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91 Jetta GL [1.8L, AT, A/C, 140k]: Heater core or overpressure?

I was driving to work this morning (temp was in the low 50's and humidity was going up in anticipation of rain) after not having driven the car yesterday.

The car in question is a '91 German-made VW Jetta 1.8L GL with automatic transmission and ~140k on the odometer.

The climate control was set to off (i.e. all the way to the left on both sliders). I noticed some fogginess starting to build up so I shifted to defrost (the fan control was at a 1) while leaving the lower (temperature) slider on the cold end.

Seeing no change in the fogginess, I pushed the temp slider to the hot end (right).

At least I think this is what I did, but I can't recall for sure due to what came next.

Vapor billowed out of all of the vents (most appeared to come from those directly by the windshield) and filled my car to the point that I almost had to stop since I could barely see out.

The vapor at first smelled a bit dusty/musty, but then smelled oh-so-slightly sweet, then seemed to have no smell whatsover (tho' I have to admit to not having the best sense of smell in the world).

After 5 seconds of this, the intensity of vapor trailed off as I was left in a car with all windows fogged.

I flicked the temperature down to the cold end and the windows started to clear.

On the way home, I confirmed that it was definitely putting the bottom slider of the climate control to hot that caused the interior fog bank. It doesn't matter where the top slider is (defrost or just external air).

After running it for about 5 minutes, stopping for 10 minutes to do an errand, then restarting, I noticed a slight fogging again of the windows and slid to defrost and hot. This time, instant vapor and blazing hot output from the vents. Greasy residue left on the windows after the open windows and sunroof cleared out the interior.

All the while the temp gauge read about straight up.

I stopped for about 20 minutes, let the engine cool, to within the low temp (white) zone on the gauge, then put in about a reservoir full of coolant and drove the rest of the way home.

After cooling for a few hours, I noticed that the coolant level had again dropped and there was a bit of coolant on the floor. It was located on the driver's side of center of the car toward the back of the engine compartment... definitely not under the pump.

I looked through Bentley and did what I could in the way of diagnostics.

So, the first thing that occurred to me was that the fan was not coming on and that things were getting overpressured. This happened a few years ago (fan siezed) and blew out my A/C.

I don't know if the radiator fan was coming on, but I ran the Fan/Radiator Thermoswitch tests in section 4.4 of Bentley. The fan's low and high speeds come on appropriately when jumpered.

However, is there a conclusive test for the radiator thermoswitch being bad?

Or does one just replace it to rule it out as a problem?

I tested the after-run switch, and again the fan came on when the black wire was grounded.... and the fan wasn't running otherwise (the engine was several hours cool at this point).

One last thing I could check was the passenger compartment floor.

Sure enough, there were a few splatters and drips of coolant on both interior sides under the dash.

Does this definitely mean heater core?

Or is the core leaking due to being overpressured (from the fan - for example - not coming on)?

I'd definitely like to fix this if I could - or know if I'm in over my head - so any advice would be most appreciated.

Having had my '90 Golf's heater core replaced due to the recall before it took its own life, I have no experience of a heater core going south.

Thanks, Scott

Reply to
s2zeller
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That is a classic case of heater core failure. You have a leaking heater core or hose. It needs to be replaced. I suggest replacing both the core and the hoses as the labor is going to be expensive and no matter which (hose or core) it may be, the other is going to fail as soon as you get it all put back together.

Reply to
Joseph Meehan

matter which

That's what I was afraid of after doing some more research last night.

I also see that the '91 *may* be unofficially covered in the heater core recall (as some folks seem to have gotten it fixed on VW's tab). Any surefire way to get them to fix it (i.e. contact VWoA first)?

Alternatively, are there any step-by-step guides for doing it myself?

Thanks, Scott

Reply to
s2zeller

FYI my GTI is a '91 and it was covered under the recall. Built in 11/90.

Reply to
Matt B.

replacing

myself?

Did you get a notice for it?

I am the original owner and haven't for this car (but did for my '90 Golf). I do have the '91's "birth" certificate at home somewhere. I'll have to dig it out and check.

Thanks, Scott

Reply to
s2zeller

The procedure is you must take it to the dealer first to have them verify it is the core leaking. Then the dealer may call VWoA or give you the number to call.

Reply to
Woodchuck

I don't recall getting a notice (this was like 14 years ago) but I think I had taken it in for its first oil change or something like that and the dealer put in the VIN and found that it needed the core replaced under the recall. also did the fuel line clamp recall too.

Reply to
Matt B.

As a follow-up, it was definitely the heater core.

However, I learned the downside of having a German-made A2.... not covered by the SD recall (even tho' it was manufactured in late 1990).

Thanks, Scott

Reply to
s2zeller

As an addendum...

The kind of weird thing (isn't there always something) was that the service manager said that this would be an easier swap out than they expected and would *only* cost $600 instead of the usual $1000.

Now, when my '90 Mexican-made Golf had the recall done, I do recall it being pretty pricey and difficult (had I had to pay for it).

Anyone know why this newer car would be easier?

They also mentioned having to get an adapter. Are the old cores no longer available?

Thanks, Scott

Reply to
s2zeller

They're charging $100/hour?

Procedures have been officially documented that do not require removal of the dashboard and discharge of the airconditioning system. The swap could take as little as 2 hours, but 4 hours is probably more like it in practice.

Allow 6 to 8 hours if you're doing it yourself using 2 left thumbs.

Adapter? Maybe the high-pressure bypass. That was fitted to the later models in a recall. The valves have a life of about 4 years before they cut off the heater completely in stop-go traffic.

The new cores are the same as in the Mk4 Golf/Jetta/Bora/...

Reply to
Bernd Felsche

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