2004 Monte SS

I live in the midwest where it's about 15 degrees today. I drove home about 30 minutes and the whole way home my engine temp said 185 (normal) and I had good heat within the car. After I got off the interstate I rolled my window down real quick and my hands got cold. I turned my blower on high and that's when things got weird. The blower spooled up with heat, then it gradually got colder and colder. At the same time the heat was getting colder and colder the engine temp was rising, eventually settling on about 225. I turned the blower back down, the heat got very hot again, and the engine temp went back down to 185. When I got home I tried to repeat it in the driveway, I couldn't do it. I turned the car off, let it sit 30 seconds, turned it back on, and now, no matter what blower speed, the air temp is moderately lukewarm, certainly not real hot.

It sounds like a typical thermostat failure, but I'm having trouble rectifying why my engine temp went up and the heat went away. Would a bad heater core show itself some other way?

 

When the car is cold, pop the cap on the radiator, make sure you have fluid. If you lost fluid, warm air messes with temp sensor readings and prevents you from having heat in the car (as hot air in the heater core does not produce what you need to warm the inside of the car).

If it's full, then I'd try change the T-stat (heck if it's not full, you may want to leak check it, but could still be a good time to change the T-stat if it's been a while).

 

I popped the cap and couldn't see any fluid. Since the neck to fill the radiator is on an angle I, obviously, couldn't see all the way down, but I presume it should have had coolant to around the top of the radiator? Ideally, it should always be level with the cold fill line in the overfill, right? So, fill the radiator to the top, close the system then let it cycle through and just keep topping off the overfill tank until my cold coolant always meets the line in the overfill?

Unrelated, but possibly related, when I look down the neck of the filler tube (and on the bottom of the cap) there's quite a bit of brown sludge. Please tell me this is just dirt and not oil coming in through (possibly) the LIM gaskets. I also lose a quart of oil every 4k miles, and it's not burning out through my exhaust. Or at least it's not in large enough quantities to turn my tail pipes black with soot.

 

Sounds like a gaskit

 

If you have not flushed the cooling system in a while, that could simply and probably is just Dex cool breaking down. It happens. If you don't know the last time the coolant was flushed, I'd say you're due.
I have to flush the coolant on my '02 Grand Am. It went through a similar symptom (had heat and then NO heat). I was half gallon low on coolant, I topped it off week ago and it's been fine (I'm going to try and ride this out until spring/summer). But looking at Dex sludge, it's DUE for a flush.
And FYI - I'm going to probably put Dex right back in.

Back to filling, the line on the overflow bottle is not critical. Just fill the radiator as best you can, feel free to fill to the line on the overflow bottle. See what happens. If all is fine, plan a coolant flush in spring.

 

Thanks Maniac. I've lowered the coolant level once before to clean my throttle body, but I've never emptied in and I've certainly never flushed it. At 130k miles it certainly seems reasonable to need a flush. Since it's winter I presume I need to fill with 100% Dex, rather than a 50/50?

Just so I can easily find this in the spring when it warms up, when you reference flushing, are you saying a whole system flush or just the radiator? What's your preferred methodology for completing this task? I did a quick check on the site and there seems to be a couple different thoughts.

 

You HAVE to add water to activate any antifreeze

 

Alright, it only took about 20 ounces (so not much) to get the radiator back up to the top. I also added a little bit to the overfill. I suppose if I keep having heat issues I'll probably start with the thermostat.

 

I always run a 50/50 mix of any antifreeze and water.
Also, not sure if I needed to mention, if you fill the radiator fast it may take a couple seconds for the coolant to settle and reveal you still need to add more. Don't be alarmed if you still need to top off one more time.

As for a flush, FULL coolant system. Normally you can add a product to help purge scale and gunk. A couple of companies make a flush kit to help (and that's what I've normally used, a kit and an additive).

 

The best way to know would be the thermostat. Without one, the engine should not go past 160 degrees. If it does, then you need to look somewhere else for your issue.