White smoke coming from A/C vents...

[Mounty99]

Back story. Problem started today. White smoke billowing from the A/C vents inside the truck. Sweet smell (coolant). Coolant reservoir not really any different than normal (I have to top it off monthly). Mountaineer is coming out of a tough Texas summer where A/C was often cranked way up.

--Guessing maybe heater core? But should the smoke be coming out if only running the A/C? Anything else to check, etc?
--From older threads, seems like options are to replace core, bypass core, or throw in some of Koda's favorite (KSeal)?

I'm not the best mechanic, but you guys have helped me tremendously over the years. Love the Merc & money always seems tight, so any advice to get her back up to speed is much appreciated!

 

[Mounty99]

Ok, think I may just bypass and buy myself some time. Won't need heater for few more months. Is there a proper way by bypass? Can't seem to find a "how to" for it. I haul young kids around in this and don't want to screw it up! Thanks again.

 

[974X4BLACKSPORT]

If you just want to bypass the heater core, you just connect the heater core inlet hose (usually the larger 3/4" hose that comes from the intake manifold on older v8's like the 5.0) and connect it to the barb on the water pump (usually the smaller hose 5/8"). The hot water comes out the intake manifold and goes back to the water pump, or near by fitting for re circulation when the heater core is bypassed like this.

 

[J_C]

I was under the impression that you should have a heater valve that closes coolant flow to the core when it's set to cold, no? I suppose it could be leaking by now...

 

[fast_dave]

@Mounty99

I read your well-written write up, and here's my .02

OK - The Heater Valve is on the passenger side, which is also the same side that the fresh air intake is on (base of the windshield) - which is where your A/C gets fresh air from...

So, with that said, PERHAPS - since you mention that you don't see any significant coolant loss - your Heater Valve is leaking (this valve is a frequent coolant leaker from the underside) either directly on the exhaust manifold OR the heater valve is leaking an the coolant is flowing down the underside of a heater hose and eventually dripping on the exhaust manifold.

Before you do anything drastic - I'd check - with your hands - the underside of the heater valve, and the undersides of all the hoses leading to and from the heater valve.

Maybe you'll get lucky and you only have a heater valve or heater hose problem

Hope that helps & wishing you good luck!

 

[Mounty99]

Before you do anything drastic - I'd check - with your hands - the underside of the heater valve, and the undersides of all the hoses leading to and from the heater valve.

Thanks FastDave. I didn't really see any leak there from earlier inspection, but I'll definitely double check that area.

If you just want to bypass the heater core, you just connect the heater core inlet hose (usually the larger 3/4" hose that comes from the intake manifold on older v8's like the 5.0) and connect it to the barb on the water pump (usually the smaller hose 5/8").

Thanks. I was thinking both hoses (inlet to heater and outlet) are 5/8? Am going by the the rock auto parts sizes. Is this correct? Am I able to just remove these two hoses, connect together, and good to go?

1999 MERCURY MOUNTAINEER 5.0L V8 Heater Hose / Pipe | RockAuto

 

[fast_dave]

Thanks FastDave. I didn't really see any leak there from earlier inspection, but I'll definitely double check that area.

@Mounty99

It's easy not to see a leak in that area - especially if it's a leak that only shows it's head under high pressure/while driving.

When I read what you wrote, the standout clue is you're saying you're seeing steam come out of the vents.

For there to be white steam to becoming out of the vents, I'd bet coolant is hitting the exhaust manifold, turning into steam, and then getting sucked into the cabin.

This pathway into the cabin is occurring either at the base of the passenger side windshield (climate control fresh air intake), or through/past the Evaporator Box - located on the passenger side of the engine compartment.

Additionally the plot thickens when you take into account that the Evaporator Box is located right below the heater valve & heater hoses, and is three inches or so right next to the exhaust manifold.

The effects of a bad heater core are usually three-fold (that's why I think you have a different problem);

* sweet smell in cabin (you have that)
*humidity on the inside of the windshield (you don't mention having this),
*and coolant pooling under the carpet on the passenger side (you also don't mention having this).

HTH & good luck!

BTW - the heater valve usually fails right at the point where the round/thin steel arm for the butterfly valve enters into the heater valve body.

 

[Mounty99]

* sweet smell in cabin (you have that)
*humidity on the inside of the windshield (you don't mention having this),
*and coolant pooling under the carpet on the passenger side (you also don't mention having this)

Thanks Dave. Core basically started leaking big time the other day, flooding my floorboard with coolant. So now officially had all three symptoms!

I did bypass the heater core with a 5/8 Ushaped hose, etc...and all seems to be good now. Air blows so much colder. Wish I would have done this bypass back in April! Anyway, thanks to all for the advice and suggestions

 

[fast_dave]

@Mounty99

No problem, I'm happy to offer you any assistance, and I'm sorry to her about the heater core finally letting go.
Search the forum for write-ups, ask questions, procure parts, and fix it when it isn't so hot out.

Take care and stay in touch!