Fintail Heater Core R&R - Mercedes-Benz Forum

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post #1 of 1 (permalink) Old 11-14-2010, 05:22 PM Thread Starter
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Date registered: Nov 2008
Vehicle: 1981 300TD 310k--1966 230 165k--1970 280se 172k
Location: Ohio City, Ohio
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Fintail Heater Core R&R

I just finished this job so I thought I would post my experience to help others taking on this task. My cores were bypassed and I wasn't sure if it was stuck valves or a leaking core. Here's my step by step:

1) Drain off a gallon or so of coolant.

2) Pull the steel crossover tube from heater outlet hoses under the hood and carefully pull the grommets on the firewall that buffer the two hoses. Pull the lower supply hose from tube where it passes through the firewall. Leave the grommet. Remove the ashtray and glove box.

3) Remove the under dash panel. You will see the two valves for each core half. Carefully remove the retaining screws that secure the bowden cable levers after marking their positions on the valve housing.

4) Remove the two levers and cross cable that actuate the up/down diverter flaps. Be careful with the brittle plastic.

5) Unplug the blower fan socket and remove the two screws that hold the male half to the front of the heater core case. Push it into the case so that it clears.

6) There are 4 steel retaining clips that hold the case together. Two are located in the bottom and two in the top. Unsnap the clips using a screwdriver. the bottom ones will fall down but the top ones will stay.

7) Unscrew the 10mm screw at the very top that secures the case front to the underside of the dashboard.

8) Pull the front of the case off. You will see the two cores held snugly in the case and 45 years of debris. Vacuum as much of it as you can.

9) Use or make a tool that can loosen the cotter key clamps that hold the valves to the intermediate hose (between the valves and the manifold). I had to use a hacksaw blade to break them totally loose.

10) Take a small sharp chisel and cut the hoses so it they are free of the valves. Do the same for the top tubes. The cores will not come out with the clamps and hose attached at the top. It's tight, especially the one on the left.

11) You can now pull the cores out. Easier said than done. There is a thin foam surrounding the cores that adhered itself over time to the cases at the very top. I made a tool to grab around the inlet tube at the top and began pulling there and at the valves. Be careful--it is easy to break the solder joint or deform the core where the tubes are joined. I had to use a thin putty knife and a long piece of sharp aluminum to free the foam from the case.

12) You will see that there is a slot in the top of the case allowing you to clear the inlet tube as you pull the cores forward. Once the foam around the cores are broken free of the case, wiggle the core forward and tilt the bottom out and twist to the center and the cores should come out. There is barely enough clearance between them and the bottom of the dash. I probably should have taken the radio out to help this step.

13) Carefully pull the manifold tube out by pushing in on the right side and pulling on the left until it clears the firewall grommet and comes completely out of the car over the trans hump.

14) On the bench, disassemble the valves using the tutorial on the Ponton site. Carefully remove the foam core surround and take the cores and manifold tube to a radiator shop for boiling and pressure testing. I saw that I had a leak at one of the inlet tubes, so I re-soldered both just to be sure. You will need all the strength you can get at this joint to get the cores back in and the new hoses aligned without damaging anything.

15) Completely clean out the case and spray some silicone on the inside surfaces.

16) After rebuilding the valves using the same Ponton tutorial, use the old hoses as a template to cut new ones. 5/8" heater hose works for the outlets and also the valves to manifold. Use 3/4" for the manifold to block connection.

17) Clean all metal hose connections with steel wool or emery paper. Clamp the new hoses to the manifold and the top outlet pipes on the cores. Try to angle the top hoses so the natural curvature of the hoses approximates getting the hose to the middle of the firewall hole and more or less perpendicular to the firewall.

18) I took this opportunity to get some lubricant on the blower motor shaft as a preventative measure. Not sure if it did any good. You can barely get a spray straw to the shaft.

19) Install the manifold tube in reverse of removal. Spray some silicone or grease on the firewall grommet to ease installation.

20) After using electrical tape to re-secure the foam to the cores it's now time to reinstall. I used a dremel to grind out the metal at the end of the slots in the upper case. The hose and clamp will not fit through the slot otherwise. At the factory, they must have installed the cores, then the hose and clamp. Since I was not able to find the little cotter clamps that can be tightened longitudinally to the hose, I saw no other way--there is no possibility of getting a driver in there to tighten the worm clamps. You will also need to position the clamp at about 2 o'clock on the left core and 10 o'clock on the right core to prevent interference with the underside of the dash. Do not rotate the clamps to far "in" or you will hit the buckles that secure the diverter housing to the core case. Be sure to use the proper size clamps. You can't afford any excess material due to the tight clearance.

21) OK, rotate, push, and generally fuss the cores back in. Seat the valves in the hose while you do this (remember to put the clamps on first) and get the top hose to pass through the firewall. Tighten the hose clamps at the valves being sure the cores are completely seated.

22) Resecure the blower socket to the front case. Fit front case. Clip the 4 steel retaining clips at the four corners to hold the front to the case body. Tighten the 10mm bolt at the very top to the dash. Reinstall all levers, plugs and cables.

23) Spray firewall grommets with silicone or coat mating surfaces with a light coat of grease and carefully seat them in the firewall with a dull screwdriver. Reinsert and clamp the crossover tube and the feed hose from the block.

24) Add coolant. Get car to temp and test for heat. Check all connections for leaks. Reinstall underdash panel.

This job wasn't as onerous as it sounds. Time consuming (2-six hour days) and the cuss quotient is pretty high.

Having heat and defrost is a good thing.

1981 300TD--310k miles
1970 280sel--172k miles
1966 230--162k miles
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