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dancing temp gauge


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16 replies to this topic

#1 cricket

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Posted 22 November 2006 - 07:37 PM

My 98 Forester's temp gauge tends to drop down to the bottom for no apparent reason. Today I was doing 70 on the highway, and the temp needle just plunked to the bottom of the gauge. It had been holding steady about half way up for several minutes. What's the problem? or is this normal? It was was well over 32F at the time. Thanks!

#2 ericem

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Posted 22 November 2006 - 07:43 PM

sounds liek all u need is a new temp sesnor, 20 bucks. Someone here will say its the thermostat i know someone will, but it is most likely the temp sensor and its way easier to change the temp sensor then a thermostat.

#3 porcupine73

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Posted 22 November 2006 - 09:04 PM

The temp sensor might not be a bad thing to try, especially if you don't want to mess around checking connections and stuff. Note there are two temp sensors - one for the ECU fuel maps, the other for the temp gauge. Does it bottom out suddenly or slowly (if you were able to notice)?

#4 Suzam

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Posted 22 November 2006 - 09:06 PM

Could be a bad connection on the temp sensor. Check the wiring itself and make sure it's secure. That would explain an intermittent problem.

#5 Manarius

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Posted 22 November 2006 - 10:14 PM

Could be a bad connection on the temp sensor. Check the wiring itself and make sure it's secure. That would explain an intermittent problem.

Yeah, a bad connection to the sensor that sends to the gauge, not the Coolant Temp Sensor we find under the Intake.

#6 gbhrps

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Posted 23 November 2006 - 06:17 PM

If you have the tools, the place to work, and the time, pull the coolant temp sensor. The temp sensor in my 55 Thunderbird started becoming erratic this summer, with readings all over the guage, changing several times in a 5 minute period from 25% to 85% to 0% to 90% and back to 60% readings. I pulled it and put it in a cold pan of water on the stove and hooked a multimeter to its body and the terminal. As I turned up the heat to get the water to a boil, the multimeter readings did exactly the same dance as the temperature guage had done in the car. Obviously the temp sender was bad. Good Luck!

#7 Setright

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Posted 24 November 2006 - 01:57 AM

WAIT!


Is it possible that your car is equipped with a non-genuine thermostat?

Drops on the freeway, climbs back to normal in city traffic?

Fit genuine thermostat, problem solved.

#8 cricket

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Posted 14 December 2006 - 04:29 PM

For those of you keeping track of this.... According to the shop, it's the thermostat. The shop INSTALLED the thermostat because there was NO thermostat to begin with. But I don't see how the lack of a thermostat would make the needle suddenly drop. Maybe not enough in the pressure? And why would it go up and then down... I have a feeling I'll need to replace the sensor anyway.


My 98 Forester's temp gauge tends to drop down to the bottom for no apparent reason. Today I was doing 70 on the highway, and the temp needle just plunked to the bottom of the gauge. It had been holding steady about half way up for several minutes. What's the problem? or is this normal? It was was well over 32F at the time. Thanks!



#9 johnceggleston

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Posted 14 December 2006 - 04:44 PM

how could it not have a thermostat? the temp guage would never move if it were missing, it certainly wouldn't reach the mid point on the guage. you'd have almost no heat. ?.?.? the ecu would always think it was just starting up. maybe in texas it's hot enough...

how long have you had this car.?

For those of you keeping track of this.... According to the shop, it's the thermostat. The shop INSTALLED the thermostat because there was NO thermostat to begin with. But I don't see how the lack of a thermostat would make the needle suddenly drop. Maybe not enough in the pressure? And why would it go up and then down... I have a feeling I'll need to replace the sensor anyway.



#10 nipper

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Posted 14 December 2006 - 05:29 PM

Makes sense. Local driving there isnt enough air moving over the radiator to pull out all the heat. Highway driving the amount of air through the radiator will remove all the heat and cool the engine.
Subaru thermostates are 180-190 degrees. At mid point on the temp gauge that is around 190-200 degrees reading off the ecu using a scangauge. As you can see it doesnt take much to pull the heat out of the engine without the thermostat.
This is not a big heat producing engine when its cold outside. Thats why you get no heat without a thermostat.

nipper

#11 cricket

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Posted 14 December 2006 - 05:48 PM

It's Houston Texas! I've had it a couple of months now.


how could it not have a thermostat? the temp guage would never move if it were missing, it certainly wouldn't reach the mid point on the guage. you'd have almost no heat. ?.?.? the ecu would always think it was just starting up. maybe in texas it's hot enough...

how long have you had this car.?



#12 Legacy777

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Posted 15 December 2006 - 12:42 PM

Hey.....another Houstonian :)

Do you know if the shop put in a subaru thermostat? If not, you still may have some issues. Don't ask me why, but Subaru engines act weird if they don't have a subaru thermostat in them.

BTW, you may want to check out the texas forum on http://forums.nasioc.com/forums

There are local get togethers every week, and state meets at times throughout the year.

If you still have problems with the car, let me know, I could take a look at it.

Josh

#13 cricket

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Posted 15 December 2006 - 06:48 PM

Thanks! I forgot to mention.... I took it into the shop because the check engine light came on. Two codes: misfire, and fuel sending unit. New wires took care of the misfire. Subaru wanted $130 for the sending unit. I figured I'd go ahead and change the pump and strainer while I'm in there. Subaru wanted $445 for the pump. Wow. I hope I didn't do the wrong thing by buying the pump, strainer AND strainer for around $120 altogether off ebay. I got the Bosch pump and OEM Subaru sending unit.


Hey.....another Houstonian :)

Do you know if the shop put in a subaru thermostat? If not, you still may have some issues. Don't ask me why, but Subaru engines act weird if they don't have a subaru thermostat in them.

BTW, you may want to check out the texas forum on http://forums.nasioc.com/forums

There are local get togethers every week, and state meets at times throughout the year.

If you still have problems with the car, let me know, I could take a look at it.

Josh



#14 cricket

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Posted 15 December 2006 - 06:50 PM

Do you know if the shop put in a subaru thermostat?


I don't know. I do know that the second thermostat they put in (the first one failed and caused overheating) is a "premium" thermostat.

#15 nipper

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Posted 15 December 2006 - 07:01 PM

Thanks! I forgot to mention.... I took it into the shop because the check engine light came on. Two codes: misfire, and fuel sending unit. New wires took care of the misfire. Subaru wanted $130 for the sending unit. I figured I'd go ahead and change the pump and strainer while I'm in there. Subaru wanted $445 for the pump. Wow. I hope I didn't do the wrong thing by buying the pump, strainer AND strainer for around $120 altogether off ebay. I got the Bosch pump and OEM Subaru sending unit.


er um....

You wont get a code for a fuel sender. Its not even part of the ECU circuit.
Subarus have notorously bad fuel senders that can usually be made better with Techron fuel additive.
Personally i would say unless the sender is dead, do the techron thing.
I have never bought major parts off ebay that were not OE. Luckily its something thats easy to get to.

nipper

#16 cricket

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Posted 15 December 2006 - 11:02 PM

Okay, thanks. Funny the shop even gave me the number of the code. For fuel sending unit, the fuel gauge thing at the tank. I could be mistaken. I have noticed that whenever the fuel gauge needle takes a sudden dive to "empty", the check engine light comes on shortly after that. Then, when I put some gas in the tank and the needle comes back to life and settles at its correct position, the check engine turns off. :confused:

er um....

You wont get a code for a fuel sender. Its not even part of the ECU circuit.
Subarus have notorously bad fuel senders that can usually be made better with Techron fuel additive.
Personally i would say unless the sender is dead, do the techron thing.
I have never bought major parts off ebay that were not OE. Luckily its something thats easy to get to.

nipper



#17 nipper

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Posted 15 December 2006 - 11:09 PM

Okay, thanks. Funny the shop even gave me the number of the code. For fuel sending unit, the fuel gauge thing at the tank. I could be mistaken. I have noticed that whenever the fuel gauge needle takes a sudden dive to "empty", the check engine light comes on shortly after that. Then, when I put some gas in the tank and the needle comes back to life and settles at its correct position, the check engine turns off. :confused:


Ok next time that happen have the codes read at an autopart sotre for free. I think that has more to do with your EVAP system then anything else.

What code number did they give you.

nipper




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