2003 A4 1.8t quattro. 156k miles. head gasket blew on old motor at 100k or so, had a new motor put in with 60k on it, had a new timing belt and water pump put on that motor. ran fine for about 50k, now having coolant issues. recently had the coolant light come on, and the level was pretty low so i added as i have before. i had not checked the level in months. since adding, i get the "COOLANT" warning with the thermometer, and my temp gauge does crazy stuff. when i turn the key to ON without starting the car, my temperature needle maxes out. when i start and run the car, the top radiator hose gets really hot and the bottom one doesnt change. do i have a blockage? or did my new water pump already go? when i crack the bolt on the hard line, some air bubbly coolant sputters out at pressure, there is definitely pressure in the system. any input is greatly appreciated! thanks!

 

temperature gauge needle will occasionally drop down to half, or zero, then shoot back up to full where it sits most of the time. coolant warning will go away for a few moments, then come back, then go away for a few moments. i suspected air bubbles. tried "burping" by crackign the bolt on the hard line atop the engine and squeexzing the rubber hoses. doesn't seem to have changed anything.

 

to give more context, i have driven it around 20 miles at a time in this state, stopping every few miles to make sure there was no steam or anything. i WILL say i have sort of "smelled hot" a couple times since this started happening, but never a lick of steam. thanks for reading! and please let me know if any other information ic ould offer could help narrow down the problem. thanks again!

 

Could be the coolant temp sensor flaking out. However, I suspect there is still some air in the coolant system. Also look for possible small leaks on either end of the radiator where the plastic reservoirs meet the aluminum cooling cores. These can leak allowing air in and preventing the coolant system from pressurizing properly. The low coolant light is controlled by a float in the reservoir where your fill the cooling system. It sounds like it's burping coolant in and out which also means there is still lots of air in the system.

 

thanks for your reply! how do i go about burp[ing it properly? run it with the blue cap off? run it and keep occasionally cracking the bolt on top of the hard line thats on top of the engine? thanks!

 

I've had good success in filling the coolant reservoir with the bleeder open. Fill it till it's about ready to overflow. Gently squeeze the one of the radiator hoses to push the air out. It should pull some of the coolant in when you release it. You may have to do this a few times to get all the air out. Hell, sometimes I'll pinch off the overflow pipe on the reservoir and give a little mouth to mouth resuscitation with someone watching the bleeder hole ready to close it when coolant starts running out. It's really love to get one of the vacuum bleeder kits for coolant systems though.

 

thanks dave! should i be adding coolant and squeezing the tube with the engine running or off? thanks! also, which tube should i squeeze! im squeezing the fatter one that goes up top on the reservoir, bubbles seem to be coming out but sucking right back in. should i be pinching the overflow hose shut while doing this? thanks and sorry for the questions, i want to make sure im doing this right.

thanks again for all help!

steve

 

also if you wouldnt mind explaining in a little more detail your mouth to mouth technique, id happily try anything to get rid of this issue. its very unnerving not knowing if your engine is actually overheating or not. i ride it on the highway and on back roads and the temperature shoots from the center to maximum to center to maximum, each time it goes back to center, the COOLANT warning goes away until it spikes again.

 

When squeezing the hose (any of them really), if you get some coolant to come out, you shouldn't release the grip on the hose until you've closed the bleeder or it will suck air back in.

The mouth to mouth technique is not really a "recommended" thing.. LOL but.. pinching off the small hose that directs overflow coolant to the ground in the event of an over pressure situation helps you pressurize the reservoir much easier. Some of the newer types don't have this feature though. Anyway, while the bleeder is open and someone right there at it to quickly close it when coolant starts to flow out, you pressurize the reservoir by forcing air into it like you could be giving CPR to someone. It really doesn't take much pressure to get the coolant coming out. It really only takes just a little bit or air in these things to cause the issue.

Some of these things are harder to bleed than others for some reason. You could take it to a shop that has a vacuum system to refill the coolant. Preferably a reputable German Car shop that is familiar with VW/Audi.

 

ok cool, thanks! now should i be adding coolant and squeezing with the car running or off? thanks again man!