YACT - Overheating Problems...Thermostat?

[PricklyPete]

I have a Mazda Millenia S ('99) that is having a somewhat odd overheating problem. I say odd because it doesn't just overheat and be done with it. The car behaves differently whether I'm driving on the highway or I'm driving around town.

When I'm driving on the highway (most of my driving), the car will slowly overheat until it nearly hits the top of the gage. After a short period of time (1 minute), the needle will drop significantly to normal operating temperatures (needle directly at the "50%" mark on guage). Sometimes the needle will to to 3/4 position on the guage and sit there for an extended period of time (5 minutes), then slowly creep up again to almost the top of the guage and then drop significantly to normal driving temperatures. There will be long periods of time where the guage will stay at normal operating temperatures (15+ minutes).

When driving around town, the car tends to stay in the 3/4 position...occasionally dropping down to normal driving temperatures and occasionally heating up to almost the top of the guage.

I am no car expert, but I was thinking that the Thermostat may be malfunctioning...where it doesn't open up properly until the car gets very hot. This would kind of explain why the temperature would drop to normal driving temperatures so quickly...but when I mean quickly...it's literally a couple fo seconds. I can't imagine that the car would really cool down that quickly from the Thermostat opening up all the way.

Any other suggestions on what could be causing the problem?

I was planning on trying to replace the Thermostat this weekend to see if that will fix the problem. Am I ruining my car by driving it till then with these occasional heat spikes and the occasional extended period of time where the car is running at 3/4 temps (I realize that this gives you no idea of what the actual temperature is...but alas my car does not give any indication either). I don't want to ruin my car, but I would like to do this myself if possible.

Thanks.

 

[Shockwave]

Thermostat or possible low coolant would be about the only 2 obvious culprits. However, I've had very few thermostats fail, and never on a car that new. Flip side, you can snag them for around 15 or 20 bucks so its a cheap fix and if it doesnt work your not out a whole helluva lot.
And in my experience with stuck thermostats, the tempature drop was VERY fast.

 

[Quixfire]

Originally posted by: Shockwave
Thermostat or possible low coolant would be about the only 2 obvious culprits. However, I've had very few thermostats fail, and never on a car that new. Flip side, you can snag them for around 15 or 20 bucks so its a cheap fix and if it doesnt work your not out a whole helluva lot.
And in my experience with stuck thermostats, the tempature drop was VERY fast.

I agree with Shockwaves assessment. I would also make sure to bleed any air out of the system to make sure there isn't an air pocket causing this problem.

 

[GalvanizedYankee]

I would use a quick flush product, as per instructions and replace the coolant, when you change the T-stat.

Make sure the radiator cap is in good condition, at 5 years a new one might be a good idea.

Make sure the lower radiator hose has not gone soft causing it to collapse during suction. It happens and snuffs coolant flow.

Use a flash light to see if the cooling fins are clogged w/bugs. Light should easily be seen on the other side.

If that car has an electric fan make sure it is cycling. After a drive let the car idle, you should be able to hear it turn on
after a few minuets then shut off.

Just my $.02


EDIT: When you flush and/or fill make sure the heater is turned on all the way. This will clear air out of that part of the system.

 

[PricklyPete]

Thanks guys. I'll check all of the things you have mentioned. I think the Thermostat at Autozone is like $15, so if that is the problem I don't see it being an expensive fix.

Am I hurting my car if I drive it till this weekend with the occasional spikes in temperature?

 

[JulesMaximus]

Have you ever flushed the cooling system? This should be done every year as part of your annual maintenance. How many miles are on the car?

I would start by replacing the thermostat and flushing the cooling system.

I also would not continue to drive a car with the temp gauge reading in the red. You are just asking for major engine damage by doing this.

 

[Quixfire]

Originally posted by: PricklyPete
Thanks guys. I'll check all of the things you have mentioned. I think the Thermostat at Autozone is like $15, so if that is the problem I don't see it being an expensive fix.

Am I hurting my car if I drive it till this weekend with the occasional spikes in temperature?

If there is an air pocket trapped in the system you could be super heating the coolant into steam which could cause damage to the engine. I would check for air in the system first as soon as possible.

 

[Shockwave]

Originally posted by: PricklyPete
Thanks guys. I'll check all of the things you have mentioned. I think the Thermostat at Autozone is like $15, so if that is the problem I don't see it being an expensive fix.

Am I hurting my car if I drive it till this weekend with the occasional spikes in temperature?

Well, it sure aint good. If you do, once you get it fixed get an oil change as well. High temps will break down the oil faster. Another thing you can do is pop the hood but keep the saftey latch secure. Think of it as the poor mans Ram Air system. It'll help to keep air circulating when your at speed.
While I would check the radiator and hoses, your particular problem doesnt sound too much like that type of problem. However, Murphy's Law has never failed me so....

 

[PricklyPete]

I was definitely planning on changing the oil again even though it has only been 2 weeks since the last change.

What is the best way to bleed the air out of the cooling system?

Does flushing the cooling system just involve draining the coolant and then replacing or is there something more involved. I bought the car used with 29K and I have put 41k on it in the last year and a half. I changed the coolant about 38k, but haven't touched it since then.

 

[Quixfire]

There should be a bleeder type screw in the thermostat housing or where the upper radiator hose connects to the engine. Open the bleeder up and watch for air bubbles, close when no more air comes out.

 

[PricklyPete]

Originally posted by: Quixfire
There should be a bleeder type screw in the thermostat housing or where the upper radiator hose connects to the engine. Open the bleeder up and watch for air bubbles, close when no more air comes out.

Thanks, I'll try and take a look for that.

 

[Shockwave]

Originally posted by: PricklyPete
I was definitely planning on changing the oil again even though it has only been 2 weeks since the last change.

What is the best way to bleed the air out of the cooling system?

Does flushing the cooling system just involve draining the coolant and then replacing or is there something more involved. I bought the car used with 29K and I have put 41k on it in the last year and a half. I changed the coolant about 38k, but haven't touched it since then.

I've got 115,000 on my coolant...

 

[Brutuskend]

Is the cooling fan belt driven or electric?

 

[PricklyPete]

Originally posted by: Brutuskend
Is the cooling fan belt driven or electric?

It is electric.

 

[PricklyPete]

Thanks for all of the suggestions. I "flushed" my coolant and this seems to have fixed the problem for now. I will update if it reappears.

 

[0roo0roo]

was it dirty?

 

[Ornery]

Originally posted by: Brutuskend
Is the cooling fan belt driven or electric?

That's the first thing I wondered. Make sure the damn thing is spinning!

 

[iamwiz82]

Originally posted by: Ornery

Originally posted by: Brutuskend
Is the cooling fan belt driven or electric?

That's the first thing I wondered. Make sure the damn thing is spinning!

Well, on the freeway there should be enough air moving through that the fan is not necessary. My car turns off the electric fan at 63mph.

 

[CraigRT]

Originally posted by: PricklyPete
Thanks for all of the suggestions. I "flushed" my coolant and this seems to have fixed the problem for now. I will update if it reappears.

so was there not much of it? glad it fixed the problem.

 

[Ornery]

"Well, on the freeway there should be enough air moving through that the fan is not necessary. My car turns off the electric fan at 63mph."

Right, that perfectly matches the description of his problem. After it's been warmed up, leave it running and look under the hood. If the fan ain't spinning, something's broke. Could be the fan motor, switch, connection or temp sensor.

 

[PricklyPete]

Originally posted by: Ornery

Originally posted by: Brutuskend
Is the cooling fan belt driven or electric?

That's the first thing I wondered. Make sure the damn thing is spinning!

The fan is working.

 

[PricklyPete]

I don't know how dirty the coolant gets, but it wasn't what I would consider dirty. flushing may have just freed some stuff up in there. I don't know. Regardless it seems to be working fine...hasn't gotten above normal temps yet and I've driven it 40+ miles already (long commute).

 

[PricklyPete]

Originally posted by: CraigRT

Originally posted by: PricklyPete
Thanks for all of the suggestions. I "flushed" my coolant and this seems to have fixed the problem for now. I will update if it reappears.

so was there not much of it? glad it fixed the problem.

The coolant was a little low, but still within the "acceptable" range according to the resevoir.

 

[JulesMaximus]

Originally posted by: Shockwave

Originally posted by: PricklyPete
I was definitely planning on changing the oil again even though it has only been 2 weeks since the last change.

What is the best way to bleed the air out of the cooling system?

Does flushing the cooling system just involve draining the coolant and then replacing or is there something more involved. I bought the car used with 29K and I have put 41k on it in the last year and a half. I changed the coolant about 38k, but haven't touched it since then.

I've got 115,000 on my coolant...

Yikes! I'd hate to see the inside of your engine and radiator. I just bought a car with 67k miles on it and the first thing I did was flush the coolant (I don't think the pervious owner ever did this) and it was pretty ugly. It failed the coolant test also (test is to determine how the coolant handles high/low temps) Trust me, you don't want your coolant boiling or freezing inside your engine.

How often do you change your oil?

The person I bought my Rodeo from was lax on following the routine maintenance (I didn't know this until after I bought it and started fixing some of the minor things that were wrong with it). It had a bit of sludge built up in the engine so I've been changing the oil every 1,000 miles. It keeps coming out cleaner and the oil pressure is starting to go up to around 55-60 (it was hovering around 45 for a while-which isn't out of the norm for this vehicle though).

I even had the differential fluid and transmission fluid changed.

 

[Quixfire]

Originally posted by: PricklyPete
I don't know how dirty the coolant gets, but it wasn't what I would consider dirty. flushing may have just freed some stuff up in there. I don't know. Regardless it seems to be working fine...hasn't gotten above normal temps yet and I've driven it 40+ miles already (long commute).

That just confirms what I thought, an air pocket in the system. Flushing the coolant removes the air pocket and you thermostat is now working normally.

A pocket will get caught between the coolant and the thermostat creating a barrier to prevent the thermostat from opening due to pressure. Removing this air from the system allow the thermostat to work normally.

I glad you got it fixed.