Hello! As part of the cooling system basic update, I bought a Motorad thermostat to replace the current one. It comes with an o-ring which I thought was for protection of the product. However, when I removed the housing, I saw that the current one sat in there wearing an o-ring. There was no paper gasket residue for me to remove. With the o-ring adding some thickness to the edge of the disc, a paper gasket wouldn't be flush against either surface. I installed the new one with the o-ring (sealer applied). Now I noticed that the old thermostat was also a Motorad, which meant the replacement was maybe a DIY job and not per Mazda spec. Should I remove the o-ring and insert the gasket? Haynes mention the gasket but not the o-ring. Monochrome pictures don't show clearly. I can wait and see if anything leaks from the housing or if it overheats. As for the choice of thermostat, it's a Fail-Safe unit that I ordered along with other parts. I wasn't aware that OEM is strongly preferred.

 

OEM best!

 

There was never an o-ring on the thermostat nor was there ever sealer. You need each gasket surface to be clean and true and you will want to install a Mazda brand thermostat and gasket. It has happened that non oem thermostats have caused overheating issues.

 

Thank you both. I will redo this part at the next flush. Is there any way to make less of a mess to drain the coolant from the lower hose? The radiator side of the lower hose points at the belly cover and the liquid ends up flowing from the various lots and holes. :-/

 

Make sure the small hole in the t-stat is on the top most side. It helps air bleed.

 

Prestone makes a neat "drain" kit which is a 'T' nozzle that fits to the FRONT heater hose (the one that hooks to the bottom rad hose fitting on the rad). You cut the hose and insert the "T". It has a threaded cap so you can drain more cleanly from there. That said I always remove the belly pan to do this regardless. As you noted, its a lot messier controlling coolant flow. With the Pan off, just slide a tray under the rad and draining is clean and simple.

Stu Aull
80GS
AK>AZ

 

The OEM thermostat and gasket should arrive next week. In the mean time, I haven't had the opportunity to properly burp the system (due to heavy smoke at startup and driveabilty concerns). How long does it typically take to get up to operating temperature if it is idling? The coolant temp indicator didn't seem to move a bit after five minutes.

 

Are you sure the sensor is connected? It's under the oil pedestal not fare from the oil pressure sensor.

 

Thank you! Did you mean the oil filter pedestal? I don't know what it looks like. On my NA Miata, there is a fan switch sensor right on top of the thermostat housing, whereas the temp sensor is on the side of the engine. Should I look for something that's brass in color and smaller than a pinky?

 

Yes, the oil pedestal. The sensor on the back of the water pump housing controls the automatic choke. The sensor below the oil pedestal is for the gauge.

"Should I look for something that's brass in color and smaller than a pinky" - yes. Kind of bullet shaped that takes a female bullet type connector.

 

I took the car out for a half-hour drive this evening and the temperature indicator moved slightly to about 1/8 of the spectrum. I suppose that means the sensor is connected. However, it was 70-80 mph and 3K+ rpm for the most part, I'd expect the temp to be at least mid-way like on my MX-5. Perhaps the sensor needs to be replaced? :-0 I'd hate to overheat the engine and not know about it.

 

Yeah, the sensor is connected if the gauge needle moves. You might want to clean the connection and be sure it's making good contact, as it's a resistance-based sensor.

On the engine heat range - after putting in an aluminum KOYORAD a year ago, the gauge needle barely moves past the C to the first mark. Without changing the sensor or anything, it used to run at about 1/3 up the range, but now barely makes it off the stop pin - and this is in 110F temperatures in the middle of the desert. When I put my hand on the top of the radiator, it's definitely losing a ton of heat there, and the engine temps stay low. One of the best improvements I've made after limping the stock brass radiator along for many years with rodding out and cleaning.

 

With a normal cooling system and the gauge being good and the sensor good, the gauge should get up to about 1/4 to 1/3 when the engine is warmed up. Take about 5 minutes for this to fully register. Running too cold can be almost as bad as too hot, builds up unburned carbon deposits. Check you connections and grounds to make sure a good signal is getting through to the gauge. As mentioned its resistance based.

 

I also like to add an aftermarket water temp and oil pressure gauges just to make sure things are running correctly.

 

Nice setup in the picture.

 

Time flies! I am cleaning the cooling system and came across this thread. The good news is that she still runs, having gone 10K+ miles in 3 years, and that I still enjoy her tremendously. There had been many struggles though. In November 2018, she did a 180 on the freeway after some drizzles. The tires were way too old though barely worn. After a clutch failure that left me stranded, clutch master/slave got replaced and the system was bled. New spring and shocks were installed because the front was sagging (having observed how a fellow SA was sitting differently/properly. I yanked off the rear view mirror by accident so a suction one is now doing the job. The battery cable was replaced. Plugs, wires, ignition coils, distributor cap, points, headlamps... I do what I can under the carport, and anything that requires her being off the ground is done by the shop. I drove her to work in SF, Stockton, and other places where safe stall parking was available.

I am getting her molded hoses this time. Also looking for bolts to fit the new thermostat housing/cover from Atkins.

 

Is the hose positioned correctly? I take the marks on the rad port and engine entry point to indicate where the ends should rest? It is sitting very close to the bottom of the blade on the pump though.