Hey i an 88 n/a vert i just replaced my radiator, waterpump, and thermostat. Im concerned because my temp gauge goes up about 1/2 when doing highway speed (60-70) but when im in town (30-45) it drops back to 1/4. Can anyone advise me what might be wrong or what to look at!?. (i've searched but the user never confirmed if he fixed it or not)

 

How's your coolant level? Does it seem to slowly disappear at all? Any swollen rad hoses?

 

Coolant level is at the brim, i have card board under the car and havent seen any leaks, and no swollen hoses...

 

That's just how the S4 temp gauge works. Normal operating temp is about 1/4~1/3rd up the gauge.
If you want to improve your cooling at cruising speeds, look at the air ducting to the radiator or a more efficient radiator.

 

ive owned 4 fc and never witness this, i got the radiator for performance radiator from tacoma, wa. Its a copper one.

 

Do you have a stock fan setup with the shroud?
or an Aftermarket electric?
You need a shroud for the fan then..for sure.
And it helps to have the plastic belly tray on the car too.

 

If this behavior is consistent (i.e., it's always hotter on the highway), you have a ducting issue.

Highway driving is the best case scenario for the cooling system- steady state, relatively low RPM and unobstructed airflow- so if you run hotter under those conditions, either air can't get in or it can't get out.

This assumes that the loop has been completely bled of air after all your work.

 

stock fan clutch, and shroud

 

ok, cuz i do have a gap the shroud is bolted down but doesnt fit snug like the factory radiator

 

The fan shroud, indeed, the fan itself, is irrelevant at highway speeds.

 

The temperature gauges on S4 and S5 gauge clusters read differently. S4 gauge is linear with normal operating temp about 1/3 of the way up. S5 really only has 3 positions, cold (bottom), operating temp (middle), and overheating (anything above middle). A stock and especially a copper radiator is easily up to the task of cooling an NA cruising on the highway.

By ducting, I'm referring to the panels that route air from the front bumper opening to the radiator core. As mentioned before, do you have the stock plastic undertray? I've run without one with no noticeable difference, but YMMV.

 

Car have AC?

 

Nope no under tray

 

It does but doesn't blow cold

 

You should put the undertray back on. That should help airflow. That being said, there's nothing wrong with your car. The thermostat is opening at 95C. It might be getting up to 95-100C, or about 212F, which is nothing. Don't worry about it. It's an n/a engine, so you don't even have to worry about it knocking from high temperatures.

If it gets over 230F/110C, then I'd be concerned. At that point the needle would be over halfway. Even though sensors do drift a bit over time, why would Mazda put a dangerous temperature halfway up the gauge?

This is why modern cars have those "idiot" temperature gauges. It's because people get hysterical over this kind of stuff, so now the gauges are typically useless. Lots of piston engines run at 220F/105C all day long off the showroom floor.