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Sun Nov 11, 2018 6:28 pm

Removed my heater core for replacement today and found this galvanized steel plate behind the core.

There was about 1/2 lb of bees and debris between this plate and the core. It looks like the plate was at an angle when installed and not hard up against the core, creating a perfect alcove for capturing debris.

What is this plate for?

Sun Nov 11, 2018 6:37 pm

All your answers are here. https://www.thesamba.com/vw/forum/viewtopic.php?t=277650

Sun Nov 11, 2018 6:59 pm

After my heater box rebuild I became convinced it has 2 functions:

1) prevent the oversized heater core from completely overheating the cabin;

2) with blower on full speed, provides enough negative pressure to flip the "flippers" & therefore
limit outside ambient air...especially helpful when defrosting &/or heating in very cold conditions...

My documentation...
1) Fan full speed, plate removed, "flippers" open to ambient air:

2) Fan full speed, plate in place, "flippers" closed due to negative pressure:

<shrug>

- Dave

Sun Nov 11, 2018 7:54 pm

That original thread is a hot mess. A lot of speculation about what the German engineers were thinking without a lot of data.

I'm partially convinced it does have something to do with building advantageous back pressure for blower motor flow, and am going to leave it in blindly because I trust the original designers of the system more than my ability to re-engineer it.

The only issue I see based on my experience is that it does provide a natural catch for debris which builds up impressively over the years.

Mon Nov 12, 2018 10:43 am

Dave
Your pictures look the same to me. Am I not seeing the difference?

Mon Nov 12, 2018 11:42 am

Michael4104 wrote: Dave
Your pictures look the same to me. Am I not seeing the difference?
I didn't see it either at first glance, but look at the angle of the flap at the edge to see the difference in movement- Looking at the flap head-on as it were, didn't show as much as looking at the edge and the amount of gap or movement between the 2 pictures.

Mon Nov 12, 2018 12:54 pm

drj434343 wrote: .... A lot of speculation about what the German engineers were thinking without a lot of data.

I'm partially convinced it does have something to do with building advantageous back pressure for blower motor flow, and am going to leave it in blindly because I trust the original designers of the system more than my ability to re-engineer it.

....

Possibly a little "data".

My 1981 and 1988 both have a Jetta 2.0 engine, the cooling system on each functions fine, but the heat box on the '81 was modified. Regardless.....

The '81 does not have that plate the '88 does.

The heat on the '88 gets significantly hotter and did same with the WBX engine.

Neil.

Tue Nov 13, 2018 10:17 am

Vanagon Nut wrote: drj434343 wrote: .... A lot of speculation about what the German engineers were thinking without a lot of data.

I'm partially convinced it does have something to do with building advantageous back pressure for blower motor flow, and am going to leave it in blindly because I trust the original designers of the system more than my ability to re-engineer it.

....

Possibly a little "data".

My 1981 and 1988 both have a Jetta 2.0 engine, the cooling system on each functions fine, but the heat box on the '81 was modified. Regardless.....

The '81 does not have that plate the '88 does.

The heat on the '88 gets significantly hotter and did same with the WBX engine.

Neil. One or two questions on that, were the Heater Cores Original, was the '81 given a core if it was Air Cooled in original form, and how many miles on each core? That alone could give a vehicle to vehicle difference in terms of heat output. Still, more useful info for the Blocking Plate saga... :wink:

Tue Nov 13, 2018 10:49 am

When I rebuilt my heater box on my 86 modifying air flow and installing a ram air shut off flap, I left that metal block plate off.

It gave off great heat, but I only live in NJ and take trips to Pennsylvania.
These aren't exactly "Cold" areas.

Last Fall we went West, getting into Montana with -9° F temperatures, snow and ice.

That heater could literally roast us out of the Van! Most often I only cracked open the hot water valve and allowed it to trickle in once the cab was warm.
I most often blended in a bit of cold ram air too.

IMHO ........ Leave off the plate, it isn't needed.

Dave

Tue Nov 13, 2018 11:09 am

'Heater cores' - pffft! Have we all gone soft? Just wear a parka and gloves while driving post-September. And with no heater cores, I have never had an interior coolant leak. You can't put a price on that.

The girlfriend says she doesn't like it, but she also didn't like it when the van caught on fire in a cow pasture 300 miles from anywhere. Plenty of heat there, and she still wasn't happy - no pleasing some people.

The cows were friendly though.

Tue Nov 13, 2018 11:50 am

jlrftype7 wrote: Vanagon Nut wrote:

Possibly a little "data".

My 1981 and 1988 both have a Jetta 2.0 engine, the cooling system on each functions fine, but the heat box on the '81 was modified. Regardless.....

The '81 does not have that plate the '88 does.

The heat on the '88 gets significantly hotter and did same with the WBX engine.

Neil. One or two questions on that, were the Heater Cores Original, was the '81 given a core if it was Air Cooled in original form, and how many miles on each core? That alone could give a vehicle to vehicle difference in terms of heat output. Still, more useful info for the Blocking Plate saga... :wink:

I'm assuming the '88 has a stock core and that it's likely original. The PO claimed the van had low miles so in theory, it has just under 100K miles. The heater fan makes rattly-squeaky noises at times, so the heat box likely hasn't been opened.

The '81 was an air cooled van. I installed a new actual VW Vanagon core at time of the engine swap. As a rough guess, the core probably has 100K miles on it.

Both vans use an OE heat control valve and the same coolant routing but the '88 doesn't use the "spider" hose etc. (see below)

Though this was done in early years of my Vanagon ownership (~2008), on my '81, one aspect of the "modified" i referred to was to change the box so it would recirculate cabin air back in and across the core; on the bench, the box actually pulled in cabin air through the side vent holes when the fresh air ram was partially or fully blocked. I never got around to making a control flap at that ram. R&D on that project got stalled so that mod certainly could be a factor in the amount of heat.

Of note, the '81 box is rather crude. Aside from the heater valve control (not on a lever, I'm lazy), it has 2 levers. One controls foot heat and when closed, routes more air to defrost. The other lever controls fresh air inflow which in turn obviously controls heat to feet and defrost.

The water pump on the '81 is the "paddle" type, purported to be less efficient at moving coolant. The '88 has the "volcano" type which is purported to move coolant better. If true, this may only be a factor at low RPM's

I live in a moderate clime so at the time of the engine swap on my '81, just having heat was amazing! It seemed to work fine and did so since then around town and on trips in warmer weather. On a recent trip south in Winter, I found out that the heater was less efficient especially at highway speeds. I don't think the core is at fault but then partially blocking the fresh air ram didn't seem to help.

Since the '81 air cooled box had a fresh air fan, it had provisions for a heater core, but the box is obviously different than WBX and likely diesel Vanagon heat boxes.

So there you have it!

Neil.

some images of the '81 heat box mods starting here:

https://photos.google.com/share/AF1QipPv5FCJYS-g1y...diSm9KWFFR

shows heater core nipple knockouts

not a great pic but shows non OE copper heater core - coolant bottle return manifold on my '88

OE Jetta heater-coolant bottle return junction on my '81. Coolant bottle return hose not really visible but its there.

Wed Jul 23, 2025 11:20 am

Is there a spacer (in the middle) between the baffle plate and the heater core of the heater box? If so, how thick is it and what material is it made of?
Raf

Wed Jul 23, 2025 11:41 am

weekenderraf wrote: Is there a spacer (in the middle) between the baffle plate and the heater core of the heater box? If so, how thick is it and what material is it made of?
Raf
No, it rests next to the core.
Here's a pic of a just opened heater box showing the core, plate and box as they came apart.

P.S. it helps if you keep your question in one place.