: Occassional burnt-smell and white smoke from under hood pass-side, drives okay though

10-23-08, 11:55 PM
Some months ago my '97 cat started to produce a strong sweet-burning-plastic smell on seemingly random occassions, usually it goes away by itself but a few times it ended in a thick white smoke coming from under the hood on the passenger side (near the A/C cabin-filter air inlet) and coolant spilling out under the car (at which point I have shut her down and let her cool.) When it is all over the coolant reservoir is near empty, but I simply add a little water and the car seems to work fine for another month until it happens again. Now I have learned that smell=low-coolant so I add some water and have avoided the smoking issue since figuring that out.

Funny thing is that the car never stops working or drives any different, the temp gauge always reads in the middle and the system was pressure tested already 3 times by three different shops and nobody can find any leaks or anything wrong.

What gives?

10-23-08, 11:59 PM
Could this have anything to do with not changing the oil in the last 16 months? (only 5k miles driven though)

10-24-08, 12:19 AM
No probably not, but it would be a good idea to get that changed for sure.

I don't know where the burnt plastic smell would come from at all. Maybe make sure the cap on your coolant is sealing properly. Have you given it a full flush and replaced all the coolant in the car?

10-24-08, 12:43 AM
The cap was not sealing properly, the ring-washer had expanded and I replaced it about a month ago with a similar sized one I had sitting around. No idea if it occurred before or as a result of this issue.

Not going to flush the system so long as it still occasionally dumps the coolant out on the floor. The coolant is original with the motor that was put in 35k miles/7 years ago.

One other point, there is noticeable black/brown sediment in the reservoir tank.

10-24-08, 02:23 AM
The leaking is probably the heater coolant control valve as these are a common issue. Heat and bad design causes them to crack.

It could also be since you're starting to notice brown/black sediment the oil to water oil cooler deep within the intake valley of the engine may be going bad and is leaking oil into the coolant stream = bad.

10-24-08, 03:05 PM
If you are adding tap water to the coolant you are contaminating the factory Dexcool in the system. I searched car forums and newsgroupsand read that Dexcool itself is fine in a cooling system that is free of contaminants and leaks, but indeed the stuff will turn into a gooey mess if mixed with anything but distilled water or if exposed to air. Mixed with green coolant or non-distilled water it changes chemical properties. It can turn into a gel that clogs the radiator, oil cooler (clinging to the outside fins), and heater core. It will destroy the corrosion inhibitors in the Dexcool causing scale and rust.

Same thing if the coolant level is allowed to go too low in the coolant reservoir. Air can enter the cooling passages and contaminate the Dexcool with the same results. It was recommended to keep the reservoir filled to the HOT level even with a cold engine. Also, those drivers who do not get their vehicles up to normal operating temperatures every trip may want to consider changing the coolant more often.

The reason for using Dexcool in our engines is that the gaskets coming in contact with coolant, including the head gaskets, are designed with Dexcool in mind. Other coolants will eat away the gaskets. Saving pennies on the non-Dexcool coolants will cost more in engine repairs later. The Dexcool PH is also important in preventing corrosion in the aluminum heads and miscellaneous coolant passages.

A brown creamy emulsion under the oil filler cap or on the dipstick is usually caused by water condensation in the crankcase. It's relatively harmless. Short trips will not boil off this water. Clean the cap and filler tube, then go for a long drive to clear the water.

If the "mayo" remains after long trips, check for oil in the coolant tank. . If there is you have a leaking oil cooler. It's buried between the cylinderheads in a coolant gallery. It will require replacement of the cooler, and flushing of the cooling system. Continued use will clog the radiator and heater core.

If there is no oil in the coolant tank, with the engine idling, check the tank for exhaust gas smell and signs of bubbles. If there are it's likely you have a blown head gasket. Not very common for this engine but it does happen.

Draining the coolant

Oil Cooler Diagrams

Changing the oil

Replacing the oil cooler

External Oil Cooler Mod

The head gasket procedure is below.


12-11-08, 03:23 PM
The problem still exists, adding UV dye to the coolant revealed nothing and now with 40F temps where I live the temp gauge fluctuates as I drive- high (but not into the red) while idling, normal one-mark-over-halfpoint while moving.

Now I also get a loud whistling noise from the driver-side of the radiator whenever the car idles while in drive, press the gas and the noise stops. Put the car in park or neutral and it usually stops immediately although a few times it continued even after shutting the engine which allowed me to get under the hood and pinpoint where in the engine bay the sound is coming from. Could the sound be related to the coolant leak?

Any ideas?

12-15-08, 11:58 AM
Mine had many similar problems to yours. It was 2 separate unrelated problems.

The coolant spilling was the heater control valve located between the firewall and upper intake plenum. Changed it and haven't had a problem since. If your coolant puddles are generally under the firewall, could be a bad heater control valve.

The burnt smell and thick white smoke were very bad valve cover gaskets. I had oil leaking onto the headers and smoking/burning. If you have a lot of oil around the bottom of your valve covers that could be it.

Neither made my car run differently either. Both jobs appear intimidating, but turned out to be very routine and simpler than they look.

The loud whistling at idle is likely a vacuum leak since there is vacuum at idle, but not while on the gas, but I wouldn't know where. I know there is a vacuum tube attached to the heater valve; could be related; could be somewhere else.

The black brown sediment...I don't know. The only time I've ever seen that was on a Taurus with incredibly bad head gaskets that someone continued to drive for another 4 months anyway until it died. Hope that's not your problem. It's a hell-ish and expensive fix.

12-30-08, 03:26 PM
Thanks for the response, it was very helpful although I cannot seem to find anyone willing to do the job of checking/changing the heater control valve.

In the meantime the leak got much worse. I now fill the reservoir and a minute later it pours out from somewhere above the frontwards passenger-side corner of the oil pan, is that where the heater control valve is?

As for the vacuum leak causing the whistling, that makes sense, I know I have a tear in one of the vacuum tubes but without coolant that seemed less urgent to fix...

Amazingly, the car still drives fine and does not heat into the red zone, albeit with the occasional smoke when the coolant drains out completely... :thepan: