Alright.

I bought an 1985 Audi coupe GT with over 200,000 miles on it. It had a bad water pump so it was over heating.

Put in a new water pump, and a new thermostate.
Now it drives fine for a while and then the water alert gauge thing goes off... and the engine gets really hot, way too hot to touch after a short period of time.

Sometimes pressure builds up in the coolent tank, so I have to keep the cap a little loose to let the pressure out.

What can be the cause of it over-heating?

It's not a cracked head, the car doesnt smoke bad at all, and water and oil dont mix anywhere.

also why does water come out the exhaust pipe?

a side note, I was wondering what kind of gas to use? I currently put permium 92 octane gas.
Also whats oil type and a good brand to use?

 

Even if the cooling system is working properly the engine and radiator is going to be hot to touch. The system will also be under pressure 5-15psi depending on the cap and condition. The electronics in old Audi's has a tendency to read anything other than what it is supposed to be. Does the fan turn on, does it cycle? I would check the fan circuit to make sure that it works, maybe even replace the thermo switch with the proper one. I would also use either an infrared or a thermocouple thermometer to get another reading to verify that the gauge is working properly.

Unless the water pump is seized it would not cause over heating. Impellers rarely fall off and I have not heard of any cases. Most of the failures are the result of leaking seal or bearing failure. Probably you have something blocking the passages or the radiator has gone south.

 

yeah the fan does turn on, and it turns on pretty often when I just sit and idle... I was thinking the radiator was dead... I will take the car to an Audi specialist and see whats up.

 

You never want to "keep the cap a little loose to let the pressure out".

Your system is designed to maintain less than 15 PSI, loosening the cap lets you boil out the coolant, when you lose some, the rest becomes less capable of keeping the engine cool.

I don't have the numbers at hand, but water boils at 212 F, 50/50 Antifreeze, maybe 250 F, at 15 PSI, maybe 285 F. If you loosen the cap, steam pockets form in the hottest parts of the engine, expand and force coolant out of the system, less coolant there, more steam pockets force more and more out of the system, till you absolutely o'heat so much the engine wont run and you destroy the engine.

If the pump is punping coolant, and if the fan does cycle on and off, you may need a radiator flush. Core may be crudded up so much that many of the tubes are plugged. Especially possible if the PO had a leak and put in any kind of "stop leak", cruds up a radiator AND a heater core.

Cheers,

George

 

really now? I was told by a few mechanics to leave that cap loose to let out pressure... Where do I get my radiator flashed?

 

He is wrong about keeping the cap lose. I was haveing a ton of problems checking and changing things till I found out it was the cap all the time. Water comeing out of the exhaust pipe is normal as long as it's just a little.

 

As long as air is passing through the radiator and the coolant is circulating, leaving the cap off is not catastrophic unless the cooling system is in bad shape or it’s 110°F and you are in slow traffic. Without the cap you will lower the boiling point and car will steam sooner. I have certainly done it when I had an unexpected leak in the radiator, heater core and when I blew a head gasket. So the mechanics are partially correct. However this is just a temporary fix for small leaks. Also the cap keeps the coolant from violently boiling out after engine shutdown. Also just because you put in a new thermostat doesn't mean that it's %100 good. I have had few occasions when brand new parts were defective. Take it out and drop it boiling water and visually check that it is opening. Also check to make sure that the fan is blowing in the right direction, sometimes previous owners misswire broken connectors. You can also try blowing out the fins of the radiator, you should be able to see through the fins. If you suspect that the radiator is bad just replace it. The aluminum radiators are NOT serviceable, just get a new one, $125 – 200, an OE Vero runs about $160.

 

Just one other thing.

You say the head is not cracked or anything, but that does not mean you dont have a head gasket leak.

I have had that, not enough for coolant, at 10 psi to get into oil galleries, you won't see coolant in the oil, but definitely enough for 200 plus psi of expanding combustion gases to enter the cooling system.

Had it on an Audi diesel, an Olds diesel, a Ford V-8 pickup. None had water in the oil, all blew coolant out of the system after warming up a bit, and violently, at that. Overheat occurred only after they lost too much coolant.

Actually, this is not to say you do NOT have a cracked head, either.

Cheers,

George

 

i have a brand new head gasket on there, so its not leaking anything.

 

From the above, you did not say that.

Blow it down, see what you have.

If you got a leak, that's the way to find it.

If you are just going to come up with new reasons not to do something, like, "I got a new head gasket", how may I help you?

Personally, I cannot.

Cheers,

George