Mx3 Heat Problem? Thermostat

[Letters11]

Hello All,
When I drive lately my car warms up fine but when the heat is on 3 or 4 my temp gauge starts to fall down to cold again (heat is blowing cold as well) as if the engine was not warmed up at all. I then turn my heat off and the gauge rises. Sometimes it does this a few times and sometimes it only happens one time. Its been about 15-30 degrees when it happens. Anyone experience this?? Thanks in advance for the help. Also, I may have a bad alternator if this could be the problem.
Thanks again!!

[Tunes67]

Check your coolant level.. if your low on coolant you may have an air bubble getting into your heater core. This would drop the temp in the heater core and cause the heater to blow cold air. Thats the simple check. If your full up on coolant.. your water pump may not be doing its job at full efficiency. If the coolant stays in the heater core too long.. it will cool off just as if it were a mini radiator. A bad alternator would have nothing to do with this issue.

Tunes67

[Letters11]

Check your coolant level.. if your low on coolant you may have an air bubble getting into your heater core.

I initially thought it was the coolant level, which i checked and was very low. I filled it up and a few days later it was doing it again. Maybe the water pump needs replacing, I dont see any other logical explanation. Thank You

[Tunes67]

Sounds like you may have a bubble in the system then if it was real low and you refilled it. However.. that begs the next question.. why was the coolant low? There are a couple of possibilities to that.

One.. the water pump has a purge hole on it.. when the bearing in the waterpump starts to go bad.. coolant gets by it and goes out the purge hole. Have you noticed any puddles under your car recently? This happens more when the car is running than at stop though.. so its hard to detect visually cause the water coming out usually vaporizes to steam and leaves little or no trace until its too late. If you refill your coolant and it keeps going low on you.. take your car to a radiator shop and have them pressure test the cooling system.. this will reveal if the water pump is leaking.

Two.. Your radiator cap is no longer holding sufficient pressure and is allowing your coolant to flow out to the run off tank and out of the system. This is a far more common and likely issue. Radiator caps do go bad over time and considering the age of our cars, this is fairly common. It is also something that is cheap and simple to replace.

Three.. You may have blown a head gasket.. This can also be difficult to detect depending on how and where the gasket failed. Sometimes its easy to find.. if you have oil in the water or water in the oil.. this shows up and is quickly noticed usually. More difficult to spot is when the gasket fails near a coolant passage that is close to one of the cylinders. What happens then is that exhaust gases can get pumped into the cooling system.. this forces coolant into the cylinder near the failed gasket. As this issue progressively gets worse you would notice white smoke from your exhaust.. this wouldnt go away even after the car is warmed up. If you suspect this kind of head gasket failure.. a radiator shop can test the coolant for exhaust chemicals in the coolant. This can be an expensive issue to resolve since the heads and block are both aluminum and prone to warp. This failure most often occurs after overheating.

Refill and replace the radiator cap first.. but monitor the coolant level daily for a while to ensure that you are no longer losing coolant.

Tunes67

[Letters11]

Sounds like you may have a bubble in the system then if it was real low and you refilled it. However.. that begs the next question.. why was the coolant low? There are a couple of possibilities to that.

One.. the water pump has a purge hole on it.. when the bearing in the waterpump starts to go bad.. coolant gets by it and goes out the purge hole. Have you noticed any puddles under your car recently? This happens more when the car is running than at stop though.. so its hard to detect visually cause the water coming out usually vaporizes to steam and leaves little or no trace until its too late. If you refill your coolant and it keeps going low on you.. take your car to a radiator shop and have them pressure test the cooling system.. this will reveal if the water pump is leaking.

Two.. Your radiator cap is no longer holding sufficient pressure and is allowing your coolant to flow out to the run off tank and out of the system. This is a far more common and likely issue. Radiator caps do go bad over time and considering the age of our cars, this is fairly common. It is also something that is cheap and simple to replace.

Three.. You may have blown a head gasket.. This can also be difficult to detect depending on how and where the gasket failed. Sometimes its easy to find.. if you have oil in the water or water in the oil.. this shows up and is quickly noticed usually. More difficult to spot is when the gasket fails near a coolant passage that is close to one of the cylinders. What happens then is that exhaust gases can get pumped into the cooling system.. this forces coolant into the cylinder near the failed gasket. As this issue progressively gets worse you would notice white smoke from your exhaust.. this wouldnt go away even after the car is warmed up. If you suspect this kind of head gasket failure.. a radiator shop can test the coolant for exhaust chemicals in the coolant. This can be an expensive issue to resolve since the heads and block are both aluminum and prone to warp. This failure most often occurs after overheating.

Refill and replace the radiator cap first.. but monitor the coolant level daily for a while to ensure that you are no longer losing coolant.

Tunes67

wow, thank you for all that information. I havent noticed any spot of water or anything leaking. The coolant level was low when i bought it and I guess it slipped my mind but it never went lower than its been. I filled it up a few days ago and have been checking it to see if the level goes down which it has not. I will keep my eye on the smoke colors and the fluid levels. Thanks so much.

[Letters11]

I took a radiator cap off another one of my mx3's to see if this would work. When it took it off the 2nd car and put it on the one with the problems, the cap just turned on like you would put a cap on a jar. When i took it off the initial car i had to turn it and then psh down and turn it again. This did not do it on mine, it just slid on. Also even when the heat works good and at normal operating temperature, the coolant is cool to the touch. When i take the cap off after i drive it, no pressure is released from the radiator. If i take the cap all the way off, some coolant leaks out but it i as if the car never warmed up. I have no idea what this could be? Could it be the piece that the cap goes onto is letting pressure out, mayb its busted? Thats the only logical explanation i can come up with Any Suggestions?? Thanks alot!

[Letters11]

I have replaced my thermostat and the heat and temp gauge worked for about 2 hours and then it started dropping again. I then got the water pump replaced. Nothing benificial happened, still dropping. If I let the car sit, it warms up nicely but when I go around a turn or down a hill or something, the gauge level drops and takes a while to warm back up unless im idling. I dont know if it would be a bubble in the system since it was drained when the water pump was replaced. Heater core maybe?? Thanks

[Daninski]

Feel your radiator, if it's very warm then the problem could still be your thermostat sticking open either because of improper installation or a faulty thermostat (even new ones). Place some card board in front of your rad to stop airflow, if that helps then your thermostat is stuck open.

[Letters11]

Feel your radiator, if it's very warm then the problem could still be your thermostat sticking open either because of improper installation or a faulty thermostat (even new ones). Place some card board in front of your rad to stop airflow, if that helps then your thermostat is stuck open.

OOOOKKKKKK. So when I feel it, the hoses should only be warm and not hot? If the thermostat is stuck open? is there any way to make sure that the thermostat is in properly. Ive done 2 on the mx-3's and they were fairly easy so i thought i did this one right thank you for the help

[Sleeper6]

Pressure test your coolant system, from the sounds of it Im afraid your looking at a head gasket issue IMO.

[Daninski]

Pressure test your coolant system, from the sounds of it Im afraid your looking at a head gasket issue IMO.

Did he say he was constantly having to add coolant? White smoke in the exhaust? Didn't read that.

[Sleeper6]

You wont always see smoke in the exhaust and might only be loosing a small amount of coolant. And if it was properly flushed when they did the w/p it shouldnt be an air pocket, also new thermostats rarely fail. And personally I don't like to guess when you can just go to your local advance and loan out a pressure tester to make sure as its much easier and cheaper then pulling the heads and checking for clean pistons. You dont need a huge blown gasket to give you issues, even a small break in the gasket can cause problems. IE not every head gasket will billow white smoke and dump coolant into oil just an fyi.

Side note, but are both your rad fans staying on when the car is running?

[Letters11]

You wont always see smoke in the exhaust and might only be loosing a small amount of coolant. And if it was properly flushed when they did the w/p it shouldnt be an air pocket, also new thermostats rarely fail. And personally I don't like to guess when you can just go to your local advance and loan out a pressure tester to make sure as its much easier and cheaper then pulling the heads and checking for clean pistons. You dont need a huge blown gasket to give you issues, even a small break in the gasket can cause problems. IE not every head gasket will billow white smoke and dump coolant into oil just an fyi.

Side note, but are both your rad fans staying on when the car is running?

Thanks. I have to stop at advanced tomorrow so I guess thats what ill do. How will I be able to tell what is what after the test is complete (never done one before). Also about the fans, Ive owned the car about 1.5 years and neither of the fans have ever been on.

[Letters11]

ok i went to advanced and they didnt have the testers and all the garages wee closed to day. I started the car with the radiator cap off. Eventually the hoses started to warm up. The coolant level in the radiator neck would go down a little bit and then the top hose would get very hot where i wouldnt be able to touch it. After it would return to being very warm the level would rise again. I did this for about 30-45 minutes, with the heat on and off and no change on my gauge. The lower hose, the whole time, would only be warm, not the slightest bit hot (if this has anything to do with it). How does the system work?? From the radiator to the upper hose, into the engine, and exits the bottom and then the cycle starts again? Im just curious becuase the top hose seems to be doing all the work and something doesnt seem right about that. Also im assuming I can eliminate a bad thermostat due to it flucuating in temperature?? Also I thin if i had a head gasket leak, i would definitly know by now and there would be more damage because this has been happenning for the past year and a half. Ok, back to the problem, any ideas with the new info? Thanks

[Letters11]

Also, the only time ive added coolant is when I bought the car to top it off. It doesnt lose any.