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Jumpy temp gauge

I am getting so frustrated being a 944 owner that I am ready to sell. It seems that when I fix a problem, two more things go wrong and I have to park the car until I get another $1500 for the mechanic. Maybe the latest problem is easily fixed, I don't know. I did do a few quick searches in the archives here before posting, but I didn't notice a problem exactly like mine.

When I bought this car a few years (and only about 12,000 miles) ago, the owner had just replaced the radiator. When I bought it, one of the cooling fans stayed on all the time and would drain the battery. I had the fan switch replaced and the stupid mechanic did not refill the coolant. Within 2 miles I blew a head gasket. Fast forward a couple of years and last fall the water pump went out. Once I saved the money I had it replaced and the mechanic (obviously not the mechanic that messed me up) replaced the thermostat at the same time. This is the second thermostat that has been put in the car since I've had it. A couple of months ago the temp started fluctuating in the car. I discovered that the passenger-side fan was not turning. I had that replaced. So in the past few years I have had the radiator, water pump, thermostat, and one fan replaced in the cooling system alone (this does not count repairs on the suspension and others). Anyway, on to my current problem.

My temp gauge is "jumpy". When I am driving, most of the time it will sit on the 1/2 way mark but it will jump up to the line just below the red box. I am so paranoid about overheating issues that this scares me. It will then drop back down to 1/2 way. It is never a smooth transition between temperatures, but it jumps so fast that the needle even shakes a little when it arrives at the new temp. Is this air in my cooling system or something worse?

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Old 07-03-2008, 03:27 AM
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Sounds like a bad ground. As you probably know, these cars need to have the grounds checked and cleaned periodically.

I hope that the mechanic paid for the new head gasket.
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Old 07-03-2008, 04:06 AM
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Any fluctuation in any of the other instruments? There is a write up (Pelican Tech actually) for pulling the cluster and cleaning the grounds in the cluster, my temp, fuel, and oil pressure all do it. Though my headlight ground is a little corroded.

There is an important ground under the driver side dash. Put head by the pedals, look up. Brown wires, towards outside (driver door) of car. Cannot miss them. =)
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Old 07-03-2008, 04:59 AM
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All other instruments are operating normally. I pulled the cluster 6 months or so ago to replace the speedo. I replaced all the dash lights at the same time.
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Old 07-03-2008, 05:16 AM
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Did you adjust the footballs and tighten the screws? =)

Also, check the two grounds I mentioned. =)
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Old 07-03-2008, 06:02 AM
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Quote:
Originally Posted by fbgh2o View Post
I hope that the mechanic paid for the new head gasket.
No. He claimed that the car had a bad head gasket when I brought it in. My attorney wrote a couple of letters but then told me that it would cost me more in trying to get my money back then I could expect to receive in compensation. I had been using this mechanic for a number of years. I now go to a German specialty shop. The first time I took the car in the mechanic told me the entire history of this particular car. The mechanic worked for the Porsche dealer when this original owner bought the car. Until I took it to this jack-leg that screwed it up, the car had only known one mechanic.
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Old 07-03-2008, 11:35 AM
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I'll check those grounds that Phoenix and Fergus suggested sometime over the holiday. I just don't see how it could be a ground issue. Maybe I did not explain the symptoms as in detail as I should. The temp guage gently rises from cold to the mid-point as it warms up. After I've driven a while, that is when it will jump from the mid point to the 3/4 mark. It does not constantly bounce back and forth, it will sit on 3/4. Eventually it will pop back down to 1/2 way - but I hold my breath the entire time.

If this is a ground issue, I am not risking damage to my car by driving it am I?
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Old 07-03-2008, 11:39 AM
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You could also bleed the system again. The temp sender gets confused when it hits air instead of coolant.
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Old 07-03-2008, 12:35 PM
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For the gauge to jump suddenly, and not slowly, you probably have an electrical, and not temperature, issue. Check the connection to the temperature sender on the block - it's the one with one wire on it. If the connection is clean and tight, the wire may be corroded or broken internally (within the insulation). Wait for the failure mode to occur and wiggle the wire at different points in its length to see if the needle bounces. This may take two people or clever positioning of a small mirror.
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Old 07-03-2008, 01:44 PM
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Quote:
Originally Posted by phoenix_iii View Post
Did you adjust the footballs and tighten the screws? =)

Also, check the two grounds I mentioned. =)
how do you adjust the footballs, aren't they held down with two nuts?
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Old 07-03-2008, 05:42 PM
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The footballs are held down by the sock.

For it to jump I would say you have 2 possible things. Both have been mentioned above. Ground issue or air in the system. One is easy, the other is messy and a pain to troubleshoot.
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Old 07-03-2008, 05:57 PM
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The footballs are held down by the sock.

For it to jump I would say you have 2 possible things. Both have been mentioned above. Ground issue or air in the system. One is easy, the other is messy and a pain to troubleshoot.
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Old 07-03-2008, 05:57 PM
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--another good indicator of bad grounds is if the temp jumps when you turn on big loads (headlights, defroster...).
Clean the grounds at the rear of the engine - made a pretty big difference in temperature indication for me - almost half a division, and reduced jumpiness.
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Old 07-05-2008, 03:10 PM
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Quote:
Originally Posted by hpservertech View Post
The footballs are held down by the sock.

For it to jump I would say you have 2 possible things. Both have been mentioned above. Ground issue or air in the system. One is easy, the other is messy and a pain to troubleshoot.

which sock would that be, the one missing in the laundry?
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Old 07-05-2008, 08:54 PM
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I had the same problem on one of my 968s - checked and cleaned grounds, went through 4 thermostats and two water pumps and 2 radiators, yes I threw parts at it. Finally bought the ice shark cables from Robby over on rennlist and now everything is steady and I have peace of mind that I can trust my gauges and my old ass cables with disintegrating insulation have been replaced in the engine bay so I have reduced the chances of an engine fire.
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Old 07-11-2008, 08:21 AM
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Holy cr4p. How come now one said bad RADIATOR CAP

Just had mine pressure tested... it's bad. It looked good, but was bad. I have jumpy temps.


Newy on it's way. Apparently this causes jumpy temps. =)
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Old 07-11-2008, 10:46 AM
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Quote:
Originally Posted by phoenix_iii View Post
Holy cr4p. How come now one said bad RADIATOR CAP

Just had mine pressure tested... it's bad. It looked good, but was bad. I have jumpy temps.


Newy on it's way. Apparently this causes jumpy temps. =)
Well? Did the new cap fix the jumpy temps? (short pause) I didn't think so.
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Old 07-15-2008, 03:23 PM
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Mine does the same thing, only the temp gauge, something inside the instrument cluster.
Whenever the temp gauge jumps up or rapidly rises, I tap the cluster window a few good times near the temp gauge and it always drops back to normal.
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Old 07-16-2008, 05:07 PM
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I'm currently having some issues going on with my car. The problem is exasperated by the fact that I NEED my car to work this week; my normal daily keeps stalling and it's in the shop. Things couldn't possibly be timed worse.

My temperature gauge has always been a little jumpy; if i tap the throttle, it comes back down. Autocrossing seems to make it run hotter (which is okay with me, I guess. A lot of cars do that...). Recently, however, I have been stranded by the car. Here's what's up:

The car seems to drive absolutely fine. It starts up okay, goes fast, etc etc. However, after I've been driving it (to the store 5 miles away, lets say), and turn it off, then turn it on when I get back into the car, it will not start. I have replaced the starter already (earlier this year). I have also replaced the battery (last month), but I don't think that's the issue anyways, because my radio/lights/windows etc all still work fine and bright. When I do get the car started (after pop starting it, which is bad, I know), the temperature is through the ROOF. My oil pressure is also low. The car runs fine; nothing out of the ordinary with the way it drives. I think it's a wrong reading on both counts.

My questions are: if the car overheats, does it have a safety setting that prevents it from being started up again? Could that cause the problem? Could cleaning the grounds help me out a bit? Would the car perform differently if my oil pressure was actually low (the level is fine, by the way.)? I don't even know where to start, exactly. I'm not a mechanic; oil changes, brakes, etc. I can do. Anything beyond that...uggh.

I'm a poor college graduate and I really don't want to spend a lot of money on my car right now. I have a cracked manifold that's already going to cost me over $2000.

I have not actually gotten around to looking at the grounds, the cap, or the thermostat (it's 10pm on Sunday, and I just got home from work. I'll attack it tomorrow...). I plan on just buying the other parts, they're not that expensive.

Is there a writeup on how to clean/check the grounds?

Sorry for the long post.
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Old 10-12-2008, 06:03 PM
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Quote:
Originally Posted by Aufgeladen944 View Post
I'm currently having some issues going on with my car. The problem is exasperated by the fact that I NEED my car to work this week; my normal daily keeps stalling and it's in the shop. Things couldn't possibly be timed worse.

My temperature gauge has always been a little jumpy; if i tap the throttle, it comes back down. Autocrossing seems to make it run hotter (which is okay with me, I guess. A lot of cars do that...). Recently, however, I have been stranded by the car. Here's what's up:

The car seems to drive absolutely fine. It starts up okay, goes fast, etc etc. However, after I've been driving it (to the store 5 miles away, lets say), and turn it off, then turn it on when I get back into the car, it will not start. I have replaced the starter already (earlier this year). I have also replaced the battery (last month), but I don't think that's the issue anyways, because my radio/lights/windows etc all still work fine and bright. When I do get the car started (after pop starting it, which is bad, I know), the temperature is through the ROOF. My oil pressure is also low. The car runs fine; nothing out of the ordinary with the way it drives. I think it's a wrong reading on both counts.

My questions are: if the car overheats, does it have a safety setting that prevents it from being started up again? Could that cause the problem? Could cleaning the grounds help me out a bit? Would the car perform differently if my oil pressure was actually low (the level is fine, by the way.)? I don't even know where to start, exactly. I'm not a mechanic; oil changes, brakes, etc. I can do. Anything beyond that...uggh.

I'm a poor college graduate and I really don't want to spend a lot of money on my car right now. I have a cracked manifold that's already going to cost me over $2000.

I have not actually gotten around to looking at the grounds, the cap, or the thermostat (it's 10pm on Sunday, and I just got home from work. I'll attack it tomorrow...). I plan on just buying the other parts, they're not that expensive.

Is there a writeup on how to clean/check the grounds?

Sorry for the long post.
You may be experiencing a high open in your ignition. I had the same problem and solved with a push button starter,bypassing ignition wire to starter solenoid. All the parts cost about $20 with the wire connectors and switches and about 2 hours of easy labor

Old 10-12-2008, 06:26 PM
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