1995 Audi 90 2.8l engine temperature low

Ok, before you all say that I need a new thermostat, I've been there. :-)
The engine temperature guage seems to regulate to the first, thin white
line at about 1/4 on the guage. There is a thick white line just below half way up the guage where I would expect the needle to settle. The needle only gets there on warm days in the summer or if I let the car idle stopped for some long period of time. Somewhat farther up the guage(just above half guage) the fans turn on, as I would expect also. The heater blows very slightly warm air if the outside temp is below, say, 45 degrees.... unless I let the car sit idling long enough to get the gauge up to or past the thick white line I mentioned before. Then the heat seems to work fine. If the outside temp is below 40 or so, the "Heat" makes my feed cold!
If I'm moving, even at slow speeds, the gauge settles back the the thin white line at about 1/4 again.
Also, the oil temp only just comes off the cold mark (60degrees C) to the first white mark at about 1/6 the guage. The engine has an oil cooler so I wouldn't expect the oil to get much above the coolant temp.
All indications are that the engine is not getting to full operating temperature. I've replaced the thermostat twice, once because it really failed. I've installed the 97 degree C thermostat, not the 87. And still, very low heater output, and the needle stays at about 1/4 on the gauge. There is no indication on the gauge as to what the temperature value is.
Any ideas?
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I am having almost the same problem with my 97 A6. I have replaced the thermostat 3 times. The coolant temp is the same as yours but my oil temp is where it is supposed to be. I was told by one garage that the previous owner had used an additive to seal up a leak in the system and now the whole thing is clogged and needs to be replaced(about $700). I haven't gotten a second opinion on it yet, though.

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What did they say needed to be replaced? Radiator? Heater core?
Gene

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The heater core.

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Sounds like your shop is looking to pick up some more money. I doubt very much that anything is 'clogged' up in your system just because the PO used BarsAll or Stop-Leak.
My son has a '98 A4 2.8 Tip. His heater core started a small leak that caused his windshield to fog badly. I can't remember the name by the stop leak product that we used but it looked like silver flakes in a small plastic tube. Stopped the leak for the last two years with no other problems.
His car gets to temperature at the middle line and stays there like the needle was nailed in place in all ambient conditions.
Tony
Archangel wrote:

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Arch, I agree with Tony, if the system was clogged you'd expect a less efficient heat exchange and an overheating engine. Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

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I wondered about the shops diagnosis also that's why I'm getting a second opinion. The second shop did a flush of the system when they did the timing belt/water pump and now we have some heat although not as hot as it should be unless we're moving. As far as the stop leak not causing the problem... well it was not just for a small leak, it turned out that the head gasket was cracked and that's how they tried to fix it. Maybe they used allot of the stuff?

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Arch, I had a similar thing happen to me except in the opposite direction - the car ran hot since the day I got it - the dealer looked at it, flushed the system, told me that it was probably plugged by rust & debris from the engine. A short time later it began to seriously overheat and I found out the head gasket was toast (heat reason #1). Had the hg replaced and they filled it with water/froze overnight in a cold snap/overheated on the highway next morning (AARRRGHHH!) and then the plastic end tank gave up and barfed all over the parking lot at work. When I was disposing of the rad I pulled the remains of the plastic tanks off - the rubber gasket on the side with all of the hose ports to the engine was broken (old break) between the hot and cold sides - short circuiting the rad (heat reason #2). The used brass Modine I put in works like a charm now. It seems that "it's plugged" seems like an easy diagnosis for an older system that isn't working as it should. Take a look into the climate control system, especially the heater valve at the back of the engine. With all sorts of vacuum leaks, stripped servo gears, worn fan brushes - makes me wish the CC system was as simple as the one in my DKW - 2 levers: hot/cold and Winter/Summer. Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

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It sounds like your diagnosis is correct - the engine is not getting up to temperature. The way the radiator fan works sounds correct when you let it idle to get it warm.
Th only thing that strikes me is that it might be possible to install the T stat upside down so that it opens too easily or maybe a gasket to seal it into place is missing.
Tony
Gene Buckwalter wrote:

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Gene, I'd get a thermometer and check the temp of the fluid running into the rad. With a 97c thermostat, the fluid should circulate in the block only for a longer period, and the regular oil temp should raise as well. The coolant temperature gauge is on the outside of the t-stat, so it is more a gauge of the temperature of the fluid in the rad than the engine, and if the t-stat is holding the temp in, then you'd expect the oil temp to go way up. I've heard of new t-stats malfunctioning - I checked the last one I put in the 5ktq on the stove before I put it in - had to use cooking oil as the water was boiling below the opening point (not that I live on a significant mountain, or anything). Tony is about right - there has to be heated coolant bypassing the thermostat. On the heater issue, have you checked that the cabin heating system is operating correctly? My '87 5ktq had only unheated air out the vents all summer - turns out that the servo motor ist kaput and wouldn't pull the bowden cable that changes the air supply from outside to from the heater core. I found the servo pack behind the glovebox and manually rotated the servo link to heat - now all I'll have to do is change it back in the spring (take THAT, "climate control system"!) There's a discussion about CC problems on Audifans today - if your system has the "fault codes", on the Type 44 system channel 8 and 9 should be within 3 units of each other if the servo is working well. Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

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The heating system seems to function as well as it can with the engine coolant temp being low....if that's really the case.
Last night I put a therocouple on the temp sensor in the pipe that comes out of he rear of the passenger side head. That seemed to read about 70C when the dash needle was where it normally rests. Then I moved the thermocouple to the radiator, right where the heated water enters it. That read about 85C or so a few minutes later, when the temp had risen above its normal operating temp.
Anyway, as you mentioned, I also beleive the only way for the temp to be low is either a bad run of thermostats or something wrong with the way it's installed. Somehow, heated coolant is getting to the radiator to lose its heat.
Is it possible that the coolant configuration on this engine is different from what the orientation instructions say that come with the thermostat? The thermostat in backwards may cause this sort of problem.
I soon need to fix an oil leak on the front of the engine so I'll be removing the timing belt and such anyway. I plan to take a very carefull look at the coolant direction and the orientation of the t-stat and replace it for good measure.
Gene

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You should also check to see if the Tstat is supposed to have one of those 'O' ring seals that snap on its edge. If it is, and it isn't there, you would get a lot of flow around the sides.
Tony
Gene Buckwalter wrote:

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I'm as sure as I can be that I installed that too. The only thing I can figure is that it's in backwards, but that seems unlikely three times....unless what-ever indication I used for direction gives me the wrong way.

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Gene, If you have a 97c thermostat installed, the temperature of the coolant exiting through the thermostat should be 97c or above. It sounds like the thermostat is letting 87c coolant pass by (which, according to the FA, is what the 078 121 113F thermostat is supposed to do for your car, anyway - it shows that the rubber gasket is between the thermostat and the cover, not between the thermostat and the block, FWIW). I'd take the thermostat out and check it on the stove, personally. A few years ago the temp gauge in the 5ktq was acting up, it would read temperature to a certain point, and then stay there. IIRC the temperature sensor, often referred to as the "Multimalfunction Device", can fail in this way as it uses a combo of mechanical and electrical devices to read the temperature. The replacement of the sensor cured the gauge woes. Look at: http://www.sjmautotechnik.com/trouble_shooting/20vmfsns.html and: http://www.sjmautotechnik.com/trouble_shooting/cooling.html#gauge Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

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Thanks, Steve. Like I said, I'll take a very close look at this when I go after an oil leak in the next few weeks. The sites you listed look very informative as well. Thanks again.
I should have done some more of this research before I pulled the heads and replaced valve guides in October. I could have killed this bird with that stone too.
Gene

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