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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old October 13th, 2003, 13:15   #1
Secret Squirrel
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Join Date: Sep 2000
Location: Lakeport, MI USA
Fuel Economy: 49 combined
Default Changing Thermostat on 98 Jetta

OK guys. Who has done it and how bad was it to do? I can see taking out the alternator. Will it be necesary to take out the A/C compressor also? I'm trying to disturb as little as possible when changing out the thermostat. Thanks in advance.

Eric
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Old October 13th, 2003, 13:29   #2
Bookerdog
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Default Changing Thermostat on 98 Jetta

Wrong direction. I'm pretty sure you should attack from the bottom. Remove the belt for the power steering pump, loosen all the bolts for the bracket and swing it out of the way. Then you should have access to the housing where the plastic outlet attached to the lower radiator hose bolts to the bottom of the water pump housing.

Take off the lower hose to drain the coolant from the radiator side. then loosen the two bolts on the outlet flange and pull it off. You'll get another flood of coolant from inside the motor. But the TStat sits in between the outlet and the waterpump housing. Not a clean job by any means, but not too bad.

This experience is based on my A2 gasser primarily, but everything is in the same location on our motors, so it should apply. I'm sure others will point out my errors if not. [img]/images/graemlins/laugh.gif[/img]
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Old October 13th, 2003, 14:04   #3
Drivbiwire
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Join Date: Oct 1998
Location: Boise, Idaho
Default Changing Thermostat on 98 Jetta

First off...If it's not malfuntioning DON'T F#$@ WITH IT!!!!

Now if it is bad and the car is not maintaining 90C or 190F (centered on the cluster then make sure you are not looking at a bad fan control or fan conection...in otehr words rule everything out before replacing the thermostat...point being they very rarely IF EVER go bad with the new G-12 Coolant.

The correct way to get at it is from the bottom, not the easiest thing to get at trust me.

DB
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Old October 13th, 2003, 14:10   #4
oilhammer
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Default Changing Thermostat on 98 Jetta

I ditto DBW comments... they rarely fail. If your car seems like it takes a long time to warm up, that's normal. And they simply won't warm up if you let them sit and idle.

I may ask, why do you want to replace it?
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Old October 13th, 2003, 16:09   #5
Secret Squirrel
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Default Changing Thermostat on 98 Jetta

Thanks for the advice guys. The reason I'm changing out the thermostat is that I believe the stat is stuck slightly if not all the way open. I have plugged in the VAG-COM to rule out the temp sender. Even during a hot summer day running in stop and go traffic and the freeway, the needle will barely even get to 120 degrees let alone 190 which is where is used to for the longest time indicate. My heater output is also a bit lackluster from what it used to be. I have experiended this symptom on other vehicles that I have owned in the past and am going by experience. Believe me, I would rather not mess with it. The least, the better.
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Old October 13th, 2003, 19:31   #6
oilhammer
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Default Changing Thermostat on 98 Jetta

Okay, no problem then. You'll need to hang the power steering pump/bracket out of the way...you don't need to disconnect the lines, there should be enough slack.

Then where the lower hose attaches to the engine there is the water neck...above that is the thermostat. Be sure and have a pan ready!
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Old October 14th, 2003, 00:21   #7
DeepSea
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Default Changing Thermostat on 98 Jetta

I just went through replacing my thermostat last week. I noticed the temp would consistently drop as I traveled through cooler valley areas, during my morning commute (70 mi, each way). To me there was no question the Tstat was stuck partially open, if not fully open. I replaced it and the temp holds center on gage throughout the trip.
All the advice for changing out the part is right on. No need to disconnect the power steering lines. I disconnected the power steering pump bracket and hung the pump out of the way using some string tied to the front bumper. Break the line going to the thermostat housing and have a large drain pan ready. If you're careful won't be too messy. Be prepared for more fluid when you break the thermostat housing seal, and when you pull the thermostat itself. Make sure to buy your parts online (much cheaper), and to replace the thermostat housing "O" ring.
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Old October 14th, 2003, 04:52   #8
Drivbiwire
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Default Changing Thermostat on 98 Jetta

Yup your thermostat failed...VW thermostats fail "Operational" in other words you won't overheat and fry your motor like a Chevy will, LOL.

The power steering pump bracket has to be removed this allows you to get at the lower hose. It's a real pain. I have only replaced one thermostat in an A3 and all the other times were in my A2 Golf 1.6 that has the identical cooling system.

DB
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Old October 14th, 2003, 07:47   #9
Bookerdog
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Default Changing Thermostat on 98 Jetta

The biggest pain is the fact that they decided there was no need at all to put a draincock anywhere in the cooling system. Is it really that hard? My wife's old '90 Camry V6 had this awesome draincock with a tube leading down, kinda like a Fumimoto for the cooling system. Changing the coolant tended to be an even easier job than doing an oil change. Then again, that motor was designed with the mechanic in mind. Everything that seemed impossible was neatly placed and sized if you followed the set procedure.

I know, I know, lifetime coolant in the resevoir, but come on, when you do have to drain it, it would be nice not to get a coolant bath. Be sure to close your eyes and shut your mouth tight when you pull off the hose and again when you pop out the TStat.

DBW, the failing "operational" must have come on with the A2. My parents first 79 Rabbit Diesel died due to a TStat that failed closed. Overheated, warped the head, and my dad cracked the block trying to torque the head bolts in the cold. That experience has always made me very gunshy of the VW thermostat.
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