1995 Jetta Temperature Gauge rises then drops suddently back to normal.

Good Afternoon!
My daughter just called me on the way from from college and said she was having a problem with her car. She said that as she is driving
the temperature will sudden rise to just below the max, then just as quickly return to the normal position.
Does anybody have any ideas as to what the problem could be?
It's a 1995 Jetta III with auto transmission.
Thanks in advance for any and all help.
Jeff
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Sticky thermostat. Especially in the winter. Replace it.
But, just in case, check the fan action - but what you describe is not typically a fan problem.
Peter Wieck Melrose Park, PA
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I've never replace a thermostat on this car - her boyfriend always did it.
How much of a pain would something like that be?
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Depends. When has the antifreeze last been changed? If it is more than three years, not much of a pain at all as you are dumping the system anyway. The stat itself is a few bucks.
Do a flush to get any sludge out of the system, use VW - approved anti- freeze, and take your time.
There are sources on the net for How-To tutorials - for example, here is one for an '03 Jetta:
http://answers.edmunds.com/question-do-picture-vw-jetta-2003-2-0-engine-thermostat-engine-23412.aspx
http://www.partsgeek.com/catalog/1995/volkswagen/jetta/cooling_system/thermostat.html
http://www.partsgeek.com/catalog/1995/volkswagen/jetta/cooling_system/thermostat_housing.html
I linked you to the housing in case it gets bunged in the process - they are brittle if abused.
You could also pay your local mechanic or draft the boyfriend to do it if you are uncomfortable with it. It is maybe 2 hours' work with the draining, purging and filling. When you refill, remember not to forget to "BURP" the system or you will have no heat - much has been written here on VW engines needing burping for proper refilling.
Peter Wieck Melrose Park, PA
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I could NEVER get even most of the air out with squeezing hoses, etc, etc. I just ran it 5-10 minutes, shut it off and let it cool, filled the ball to MAX, drove around (like to work), stopped, let cool, topped off, etc. Would take 3-5 heat cycles to get it stable.
Mark
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snipped-for-privacy@aol.com wrote:

eh, if it's got a two speed fan, it might be a failing low speed on the fan thermoswitch. Sticky thermostat, equally likely. I'd probably replace both and be done with it.
nate
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I guess it depends on what "sudden rise" actually means. A short in the wiring or a defective coolant temperature sensor could cause fluctuations with the gauge.
BTW Is this a 4 cylinder gas engine?
A new thermostat is probably a good idea but make sure that a good brand is installed! I just talked to someone that installed a new thermostat ( I don't know the brand he used) and it lasted about a month before it did not function correctly. It was stuck in the closed position and the heater core had to do the work of cooling the coolant. Well the car was driven too fast and the heater core blew causing an accident with his 1997 Jetta 2.0. Car is totalled but he is fine.
JMHO
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later,
(One out of many daves)
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In article <2a1bfc63-2db2-4493-b419-0b0b27a9ec96

Agreed with the group. Sticky thermostat.
I'll assume the 2.0l engine.
I forget (sold the '95), is the thermostat up in the head under that plastic goose neck? If so, replace that too. ~Cheap. They crack at the mounting holes and cause a leak, then you gotta dump the coolant again. If it's where I remember (see above) you're gonna be moving it around, retorquing, etc, so I'd think if it were gonna crack, it'd be a month after doin' the thermostat.
If the hoses are the least bit suspect, I'd do those too. Not so cheap, and that oil cooler plumbing (just above the oil filter mount) is a PITA to deal with. Look at the mass of hose in the area and you'll get the idea. Did mine with the front bumper off (rad fan and fan belt R&R - yep, it's got a fan belt) and it was still a PITA.
If you do the hoses, get that orange plastic dip stick tube too. You'll prolly break it yanking around (or trying to take it off so you don't), and it's cheap just to have in case.
Good luck!
Mark '95 Jetta GLS (sold) '08 Jetta SEL
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tombstone wrote:

If the wire connecting to the coolant temperature sensor gets grounded believe this would cause the temperature gauge to go to maximum. There could be a momentary ground short in that wire circuit. rich
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