through the radiator, no undertray and it bypasses the radiator and pressurizes the engine compartment. High pressure in front of the rad, high pressure behind, no air flow. Undertray keeps air out so high pressure in front, lower pressure behind; air flow through radiator.

It's better at low speed because the engine bay isn't pressurized by oncoming air and the fans draw air through the radiator.

 

I run no undertray, and have normal temps, hot in traffic and normal while moving 55 and above. The AC condenser is where the undertray would normally be. No ducting what so ever. While I plan on adding the undertray when my new hood arrives. I don't understand why this wouldn't be a consistent problem.

 

I thought it may have been the pressure idea, but the temps have been fine for awhile without the undertray. Then, all of a sudden, the high temps came on during highway driving and low temps around the city. I don't think the undertray helps that much, but i'm getting one just to be on the safe side. I just got to wait until the parts get here.

It probably doens't help to run a fmic without the undertray.

 

Actually, the undertray (and additional ducting) makes a significant difference, especially at higher speeds as others have noted. Certainly don't go to the track or drive the car hard for any extended period until you have the tray installed.


Could be a seasonal change - ambient temps are rising as summer approaches (at least where I live). Get the undertray back on the car, then if temp problems persist, replace the thermostat.

 

You guys who think an undertray doesn't help much or isn't useful don't have a clue.

Not only is it useful from an aerodynamic sense, but it most certainly forces more air through the radiator. Not only that, but here's another reason why to run one -- https://www.rx7club.com/showthread.p...ight=undertray

 

It's not the weather because it used to hold temp while it was around 70 F. While I was driving, the water temp would not hold when the outside temp was around 50 F or or less.

 

Well said!

Ouch, I run that same cooler setup, same lines and all. I knew there was a reason I felt sketchy about that line running down beneath the radiator!

 

Okay, then it does sound like the thermostat's starting to stick and/or get lazy...

And you should still run an undertray.

 

I know I still need an undertray, rocks and roadkill are nasty pieces to be cleaning out.

 

Just changed the thermostat, and everything seems to be working. Took the car on the highway and it holds temp at around 87 C. Driving around the city, the temp stays at around 87 C as well.

Now, the water temp gauge is acting up. It bounces from 260 to 300 F, and 300 to 260. It looks like it needs to be reset. How can I do this? Could I disconnect and reconnect the battery? Or do I have to remove the gauge and reset that somehow? It's a defi water temp gauge.

 

Good catch - if you let it go too long, the thermostat will eventually just stop opening at all, and you cook your engine.


Where's your sender located? You may have worked some wiring loose or caused a short, especially if it's installed in the thermostat housing (which you just R&R'd).

 

I was wrong, it WAS the t-stat. Glad you fixed it before toasting the motor. Still, get that undertray on!