Howdy all!

We've all got winter on the horizon and cold weather in the forecast and I found my trusty '99 suddenly wasn't blowing any heat! My first knee jerk reaction was the head gasket went finally (I have slooowly lost antifreeze over the last 5-7 years with no drastic change in quantities) since I had just topped up the rad a couple weeks ago. Got stopped, and she was still full with nothing looking like oil or milkshake-like going on.

If I've got coolant and the temp gauge is registering normal temps...what do I look at next? The other day I had a 6-7 ft piece of drill stem to move and slid it over the back see and under the dash, just to the right of the console. I remember setting it on the ground and then skootching it forward so it was as high up the footwell as I could get it to relieve the pressure on the console a bit. Could I have pinched or crushed something? I'm on my way out to investigate now but thought I'd ask in case someone else with more know-how in this dept may have ideas in case it's not something obvious and easy to find in the canadian dark

You have a manual control or digital climate controls?

If manual. Look on your passenger side floor closer to the center console. Up next to the bottom of the dash itself. You see the slide cable attaches and one if the cables that switches from hot to cold.



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Could possibly be a plugged heater core, if it's still the OEM unit I wouldn't be horribly surprised if that's the case. Unfortunately I don't know of any ways to test one - perhaps one can hook a garden hose to it and see if water flows through, similar to a radiator?

I really hope it's not a plugged heater core. As those are very deeply embedded into the dash and probably lots of hours to change.

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It’s not a big deal to unclog the heater core. It happens fairly often in these, and almost always if the cooling system has been ran low or neglected.

Get the engine warm, slide the temperature control to hot in the cab, go out and put you hands on the heater core hoses. If one hose is hot, and the other isn’t, it’s a plugged heater core. The side toward the shutoff valve up center high on the firewall is what controls flow, follow that hose to the core, that’s your inlet. Temp check the outlet.

OTC makes a sweet pulsating air/water gun that makes extremely short work of the job and in my opinion very worth the 50$. You can use a garden hose though.

OTC 6043 Blast-Vac Multipurpose Cleaning Gun, ASIN B000F5ECRW

Looks like it’s 67$ now, still worth it. You can flush the entire system, radiator, and cores both ways.

Other than that all that’s left is the blower or the blend door.

I used 9% vinegar to loosen calcium carbonate that was built inside my LC's heater core. Leave it inside the heater core for few days and flush, do it again and flush.

Above Blast-Vac works very well if you can use it to flush after treating with vinegar.

Use a pick to loosen the heater hose mounted to Aluminum tubes. A pliers and too much force can crush the Aluminum tubes.

Any heater cores develop leaks after being plugged? I know I sure give it a go as the cores are fairly in the dash. When we pulled my parts rig apart we were really surprised how it's in there.

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I’ve reverse flushed me heater core on my Saturn with compressed air. All kinds of chunks came out of the T-stat housing when I did it.


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Interesting and make sense. I just dread the thought of having to change a heater core in a 3rd gen.

However, I have some ideas on how to flush them without heavy damage...

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I recently had this same issue. Back flushed my heater core with a $3 coolant flush kit from Walmart. Clamped off the lines before disconnecting so I didn't have to drain the whole system. Will tell you lots of gross gunk came out of there. But now the damn thing is almost too hot!

Good luck with whatever method you go with