Hello,

I don't know if this is more appropriate in the a4 section or the mechanic section but here we go. About 6 months ago I bought a 2002 a4 1.8t quattro (manual transmission) and i've had to replace part by part on it. About 2 months in my radiator blew, causing my engine temp to sky rocket. I bought a replacement and installed it myself. Now i'm having more coolant issues and I need your help diagnosing it.

So the engine temp gauge is starting to sit just right of 50%, where you can notice a sliver of white peeking through the left side of the marker ) it would normally sit dead at 50%). Anyways, I can take this thing on the highway, and when i approach 60-65mph my temp sensor will jump to over 3/4. This doesn't happen every time I go that fast either. I'll pop it in neutral and let the temp come back down. One time, the temp went right back up as I started accelerating again, but the other couple times, I could take it back up to 75-80mph with higher RPM and the temp sensor wouldn't move, it just sits at 51%. I've run into this same incident going 30-35mph as well once or twice. Same thing there, I go neutral, let the temp come back down, and i'm able to drive again uninhibited. When the temp does skyrocket, a low coolant warning will flash on the dash but it will go away as the temp comes down. I know I have a coolant leak and it looks to be coming from somewhere under the engine. There is a small collection of coolant on the underside of the car just under the engine, and it looks to be a little more on the driver's side. Finally, when all of this started happening, I lost hot air. I can run the heater on the whole way on my 20 minute commute and nothing. I might get a glimpse of hot air for a second, but when i go to feel if it actually is blowing hot air, it's gone.

I am by no means a car expert, but i always try to fix cars myself so I have a basic understanding of what's going on. This to me sounds like a thermostat issue, and the spikes in temperature are it sticking open or closed when it shouldn't be. If i'm not mistaken, this could be the source of the hot air issue as well. I've looked at youtube to see how I would go about replacing my thermostat, and judging on its location, I think that might be the source of my leak. Does anyone see something I should be trying first to fix the problem, or another part that might be the culprit? I think i have the tools, time and patience to replace the thermostat myself, but it will be a huge pain in the butt, and I don't want to have to go through all of that if I don't have to.

Thanks in advance.

 

Update: I was able to get continuous hot air when I kept the fan on super low, like 2 bars (maybe 15%) but the second I increased the fan speed, the heat dissipated and I was just getting tempid (80F?). And as I'm parked writing this, the heat is gone.

 

Don't know much about the 1.8 engine. What you describe could be caused by a sticky thermostat. The odd part is if the temp gauge is reading hot you should be able to get all the heat you want. Also, not sure why putting it in neutral would suddenly bring the temp down. You may also want to make sure you do not have air in the system. That could also be causing your temp swings.

 

I put it neutral just to stop RPM and not rev the engine and create more heat anymore than I need to. Plus I live in Colorado and it's been cold, so that extra cold air really helps bring the temp down.

Is there a way to bleed air out of the system?