Tercel: Aggravating smell from heater

If you have to research things for your mechanic to check, you need to find a better mechanic. Is this an independent guy, dealer, chain store, or what?

You will not necessarily get a warning light from an oil or coolant leak.

There is no sensor controlled mixing of coolant before sending it to the heater. The heater temperature is regulated by varying the amount of coolant flowing through the heater core.

Coolant can leave a sickly-sweet taste at the back of your throat. If the heater core or one of the hoses connected to the heater core is leaking, you might get coolant vapor in the cabin. With the engine running, nobody sitting in the car, heater set to recirc and to the front defrosters and temperature set to hot, does the windshield start to fog up? If so, that is a sign of a heater core leak. Are you getting any coolant loss? To check, put a piece of masking or duct tape vertically on the coolant overflow reservoir and mark the coolant level. Check the coolant level periodically and see if it is gradually going down. If the radiator cap is more than 10 years old, consider replacing it.

"Ray O" wrote in news:EImdnea7uaOm2FvanZ2dnUVZ snipped-for-privacy@comcast.com:

That may depend on the year of the Tercel, whch th OP does not give.

Later Tercels did not have heater control valves, so flow to the heater core is unrestricted. Blend doors are used instead; they control air flow through the core.

Hmm. OK.

For such a control scheme, what determines the amount of coolant that flows through the heater core?

It doesn't smell sickly sweet. Just aggravating, and sometimes like burning, rubber, burning rubber, burning oil, or diesel.

No, it doesn't. In fact, that's what I have to do to unfog the windows in the winter when the car is occupied. There is no window fog at the front regardless of whether there is anyone inside.

No, not for the years over which this problem has taken place. This is just from eyeballing, but I almost never have to fill up the coolant.

Would the coolant fluctuate, but still sit around the same level? I shall try that.

Thanks.

This is a 97 Tercel.

For those designs that don't have heater control valves, when the fan is set on recirculate, does it just direct some of the intake air to the heater, and some around it?

The amount of coolant that flows through the heater core is determined by the heater control valve, which is probably mounted on the firewall in the engine compartment. The heater control valve is controlled by the temperature lever or knob inside the car. When the temperature is set all the way to red, a cable attached to the knob or lever moves the heater control valve to the full open position, and setting the temperature to cooler closes the heater control valve.

Yes, the coolant level will fluctuate when the engine is running, but when the engine is cold, it should sit at the same level.

As far as I know, all cars with heaters with coolant circulating have heater control valves. When the HVAC system is set to recirculate, the air blowing past the heater core is drawn from the interior of the car instead of the exterior of the car.

If the burning sensation is reduced when the system is set on recirculate, then the source is in the engine compartment or intake. If setting the system to recirculate doesn't make a difference, then the problem could be in the ductwork, heater core, AC evaporator, fan, or heater resistors.

Ray O wrote:

Yes, that's what the pictograms on the recirculation lever suggests.

I have no AC, so that should simplify things. Early on, one of the ways I've extensively tried to characterize the problem is by seeing how it changes between recirculate and ventilate. This didn't lead to anything conclusive, because ventilated air seems to bring with it a host of other smells. I've since tried to troubleshoot it in recirculate alone.

The ductwork was subject to an antibacterial mist treatment. The fan has been changed twice. Last time, there was some doubt cast on the resistor as a candiate culprit, but I'll bring it up with my mechanic.

Thanks you again for your ideas, Ray.

Ray O wrote:

Ray O wrote:

"Dubious Dude" wrote:

Ray O wrote:

Ray O wrote:

Thanks. It's almost warm enough to give it a shot

You're welcome! The heater resistor pack was my idea, and it is a long shot and not very likely to be the source of the smell but still worth taking a look at. Just wipe it down with rubbing alcohol to make sure nothing has built up on it. While you're in there, make sure that no critters have disturbed anything like the foam insulation or wires.

good luck!

Dubious Dude wrote in news:fqalp7$lrg$ snipped-for-privacy@aioe.org:

Recirc shuts off the intake of fresh outside air. After that you're putting the same interior air through the heater core over and over again. It's handy for very cold winter days.

"Ray O" wrote in news:LoGdneP1uPQTcFXanZ2dnUVZ snipped-for-privacy@comcast.com:

The '97'-'99 Tercel has no heater control valve. It uses blend doors to regulate circulation of air past the heater matrix.

I learned something new today! I knew that Toyotas with automatic AC use blend doors regulate air circulation but I didn't realize that the Tercel did that as well.