overheating and I searched need advice

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neodriftout

Member
The story is the same as everyone elses, on the way home from work today my 2002 mazda MP5 started to overheat out of the blue. I pulled over and put water in the radiator and see if i had any leaks and such. I didnt notice any leaks so I went on my way and it overheated again of course, now here is where my story differs from the rest. I put the heater on and it was fine the temp is normal and I drove about 15 minutes home without problems, anytime i take the heater off though it overheats.

Sooooooo what the hell can it be? DO you think there is air in the system? I tried to bleed it but i have had no success "I dont know how to bleed this system"

The fans come on so we can rule out that and there is no oil in the coolant or vice versa.

So it must be the thermostat right? but why does it work with the heat on if it is the t-stat?

Please help!!
 
when you turn on the heat in the car it opens the thermostat and runs more coolant through the heater core - making a longer trip for the coolant plus drawing heat from the engine, thus cooling your cars engine temp...

as far as bleeding the system - usually running the car with the heat on and full fan speed when the car reaches normal op temp and leaving the reserve tank open. usually for 10 minutes or so.

if your car is overheating - sounds like it could be a faulty thermostat or the wrong one - if it worked fine b4 then it rules it out and might have went bad. other reasons could be the wrong/old coolant or coolant mixture (water to coolant %), coolant sensor, or unrelated like oil change needed, oil type for outside temp needed, or internal coolant leak. apart from obvious leaks its hard to tell unless you have the coolant system tested.
 
I thinks it is the thermostat, the car ran fine for two years "As long as I owned it" and I always have it maintained regularly. The inside of the radiator is immaculate and the oil in the motor was not milky.

I tried bleeding the system the way you described so i will be getting a new thermo this weekend.

With my luck though my Rx7 will crap out now :(
 
neodriftout said:
I dont have subwoofers, seriously what does that mean?
Click to expand...

SUB= Means he subscribed for info. IMO changing your thermostat will fix the problem.
Rob
 
neodriftout said:
The story is the same as everyone elses, on the way home from work today my 2002 mazda MP5 started to overheat out of the blue. I pulled over and put water in the radiator and see if i had any leaks and such. I didnt notice any leaks so I went on my way and it overheated again of course, now here is where my story differs from the rest. I put the heater on and it was fine the temp is normal and I drove about 15 minutes home without problems, anytime i take the heater off though it overheats.

Sooooooo what the hell can it be? DO you think there is air in the system? I tried to bleed it but i have had no success "I dont know how to bleed this system"

The fans come on so we can rule out that and there is no oil in the coolant or vice versa.

So it must be the thermostat right? but why does it work with the heat on if it is the t-stat?

Please help!!
Click to expand...

I had the same Problem Buddie, and had to change the Head Gasket. Thats a typical problem that occurs when your head gasket its blown. you loose compression and overheats. so the solution is new head gasket
 
If it werent for the fact that I was just doing some normal everyday driving and I dont beat this car at all (this is just a normal none turbo run of the mill MP5 after all + I have a fast weekend track car to flog when I feel the need fo speed) I would believe you, also why when I put the heat on all the problems go away??? If it where the head gasket I would think it would always overheat no matter what.

I drove for like 15 minutes with the heat on and no problems what so ever (besides sweating) then when i got close to home I turned the heat off and it slowly started heating up again so I put it back on and it cooled back off.
 
Also I would be very pissed off if it was the head gasket. This car has been babied and cared for like a king not to mention it has barely over 70000 miles on it
 
mzdalvr said:
when you turn on the heat in the car it opens the thermostat and runs more coolant through the heater core - making a longer trip for the coolant plus drawing heat from the engine, thus cooling your cars engine temp...

Turning on the heater does not 'open' the thermostat. It is a coil spring calibrated to a temperature. Def'ly correct that the heater 'on' is like another 'radiator' to shed heat.


as far as bleeding the system - usually running the car with the heat on and full fan speed when the car reaches normal op temp and leaving the reserve tank open. usually for 10 minutes or so.

Again, close. You must run with the radiator cap off.

if your car is overheating - sounds like it could be a faulty thermostat or the wrong one - if it worked fine b4 then it rules it out and might have went bad. other reasons could be the wrong/old coolant or coolant mixture (water to coolant %), coolant sensor, or unrelated like oil change needed, oil type for outside temp needed, or internal coolant leak. apart from obvious leaks its hard to tell unless you have the coolant system tested.
Click to expand...

To test for head gasket/head: With the radiator cap off - rev the engine and see if bubbles appear. Have a garage do a exhaust gas 'sniff' check at the radiator to be 'double-sure'.

Or swap the thermostat becaue it is quick/easy/cheap and may solve the problem before troubleshooting the head/gasket.
 
I am going to go with the thermostat, and I hope thats what it is, if it isnt I dont think I will buy another mazda vehicle again aside from the rx7, My old turbo Rx7 had double the miles and I drove it daily and didnt take care of it at all and i still never blew the motor and rotaries are suppose to be unreliable :)
 
mzdalvr said:
when you turn on the heat in the car it opens the thermostat and runs more coolant through the heater core - making a longer trip for the coolant plus drawing heat from the engine, thus cooling your cars engine temp...
Click to expand...
It is my understanding that a car's thermostat is not directly controlled by anything. Most thermostats are filled with a wax that has a specific melting point (ex. 180 degrees F). When the wax is not melted, the thermostat stays closed keeping the coolant in the engine block (brilliantly simple!). This allows the engine to heat up to ideal operating temperature (ex. 180 degrees) as quickly as possible. Once 180 is reached, the wax melts causing the thermostat to expand (open). This allows the hot coolant to make its way to the radiator to be cooled.

There is a separate coolant feed that supplies hot coolant to your heater core (looks like a mini radiator). When you "turn the heat on" in your car, you are simply activating a fan that blows air across the heater core. The air is heated quickly and blows into your cabin. The heater core leg of the coolant system is always receiving hot engine coolant (ideally directly from the engine block).

Turning your heat on acts as a second radiator by radiating some heat out of the coolant system. This is a great defense against a stuck closed thermostat that is causing WAY too much heat to build up in the coolant system

If anyone cares, HowSuffWorks.com has a cool write up on thermostats/coolant systems. I'm just regurgitating
stuff from there.

OP, you should replace your thermostat first before trying anything else.
 
Purrfectangel said:
Sounds like your water pump!

How many km's on your rig?
Click to expand...
If it was the water pump turning on the heater would'nt help. It might even make it worse because the pump would have that much more strain on it to pump the water through the heater core.

It's the thermostat.
 
Well actually it helps a little. Yes it does have to work harder to pump the water through the heater core and such, your right, but at the same time it's still transferring the heat it produces to somewhere other than the engine. It could simply be and most likely is the thermastat, but if he looks that over and/or gets it fixed and it's still doing it, well then it's obviously something else....Just putting idea's out. Honestly it's the first thing that came to mind, he said it differs from other stories and from what he described it sounds like the water pump...that's why I asked how many km's on his rig?
 
(deadhorse :)unless the protege heater is like 100x more complicated than every other car ive owned or worked on, turning the heater on does not cause any extra strain or load on the water pump. Coolant is circulating through the heater core 100% of the time. when you turn on the heater it opens a little air vent and cool outside, or inside, air flows across the little mini-radiator that is the heater core. when you turn off the heater the little door closes and the outside air bypasses the heater.

turning on the heater when youre overheating seems to work pretty good in our cars and its good to know that it will work in an emergency. Id say the water pump is in top notch shape if the car can maintain a stable operating temp with just the heater.
 
I had the same issue as you. However mine was less severe. It only happened in the summer with the higher temps and when climbing hills; I would get temperatures 95 C+ when my OEM temp gauge would start climbing above the middle and near "H"

I have replaced the thermostat, coolant temperature sensor and flushed the system out with no results. I have a feeling it's the headgasket, even though mine was a minor problem it's going to get worse.
 
qualityrockola said:
(deadhorse :)unless the protege heater is like 100x more complicated than every other car ive owned or worked on, turning the heater on does not cause any extra strain or load on the water pump. Coolant is circulating through the heater core 100% of the time. when you turn on the heater it opens a little air vent and cool outside, or inside, air flows across the little mini-radiator that is the heater core. when you turn off the heater the little door closes and the outside air bypasses the heater.

turning on the heater when youre overheating seems to work pretty good in our cars and its good to know that it will work in an emergency. Id say the water pump is in top notch shape if the car can maintain a stable operating temp with just the heater.
Click to expand...
You know, thinking about it you are right! It does flow all the time. So it's just the fan and the vent opening that allows air to go through that cools it.
 
Headgasket buddie, theres no doubt about it. forget about thermostat, thats not going to help. its the headgasket, no matter if you babie up your car.. thats the real problem.
 
Well I read the first post again and I still say it's the thermastat. My car did the same thing and I took out the old one on the side of the road and it was fine. Actually I drove it like that until the first freeze hit. Then I put the new one in.

As far as bleeding the system. IMO you should not have to bleed it. If it was a mid engine car where the lines travel from front to rear, then yes you might have to. But even then I didn't have a problem with that. I had a 91 MR2 that I had the same problem with. You SHOULD just turn the car on fill it up and wait until you see it flow and then top it off.
 
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