Thermostat?

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skizot722

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I've read a lot of the previous posts on overheating, but nothing seemed to match up with what I experienced yesterday.

I got in my car after it had been sitting overnight, started it up, and drove to my friends house less than a mile away. Picked him up and started heading down the road. I heard a really loud fan noise I hadn't heard before, and figured it might be coming from another car around me. A few seconds later the "Check Engine Temperature" text displayed on the diagnostics screen. I looked over at the engine temp gauge and it was 3/4 the way up (it always sits a tad bit under half-way). I then glanced back over to the diagnostics screen to see if it was saying anything else. It wasn't, so I glanced back over at the temp gauge, and it was already pegged at the max temp end. I pulled over immediately.

I figured maybe it might have stored a code, so I ran over to the parts shop to pick up an OBD II scanner (after walking back to my friend's house and grabbing his vehicle :(). Car sat for maybe 20 minutes during that time, and when I got back with the scanner, the temp gauge was sitting at about half-way (close to where it usually sits). No codes were stored. So, I decided to start it up and get under the hood to listen for different sounds (nothing was leaking anywhere). When I started it, the temperature had lowered enough that the "Check Engine Temperature" message was gone. I let it run for about 10 minutes, and all was good. I held it at about 2200 RPM for a minute, and the temp held steady where it usually does.

I decided to drive it home, which was about a mile away, and it made it home just fine. The car is a 2002 LS V8 with 32,000 miles on it, and has never had a coolant leak. The temperature outside was in the lower 70s, and I didn't have my A/C on.

Given that:

1. Radiator fan was running just fine.
2. Water pump is mechanical (if it went bad, car wouldn't have been fine after starting it back up to drive home).
3. Coolant temp rose very quickly (radiator fan being bad would have caused a lot slower rise in temp).

I'm thinking the thermostat just got stuck (closed). What do you guys think? I assume the tstat is still mechanical on these cars, or is it electric? Is it sticking closed a common problem?
 
Either that or air in the system. a tstat swap would require proper bleeding of the coolant system. So that would fix either issue.

But if it is air, you need to find where it's coming from. Maybe replace the cap on the puke tank too?
 
I had that same problem about a year and a half ago. In my case it was the overflow reservoir and just recently I had a bunch of overheating issues but with this time I had the thermostat, hydraulic pump, and elec fan replaced. It finally was fixed after I had the pump actuator replaced by the dealership. Now if I ever have any problems with overheating or anyother major parts I'm going to take it straight to the dealership!
 
See, I didn't think it would be the resevoir itself, since he stated he's never had a leak.
 
True, true. With this damn car it could be anything!:D I just hope it's not as bad as mine was here recently...
Keep us updated skizot722.
 
Many, many thermostats are replaced, but very few are ever at fault.

I strongly suspect that you have air in the cooling system. Bleed it by the proper procedure to find out. If you do, then you do have a small leak somewhere, you just haven't detected it.

The reason for the rapid temperature gauge rise is not because engine temperature suddenly rose. It has to do with the way the electronics work. Normally, the temperature gauge shows engine coolant temperature. When one of the head temperature sensors indicates overheating (such as happens with air in the coolant), the engine computer sends a command to the instrument cluster for it to move the temperature gauge to maximum no matter what the water temperature really is.
 
joegr said:
The reason for the rapid temperature gauge rise is not because engine temperature suddenly rose. It has to do with the way the electronics work. Normally, the temperature gauge shows engine coolant temperature. When one of the head temperature sensors indicates overheating (such as happens with air in the coolant), the engine computer sends a command to the instrument cluster for it to move the temperature gauge to maximum no matter what the water temperature really is.
Click to expand...

Very interesting. I never knew that before.

I had an overheat symptom when I first bought the car. Faulty cylinder head temp sensor. They replaced it, all is well.
 
joegr said:
Many, many thermostats are replaced, but very few are ever at fault.

I strongly suspect that you have air in the cooling system. Bleed it by the proper procedure to find out. If you do, then you do have a small leak somewhere, you just haven't detected it.

The reason for the rapid temperature gauge rise is not because engine temperature suddenly rose. It has to do with the way the electronics work. Normally, the temperature gauge shows engine coolant temperature. When one of the head temperature sensors indicates overheating (such as happens with air in the coolant), the engine computer sends a command to the instrument cluster for it to move the temperature gauge to maximum no matter what the water temperature really is.
Click to expand...

Interesting. I have looked all over for leaks and didn't find any. I will look again in case I missed something. The cooling system has never been opened for anything, so if there are no leaks, I don't think there is air in the system. That thought crossed my mind, too, so I look for a good 15 minutes for leaks that night. I don't doubt that the engine temperature rose as much as the gauge specified though, because when I popped the hood, the coolant was definitely boiling in the container up by the windshield. I really suspect the thermostat, but I could be wrong because it did seem like the gauge rose fairly quickly.

Thanks for the info about the gauges though; definitely something new to me. I will spend some more time looking for leaks tonight. :)
 
when the engine temp goes up, check under the hood, check the hoses for pressure, check if the hoses are hot, and look for leaks, and if its something not visible, its probably something electrical, solenoid, actuator, something like that - this is if you bleed the system correctly too.
 
If it's boiling in the tank, check the cap on the puke tank. If it isn't getting a good seal, then it won't be pressurized. If the system isn't pressurized, the coolant will boil at a lower temperature.
 
pektel said:
If it's boiling in the tank, check the cap on the puke tank. If it isn't getting a good seal, then it won't be pressurized. If the system isn't pressurized, the coolant will boil at a lower temperature.
Click to expand...

So would it not also boil if it were actually 270 *F? I will check the cap though.
 
Sounds like the exact problem I had when I got my car. Some people don't run a proper mixture of antifreeze and water and just think that they can just add water to the cooling system when low. What happens though is that water evaporates and coolant doesn't, so if it's hot and you're almost low on coolant then some of it might have evaporated and cause the system to suck in air through the overflow spout on the degas bottle. I say bleed the system PROPERLY and go from there.
 
skizot722 said:
Interesting. I have looked all over for leaks and didn't find any. I will look again in case I missed something. The cooling system has never been opened for anything, so if there are no leaks, I don't think there is air in the system. That thought crossed my mind, too, so I look for a good 15 minutes for leaks that night. I don't doubt that the engine temperature rose as much as the gauge specified though, because when I popped the hood, the coolant was definitely boiling in the container up by the windshield. I really suspect the thermostat, but I could be wrong because it did seem like the gauge rose fairly quickly.

Thanks for the info about the gauges though; definitely something new to me. I will spend some more time looking for leaks tonight. :)
Click to expand...

Please note that you often will not be able to see evidence of small leaks. Pressure testing may be the only way to find them. I'd try the bleed procedure first, to see if there is any air trapped in the system.

You are very overdue to have your coolant flushed and replaced. (The schedule is x miles or x months, whichever comes first. While you are okay on mileage, you are past due on time.) The anti-corrosion additives and the water-pump lubricate were all used up some time ago.
You may have blocked cooling passages due to this.

Also, you are probably about due for a cracked Degas bottle. This is definitely a leak that you wouldn't usually see.
 
Thanks for the tips, joegr. I may just take it into the shop and have them replace the coolant. I would do it myself, but I don't have the tools to pressure test the system. How about the degas bottle though, is that pretty easy? The bleed procedure looks pretty straight forward.
 
skizot722 said:
Thanks for the tips, joegr. I may just take it into the shop and have them replace the coolant. I would do it myself, but I don't have the tools to pressure test the system. How about the degas bottle though, is that pretty easy? The bleed procedure looks pretty straight forward.
Click to expand...

I haven't had to replace one yet, so I'll let someone else chime in here.

If you do take it somewhere to have everything done, you probably should replace the thermostat while you are at is. (I still say it is unlikely to be the failure, but it will cost very little to change while the system is open anyway.)
 
fonsito said:
By any chance is their a 160 dg thermostat available for our cars??
Click to expand...

Why, because you want the car to run like crap, get worse mileage, and contaminate the oil more? A lower temp thermostat won't help at all with overheating. Fix the real problem. Both of my LS's have never been past the half-way mark on the gauge. They have both spent a lot of time in 100+ weather, both driving and idling with the AC on for long periods of time.
 
joegr said:
Why, because you want the car to run like crap, get worse mileage, and contaminate the oil more? A lower temp thermostat won't help at all with overheating. Fix the real problem. Both of my LS's have never been past the half-way mark on the gauge. They have both spent a lot of time in 100+ weather, both driving and idling with the AC on for long periods of time.
Click to expand...

I dont have a Overheating problem...just wanted to upgrade my thermostat like I did on my F-150 Lightning a couple of years ago
 
fonsito said:
I dont have a Overheating problem...just wanted to upgrade my thermostat like I did on my F-150 Lightning a couple of years ago
Click to expand...

Why do you think that a lower temperature thermostat is an "upgrade?"
 
the only reason you would get a lower temp tstat is if you were to upgrade your radiator, the tstat opening at a lower temp really has not too big of an effect on a 3.9 engine, it would be more beneficial to work on the fan that cools more then the tstat, the lower temp tstat would just have the engine warm up slower, but eventually be just at hot
 
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