And now it's time to play diagnose this problem

[selavia]

Okay. I don't have my car with me in Detroit; my baby is back home. My Dad went to drive it the other day and he turned the heat on and the air never got hot, it didn't even get warm. What's more the temp. gauge never got to the half way mark; only stayed at quarter of the way warm. And the car was driven for quote a while.

I'm thinking it might be the thermostat, but would that affect the temp. of the air entering the car?

I'm at a little bit of a loss since I cannot look at it myself.


Any suggestions?

Sean

 

[andreyiv]

It does sound like a stuck open thermostat and it would really affect the air entering the cabin. I'm guessing it has gotten pretty cold out and the engine just generates heat slower then the cooling system dissipates it.

Last time I had problems with the cooling system, I took an IR thermostat and kept checking the temperature of the coolant entering the radiator from the engine (the hose, not the coolant itself of course) and found out that even in the mid of summer, the thermostat would only open for short periods of time to dump the hot coolant in the radiator and then it would close for a while. The car stayed cool and seemed to function properly so I don't think it was a malfunctioning thermostat.

Hope this helped.

 

[selavia]

ok.
I'm not terribly certain I understand what you did, and what exactly it proved? Care to elaborate?

Also, my Dad said, if you let the car sit, without driving it, the temp guage reaches the half-way mark, and the vents blow air hotter than hell. I'm thinking the thermostat is stuck open.

 

[selavia]

btw, andreyiv, I love your signature picture. I got to change mine one of these days.

 

[andreyiv]

Thanks for the complement, the pic was an accident, if you look close enough there are two glowing lines on the lower quarter of the picture; a ricey maxima was leaving the parking lot and got caught in the picture (I was ready to curse him out before I saw the picture).

What I did was measure the coolant in the hose that connects the engine block and the radiator. There are two; I measured temperature of the top hose (where the engine disposes of hot coolant). I just now realized that I made a mistake in my previous explanation (the thermostat directly controls the intake of coolant, not disposal).

Anyhow, what happens is the following. In a functioning cooling system, cooler coolant is kept in the radiator (because it is being cooled by the radiator); hotter coolant is in the engine block (because it is being heated by the engine block). The thermostat controls the exchange of the hot and cold coolant between the two parts of the system. When the coolant in the engine gets too hot, it opens and lets some cool coolant in (from the radiator) and this causes the hot coolant to flow into the radiator (and get cooled off).

I just measured the temperature of the coolant exiting the engine block as the engine was warming up and a little while after it got to operating temperature. If I would have plotted those points on a graph with temperature (y-axis) vs. time (x-axis), at first, the temperature would be very slowly increasing (no flow of coolant between the block and the radiator because the block is still cold and the thermostat is closed, letting the engine warm up quicker and giving you heat in the cabin quicker). Then, the temperature would rise quickly (as the thermostat opens for the first time, making the engine take in some cold coolant and dumping some hot coolant in the radiator), next, the temperature would come down as the thermostat has closed and the radiator starts doing its job, and once again, when the engine block gets hot, the thermostat opens and the same thing happens so it would look like a sine graph.

What it proved was that even in the middle of summer (hot temperature outside) the thermostat was not always open, meaning, the cooling system wasn't working at it's full capacity, meaning, the engine still conserved some heat by keep the thermostat closed (or partially closed) in order to stay at its peak operating temperature. What it means to you is that a car with a stock open thermostat would just be overly cooled and would not get up to its operating temperature with low outside temperatures. Which yours does, which points to a stuck open thermostat.

The reason it actually got to operating temperature and had hot air blowing through the vents was because of less airflow over the radiator. It dissipated heat slower and the engine was able to catch up to it. Think of the engine as a positive number and the cooling system a negative number, when everything is working properly, the two are same but opposite, by canceling each other out, they keep the engine at a constant temperature. If its cold out and the thermostat is open all the time, that negative number is larger, much larger then the positive number and not letting the engine get up to its operating temp.

The comparisons and explanations are pretty bad and don't really hold true if you look at all the cases (like some people who are good in math may point out) but it is the best I could do after waking up from 3 hours of sleep in the afternoon.

Sorry its really long too, I hope it clears some of the confusion up though.

 

[selavia]

actually, I think it was a great explanation. Makes sense to me. Actually makes excellent sense. THanks! Now, on to the next logical question, something I should do myself, or have done?

Any particular brand to buy? Any techniques for refilling the coolant (i know air can be a problem)? Any DIY guides besides pelican's?

Thanks, Sean

 

[wood_e]

The thermostat, if stuck open would allow coolant to flow throughout the system, and if the heat was on and it was not warm than the coolant going through the heater core was not hot.

Go get a thermostat, try getting one at the dealer or NAPA.

 

[andreyiv]

Like wood_e said, you can either get one from the dealer or online, don't know about NAPA as there aren't any NAPA stores around here.

Well, lets see, I've never delt with the 4 cylinder, but on the 6 cylinder, in order to get to the thermostat, you would need to remove the engine fan (actually, the fan clutch, as the fan is sitting on the clutch and can't be taken off without the clutch (at least I don't think it can be)). In order to remove the clutch, you need a huge wrench (32mm I believe, might be different on the 4 cylinder). In order to turn the nut, you need to somehow stop the water pump from turning which could be a head ache but if you have a bunch of different length and thickness screwdrivers that you don't care for, you can do it; or you can get a special tool.

Its not a hard job and there ae a lot of write ups on it (this site has a few: http://www.geocities.com/e36rulz/DIY.html ), just look for something like, replacing the water pump or the like. Once you get the fan off, its all downhill from there, I believe there are only 4 screws holding the thermostat cover in place (I would reccomend replacing this also, they are plastic and crack, like mine did). Don't forget to buy the appropriate gaskets for the thermostat area.

Now, there is another way to replace the thermostat without removing the fan, which is breaking off one blade off the fan but it becomes such a pain in the neck to get to the housing (impossible with all the blades there) and I just don't think is worth a broken fan blade.

Coolant replacement is also a pretty simple job, once again, a few write ups on that site. Bleeding the system is the most complicated part of the whole job in my opinion. There is no dummy flag that pops up and tells you all the air is bled out of the system, its more or lesspatience and intuition. Just devote a lot of time to this and make sure you have a lot of extra coolant. Read some of the write ups on bleeding the system and if some things aren't clear, ask me, its more then enough for another post.

You can do everything yourself and it would make you feel good when your done, but there are some snags and you'd need to devote a whole day just in case something goes wrong. At the mechanic, it should cost you around 200 just for labor so its really your choice. I'll tell you this, everytime I bleed the system and there is still some air in there, I curse myself and wish I had the money to make a mechanic do it properly.

Good luck with whatever you choose to do.