My 240 D does not loose any coolant. It gets up to temperature perfectly, and has no issues regulating temperature and staying at the right operating temp. AC system works well, AC blows COLD, heat blows hot. I dont seem to be able to get any air out of the two outboard dash vents, but that is another thing for another time.

Car is mechanically perfect. No smells of any type.

When I turn up the heat in the car, I get a pretty good fogging of the windshield. It does this without fail, AC engaged or not. Eventually it goes away, but it happens every time.

What gives? I dont think it is a bad heater core, because I smell no antifreeze and loose no antifreeze.

Could it be AC condensation on the hot heater core flashing up as steam?

My 240 has a fully manual system.

Thanks!

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Warm moist air on a cold windshield will fog up until the glass warms up.

It might be made worse by extra moisture in the system. Are all your drains clear in your A/C system? No windshield gasket leaks? The air intakes in the cowls clear of debris that could hold water?

I am not sure about how a Benz works in this fashion, but in some cars the cores are vented when the engine looses vacuum. This is so they can "air-out" and prevent this problem. Since you have no air to the outer vents, I wonder if there is a larger problem that is preventing fresh air from entering, either at all times of when shutdown.

Just a random theory based on my limited HVAC knowledge.

__________________
1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

For my climate/conditions, this isnt the case. It isnt in any other vehicle.

This car is not used regularly, so it sits unused for weeks/ a month. The only time it gets wet if I can control it is when I wash it.

AC drains being clear is a good question that Ill check.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Interesting... I was under the impression that the 240D did not have vacuum in the HVAC controls though. That may be wrong.

Thing with the air not entering is that this system blows great under heat and AC. Id think that I would hear a restriction, or feel reduced airflow. The system blows!

But your point is one well taken, that Ill have to look into, thanks!

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Well like I said, I have limited knowledge. As for restriction, you would notice none if its brining in inside air instead. Again, not sure how your Benz works, but on most cars that have a recycle air function (like my 560) there is a door that will open or close to bring in outside air or not. I am not sure if your car has a recalculation ability. But again the thought being that if it does, it may be stuck closed and it may be related to your venting issue. I am sure other can chime in with better knowledge.

__________________
1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Following the KISS philosophy, the most likely cause for your fogging windshield is a leaking heater core.
I know you said that it uses no coolant, and there is no odor, but the leak could be tiny.
In my experience with any car, a fogging windshield when using the defroster has always been a leaking heater core.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

Could be that periodic fogging of hte windsheild allows water buildup that gets condensed off when you use the heat. If you use is every day for a week, you may find the cause or it will go away.

I have sealed up a heater core by pumping hot water and stop- leak through just the core. That was over a year ago and still no more leak. I used a small submersible 12v bilge pump. heard about it on this forum and it worked great.

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Hi Stevo,


I had a couple quick questions about this post from waaaay back in 2011...


Do you happen to remember which stop leak product you used? Did the leak return in the 8 years since then (probably)?


Did you just set up your bilge pump to circulate water into the heater core at the T-junction on the firewall, and grab the return (which I think is down below)?


Thanks,


Kurt

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- '79 240D - engine swap complete! Engine broken in! 28-31 mpg! Lovin' the ride!
- '86 190D (W201-126) - 2.5 NA engine, 5 speed, cloth interior, manual climate controls, 33-34 mpg (sold to forum member).

Old thread.

Still happens and still no coolant loss or leaks (knock on wood).

I’m due for a coolant change in the spring. I’ll probably add some gm walnut tablets or bars leaks powder. Just a little, don’t want to sludge up an otherwise nicely operating system...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

My 1982 240D does the same thing and always has, I've had the car 20 years now .

If it's not too cold just open the side window, otherwise turn on the AC to quickly clear the mist off the inside of the glass, as soon as the dash vents begin blowing hot air close the window or turn off the AC.....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I would suggest to check again, a freind of mine has a ford fusion and that too fogs up the windshield like this and he also said no coolant loss.

I told him to measure the coolant loss after a month or two, he found the expansion about a cup low on coolant after 2 months of daily driving it.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Mines not a daily driver, so that helps

But after a few years and a few thousand miles it’s still where I filled it to.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Humm, I dont remember what brand I used but I didn't use the whole bottle, maybe half. I did just pump it in one side and out the other at the firewall and I used hot water. I dont even remember which car I did that to, but I haven't had to deal with the problem again. It's worth a try considering the hassle of taking the heater out

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"