Jeff928S4

1989 S4

Had a coolant leak at the water manifold. Took it to the shop where they replaced the thermostat, o-rings, water manifold gaskets, etc.

Got the car back and drove it.....noticed it was heating up a tad higher than normal; also noticed that the coolant level had dropped a inch in the expansion tank. Topped it up and started doing some hose burping. Burped down about another inch or two out of the expansion tank. Topped it back up.

Drove it the next day and noticed it was down another inch in the expansion tank. Back to burping. The lower rad hose felt "empty" - very easy to squeeze. Burped another inch or two out of the expansion tank. Topped it up again.

Now, the lower hose seems to be more rigid and is heating up and the car warmed up to it normal level. **Note - fans are turning on as required when car gets to it operating temp**.

Now, this morning, I go out and I have no heat (had heat the night before). Car is fully warmed up, but blowing cold air. As it warms up, it runs a wee bit more hot than normal again. (Before, the car would max out at just below the third white line.....never went above it. Now, it gets up to the line and juuuuust about goes past it, then the fans kick in and it goes down.)

I suspect the shop did not re-fill the coolant correctly. After all my "burping", could there still be enough air in the system to make it run a bit more hot and have it not blow cold air?

Garth S

Jeff,
Should the heater valve fail, it fails wide open = lots of heat ( valve located under the air box) .... so that's not the problem .... nor is it likely an airlock, as you've already had heat: IIRC, you recently posted re. a knocking noise under the dash.
Wally gave you excellent direction as to how to rectify that ( orange vac line, etc ... for it sounded as if the comb flap has a defective vacuum pot). Depending on what action you took there, I suspect that you have the wrong flap closed = no heat.
As for trapped air, if you think some is still present, park the car facing an incline: open the top thermo sensor on the water bridge or the 1/2" hose on the rad as mentioned previously - and assure that there are no bubbles in the escaping coolant ( cold to warm engine - NOT hot). If by chance there is a lot of air ( and BTW, the heater valve must be wide open when air bleeding is done), that could be the problem. However, I'm speculating that they are separate issues ....
To avoid a third, check for any coolant leaks ...

Jeff928S4

I do suspect the thermostat to be working, as my fans turn on etc.

Jeff928S4

Garth, I just ran outside and located the orange hose Wally suggested I cut and plug.

Now, my question is, will this hose end up being replaced when the comb is fixed? Once I cut it and plug it, does it stay that way?

Just checking before I go snipping.

Jeff928S4

I just ran out again and did the "look in the center vents to see if the comb is flapping" thing (as per Wally's instructions) and did not see any movement to accompany the "flapping" sound (even though the noise is coming directly from the area behind the center vent).

I did not cut the orange hose.

Running out now to unscrew the temp sensor to check for air.......

Jeff928S4

I just opened the temp sensor on the right (the side closest to the drivers side) and it bubbled like an opened bottle of Chapagne.

I appear to be leak-free. Garth, I hosed the car down yesterday with garden hose to remove all old, spilled coolant, as you said and no "new" coolant is present.

I am now down another inch on the expansion tank......and the hoses feel "empty" again. Must be a ton o' air in there!

Could the air be "making its rounds"? Meaning, could I have had heat last night and today the air made its way to the heater core? I did do a lot of burping last night after shutdown.....maybe I moved the air?

Garth S

Jeff,
Right .. don't cut anything just yet! If you found air once, repeat after a brief run until you run out of 'champagne' ...
So - why was air trapped in the system? As Borland said, the design is self bleeding; however, that is not always the case - even when the thermostat is installed correctly ( they do not all have air bleed holes - although a 1/8" drill will fix that!). Continue until the coolant level is stable in the expansion tank - although you should be very close, if not already there.
If you keep getting 'air' in abundance, then there is another issue which we need not discuss just yet ....
As for the heater valve, you can watch the actuator arm move when the heat control lever is moved: no vac = open = heat. Touch the firewall side of the heater hose - if hot when heat is called for and no cabin heat available, then there is a flap issue.

Jeff928S4

Don't scare a fella like that!!

Going for a quick run now and will check that hose once the car is hot and report back! (I suspect the hose I am looking for will be around the Hot Water Valve area, no?).

Jeff928S4

Just got back from a quick trip and the heat has returned.....................sort of.

The temp out of the vents got a tad warmer as I drove, but I also noticed that the temp went higher as the revs went up. If I held it at 3000 rpms, it was fully hot......but as soon as I left off the gas, the temp dropped again.

Now, with my limited knowledge of these cars to date, can I assume that this means either:

1. The revs are related to vacuum and the higher the revs, the better the vacuum, which = better heat?

or

2. The revs are related to coolant flow and the increased flow raises the heat?

or

3. Put the keys down, step away from the car.......I have no clue what I'm talking about.

or

4. The right answer (Insert here ___________________).

Garth S

I kinda like #3 ..

Was the thermostat installed first .... and the O-ring placed on top? tres important!
Also, the rear t-stat seal was replaced - yes?
Anyway, the 928 should readily achieve operating temp and sustain it regardless of idle, WOT, winter, summer, etc. If the t-stat is either not opening correctly (even though it is new), or is not installed correctly .... correct coolant flow will be comprimised.

Jeff928S4

Yes, I assume the thermostat was installed correctly.....I printed out a blow-up of the entire water manifold, thermostat housing, etc for them to use and I had to show him that the large "O-ring" was the right one to put infront of the thermostat (the older ring had formed to the shape of the housing). The ribbed seal behind the thermostat was also replaced.

I did a seach on the temp being related to engine speed and found little to work with. Could air in the system be causing the change in temp of the heat?

Bill Ball

The heater box should get flow regardless of the T-stat installation. It's on a loop that comes out of the rear of the block and is not controlled by the T-stat in the water bridge. Somebody correct me if this is wrong. And the failure mode of the heater contol valve is heat on. So, other than it being colder than H in your part of the world, I'm not sure what is happening. You have bled enough air, I would think, but judging from the falling water levels, maybe not. You have shown air in the lines. Maybe more. The other bad possibility is a failing water pump, such as a loose impeller that is only effective at high RPM. Strange coincidence for a water bridge rehab.

Bill Ball

Also, the lower radiator hose will be flaccid at first and will not fill until the T-stat closes off the bypass. After that it should get really hot and as hard as a pipe. If it is only warm and not real firm, then the T-stat OR water pump is not doing its job. Get your leather gloves out and run the car, when the fans come on, the hose should get hot and hard.

Jeff928S4

True.....but hopefully it is NOT a strange coincidence.

There is definately some air still in there, I can feel it in the hoses. When I squeeze them, I can hear the coolant moving......especially in the lower hose - and it was quite evident when I opened up that Temp sensor that air was trying to get out.

I'm taking it back to the shop tomorrow morning and have them try and get the air out - I'll suggest re-filling it with the upper return hose on the rad (the 'lil one) open. That should help.

Bill Ball

Yes, you could still have gobs of compressible air in the system. That would be consistent with the symptoms. I've never had much of an issue getting the air out. A bunch of firm squeezes on the lower and upper hoses after the fans comes on usually drives it out to the overflow. Anyway, if the hoses do not get real firm and hot after they assure all the air is expelled, then there is another issue.