"Overheating" Well kinda, sorta. It's complicated.

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[Chris]

So my car has been doing this ever since I purchased it almost 5 years ago. After running for a little while, the temp gauge creeps all the way up to 260 and the overheat light comes on. Then it'll suddenly jump down quickly and hover around 235-ish. The thermostat seems to never open, and no coolant flows through the upper radiator hose. I bled the system few hundred times (I shit you not) and nothing has ever fixed this problem. The coolant temp sensor is about an inch away from the thermostat, so it's not bullshitting me with false readings. It's hot enough for the thermostat to open, it just doesn't.

I finally gave up and replaced the thermostat, which didn't fix the problem at all. BUT, now the car was eating coolant. Not much, but enough that I every other day I had to add about a half gallon because the "Low Coolant" light would come on. Then one day while my car was idling, I heard a hiss - like someone opened up a can of soda - to turn around and see my car engulfed in a cloud of steam. I shut the car off and opened the hood - and my radiator cap was just GONE.

Pissed off, I pulled the thermostat out of the car and replaced it with a gutted t-stat so there would be some restriction in the line. I ran the car like this for a couple of months. I had about 80% of the radiator blocked off (on the bottom) so the car would warm up to operating temperature and OD would work (oh, and having heat this far up north is nice too). Well, this worked awesome until lately when I started using the A/C. Boy did that temperature gauge climb quick with the A/C on and 80% of the radiator blocked! The good thing was the car never consumed ANY coolant with the t-stat removed.

Since I need heat in the mornings on my drive to work and A/C on my drive home (VT spring means crazy weather. 35* in the morning, and 85* in the afternoon), I decided to put the t-stat back in. When I did this I completely flushed the system with water. I spent two hours flushing the system and bleeding the air out of all the lines and engine block. There wasn't a drop of air in that thing.

Well it's been three days since I did that. The car is back to overheating, but not quite as bad. The first time it overheated it stood at 260* with the warning light solid for about 30 seconds, then quickly dropped down to 235*. Since then, the car never gets over 235* - but 235* is still "overheating" IMO because my '91 has never gone over 200*. Now it's consuming a complete gallon of water for every 50 miles I drive.

There's no oil in the water, or water in the oil. I'm thinking the LIM is on it's way out now, but that's a symptom of the larger problem. The car acts up no matter what I'm doing. I could be cruising at 70mph, 50mph, 30mph or just sitting and idling. The cooling fans work properly, and I even upgraded both cooling fans to 95+ primary fans (The voltage meter takes a dive when both kick on at the same time!).

I hate this car and all it's little bullshit problems.

[Chris]

Well it seems that I lied, it is still overheating - I just stopped paying attention to the temperature gauge.



A two mile, 3 minute drive is all it takes for it to overheat:




Within 30 seconds it boils over, dumping fluid into the overflow tank and dropping the temp:




As soon as it does this, I'm now about a gallon lower on coolant:




Like I said, the thermostat NEVER opens up. I've tried three different thermostats and none of them open.

[crazy k]

Your car probably does not leak coolant into the oil, as it does not have the gasket problems as the 94+ 3100 SFI.


sounds like what my 92 vert did... as did my 93 vert.... when the throttle body hoses in both cars went out, and it could also be a heater core leak, like my 95 CS had.  When you have a leak on the HOT side of the system before the thermostat, the car will piss coolant under pressure while the T-stat is closed.  



the temp sensor that gives you the gauge reading is on the rear head, not by the T-stat.  the T-stat area sensor is for the ECM/PCM only.  this is true on all of our engines through the end of the 1995 model year.  in 96+, a 3 wire sensor was used.

IMO (and it is backed by facts) that the two separate sensors are superior as the area most prone to overheat is the rear head (most often damaged when an engine overheats) and they are more responsive (they bounce around a bit as the temp fluctuates) and they take a reading of the temperature of the head, and not the coolant, which may not be present if you have a leak.    
CASE IN POINT: a vehicle equipped with a CS DIC can tell you the engine temperature which it gets from the datastream broadcast by the PCM.  This vehicle sprung a leak in the feed line to the heater core, which was not found for a few days even after searching.   The cluster gauge would go to redline illuminating the overheat light, but the DIC would display the temperature as a lukewarm 86 degrees.   The head was overheating and the sensor in it relayed the problem info gauge cluster, but the DIC received it's reading through the ECM sensor location in the engine.  If this vehicle had a 3 wire temp sensor it would not have informed the driver that there was a problem. (btw, this car had no working low coolant light and I don't don't know what or when it would have said... it was not mine)




can you see coolant leaking on the ground?
can you smell coolant under the hood?
can you smell it when the heat is on?
does your exhaust smell rich?

[Jay]

Radiator cap bad?

[Chris]

Your car probably does not leak coolant into the oil, as it does not have the gasket problems as the 94+ 3100 SFI.


sounds like what my 92 vert did... as did my 93 vert.... when the throttle body hoses in both cars went out, and it could also be a heater core leak, like my 95 CS had.  When you have a leak on the HOT side of the system before the thermostat, the car will piss coolant under pressure while the T-stat is closed.  



the temp sensor that gives you the gauge reading is on the rear head, not by the T-stat.  the T-stat area sensor is for the ECM/PCM only.  this is true on all of our engines through the end of the 1995 model year.  in 96+, a 3 wire sensor was used.

IMO (and it is backed by facts) that the two separate sensors are superior as the area most prone to overheat is the rear head (most often damaged when an engine overheats) and they are more responsive (they bounce around a bit as the temp fluctuates) and they take a reading of the temperature of the head, and not the coolant, which may not be present if you have a leak.    
CASE IN POINT: a vehicle equipped with a CS DIC can tell you the engine temperature which it gets from the datastream broadcast by the PCM.  This vehicle sprung a leak in the feed line to the heater core, which was not found for a few days even after searching.   The cluster gauge would go to redline illuminating the overheat light, but the DIC would display the temperature as a lukewarm 86 degrees.   The head was overheating and the sensor in it relayed the problem info gauge cluster, but the DIC received it's reading through the ECM sensor location in the engine.  If this vehicle had a 3 wire temp sensor it would not have informed the driver that there was a problem. (btw, this car had no working low coolant light and I don't don't know what or when it would have said... it was not mine)




can you see coolant leaking on the ground?
can you smell coolant under the hood?
can you smell it when the heat is on?
does your exhaust smell rich?

I replaced the heater core about 2 years ago because it had a pinhole in it that would spray coolant on my windshield. The coolant temperature sensor is directly under the thermostat, because that's where I had to install it (My car came with 80MPH speedo and idiot lights, I upgraded to euro cluster and replaced the switch with the sensor. I believe my Chilton's manual verified this was the correct placement? If I recall there were two switches - one for the idiot light and another for the fans? I don't know it was a long time ago.)

There is no smell of coolant under the hood because the car is running straight water. Since it goes through 1-2 gallons a day, the coolant is long gone. The exhaust doesn't smell either due to the same problem (no coolant, just straight water). When the car HAD coolant in it, I don't recall there being any smell from the tailpipe or under the hood.

Radiator cap bad?

Nope, replaced it when it took a vacation.

[crazy k]

Again.... you have TWO temp sensors

1: a two prong sensor for the ECM/PCM located by the T-stat: it provides information to the PCM, which uses the data to turn on the fans and regulate fuel mixture.
http://info.rockauto.com/getimage/getimage.php?imagekey=951153&imageurl=http%3A//info.rockauto.com/SMP/TX3T_FULL.jpg
2: a single wire sensor (green wire) located on the drivers side rear corner of the head: it can be either a switch or a sender, and it provides data to the gauges.
http://info.rockauto.com/getimage/getimage.php?imagekey=341156&imageurl=http%3A//info.rockauto.com/ACDelco/10232601.jpg

remember now?


Another problem with running pure water is that it boils too easily and is even more prone to blowing out the system.   If you have run the car through the winter with pure water in it, you could easily have damaged items including the heater core again.   antifreeze isn;t cheap, so I would first inspect and see if you can find any leaks.  then, I think you should re-fill the car with anitfreeze, and try to determine where it is coming out.

[Chris]

That 1st temp sensor is the one I replaced... Guess it was the wrong one, that's what I get for listening to the guy behind the parts counter.

The only reason I'm running pure water is because it pukes out the coolant as soon as it warms up. It had coolant in it all through the winter, it's had coolant in it up until about two weeks ago when the problem got worse. It use to always just get hot and then cool down rapidly; but a few weeks ago it started puking out the coolant. That's when I changed the thermostat, bled the system and eventually just took the thermostat out and blocked off the radiator. That worked fine until it was getting to the point of using the heat in the mornings and the A/C in the afternoon. It would get dangerously hot with the A/C on - although it wouldn't boil over or puke any coolant. I bled all the air out of the system, flushed it and put the t-stat back in. I then let the car warm up and purged the air from pulling the radiator hose and it's been getting worse ever since.

I don't want to put any antifreeze in it at this point. It goes through 1-2 gallons a day - and at $15/gallon for antifreeze, I'm not going to put any in until I can get this fixed.

If it wasn't for needing heat in the morning and gas was so cheap that I didn't care about the 15MPG it gets from running rich - I'd just pull the t-stat and leave it alone.

[crazy k]

wait....  if you have the wrong type of sender for you gauge... it should either read fully pegged either all the way over heated or stone cold.  

get the correct sender, and see what your temp REALLY is.

[Chris]

wait....  if you have the wrong type of sender for you gauge... it should either read fully pegged either all the way over heated or stone cold.  

get the correct sender, and see what your temp REALLY is.

Wait, nope.. Nevermind I lied. I was thinking the Lumina and picturing the 2.8 in my truck. I just went outside and looked, and yes - I replaced the correct one. It's a one-wire sensor, and a PITA to get to. I remember replacing it because the autoparts store gave me the wrong one (the one under the thermostat). Im ny S10, the 2.8 engine uses one switch for the idiot lights (two wire, similar to the ECM sensor on the 3.1) that I had to replace because it went bad, and another sensor for the ECM right next to it.

Sorry, my mistake.

[crazy k]

wait....  if you have the wrong type of sender for you gauge... it should either read fully pegged either all the way over heated or stone cold.  

get the correct sender, and see what your temp REALLY is.

Wait, nope.. Nevermind I lied. I was thinking the Lumina and picturing the 2.8 in my truck. I just went outside and looked, and yes - I replaced the correct one. It's a one-wire sensor, and a PITA to get to. I remember replacing it because the autoparts store gave me the wrong one (the one under the thermostat). Im ny S10, the 2.8 engine uses one switch for the idiot lights (two wire, similar to the ECM sensor on the 3.1) that I had to replace because it went bad, and another sensor for the ECM right next to it.

Sorry, my mistake.

<3   I forgive you!


You probably have a coolant leak.  see if it can be located.   replace the radiator cap with a new one, if you haven't already.  

Where does coolant leave the vehicle from when it overheats?  is it all flowing out of the reservoir overflow?

[Chris]

<3   I forgive you!


You probably have a coolant leak.  see if it can be located.   replace the radiator cap with a new one, if you haven't already.  

Where does coolant leave the vehicle from when it overheats?  is it all flowing out of the reservoir overflow?

It doesn't loose any coolant if I remove the thermostat. The cap has been replaced. When the coolant decides to part ways with my car, it all leaves through the overflow tank. If I don't re-fill the radiator and just deal with the "low coolant" light coming on and off, it won't overheat to the point where the idiot light will illuminate - but it still won't open the thermostat.

[crazy k]

I want you to do this:

take a working t-stat, and drill a very small "bleed" hole in it.  this will allow air to pass, while restricting coolant.   It will prevent vapor lock in the cooling system, when steam/air/vapor builds up behind the tstat, causing it not to be in contact with the hot coolant, and therefore not open. I usually make a 1/32 size hole in all my tstats...  

oh... and remove all the cardboard, and let us know how it progresses...



They even make a tstat with a built in bleed valve that allows air to pass but has a "float" that seals the hole when coolant hits it, but I don't know where to buy one...

[Chris]

I want you to do this:

take a working t-stat, and drill a very small "bleed" hole in it.  this will allow air to pass, while restricting coolant.   It will prevent vapor lock in the cooling system, when steam/air/vapor builds up behind the tstat, causing it not to be in contact with the hot coolant, and therefore not open. I usually make a 1/32 size hole in all my tstats...  They even make a tstat with a built in bleed valve that allows air to pass but has a "float" that seals the hole when coolant hits it, but I don't know where to buy one...

This is a cool idea, I'll try this.

oh... and remove all the cardboard, and let us know how it progresses...

I did that a while ago. I removed the cardboard and installed the t-stat.

[crazy k]

I want you to do this:

take a working t-stat, and drill a very small "bleed" hole in it.  this will allow air to pass, while restricting coolant.   It will prevent vapor lock in the cooling system, when steam/air/vapor builds up behind the tstat, causing it not to be in contact with the hot coolant, and therefore not open. I usually make a 1/32 size hole in all my tstats...  They even make a tstat with a built in bleed valve that allows air to pass but has a "float" that seals the hole when coolant hits it, but I don't know where to buy one...

This is a cool idea, I'll try this.

I usally go most of the way though the t-stat on the flange of the housing with a 1/8th-ish drill bit and finish either with a smaller bit or even a hammer and a thumbtack/drywall screw/sharp pointy object to pierce the tiny hole.   the hole should ideally be tiny to reduce near all coolant flow.

[Chris]

Well, I drilled a hole in the t-stat last night... While I was at it I replaced the gasket on top of my water pump that has now decided to start leaking. Filled the car up with water and bled the air from the system. This is as high as the temp gauge got on the drive from my girlfriend's to my house (45 minute drive)



On my way to work this morning, this is as high as it got:




I know at what points in the road the car overheats, so I kept a close eye on my gauge and it never overheated once. Yay to not having to add a gallon of fluid every time I stop!


BUT....


It's still not circulating coolant. Thermostat is still not opening up (I can clamp the hose shut with my hands and not feel water rushing past it). I don't know what the deal is. Today when I get to my girlfriend's I'm going to pull the upper rad hose at the t-stat housing and run the car up to operating temp to I can visually see it not circulating fluid (to confirm).