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Discussion Starter #1
Hi fellas, my '94 f350 7.3 has been running great since my last visit but now I have had a wafting vapor rising from the windshield defroster vent on the driver side. I turned off the AC and it quit.

This happened on the return trip from Tulsa- running @75mph- ambient temp. 98*. I pulled off the road and checked under the hood and found no hoses or anything leaking.

Has anyone ever had this happen to them- this is a first for me.
 

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Leaking heater core?
 

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Discussion Starter #3
I wanted to add that the 'wafting vapor' quit not the AC. The AC has been working just fine since this happened.
Sorry for the second post but I couldn't figure out how to edit my previous post after posting it?
 

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I know.. the wafting vapor could be coolant - does it smell sweet?
 

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Are you low on coolant? Maybe the up pipes are leaking.
 

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Discussion Starter #7
I know.. the wafting vapor could be coolant - does it smell sweet?
Now that you mention it -there was a faint sweet smell (asked the wife- her smeller still works). Guess that confirms coolant leak- heater core R+R coming up.

Is the core removable behind the glove box or does the dash need to be disassembled?
 

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Dead giveaway on a heater core is a fog on the windows that smears when you wipe it, check the hoses where they go through the firewall, I've had a leak there put coolant in the heater box.

Slight chance the a/c evaporator drain is clogged also, when you park the truck after running the a/c for a while, do you get a puddle behind the passenger front tire?

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Discussion Starter #9
I'll check the windshield for smearing when wiped. And I like the possibility of a loose hose clamp. fingers crossed.
 

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Good luck! I'm remembering it's easy to do, pull glovebox, and remove a panel, BUT, it's been several years and many disasters since I did one in that body style.

Let us know what ya find bud!

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Discussion Starter #12
Well I checked the windshield for coolant residue on the inside- none. Took it for another 150 mile drive and there was no vapor/misting coming from the defroster. The AC condensate drains behind the passenger side front tire as observed during and after the drive.? BTN97, I checked the heater hoses (which are clamped with spring clamps) and saw no signs of coolant leak, but am wondering whether I should replace the hoses and use a proper screw clamp on them? what do you think?
 

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Personally I don't like the spring clamps, but I hesitate to disturb anything that isn't leaking, unless it's just time to change the hoses.

Can you be a little clearer as to "wafting vapor"? Do you mean smoke? Was water condensing on the windshield?

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Discussion Starter #14
I'm not a spring clamp user and I too don't like disturbing them unless necessary but the hoses do have some age on them so may have a small intermitent seepage problem as the hoses become dry from age- possibly?
Since there was no condensation on the windshield maybe it could have been smoke ? But from where as everything seems to be working fine so where would smoke come from and exit out the defroster?
 

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Sbluke suggested maybe your up pipes could be leaking in an earlier post, other than that electrical behind the dash is all I can think of, puzzling.

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Discussion Starter #16
Do you mean - exhaust? up pipes? How would a leaking exhaust get into the ventilating/ AC system? And yes I am puzzled also.
 

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Discussion Starter #17
Well, my son-n-law had to borrow the truck for his work/ we'll see how it goes.
 

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Discussion Starter #18
I've been thinking of buying/installing a coolant filter such as dieselsite.com offers and replacing the heater hoses, with the addition of a shutoff/ bypass to eliminate the heater core heat from the AC shared box during the summer months. This way the coolant will still be filtered but just not going thru the heater core. Does this seem doable?
Update: I got my truck back and my son-n-law said he had no problems. He then told me that @3 years ago when they borrowed the truck to move from Louisanna back to Okla. that the same wafting vapor/smoke happened to them once- they had the truck for a month and it didn't happen again until the other day- so I am just going to pray that it never blows up.
 
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