Temp gage is solid red, air conditioner is now blowing hot air. Filled coolant reservoir and it emptied while driving but mechanic found no leak with pressure test. Is this a thermostat issue?

No your car will not overheat, but it is advisable to my 50% coolant on the water to prevent deposits of rust and other debris that may affect the effectiveness of the cooling system.

Sometimes when you open cooling system, air gets in, it can cause problems with temp gage.
How hot does it get in degrees F? Is the coolant boiling over? Are you losing coolant? Use a non-contact infra red temp gun to take engine temp, At least we will have a degrees F reading. Most temp gages say hi or lo, cold or hot. I don't know about yours?
Can you check for combustion gases in the coolant?

start by checking the cabin filter and replacing if necessary. That's the source of outside air.

Sorry to say you probably have engine troubles.
A leaking head gasket will drink the coolant and cause the bubbles to form.
A mechanic can check for leaks by pressurizing the cooling system and also checking for exhaust gas in the radiator.

Sounds like to me your mechanic is on the right track by having the rad cap changed. If the coolant becomes low again in the near future and there is no visible fluid leak on outside of engine or on floor/ground then your problem is internal and possibly a head gasket.

Probably a stuck open thermostat or the thermostat is the wrong temp range for your vehicle.

Most Suzukis A/C systems will cut out when the engine tempurature is too high (to reduce the load on the engine). Also, in this condition, when the A/C compressor cuts out, the A/C thermo fan (electric - in front of the condensor) may come on ( to try and cool the engine). Combined with the fact that your temp gage says the engine is hot, I would be checking your cooling system very closely. It could be as simple as leaves blocking the air flow through the radiator (between the condensor and radiator), or as serious as the internal cores of the radiator being blocked (different sorts of coolant being used can sometimes produce solid matter that can do this).

looks like you have done everything but the problem with your car is that the cylider head gasket has gone have a look at the dipstick or remove the oil filler cap if it looks like mayo then 100% head gasket has failed you said no water on the floor so it must have gone into engine only way this can happen is head gasket failing, if you have put lot of water in to the cooling system then your sump will be full of oil water mix.

let us know your findings so we can help you more if you need it

I hate to tell you this but its possible...

You have a leak. Look around on the driveway and try to determine if you have an external leak as opposed to an internal leak. If you see no coolant on the ground, suspect a blown head gasket. Do not continue to drive this car in this condition. If it does indeed have a blown head gasket, serious engine damage will occur.

Check your exhaust for white smoke. Chances are good you have a blown head gasket and coolant is leaking into the engines combustion chambers and is essentially burning off. Also check your oil, if it looks like caf mocha, this will confirm coolant is leaking into the oil via the blown head gasket

Did you bleed the air oout of the cooling system - Their is a bleeding next to the therostat housing.


1 - When the vehicle is cold remove the rad(tank) cap and top up the level if needed

2 - start the vehicle with the rad cap off and leave the car run until you can see that the therostat has openned(look in tank/rad) to see fuild flow then open the bleeder slowly to let any air out of the cooling system. Once you have coolant flowing out of the bleeder close the bleeder and install the rad/tank cap.

NOTE - Be careful with the engine running and hot Coolant.

You make need to bleeding system 2-3 time to get all the all out. Once all the air is out of the system you problem should be solved. If air returns to the coolant system have the system checked for possible head gasket leaking air into the coolant system