1998 Audi A4 2.8 Quattro - Manual - 170k

I have not had the car long and I just started having an overheating issue that I need help diagnosing. This first happened when I was heading home on the freeway, I made it home before the coolant temp reached a notch below max. If it were to go any hotter, I would have pulled over and let it cool.

I have driven it once more to perform a drive test and below are my results, the test was performed with an outside temp of 60 degrees Fahrenheit. It again reached one notch below max before I ended the test.

-During this test, I jumped on the freeway for about 7-10 minutes, the coolant temp reached mid-level. I got off the freeway and took city roads back, after about another 8-10 minutes, it reached one notch below max hot.

-The coolant temp needle slowly rose during the drive, no abrupt changes in the reading.

-The oil temp needle also slowly rose while driving. After the 15-20 minutes of driving, it reached nearly mid level, about 240 degrees Fahrenheit.

-The interior blower blows nice and hot after about 5 minutes of driving. During this test, I had the interior fan mid-low speed and on 74 degrees Fahrenheit.

-After the coolant temp level was very high, I checked the top right of the radiator, it was very hot. The left part of the radiator was warm, but not nearly as hot. The hot coolant comes in the right side, and moves through the radiator, coming out the left side.

-Everytime I checked the radiator fan, it was spinning. I checked it on startup, when the coolant temp was mid-level, and when the coolant temp was nearly max.

-The secondary fan was not spinning when I checked it at near max coolant temp. I just went down to check its operation further and it spins when I turn the A/C on, and it stops spinning when I turn the A/C off. I think this is normal operation.

-Before I got home, when the coolant temp was one notch below max, I turned on the interior fan blower to max, and max hot. The needle started to drop slowly.

I have not had the car long and have not done any work on it as of yet. I also unfortunately do not have any maintenance history on the car.

Please let me know your thoughts and if I can run any other tests to further help diagnose.

Thanks so much for your help!

10/19 Update: More info on driving the car: On the freeway, the coolant temp will slowly rise and eventually it will reach near max temp. In city driving, it will do the same, but the difference is when I stop at a red light, the coolant temp will slowly lower. While doing this second drive test, I had my heater on blast the entire time. It helped cool the engine, especially while at a stop light.

 

I would think that if it's near overheating and your auxiliary fan isn't running, you have a problem there. Just my educated guess??

 

The difference in temperature between the top and bottom radiator hoses point in the direction of an obstruction (Foreign or a faulty thermostat stuck in the closed position) or a bad water pump.

 

Thanks so much for your help. Is there any other tests I can do to further diagnose the issue? Or should I just start with a coolant flush and see if that fixes the problem?

 

Wih what we know, I'm feeling this theory too. A blocked radiator would prevent hot coolant from getting to the aux fan sensor on the lower radiator hose. Someone might have used some of that stopleak crap on it. If you drain the coolant, then put a garden hose on the top fitting what kind of flow do you get. If younsee stop leak in there, you will prob have a prob at the oil cooler too.

 

I think I have diagnosed my issue, or at the very least diagnosed part of my issue.

I tested my fan clutch today and it is shot. The fan spins, but just barely. And at way above operating temperature, it should spin at high revolutions. I used a paper towel roll and I could stop it with no force. Even without a paper towel roll, you can see the blades barely spinning. This is definitely a problem and I will replace it and post the results.

There could still be a block in the radiator, or a issue with an stuck thermostat. Or possibly even a bad water pump. I am really not sure, what are your guy's thoughts now that I have found the fan clutch is toast?

 

Baby Steps. Fix the known problem then move to the next step. It may be that a properly operating fan will solve the problem. If not, then check the radiator flow. T-stats and water pumps are for later.