'95...fog coming out of vents when heater on...???

[Tominator2000]

Hello all! This Marquis has 170,000 miles on it and has had regular maintainence and runs great.

Last week my wife complained of 'smoke' coming out of the vents while the heater is on. I just added a quart of coolant to the overflow. First ever. The windsheild and side windows fog severly.

I'm assuming a bad heater core. Is this a correct diagnosis?

The temp guage stays in the normal range.

Thanks in advance!

[cobradude360]

u said u added a qurt of coolent to it and it was the first time ever do u mean uve never flushed the system or its the 1st time uve ever had to add any ? and i have no clue have u seen this accualty happen and does it smell werid at all?

[6502dude]

Sounds like your heater core is leaking.

Dealer generally will charge 6 hours (or more) for replacement. This gets pretty expensive

Doing job yourself is not difficult, but entire dash must come out to get at plenum assembly.

BTW, only one screw needs to be removed under wiper motor - not three as noted in most service manuals.

This is not a job I would want to do in the winter. If you live in a climate that is moderate (southern US), try bypassing heater core until it can be replaced. Antifreeze fumes can be toxic.

Good luck.

[Tominator2000]

The cooling system has been flushed every 2 years. The odd thing is that there is no smell and it is pure water as far as I can tell.

Thanks for the verification. I'll be attempting the repair myself.

Until then I've told my wife to keep a window down and use the AC with the temp control on warm.

[cobradude360]

good call dont wanna hurt ne one