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  #1  
Old 03-07-2002, 08:45 PM
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Question 126 Windshield Defroster Heat Exchanger ?

1987 300SDL loosing coolant slowly but getting worse, smell of coolant in the passenger compartment, slight hissing sound heard immediately after shutdown, coolant dripping under car after shutdown. Can't have this aluminum head overheating!
Quick check of monovalve area shows no leaks. I assume that my heater core has sprung a leak.
You know where that is. Takes almost a day to remove the underdash parts and ashtray, radio, center console, upper ( this upper was stuck something fierce and took hours of very careful pulling and prying to get loose without breakage) and lower wood switch panels to get access to the heater /AC box. I was eventually able to reach into the box where I find it dry! I find and disconnect the drain from the box and its dry! What the *%@! ?

I stop where Iím at and crawl under the car. Remove the panels and start searching for the origin of the leak. Looks like itís coming from above the tranny. While I'm laying on my back a drop of coolant lands on my arm! A thorough search leads me to a drain emptying into the passenger wheel well which partially empties onto the plastic belly panel. This drain empties the windshield wiper motor/mechanism bay just under the windshield front.

Remove the wiper arms the foam seal strip and the plastic grating and I find fresh coolant in the bay area draining towards the passenger drain and a large cutout in the center. a close examination shows fresh coolant on a small 1/4 inch hose coming from a fitting just below the windshield. I replace the battery and start her up. I can observe what appears to be a slow leak from the fitting at the upper end of the hose with coolant running down to the lower end where this short (5") hose attaches to a hard pipe. I watch for five minutes where it drips steady with the engine running.

I shut down the engine and I'm looking at the area when al of a sudden I see a small jet of coolant shooting from under the edge of the windshield back towards the firewall! This creates a steady flow of coolant running out of the wheel well drain and down over the tranny. I get a small mirror and look up under the windshield edge where I can see a small hole corroded into the flat bottom side of the defroster heat exchanger. It appears that immediately after shutdown the coolant in the block gets hotter without water pump flow and pressure increases pushing the expanding coolant out of this hole. I had already noticed this post shutdown phenomena when I watched the coolant reservoir fill up right after a shut down.

Does anyone know if this failed heat exchanger can be replaced without removing the dash or windshield? If so how? It looks like a large, thin, flat sandwich where the coolant is inside. It has an inlet and an outlet formed into its forward bottom edge. The inlet is connected to the small fitting at the bottom of the monovalve and the outlet is connected via a small piece of hose to a hard return pipe leading into the engine compartment.

It looks like I will just bypass the heat exchanger for now but I'd like to get it fixed right as I will assume that the defroster efficiency with be reduced without it.

Any experiences or opinions are welcome and appreciated. Thanks.
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Old 03-07-2002, 08:58 PM
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Bb,

That plate is used, I believe, to melt ice/snowaccumilations by the wipers.

I've replaced mine by the manual. Remove the wiper motor and linkage assy. & then slide it out. Part of the plastic trim/cover at the base of the windshield was also removed if I remember correctly. I believe the plate is slid down and toward the driver's side of the opening to allow removal.

If anyone is going to keep these cars and do some work on them shop manuals are a prudent investment.

The switch of plates will probably require about 1 1/2 hours.
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Old 03-07-2002, 09:56 PM
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Thumbs up Removal!

Thank you for the good news! It appeared that it would be accessible via the method you've outlined. Although with the mild winter we've been having here I'll be able to do this at my leisure and I will simply bypass it for the immediate future.

As for you advice regarding the manuals I concur. I have not been able to find or purchase anything except the engine manual in print so far as these manuals are no longer in print nor available from MBUSA. I have obtained a collection of manuals on CD but a rather lengthily search has been fruitless for me so far.

If you by chance can recall which manual this information is in or the numerical job code for the procedure I would appreciate any info, then I could then go straight to the appropriate PDF file on my CD. If you can recall how the white plastic clips holding this part are released that would be very interesting also! Thanks again.
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Old 03-07-2002, 10:14 PM
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BillyBob:
Found the work instructions on the MB disc. Op code is 83-142.
Go into Climate Control Manual, click on ACC Section 1: Heating Ventilation and Air Conditioning, you'll find it in there.
Gilly
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Old 03-07-2002, 10:29 PM
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Bb,

Service manual

Automatic climate control

Model 126

83-142 and 83-860

Clip info covered in pic in 83-142.

Every now and then these manuals show up on E Bay. I'm currently searching for a 560 engine manual if you happen to find one.

If you happen to hear of anyone searching for a good 300 SDL, one of mine is now for sale.
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Old 03-07-2002, 11:19 PM
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Thumbs up Thanks!

Thank you very much, gentlemen. I appreciate your time, experience, and effort.

I will keep an eye out for that engine manual Howard, and for future reference what year is it and what is the engine model number?

P. S. regarding your 300SDL thanks for the offer but my wife tells me I've got all I can handle for the immedate future; but there does seem to be at least one or two folks in the diesel forum that have expressed an interest in this model recently. Turbodiesel is one I believe. You could give him a shout.

Last edited by Billybob; 03-07-2002 at 11:25 PM.
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Old 09-22-2007, 04:30 PM
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is that the right item? I'm going to be checking this while the false-bulkhead is removed from the car.




I notice a slight coolant smell (smell like old people, really.) along with the release of pressure after shutdown.
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Old 09-23-2007, 09:31 PM
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Part 110 is the correct item. A five year old thread is still of help!
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  #9  
Old 09-23-2007, 09:38 PM
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bypassed.



I hope it solves the problem - I don't look forward to ripping out the dash.
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Old 09-23-2007, 09:45 PM
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Dash need not be removed. See my 5 yr. old post above. One to 1 1/2 hours to r & r.

If you have no ice/snow buildup a by pass will work fine.
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Old 09-23-2007, 10:03 PM
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Hmm, maybe mine leaks a bit too....on rare occassion I will smell coolant (haven't in a looong time though) I never thought of that one. If I start smelling coolant again I know where I'll be looking!
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  #12  
Old 09-25-2007, 07:38 PM
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Quote:
Originally Posted by Howard Shedd View Post
Dash need not be removed. See my 5 yr. old post above. One to 1 1/2 hours to r & r.

If you have no ice/snow buildup a by pass will work fine.
I'd have to remove it to do the heatercore - if this dosnt work.



we use snowbrushes here - no time to let the car warm up and then drive. I have a feeling I wont miss it
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