PDA

View Full Version : Slowly Overheating...another coolant dilemma



Elicit4orce
10-28-2012, 06:48 PM
Hey all,

I have a 98 Audi A4 1.8t (automatic) that has recently started to slowly overheat.
Here is the history:

Did a timing belt/waterpump change with thermostat 6 months ago.
Has a slow leak on the back of the engine where the coolant flange is located, I often top off with G12 coolant time to time until i can fix that issue.

2 days ago, right after i recently change my fuel pump (it stopped working)... I noticed that the Coolant temp. Gauge would slowly rise more towards (Hot).
I opened the hood and saw that the Auxilary fan was not turning on. I double checked to see if it would work with the A/C, and it DID! (it also turns on when I put the heat on, and the heater works as well).
I instantly think its the Thermo Switch located right above the lower radiator hose. I go under to feel the lower radiator hose and its just semi cold/warm. I
climb back up and feel the top radiator hose and its hot. I think Bingo! it has to be the Thermostat (even though i changed it 6 months ago) but it can go faulty right?
I used an old version of Vag-Com to check the temperature of the Coolant and it stays at 91 degrees ( I forget if its F or Celsius). So i figure that the thermostat is closed shut and not allow any circulation which doesn't allow the thermo switch to activate the auxiliary fan to actually go on.

I did the Thermostat change today and even tried to fix the coolant flange at the same time (someone put massive amount of gasket maker around the flange so it has leaked before). I put it all back together and still the problem is unresolved. I might have to double up on the gasket maker on the flange because need to save up on new Coolant pipe. My main concern is the slow overheating issue. What other possibilities are there?

*I dont see any coolant circulation since the return hose is not spitting coolant back into the reservoir
*Upper coolant hose feels hot when the engine is hot, lower radiator hose feels semi warm
*auxilary fan not turning on ( I see the Vag-Com coolant temp stays at 91 Degrees).


Please help, only car I use for work and school.

Thanks

bps4
10-28-2012, 07:26 PM
buy an infrared thermometer gun, they are pretty cheap and will hep guide you to exactly what is faulty CTS might just be bad

Elicit4orce
10-29-2012, 10:38 AM
Coolant Temp Sensor seems fine, If it wasn't... wouldn't the coolant gauge not be working at all or give me inaccurate readings?
I also thought about the Thermo sensor on the radiator but realized it will only activate if it reaches a certain temp like 91 degrees. However,
I feel the lower radiator hose is only luke warm while the top radiator hose is HOT. I am looking at the reservoir and i don't see any circulation going...
I already changed thermostat and that didn't work. I tried bleeding the coolant system and noticed no bubbles coming out for a good 10 minutes while leaving the car on idle
(I dont even think it was warming up at all).

bps4
10-29-2012, 11:03 AM
How do you know it is giving you accurate readings? The aux fan comes on at specified temperatures based on the switch on the lower rad hose. Your FCM and that aux fan are both good based on the AC test you did. It's either that aux fan switch on the lower radiator hose is bad, or maybe your radiator is clogged? That's why i suggested the IR gun, measure the temp at the lower rad hose and see if that AUX fan should be coming on based on the thresholds. You would have your answer.

TheKid84
10-29-2012, 11:18 AM
i will say 80% is the water pump, check it out , the plastic impeller cracks and starts to slip on the metal.. If you want more help let me know...

Elicit4orce
10-29-2012, 02:25 PM
well the coolant temp gauge rises slowly as it should with the temp. on idle and goes higher when driving which is close to the feel of the engine being hot.
I will look for my Thermo gun asap, and check the temp on the radiator hoses.
How about the the coolant circulation? Am I wrong that looking at the reservoir where the small hose connecting to the pipe is suppose to have some coolant flowing back into the reservoir?
I will try to drain the coolant again and see if the Radiator is clogged (which i also replaced 6 months ago). what other area can be clogged and what causes this?

Thanks for your help bps4

Elicit4orce
10-29-2012, 02:26 PM
TheKid84 - I replaced the water pump 6 months ago as well with the timing belt... bought the kit from Blauparts.com

bps4
10-29-2012, 02:46 PM
well the coolant temp gauge rises slowly as it should with the temp. on idle and goes higher when driving which is close to the feel of the engine being hot.
I will look for my Thermo gun asap, and check the temp on the radiator hoses.
How about the the coolant circulation? Am I wrong that looking at the reservoir where the small hose connecting to the pipe is suppose to have some coolant flowing back into the reservoir?
I will try to drain the coolant again and see if the Radiator is clogged (which i also replaced 6 months ago). what other area can be clogged and what causes this?

Thanks for your help bps4

I'd focus on the functioning of the elements of the cooling system otherwise you might go crazy with guesswork. These are the thresholds for that thremoswitch on the lower rad hose. I'd be interested to know what your IR gun reads as compared with what VAG says.

13 - Radiator fan thermoswitch (-F18-), 35 Nm For electric fan
Switching temperatures: Stage 1
on: 92...97 C
off: 84...91 C
Switching temperatures: Stage 2
on: 99...105 C
off: 91...98 C

When you said: *auxilary fan not turning on ( I see the Vag-Com coolant temp stays at 91 Degrees).

Did this include when the needle was past the middle? I don't think the aux fan switch would "care" either way since it operates and sends signals on its own.

Elicit4orce
10-29-2012, 05:04 PM
ok so im on VAG COM again reading about 94 degree Celsius... the needle is on the Line right before the "Big H"... the 6th line out of 7.
I did a IR gun reading which shows the following:

Top radiator hose is showing about 160 degree F
Bottom Radiator hose shows about 115 Degree F

Stage 1 fan didn't turn on at all...

bps4
10-29-2012, 05:29 PM
ok so im on VAG COM again reading about 94 degree Celsius... the needle is on the Line right before the "Big H"... the 6th line out of 7.
I did a IR gun reading which shows the following:

Top radiator hose is showing about 160 degree F
Bottom Radiator hose shows about 115 Degree F

Stage 1 fan didn't turn on at all...

Just to clarify your gun was on Fahrenheit? Also do you have heat in the cabin?

bps4
10-29-2012, 05:50 PM
Even though you just changed it, I'd say your thermostat is stuck closed

This is from the Audi B5 S4 self study guide, I'm sure it's not going to be too far off in theory:

When the coolant thermostat is closed, the coolant flows back to the coolant pump along the short-circuit line as well as the heat exchanger.
When the coolant thermostat is open, the coolant flows back to the coolant thermostat through the radiator (primary flow) or through the oil cooler and expansion tank (secondary
flow).

It seems like coolant is not flowing through the radiator in your case based on the difference between the VAG reading and what you are measuring with the gun. The stuck thermostat will cause you to overheat pretty quickly since there is no means of cooling. I think you said you already replaced the t-stat though?

Elicit4orce
10-29-2012, 07:08 PM
So i just flushed out the radiator by disconnecting the top hose from the coolant pipe and the lower hose from the housing of the thermostat. My pressure water hose went through well so no clogged radiator. I then used the same hose and left it connected to the coolant pipe while leaving the drain right next to the thermostat housing open, pressured water went through...

Yes the gun is used in Fahrenheit. I do have heat flowing through my cabin. Yep, not only was the original thermostat was changed along with the water pump (6 months ago), I changed it again yesterday and still having the same issue. This is very bazaar...

bps4
10-29-2012, 07:24 PM
Would you be able to get a coolant flow diagram for your engine? They have something like that for the b5 s4 called a self study guide. That might help tell you where there could be some kind of an issue with flow in the system by measuring temp at a few different points in the system. If you are seeing very different temperature readings like you are, it seems like something isn't flowing correctly.

Elicit4orce
10-29-2012, 08:46 PM
im going to try and test the thermostat that i replaced on a pot to see if it opens up at certain temperature.
Now I am also thinking if improper ratio of 50/50 coolant with distilled water could affect thermostat to no open but i could be over thinking it.
ima try to find that diagram on my service manual

TheKid84
10-30-2012, 12:05 AM
TheKid84 - I replaced the water pump 6 months ago as well with the timing belt... bought the kit from Blauparts.com

woops sorry for that :] I missed that line with you replacing the water pump etc.

Elicit4orce
10-30-2012, 07:34 AM
Its cool, I should still see if the water pump impeller is spinning at all through the thermostat hole. Like i said, this problem is oddly new to me.

Elicit4orce
10-31-2012, 12:13 PM
So the good news is i don't have it overheating anymore, bad news is that the problem is still present only when i leave the thermostat installed.
I saw the metal impeller spin through the thermostat/draining hole (water pump is good). I thought if I bled the system that it would go away but didn't...
I connected the coolant lines without the thermostat and i see a good flow and obviously the upper and lower radiator hoses has the same temperature going (coolant temp. gauge stays normal). However, when just idling, I saw the coolant temp. gauge go one line above normal... and I didn't see the auxiliary fan turn on at all. That would tell me that the temp switch or even the electrical line that goes to it is fault? wouldn't that be mentioned on Vag -COM if short ?

bps4
10-31-2012, 12:18 PM
So the good news is i don't have it overheating anymore, bad news is that the problem is still present only when i leave the thermostat installed.
I saw the metal impeller spin through the thermostat/draining hole (water pump is good). I thought if I bled the system that it would go away but didn't...
I connected the coolant lines without the thermostat and i see a good flow and obviously the upper and lower radiator hoses has the same temperature going (coolant temp. gauge stays normal). However, when just idling, I saw the coolant temp. gauge go one line above normal... and I didn't see the auxiliary fan turn on at all. That would tell me that the temp switch or even the electrical line that goes to it is fault? wouldn't that be mentioned on Vag -COM if short ?

aux fan switch is mechanical only, it doesn't read in VAG. If you turn your AC on and get the aux fan spinning, that aux fan switch is just bad

Elicit4orce
10-31-2012, 12:59 PM
So what I am going to do is buy the switch and flush the system. I have a feeling sediments are clogging the thermostat when it opens...
I will attempt this weekend and try to buy the switch on autohausaz.com

*we are talking about the same fan right? Isn't the aux fan the one closest to the air filter and connected by wire only? Not sure
what you mean by mechanical only, but I understand that Vag-com wont read it out...just the fan will