Hey guys ... a weird one that has me a little stumped. (1989 300E; 181,000+ miles btw)

About a week or so ago, I started seeing symptoms of thermostat failure - whereas before, the temp. gauge would pretty much stay dead-on half-way up the scale, with only a slight raising of the temp in stop-and-go traffic, all of a sudden it started reading a little low during freeway driving and it would start heading for the 100-120 mark when stuck in traffic.

Tonight I drove 45 miles one-way to Long Beach, and afterwards when I got in the car to go back home, I noticed that it started running hot almost immediately ... I get on the highway and it starts to head towards the 120°C mark. Put the heater on full blast, lowered the windows, kept driving ... it didn't go down. Kept sitting right near 120, I was freaking that it was going to head for the red zone at any moment, and I was in a bad area - no gas stations for miles, driving through a bad part of the city (LA), etc.

Eventually I got up to a neutral zone and found a gas station right off the off-ramp and pulled off ... after letting it cool a bit, I found that it had lost a fair bit of coolant (just had it flushed and all-new coolant put in last weekend after discovering the apparent thermo issue, just in case). Topped it back up with water ... then I noticed something.

In the right-hair air intake vent at the base of the windshield, a party flyer that someone had put on the car had somehow slipped down and had completely covered the air intake grill! Well gee, no wonder it was overheating.

I took it out, and it seems that between removing it and topping up the coolant, I was good to go again

So now I'm back to the "runs slightly lower than normal temperature when on the freeway" state, albeit clearly with a busted thermostat.

Anyway, what's weird to me is, I could see this having been the problem if both of the air intakes at the base of the windshield had been blocked ... I mean, I realize it's not good to have either of 'em blocked, but I wouldn't think just one of them being blocked would cause the temperature to skyrocket like it did.

Does this behavior make any sense to anyone? Could the blockage of the air intake also have caused (perhaps indirectly) the thermostat to blow out? (arrrgh, and I just had the thermostat replaced several months ago, too - my fan belt blew up on the freeway and the whole thing overheated by the time I could get off the road, it was kinda scary)

 

Unrelated events.
Engine cooling system is a closed loop that includes the radiator, radiator cap, thermostat, fan, and water pump.
Above normal operating temperatures normally are caused by a faulty thermostat or fan not functioning.

 

The air intake grills at the base of the windshield are for the A/C/C system fresh air intake only. That may starve your brain for oxygen when driving.
Maybe your gauge isn't functioning properly, radiator has blockages, or the radiator cooling fans are malfunctioning. If you mix your coolant stronger it's harder to cool.
The normal temp is 90 deg. C. & can run up to 105 in traffic w/o A/C engaged, but will tend to stay at 90 w. A/C engaged, if everything is in order. In colder weather it can run below 80 if full heat inside is demanded especially smaller engines.
Often overlooked are radiator caps, they should hold 1.4 bar of pressure on the system, If not can also cause overheating around town and cool off on the highway.
And remember new parts doesn't mean good parts, test them.
Rich

 

I think you were a little low on coolant in the first place and that was causing your overheating problem. I've had this happen before.

LA sounds like a great place to live! Areas of town where you can't pull over and check your car? I'm there, dude! Sorry, I just think that's frickin' hysterical.

 

Thanks everyone. I was scratching my head a bit over that - I wasn't sure what role those air intakes had, just thought maybe it was an additive one in addition to the coolant system, but as RBYCC said it's a closed loop. Scratch that theory

Now I'm a bit confused - so if something was malfunctioning (I've never seen any indication that the temperature gauge wasn't working properly, but I suppose anything's possible), I'm curious how merely pulling off the road and turning the car off seemed to have "solved" it.

Needless to say, my mechanic's getting a call first thing tomorrow. I'm sure the thermostat's shot at a very minimum.

Oh, and shdoug - I realize it's funny to a Nebraskan, but reality is reality - while I try to avoid bad parts of town, they exist. The real issues for me last night were the fact that on the Long Beach (710) Freeway, turnoffs with visible gas stations right alongside the freeway are nearly non-existent, and by the time I reached the Golden State (5) Freeway and found an exit that did have one handy, it was in a part of town where the presence of gang bangers was a distinct possibility. (It was also 1:45 AM.) I'd rather have it be more like Omaha, but that's life in the big city.