Ryan'sAudiA4

Okay, changed the thermostat, and coolant temp sensor. Car runs great downhill, flat ground and little hills but once I get to a steep hill or grade, it'll get half way up the hill with no problems, then it'll slightly overheat, and the coolant will fill the entire reservoir with coolant and bubble in the reservoir for about 5 minutes, then it'll drop below the minimum line and go back down to half. And then its smooth sailing until I go back up a hill. I've bled the system using the hole on the passenger heater hose and with the cap off, so don't think its any air in the system. Heat is good. And the radiator fan is always running, even from a dead cold in 30degree weather at 6 am. Any help please. Really need to figure this out quickly so I can get it fixed. I'm new to this forum and new to cars so don't know much. Just need some good honest help. Thank you.

David.Norton

Welcome Ryan;
A little hard to tell without seeing it, but it sounds like your system is not going under pressure, so either there is still air trapped in the system, or you have a leak, letting the system boil. I've seen split hoses, cracked tanks, and bad caps cause problems like this. I wouldn't just start changing parts, that can get expensive fast, start by using a good light to just look for the leak, getting the car up to temperature before you start can force the leak, making it easier to find. Good luck with it.

Ryan'sAudiA4

Well I know I don't have any leaks. Only leak its had since I owned it was the first, and I changed the radiator cap couple months ago. Do you think all these overheating and getting hot could have ruined the new cap in anyway? Thanks alot!

jseklund

Is this a 2.8 or a 1.8T?

How do you know you don't have any coolant leaks? My first thought was that you have an opening in the system that is allowing the coolant to boil...

Ryan'sAudiA4

It's the 1.8t and I've laid down cardboard, paper, everytime I drive it to see if I start leaking. When I first bought it, I had a crack in the plastic piece where the temp sensor plugs in, but changed that and haven't had any problems with the car until this.

David.Norton

I would suggest you look for a split hose, I've had them so that they would only open under load, there wouldn't be any leak once I stopped it or under idle. Also, I hate to mention it because it can get expensive fast, but have you checked your oil for coolant, or does the car have white smoke, because it could be leaking internal to the engine.

jseklund

Ummm...the temp sensor plugs into a metal pipe....it is green? Are we talking the same part?

Ryan'sAudiA4

What's the easiest way to check for split hoses? And doesn't smoke and oil is clean. And I'm not sure. Mine is black and plastic? Lol

jseklund

Do you have the plastic engine pan under your car still? The coolant could be collecting in the pan. There is a green sensor in the coolant pipe at the top of the engine. Typically the seal fails and coolant comes out....often under pressure...when the engine is warm.

If the coolant is warm coming out of the heater core, your heat works, and the coolant is boiling, I think that is a good indicator that the coolant is moving through the engine properly, but you have a leak preventing the coolant from pressurizing.

All of the rubber hoses that have hot coolant in them can be gently stretched and compressed to see if cracks open.

You can also use an air confessor with a blower nozzle to see if the system holds pressure, but keep the pressure as low as you can ...5-10 PSI.

David.Norton

Run it up to temperature so that it is starting to overheat, pull it over, pop the hood, and with a good light look under the hood for steam jets (leave the engine on). They don't have to be big to prevent the system going under pressure.