Broken temp. gauge or thermostat? - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• Broken temp. gauge or thermostat? by 6011 on 10 Jul, 2007 22:55
• Ok, here's the deal. I was driving on the highway when I noticed that my temp. gauge was reading way low in the white range. I haven't had my jetta long but it has always run in with the needle more or less straight up once it's warm. There is warm air from the heater and the rad hoses and rad are hot but I don't have one of those laser thermometers to tell how hot. The gauge does creep up toward the warm side if I am stopped or driving slowly up a hill (not much air through the rad). This makes me think that the thermostat is stuck open but this has never happened to my in any car so I just thought I would see what others think. I hear it is a *** to change the thermostat, you have to remove the power steering pump? or is it better to remove the alternator and go from the top? Any other advice?
  
  thanks
• #1 by jtanguay on 11 Jul, 2007 04:33
• yep sounds to me like a t-stat for sure!  i had the opposite of what you described when my t-stat was nearly stuck closed.  it let a small amount of coolant flow through the rad... great for winter, but sucky for summer!
  
  definitely need to remove the power steering pump.  i've done it probably 20 times now?  :lol: it only gets easier the more you do it.  once it's off you expose the flange, remove that and you will need a new o-ring for the t-stat.  the old one will probably be all stretched out like @#$@#.
  
  i would personally rather have an easy access t-stat like most gm's, but i'm sure there is a good reason for having it at the lowest point.  you can re-use the old fluid, but considering the cost you might as well replace it.  also do a flush if you don't know the last time it was done (might as well since it's off)
• #2 by Darth Garry on 11 Jul, 2007 05:42
• And then don't put the power steering pump back on
  
  Just kidding.
  
  I just did a thermostat last weekend, but don't have power steering so can't commet on the difficulty.
  
  I agree that it sounds like the thermostat is stuck open.  I know some of the newer 'stats are teh "fail open" type.  I wonder if it's one of those you have in your car.
  
  Later,
  
  Garry
• #3 by burn_your_money on 11 Jul, 2007 06:08
• After doing this on my car with PS a few times I got fed up and snipped the PS lines and threw the pump in the scrap pile. It's not that big of deal, just like an 30 minutes to remove the pump. Once you know where all the bolts are that need to be removed it gets easier.
  If you have an AAZ it will be alot easier though
  
  I agree that it's probably the thermostat and to do a complete flush while you are in there
• #4 by 6011 on 11 Jul, 2007 18:27
• thanks for the replies, I forgot to mention that it is and 88 jetta so a 1.6 td. I replaced the timing belt about a month ago and had to loosen the  pump to remove the belt. I put antisize on the tensioner thingy at that time. I will do a good flush and replace the coolant. I already had the rad out to fix a leak. I thought I should to the thermostat then but I was dumb and didn't. At least it is not a bad time for it to stick open, the temps are in the high 30s right now here.
  
  One more thing, any input on what temp thermostat to buy? Assuming I have a choice that is.
  
  thanks
• #5 by burn_your_money on 11 Jul, 2007 20:35
• I always run the hottest, never had a problem
• #6 by myke_w on 12 Jul, 2007 00:29
• ditto 87c
• #7 by burn_your_money on 12 Jul, 2007 05:34
• Isn't 87 stock? I thought I had a 92 or something
• #8 by myke_w on 12 Jul, 2007 06:00
• in my catalog, optional ones are 71c and 80c
• #9 by burn_your_money on 12 Jul, 2007 12:55
• Hmm interesting. I'll have to check next time I'm at c-tire
• #10 by 6011 on 13 Jul, 2007 19:45
• I ordered the 92* one seen here: click here
  I also got a water pump since it was only $36 and a new plastic thermostat housing just in case. I think it was someone here that posted the link to http://importcarpartscanada.ca/ This is the second time I have ordered from them and I am very happy. Good prices and fast shipping. What ever is in Vancouver comes the next day and the stuff from Toronto a couple of days later. On my first order, they shipped everything from Vancouver except 2 little 17 cent copper washers for the oil plug. They came in their own little box from Toronto. Probably cost them way more than they are worth to ship.
  
  
  
  URL edited by burn_your_money
• #11 by coke on 13 Jul, 2007 19:49
• You'll have fun replacing the water pump. I just went through it and I don't think you can avoid having to take the timing belt and intermediate shaft pulley off.
• #12 by Darth Garry on 14 Jul, 2007 06:35
• I don't think the int shaft pully has to come out but most of the other ones do.  
  
  I ran 71 degree thermostat for a long time because I immaturely believed cooler was better, boy was I wrong!  The truck runs quieter and has more power with the right temp (87).  There is a 91, but 87 seems to do the trick here.  I hope that the 18000 miles I put on it with a 71 degree stat didn't do any long term harm.  Time will tell, I guess.  Oh yeah, it also has heat now
  
  Garry
• #13 by 6011 on 14 Jul, 2007 22:52
• Holy crap that was a PITA! I am not feeling so fond of "German engineering" right now. Some time ago I helped a friend replace a water pump on a 94 gas jetta and I don't recall it beeing that hard.... maybe because there was no injector pump blocking the top bolts! The one on the left was visible at least and reachable with a 3/8" drive universal joint but the one the right (looking at the engine) was only barely reachable with a 1/4" socket and universal. The bolt was too tight for a 1/4" drive rachet thought so I had to use a 3/8" one. If there was a hole in the alternator bracket it would be so much easyer. I tried grinding off some useless metal but it didn't help much. Then two of the bolts holding the water pump to the water pump housing broke, got them out and replaced all 8 with new. Sore right hand from a slipped wrench and back of hand impact and a hammer-smashed thumb on the right to top it all off.
  
  Oh yea, as it turns out the thermostat was broken. The brass cage that holds the spring had cracked. The 92* tstat. makes the temp gauge read at the right edge of the center coolant warning LED. The 87* one had the needle right dead center of the LED. I think it is at most the width of the needle over to the hot side.
• #14 by bigblockchev on 14 Jul, 2007 23:00
• When I did mine last time I had a bear of a time with the same bolt as you did so I carefully drilled a hole in the bracket to make it easier next time. Which hopefully is never. Cheers Dan