Hi guys, my 240D is forced to sit outside in the Pacific NW. As we are into Fall and soon Winter, I've noticed that the changes in temp and the moisture in the air causes massive amounts of condensation to form on the inner trunk surface. The floor of the trunk is dry (I've fixed all the leaks from trunk seal and rear window), but the inner surface of the trunk lid has massive amounts of condensation, likely from the combination of moist air and big swings in temperature throughout the day.

What do you guys do to combat or avoid this?

Thanks,

Packman

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83 240D - 4 speed manual - Manilla Beige
189K miles, Tachometer mod, cool wooden shift knob from PeachParts, CocoMats, Original factory paint, manual windows, manual sunroof. Starting to add AudioWrap to this car too!

I'm in the same boat as you. I'm curious to see what others have to say.

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Ventilation would help. Does your car have vents down low in the trunk? ( the area where the quarter panel meets the well. ) I'd be real tempted to use some small computer muffin fans to keep air moving. To get real tricky, use a humidastat / timer and -or solar panel.

Are you sure you don't have a leak. My antenna grommet was leaking on my car when I bought it. There were a few rust throughs on both sides where the area behind the wheel well meets the back panel.

I didn't notice much until I took out the plastic panels that fit into the wheel wells.

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.

I'm also wondering if you don't have a leak somewhere. I don't have any significant condensation in either of my 240D's, although I definitely have a leaky trunk seal in the '83. A "massive amount" seems only attainable if moisture is getting in somehow.

In addition to the antenna seal, I'd be real suspicious of a leaking tail light. Those can be tricky to find.

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'79 240D

Hi guys,

Thanks for all the helpful suggestions. I've checked the rear windshield seal (OK), the trunk seal (OK), and just pulled out the carpeting, metal panel in front of the gas tank, plastic well liners, and popped out the tail lights.

There isn't really a whole lot of water in the wheel wells, just a few drops here and there, mostly (I think) from the condensation.

The gaskets around the tail lights are old, but my garden hose testing seems to indicate that they are holding up fine. All the same, I have removed them, cleaned them off, and am spraying them with a little flex seal to coat the gaskets to 'beef them up'. I'll reinsert and then check again. https://www.getflexseal.com/

Thanks again,

Packman

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83 240D - 4 speed manual - Manilla Beige
189K miles, Tachometer mod, cool wooden shift knob from PeachParts, CocoMats, Original factory paint, manual windows, manual sunroof. Starting to add AudioWrap to this car too!

THe area between the trunk lid and the rear window tends to rot out due to old window seal on rear windshield.

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Closing the store
Benzbonz.biz on your smart phone or tablet.

Save all those desiccant packets from pill bottles and chuck them in your trunk?

Baby diapers are also very moisture absorbing maybe pull the absorbent pack out of several set them strategically in the trunk see if the swell up?

This is such a strange problem to me because all the moisture in the air where I live falls to the ground as snow. I swear Alberta is dryer than a desert in winter.

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Cheers!
Scott McPhee

1987 300D

I put a box of damp rid ,and change when needed

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

It might be tricky to figure out a good way to accomplish it but if absolutly no leaks is certain. Insulation is one way. Some form of forced ventalation might be engineered in as well.

First though make sure what you are experiencing is what it is. This should be easy by just checking other cars in your vicinity. This effect is somewhat unknown on the east coast of Canada to the best of my knowlege. Although the principal moisture showing on the underside of the trunk lid is more typical of condensation as you mention than leakage I would suspect.

There was another thread on this a month or so ago but it tapered off inconclusive. I seem to recall that the OP on that one wasn't in the PNW.

There are several usual answers for moisture in the trunk, but the part that baffles me is the condensate effect on the trunklid.

That suggests that you either have standing water in the trunk, which apparently you haven't, or somehow moisture is being drawn into the trunk from outside and rising to the trunklid. I associate condensate with either pooled water reacting to temperature, or moist air movement.

Uber-weird and I can't offer any explanation... unless it's a generalized problem of all the seals being old and allowing moist air to enter, through some vacuum effect when the car is moving?

I had a serious but generalized moisture problem in the trunk last fall and winter (everything in the trunk was damp but no pooled water), but only slight condensate on the trunklid. All I did was to carefully clean around the trunk seal this summer and I left the trunk open in direct sun a couple of very hot days and 'massaged' the seal in one spot where it had deformed slightly. The sun seemed to help straighten it out.

Anyway no problems so far this fall.

The area where I live has the opposite problem to where Scott speaks about... we have very high humidity levels most of the year (and I live in a particularly bad spot that doesn't improve matters).

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

This is what I do with backup CDs/DVDs that are stored long term

As for the trunk, some kind of vent is your best bet. My quarters were rusted out and the trunk never had a condensation problem (living in the humid NE)

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

Other sources of leaks:

1. Trunk lid star - 13mm bolt to remove star and inspect.
2. Trunk lid emblems - holes on each side holding down the emblems. Tiny grommets holding emblems in place may have fallen off.
3. Antenna mast seal - there are two, outer and inner.
4. Quarter panel moulding fasteners - if they go bad they can allow moisture inside. There is a maybe 8 or 10mm bolt at the corner of the quarter panel holding this trim piece to the car.
5. Tail light seals and seals under tail light
6. Fuel filler neck seal - allows water into trunk if not sealing properly.
7. Trunk lid "stops" on either side/rear corner of trunk lid

If water gets in and pools, when ambient temps go up the water collects on the inner surface of trunk lid.

Thanks for the tips. They are all thoughtful and useful. I have inspected all the seals, and have placed a little extra silicone sealant around the seals just to make sure. I will also climb in the trunk with a flashlight while the kids use the garden hose and see if I can detect any leaks.

Thanks you guys and I will update when possible.

Packman

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83 240D - 4 speed manual - Manilla Beige
189K miles, Tachometer mod, cool wooden shift knob from PeachParts, CocoMats, Original factory paint, manual windows, manual sunroof. Starting to add AudioWrap to this car too!

The trunk of my car had #3 and #4. It was evident when the plastic panel was removed from sill. It rusted out in the affected areas. I had holes at the bottom under the panels big enough that you could put your fingers through once you put your fingers through the rust.

Every time it got cool it felt like there was moisture evident on the inside surfaces.

Like beige said, the drains were clogged with debris.

,

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85 Merc 300D - Unwinding 31 years of wear
86 VW TD
Mahindra Diesel
Iseki Diesel

In 2007 I didn't own a diesel.