littleball_s4

Hello, dear community. I have a problem and I ask for your wise advice.

My 87 S4 blew yet another hose yesterday. I lifted the air filter at the side of the road and repair it (The one from heater valve to heater).

In my way home I realized the hose blew because something was wrong: the car was overheating a little bit (a bit over second white line while cruising).

When I got home, at idle, I heard that both fans were off (despite the temp a bit over the second white line).

This morning I went to check fuses, all ok. When I bridged the airbox temp sensor, and pushed down the hood switch, nothing happened. (It should have started the fans, IIRC). I turned ignition on. With the sensor shorted, only passenger fan kicks, very fast and swiching to fast sometimes.

I've checked visually the fan connector, driver's side. It seems ok, no excessive corrosion in the female contacts.

From here, I will clean the battery terminals and check if I have current on the fan conector. But then I have no idea what to do next if the test, as I expect, is negative.

Questions:

1) What's the easy way (for testing) to force both fans to kick? Like I did, Ignition + bridge in the engine top temp sensor?

2) Next diagnose step? Where do power for the fans come from? Back of the fuse panel? Fan controller (I don't even know where it is)? Is the XVIII relay important in my situation?

Thanks for your help!

ammonman

To test the other fan swap the plug from the running fan to the non-running fan. If the non-running fan now runs the issue is not the fan motors but either the control unit or the final stage amp. The workshop manual has a very good troubleshooting section on the fan/flap system.

Mike

pjg

Good info here:

http://www.928gt.com/T-WallyHVAC.aspx

WallyP

Your car may not be overheating at all. The temperature gauge is not a very precise instrument. A little bit over the second white line may not indicate that the engine is overheating. The engine should run at about 90 deg C. An overheating engine feels very hot and smells very hot.

The cooling system cap should maintain one bar of pressure when the engine is warmed up, and this pressure should not increase when the engine overheats, so the temperature should have very little to do with the failure of the hose.

Each of the fans has its own fuse - #28 and #29. Check these two fuses and their contacts where they plug in very carefully.

Both fans should run at the same time and at the same speeds. Both fans should run when the A/C is operating.

If only one fan runs, you can swap the power connections to the fans. This will immediately tell you whether the problem is the fan or the power to the fan.

The fan controller is under the removable cover on the passenger door sill. The fans are powered thru the fan power unit on the right side of the front valence panel. ("Right" is always driver's right while seated.)

The fans are powered thru the medium-sized red wires on the positive battery terminal.

littleball_s4

Thank you all!

Update.

I cleaned the contacts on the fuses, I cleaned the contacts on the fan and now both fans kick in when I bridge the airbox sensor and turn ignition on. But my happyness didn't last long.

I started the engine, the car warmed up to the second white line. No fans. I went and check the tubes, the top one was warm, but not as hot as the expansion tank. It had water inside, I would say, but warm water, not hot.

Stop engine. Let it cool down a bit. I should have let it run yesterday with the cap open to let all air out, I think. I open the cap and the water start to boil (****). I close it inmediately.

So I let it cool down, repeat with the cap open and pumping the tubes this time. I bridge the sensor and put both fans at full speed from the start. No change. Still the radiator is only warm when the water starts boiling.

Another thing, heater does not work. And another one, when the water boiled, it brings some brown stuff up, greasy, like the stupid thing people put into the coolant when they try to fix a radiator leak.

So this turns into a bad pump/thermostat?

Next steps?

Thanks for helping.

dr bob

With the brown crud, this is an opportunity to put new coolant in after flushing the old crud out.

Assuming that the other hoses are the same age as the one that came apart between the heater valve and the heater core, having the system drained might be the perfect opportunity to put new hoses in.


But to your immediate problem:

When the coolant level gets low and the system is opened to atmosphere, you'll ofetn find that there's an air bubble in the top of the water bridge. This happens to be where the thermostat lives, so the thermostat won't open to allow circulation though the radiator. Same air bubble keeps coolant from the temp sensor so the gauge doesn't necessarily read correctly.

What to do: Fill the coolant reservoir all the way to the top. Start the cool engine, turn the heater on to max temp. No worries about fan speed, just get the temp slider over to the right to get the heater valve open. Set the engine speed at maybe 1500 rpm. As the engine warms, initially the level in the bottle will drop as the pump flls more and more of the system. Keep the reservoir level right at the top. Some will advise you to squeeze the top hose, but I'm not sure it does anything. Can't hurt. Anyway, the faster idle will give a bit more coolant flow and will help push air bubbles out of the bridge.

You can loosen the vent hose on the top of the radiator and burp the air out there too, but ultimately the lower hose won't purge until the thermostat opens. That nipple on the radiator is fragile with age, so use care when you handle it if you decide to follow this step.

After all this, as the engine comes up to thermostat temp, the thermostat will finally open and allow coolant to flow. Fans are operated by a temp sensor bottom front driver's side (on LHD cars) of the radiator, so they won't start until the thermostat allows hot engine coolant to pass through and into the radiator outlet tank where the sensor lives. The fans will start. This is your cue that it's OK to pull the screwdriver out of the throttle linkage and let teh idle fall back to normal.

During this whoe exercise, the coolant in the reservoir will start to expand and run down the drain line, and ultimately it will expand enough to overflow the neck. Good time to put the new coolant reservoir cap on there to mage the mess. Go drive the car normally and get coolant and air separated properly. Let the car cool when you get back, and verify the coolant level in the reservoir, topping up as necessary.

littleball_s4

Thanks for the advice.

I've flushed the coolant many times in the past, I never had this problem.

To be sure, I've followed your instructions precisely. I didn't open the radiator vent.

Temp went up to the second white line, where the coolant starts to boil. Heater was not heating and driver side of the cooler was cold (maybe 5º above ambient). The other side was really hot (I couldn't keep my finger for one second) Fans never started. Heater valve opens and closes properly (opens if I select heat, closes if I select cold).

Reservoir was slightly overflowing during the second half of the test. I noticed the level went down when I rev a bit, so pump must be doing something.

Can the thermostat prevent heater from working? Is it easy to check? Could it be both the radiator and the heater are blocked with the brown ****?

Thanks again!

dr bob

Heater works when the pump is pumping and the heater valve is open, regardless of thermostat position.

You might think about replacing the thermostat since it's relatively simple and inexpensive. That should get it off the possible-causes list, although the likelyhood is low. Replace the seal behind the thermostat at the same time along with the front o-ring.


You can fill the reservoir completely while cold, and loosen each of the two temp sensors in the bridge to get all the air out of the water bridge. Your temp symptoms still point to air in there and no thermostat opening. If the top hose is 'hard" with the engine running and that top hose is hot/bottom hose is cold, the pump would be the cause of that hose being hard and may be moved lower on the possible-causes list.

On the heater non-function, verify that the valve is actually opening. Many of us tie the valve closed for the summer months to keep the heater core from heat-soaking the interior on engine shutdown. Maybe yours is tied closed. It's also tempting to tie it closed if you havre HVAC vacuum problems in the car's history, since the early symptoms list for vacuum leaks includes "heater valve not closing". Fire may have roasted vacuum plumbing and made securing the valve a patch-work solution too. Lots of possibilities there.

littleball_s4

Thanks, I will do tomorrow (it's late here). I'll start with the temp sensors burp, then I'll check Tstat.

Heater valve is ok. I can see it moving when I move the slider to each side. Heater was working ok before all the mess started. I suspect there is a common cause, but I can't think of one, unless the heater is also full of air.

I'll keep you posted, thanks for the help.

Mrmerlin

from the info provided it sounds like either the thermostat is not working or the radiator is clogged.

BUT before you do more you need to get better info.

start by getting an IR gun and get the temps of the radiator inlet and outlet also of the water bridge.

if the inlet to the radiator temps are about 85c then all is good the return hose will be about 5 C less than the top hose.
If your numbers are more than this then
I would do a basic coolant system refresh to include

new heater control valve
new short hose for the valve
new coolant bottle cap ,
2 gallons of fresh coolant
and 2 gallons of distilled water.
a new thermostat
and the rear sealing ring
and the front O ring.


make sure to drain the block prior to installing any of the new coolant
it holds about 2.5 gallons of coolant, drain both sides.

Please report back after testing and replacement of above listed parts

littleball_s4

Hi,

Still struggling.

I measured 91ºC top hose, 44ºbottom hose. Driver side of radiator was cold (couldn't point IR there). I Burped on the sensors. No air there. Not bother to check if it was better.

I Pull T-stat. It was more like a meat ball, a perfect sphere of crud. Clean with tap water, all seals ok, the one of the block a bit hard, but all ok. Test in the kitchen, it opens 9mm in boling water.

Reinstall everything, fill with sensor out, to expel all air, close sensor, follow warm-up procedure. Fans kicks between the two white lines, 81ºC bottom hose, 72ºC top. Heat (fans) cycles one or two mm up and down the temp gauge. ALL SEEM OK! It idles for 10 minutes with correct temperature. I take her for a test drive, all seem ok. I stop to check leaks and let a bit of air out the expansion tank, which have good level. 88-83ºC. I drive another 20 minutes a bit harder, the thing is solid.

Then I go back to my house, and in the last 200m the thing starts to overheat, pass the second white line. I stop, no leaks. Fans are off. 90º top, 70º bottom.
****. I manually set both fans to full power, but at idle the thing keeps overheating. now it's 100ºC in the water bridge, needle is close to redline. I stop the car.

In frustration, I let the car cool down only 15minutes, I take the t-stat out again, meatball again.

So I go to a complete flush. I flush every channel in back and forth ways with a garden hose. I take out like a ton of brown stuff. But, you know, I still think there is plenty inside. The thing sticks to the walls, does not solve in water, the colder you go, the more sticky. Every hose I pull, if I put a finger in it, It comes back brown.

So I think maybe it's good to continue flushing with engine on, maybe for some hours. I pull the temp sensor in the water bridge, let a bit of tap water flow in the expansion tank (it overflows in the sensor) and start the engine. But the water pouring directly in the spark plug cables doesn't please her, so she starts on four cilinders. I stop and let her dry up.

And meanwhile I use the time to type the report.

I can't think in a good way to take all the crud out. The most I take it out from the tstat. But, even if it's true that I clean it in less than 30 minutes now, I don't feel like doing it again and again! The lower bolt (aka bolt from hell) is a quarter turn per second.

Any ideas? Any detergent/additive able to undo this mess? I think no new parts will help until I clean the internals a bit.

Thanks for being there.

fraggle

Time for pro cleaning work it sounds.

What deteriorated in there?? Yuck!

littleball_s4

Nothing, it's Anti-leak "magic" fluid. They did it in my last visit to a workshop, I was really mad on them when I found out. But it was like 3 or 4 years ago, I flushed the system several times since that visit, and didn't find so much. I thought it was long gone, but gone my ***. Maybe the thing is getting old, or my last coolant change made some chemical reaction or god-knows what.

Mrmerlin

I would drain the coolant out then fill with water then add about 4 OZ of TIDE clothes detergent ,
Drive the car for about 20 mins with the heater open to full,
shut off let cool then drive it again for 20 mins then drain it out then flush it.
The tide should wash the rubber hoses insides off,
and also remove any oils that have accumulated.
The only problem with this is that you may wind up with a blown headgasket as the sealant may be plugging a hole in the HGs,
anyway you may also have to replace all of the hoses once the internals are cleared up as once they get oil on them they get weak and can easily slip off the connection points or just burst.
Your radiator also sounds like it may need some work done to it if after the wash cycle the temps dont normalize.

Alan

Actually the only way you can know if the heater valve is OK is to take it out and check its functional operation (flow). That the actuator moves with vacuum is good - but the ball valve linkage may not be good esp. if it was gunked up with the crud.

I think you'll have to take it our to verify flow when it is supposedly open... if no that will at least be an easy fix. maybe worth flushing the heater core in reverse to disloge the crud too...

Alan