Need fast input: ECT sensor check engine light

[nogirlsatgt]

While driving home on the highway today, my check engine light came on. I immediately noticed the temperature gauge was pegged on hot, turned the heat on full blast, and pulled off the road. The coolant in the overflow tank was boiling, and a lot of steam came from that area (front drivers side) right as I pulled over.

I continued to run the heat while making some phone calls . . . draining the battery in the process. Ended up roll-starting on I-91 by myself, not fun.

By the time I addressed the dead battery situation, the temp gauge was back to normal, and the check engine light was no longer on. I was right by an exit and pulled off.

There was an Autozone just off the exit, and they connected their code-scan tool. The worker told me it was reading a faulty ECT sensor code and that "if the ECT sensor fails, the fan won't come on and you will overheat".

The engine was waaaay to hot to try and replace the sensor in the parking lot, so I bought a new sensor, and drove home along surface roads with the heat blasting. The temp gauge would start to creep up, and then I'd get a blast of heat and it would drop down to slightly above normal. I stopped at another autoparts store and bought some pre-mix coolant by my house.

The car is parked outside now, cooling for awhile so I can replace the ECT sensor (looks like an easy job) and refill the coolant. HOPEFULLY this addresses the issue.

Any thoughts or input as to why the CEL just "went away"? Could it have had to do with the battery going dead?

 

[aMaff]

dead battery would clear the CEL.

Also, my guess is that it's the thermostat. There've been a lot of them going kaput recently.

 

[nogirlsatgt]

dead battery would clear the CEL.

But it would still be stored in the ECU so the guy could pull it, right?

I just changed out the ECT sensor (2 minute job), and replaced a lot of coolant. The car still runs hot, but with the heat on it's fine. The radiator fan DOES in fact come on when the car warms up now. Maybe I didn't do a good enough job burping air out to replace the coolant lost earlier in the day? When I shut it off again, I heard weird noises coming from the radiator filler neck . . . almost like air was being "sucked in" under the cap. If the cap wasn't sealing tight, it would certainly cause issues right?

What is the best way to go about verifying the thermostat is bad?

 

[aMaff]

1. No, it wouldn't store the code if the battery was fully done. If he pulled it, then the batter wasn't actually dead. The CEL may have just been due to the fact that you overheated the engine. That's my bet

2. If it's still running hot, it's not fixed.

3. Could be the cap. It's a less than $10 part. Change it, it couldn't hurt

4. If you're going to test the thermostat you may as well replace it. But if you must test it, pull it and put it in the fridge while you boil a pot of water. Once it's nice 'n hot, throw the thermostat into the water. If it moves, it's good. If it doesn't, then it's bad.

Like I said, you're almost better off just throwing another one in there lol. If you do the cap and the t-stat, you're out like $30 max. Both really inexpensive parts.

 

[nogirlsatgt]

Like I said, you're almost better off just throwing another one in there lol. If you do the cap and the t-stat, you're out like $30 max. Both really inexpensive parts.

True enough. God I'm hoping it's not a head gasket.

 

[aMaff]

doubtful. Easy check is to see if you find any water in the oil. If you don't, it's probably not the head gasket.

You're lucky you killed it before it was too late. If you had let it REALLY overheat, you could have warped the head. If, once it's cooled down, it's running properly, the head's probably fine.

EDIT: I just 'read' your user name. Is that the usual Georgia Tech line? lol

If so, you should go ahead and introduce yourself in the GA section. We're pretty much always up to something (bowling, wrench meets, autocrossing, etc)

Hey!! Are you new to the GA section? Post here!

 

[dezine]

I had overheating issues with my P5 awhile back and turned out to be that the thermostat was bad. Seems to happen a lot recently with a lot of people.

 

[nogirlsatgt]

If, once it's cooled down, it's running properly, the head's probably fine.

If by "runs properly" you mean "Runs hot, but otherwise not a lot of difference from normal", then that is where I'm at. That'll sure help me sleep better tonight before doing the Tstat tomorrow.

EDIT: I just 'read' your user name. Is that the usual Georgia Tech line? lol

If so, you should go ahead and introduce yourself in the GA section. We're pretty much always up to something (bowling, wrench meets, autocrossing, etc)

Hey!! Are you new to the GA section? Post here!

Yeah . . . I used it as my AIM screename since I started in 2001, and it just kinda stuck. Yes, the ratio sucks, but anyone who can actually talk to girls can pretty much have a field day there.

I grew up in Decatur, but recently moved to MA for work after graduating.

 

[aMaff]

If by "runs properly" you mean "Runs hot, but otherwise not a lot of difference from normal", then that is where I'm at. That'll sure help me sleep better tonight before doing the Tstat tomorrow.

hahaa yeah, it's gonna run hot if the tstat's not opening, I just mean it's not idling funny, stumbling, or anything funny like that.

Yeah . . . I used it as my AIM screename since I started in 2001, and it just kinda stuck. Yes, the ratio sucks, but anyone who can actually talk to girls can pretty much have a field day there.

I grew up in Decatur, but recently moved to MA for work after graduating.

ah, gotcha. You go from GA to Mass huh? That sucks! *ducks hoping the NEPOC police doesn't show up*
I was up in Mass last summer for training for work and the New England Protege Owners Club rolled out the red carpet for me and we had a great time. You definitely want to go search out their section if you haven't already

 

[nogirlsatgt]

New Tstat in, new cap on. Idled for ~10 min with no issues (gauge stayed ~ half). Havent gone for a rode test yet, but I AM testing the old Tstat . . . just because I already took the morning off work and just want to play with it.

When I was (limping) home last night with the heat on full blast, the air would kinda "cycle" between hot/cold. It would swing between reallllly hot and not even warm every few minutes. If the thermostat was functioning normally, it seems like there would be a more more "even" temperature of coolant throughout the system (?).

EDIT: Pics of Tstat-testing uploading now

 

[aMaff]

EDIT: Pics of Tstat-testing uploading now

Survey says?

 

[nogirlsatgt]

Survey says?

Didn't feel like resizing them to upload, BUT . . .

- 5 minutes in the freezer
*then*
- 5 minutes in rapidly boiling water
*then*
- Inspection

It looked exactly the same before/after. After coming out of the water, I certainly couldn't see any orifice or passage that had opened enough to let any appreciable amount of fluid get through. Still looked sealed up very well.

That gave me enough confidance for an extended test drive, after first letting the car get warm at idle: about 10 minutes of open cruising at 30 mph, followed by 70 mph for ~2 miles on the highway, and finished up with a little stop-and-go traffic for about 10 minutes. The temp gauge never got past half way, so I thiiiiiiiink all my be good, although I'll eagle-eye the temp gauge for a few days.

I had a brief scare when parking again, as steam started coming from the engine bay although the gauge still indicated all was well. I popped the hood and the overflow tank was at a normal level, and I couldn't hear any boiling. I think I was just "burning off" the coolant that puked onto other parts when doing the Tstat, or my spillage from topping the radiator off (I spilled a lot, no funnel).

Thanks for all the help!!