Overheating '86 5000 TQ

Hi, my '86 5000 TQ has been run above 100C temperatures for the past couple hundred of kilometers and finally today it overheated twice, (coolant leaked out and the temperature warning light came on), once at
night when I was driving it slowly home. I was afraid that perhaps the head gasket is blown but the car drives great and I cannot see any tell-tale exhaust, which leads me to think that either it needs a new thermostat or a radiator flush. Is there anything else that could be causing this?
TIA cp
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cp, chances are that it's a blown head gasket. Pull the plugs and check the colour. If one plug is a different colour, chances are the cylinder is leaking. You can do a compression test (small differences can tell of a head gasket leak). I was also told to pull the plugs with the engine warm, and hold an inspection mirror over the plug holes, if it fogs, there's a coolant leak. Unfortunately, every time the engine overheats, there's a risk of head warping as the aluminum head and cast iron block do not behave the same as they cool down - so the failure will only get worse. (BTDT - hg replaced, head planed) If it isn't a hg leak (I'm sure you're hoping that it's not), check the temperature of the rad. If there is a noticible temperature gradient - like the engine side is hotter than the fender side, the gasket between the hot and cold ports may have failed and coolant is bypassing the rad. (BTDT - brass radiator replaced failed plastic rad)) If you're planning on doing a flush&fill, make sure they do it with the rad disconnected and then do the rad separately to avoid rust & junk from the engine clogging the rad. The thermostat is easy to test - put it in cooking oil on the stove with a thermometer in the pot - make sure it opens at the temp stamped on the flange. It doesn't sound like a t-stat failure, though, usually they fail open and your car will take forever to warm up. Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

couple hundred of kilometers and finally today it overheated

once at night when I was driving it slowly home. I was afraid

cannot see any tell-tale exhaust, which leads me to think that

else that could be causing this?

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Hi Steve, thank you for your help, I will check this out, I SOOOOOO hope that this isn't a bad head gasket! :-\\\\\\\\\
cp

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Steve, I've checked the oil and coolant, both look as they should. The oil is 2000km old and still looks like new. The coolant is bright green, still think it could be a blown gasket?
Thank you again, people like you put the 'news' in newsgroup :-)
cp

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Is your radiator cooling fan running when it should?
- Low speed when the air conditioner is on - Fan speed two when at the larger 100C mark or just a bit higher. - Speed three when close to next higher mark. (Usually happens in stopped traffic)
If not you may have: - a bad thermo switch on the bottom of the radiator - any of three fan relays not operating - failed resistor pack on frame under radiator - Seized fan bearings
If it doesn't look like a head gasket you might also want to pull the thermostat to check its operation.
Clogged radiator is possible. If lower radiator hose is a lot cooler than the top one the rad is probably clogged.
Steve's suggestion of a bad baffel in the rad is also quite possible.
Tonyj just sold: '91 100q 5spd (4th T44) current 98.5 A4 1.8TQ 5spd APR
cp wrote:

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cp, Of course, maybe the easiest thing - checking to see if the fan is working - would be the most obvious first step in diagnosis. My bad. 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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Thank you Tony and Steve! I am going to print your posts out for the mechanic,

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Oops, I was going to add a '!' and 'cp' :-)
cp
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cp, This may open a firestorm debate here, but from what you describe, the coolant you're using doesn't sound like true "phosphate free" coolant that the engines in the 5k's, etc. need. It may say "Phosphate Free" on the label, but in many cases, it's more like "Reduced Phosphate" - you can search on the net, and on Audifans, and read discussions about that for an eternity. Getting back to the root problem, overheating, a head gasket leak can manifest itself in a number of ways. The head gasket in my 5ktq was leaking in the back cylinder, between a water jacket passageway through the HG and into the cylinder. The leak was intermittent, and would only manifest itself when the car got warm - or hot. The coolant appeared blue (VAG coolant) and didn't have obvious oil in it, but I was losing coolant. The plugs were all a nice tan colour, but the back plug had a wierd colour to it, sorta whitish, maybe slightly orange. When the head was taken off the engine, the leak through the hg was obvious. The worst part was that the inflow of coolant in the cylinder had increased the wear on the cylinder walls as the oil was being washed off by, and burned with, the coolant. As a result the bore was slightly larger than the other cylinders, the mechanic who fixed the car said that it was noticible but not terminal. Unfortunately, with the number of overheats you've had, there's a good chance that the head has warped and if there wasn't a hg leak before, there may be one now. The lack of oil in coolant, coolant in oil, etc. etc. is not an acid test to disprove a hg leak - as Tony said, check fan operation, then check the rad, and other fairly easy stuff. In the more advanced testing (which isn't all that hard if you can get the tools) if the coolant is washing out cylinder #5 (as mine was), you'll see a difference in a compression test. That's all for the news, over to Fred for the weather......;-) Cheers! Steve Sears 1987 Audi 5kTQ - Unsettled front stationary to the north (of my cubicle) 1980 Audi 5k - stationary trough in the west 1962 and '64 Auto Union DKW Junior deLuxes - fog bank moving in with the summer (SPAM Blocker NOTE: Remove SHOES to reply)

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couple hundred of kilometers and finally today it overheated

once at night when I was driving it slowly home. I was afraid

cannot see any tell-tale exhaust, which leads me to think that

else that could be causing this?

I would guess you'd need more than a flush - likely a new radiator. If there's no tell-tale smoke and you didn't lose a lot of coolant, I doubt you've blown the head gasket. Good luck!
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I hope you're right! I'm going to try all the steps that have been suggested! :-)
cp
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