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View Full Version : Baffled, water temp issues



BoostFrenzy
10-14-2006, 03:17 PM
Replaced the thermostat two times now (aftermarket and OEM!), it gets up to temp fine and stays 93-95c while driving around, no overheating/no underheating, but if I sustain 4000-4200rpm it will begin coming down like a rock! what is causing that? If i slow the engine speed back down it goes back to normal [confused]

Neo1130
10-14-2006, 04:31 PM
What coolant ration are you using? Should be a 50/50 G12/water mix...

BoostFrenzy
10-14-2006, 04:35 PM
yeah i am

Neo1130
10-14-2006, 06:23 PM
So, what gear are you in when it comes down like that? Have you changed out the coolant temp sensor yet?

BoostFrenzy
10-14-2006, 07:40 PM
yes, changed the ECT last week to make sure that wasn't the problem, i'm logging with vag-com, using the test mode of the climate control and the gauge to get my readings... and they all agree

it'll idle/cruise just fine, but if i go over 3000-3500rpm it'll drop to ~65c, if i sustain 4000rpm, it'll go down to 58-60c... am i installing the thermostats wrong?!?! the lower rad hose is also very cold like the tstat is forever open?

here's how i changed the stat (1.8tq):

-removed bolt from water pump to drain coolant
-removed hose from housing to drain more coolant
-removed old tstat/oring
-place new tstat in wp housing with the spring/backside "inside" the housing, o-ring in front so the plastic elbow will press on the o-ring to keep the tstat in place (which i might add is very difficult to hold the tstat/oring in place when you put the elbow back on
-fill coolant, remove expansion tank and cock upward so it's the highest point in the system, run full heat engine running and burp system till no more air bubbles come out, holding throttle @ 2000rpm for 1 minute when done

then the above happens :/

Quattrocket
10-14-2006, 08:55 PM
my GF had the opposite prob. at highway speeds her temp would slowly climb. her prob was the water pump. thats an odd problem. good luck though.

BoostFrenzy
10-15-2006, 02:53 PM
bump for help

BoostFrenzy
10-15-2006, 11:10 PM
more bump for help

Neo1130
10-15-2006, 11:22 PM
I will try and help you as much as possible on this and think of everything that I can, so this may be a bunch of random questions and whatnot...

Is your A/C on when you do this? If so, turn it off and see what it does then... Are you using the right thermostats? The stock one is 90*C right? If you are not using a 90* stat, do that... Check for any kinked/blocked hoses/lines too... This is what I can think of off the top of my head right now...

BoostFrenzy
10-15-2006, 11:31 PM
yes A/C is off at all times, current tstat is rated @ 91c, going to pick one up from the audi dealer in the morning... i've kind of ruled out blockages / water pump issues because even if i let it idle for 20 minutes the temp still doesn't go over ~96c and driving normally for miles upon miles it never overheats, just has a problem under-heating when i bring the revs past 3000rpm and sustain it

iin10ded
10-16-2006, 12:44 AM
ok thats weird. i just redid my cooling system os im curious as to whats goin on here. ill check the bentley in the am but that sounds like correct tstat orientation. it is a wicked PITA to get situated up in there right..

regardless it doesnt sound like a tstat problem - because the car acts 'normal' until your rpms increase. if it was seated incorrectly it would either overcool or undercool, not give the symptoms youre describing [i think...]

it sounds electrical. the gauges all agreeing might be because theyall get a reading from the same F'd sensor? id replace the sensor just because [ive got a new one i need to sell if you need one]

i also wonder if the h20 pump could be overdriving somehow? do your belts recently? i have heard that the continental branded h20 pump belts are slightly different profile in the "V" and cause the cars to run warm because the pump is underdriven slightly.

BoostFrenzy
10-16-2006, 03:18 AM
Originally posted by iin10ded
ok thats weird. i just redid my cooling system os im curious as to whats goin on here. ill check the bentley in the am but that sounds like correct tstat orientation. it is a wicked PITA to get situated up in there right..

regardless it doesnt sound like a tstat problem - because the car acts 'normal' until your rpms increase. if it was seated incorrectly it would either overcool or undercool, not give the symptoms youre describing [i think...]

it sounds electrical. the gauges all agreeing might be because theyall get a reading from the same F'd sensor? id replace the sensor just because [ive got a new one i need to sell if you need one]

i also wonder if the h20 pump could be overdriving somehow? do your belts recently? i have heard that the continental branded h20 pump belts are slightly different profile in the "V" and cause the cars to run warm because the pump is underdriven slightly.

did you read the thread? it runs proper operating temps idle/cruise, temp sensor is new and it's when i sustain 3000+rpm that it drastically undercools.