B6 S4 Overheating after reinstall

B6/7 S4/RS4
#1

To give some background info, I replaced my 04 S4 engine with an engine out of an 08 S4 Cabriolet. I have everything back together and running, but I can’t seem to figure out why the car keeps overheating. When I run the heater, it gets hot as the car gets up to temperature. But once up to temp (12’ O’clock) and the radiator fans kick on, the air gets cold and the temp needle starts to creep up until the overheat warning comes on. At this point there are bubbles non stop in the expansion tank for several minutes, sometimes coolant comes out of the bottom of the tank. There is clicking which sounds like it is coming from the cap.

I pulled the top heater core line and let the coolant come out of the bleeder hole, but I can’t figure this out. I even replaced the thermostat thinking it may be stuck closed (which was a nightmare with that spring!!), but no change.
I triple checked all of the lines to the top of the engine so i’m pretty confident they are all on correctly. The only other issue I’m getting is a loud, almost whistling sound at all RPM’s. I think I have it narrowed down to a bad PCV valve.

Any thoughts or similar experiences? Thanks!

#2

Any ideas on this issue? I have tried squeezing the coolant tube, opened the heater hose bleeder hole. Coolant sprays out. I can’t find a leak, other than a noisy PCV valve that needs replaced. I’ve drained and replaced the thermostat, no change. Would a thermostat that’s stuck closed cause these symptoms?

Thanks!

#3

I’m not 100% sure but I believe if it’s closed there shouldn’t be any coolant in the upper radiator hose.

#4

Sorry usually me or jimmy will chime in.

have you checked your rad to see if it flows well and there isnt possible debrits in it. If you have an open stat the car usually wont get up to temp. There is a chance that the water pump might be not working well.

If you can check the coolant system pressure with an approperate gauge that is a good start to make sure the coolant is actually flowing properly. You can check this the risky way by leaving the coolant res a little on the low side and once the car is up to temp slowly and I mean slowly open the cap on the res dont actually open the cap all the way just enough to see if the system has pressure.

If you drive the car with the heat on will the temp go down. And lastly check the oil just to make sure there is no coolant in the oil. Its not likely but a bad head gasket will cause that issue as well. But its very very very rare to ever see a bad headgasket

#5

Justin, I haven’t been able to get time to read or post very much lately. Today is an odd moment because I am waiting to get a replacement Note7 so my phone doesn’t catch fire or explode.

kick3points, drive the car around where you live, when you get close to operating temp then pull back in your driveway, and watch the coolant gauge for 5 minutes with the engine running at idle. Does it overheat or not? I have had a few water pumps fail on 1.8Ts like that. It would only overheat while driving but at idle it was fine. Never seen a water pump fail on a BHF 4.2 but there is a first for everything.

I might also try backwards flushing the radiators and side heat exchangers with a garden hose. Disconnect the lines and flow water through the radiator/heat exchangers backwards of flow. If you are not sure which way the coolant flows then do it both ways. That should push any crap that is stuck in them out. I do it all the time with heater cores, which are in effect are radiators that Audi blows air past to heat up the cabin.

Justin does bring up a good point about checking for oil in the coolant. Open the coolant tank cap and look for milkshake brown colored coolant on the bottom of the cap and flowing around inside in the tank. In my experience it is more likely that the oil cooler fails than a head gasket but still worth looking for oil in the coolant.

#6

Thanks for the info guys. I’ll start checking the items mentioned. I’ve actually only started the engine in the garage, so it’s overheating while at idle. I didn’t take it out for a drive yet since it started overheating once it warms up.

I had no problems with overheating prior to replacing the engine, its the same radiator and water pump. I’ve searched all over and there are lots of posts talking about an air bubble/pocket that is difficult to work through. I’ll def. check the oil for coolant, and I’ll do the pressure testing as well.

One thing I didn’t mention is that when I pull the heater hose back to expose the bleeder hole, the coolant does seem to have good pressure, as it sprays almost up to the hood at idle. Is this the best way to bleed the system?

#7

The best thing to do is to make sure you have hot air blowing through the vents. That shows that the coolant is getting past the heater core.

After that the best place to vent the system would be at the heater core where the hose actually has a small weep hole. Or you can just leave the cap off the coolant tank over night. That generally works for me.

#8

Well I figured out the problem. I was looking at the old engine I pulled and noticed the item in the pic. I remember the new engine just having one of those just sitting on it when it arrived. I followed the manual when installing everything, BUT the water pump. So I missed it!! So after a couple weeks of chasing this down I finally have the answer. Thanks for all the help guys.

http://i87.photobucket.com/albums/k150/kick3pts/Mobile%20Uploads/C16094DD-7261-4F71-A2AE-B4EBAD0291E6.jpg

#9

LOL well that would do it. If you dont have the drive shaft your not going to get a lot of drive. let us know how it all turns out after you get a few miles back on the car.