Overheating, advice needed

[Mystikal]

Noticed last night that my car (on the highway) was consistently running at the edge of the normal range of the temp gauge, it usually sits just past 12 o'clock. Today on my way out, within 2 miles of my house it was past that line, and within 2.5 miles it was flirting with red (I was pulling over on the freeway by then). I let it cool, then brought it back home (never going deep into red, just at the edge near the end of the drive).

Anyways, current observations:
- All rad hoses are hot, including to the expansion tank
- No obvious coolant leaks
- Normal coolant level
- After parking, engine gradually cools down to 12 o'clock after just 15 mins (shouldn't it take much longer after being in the red?)
- HVAC blows HOT air as the needle climbs, then completely switches to cool air as the engine goes into red
- Primary fan is spinning
- Aux fan hasn't been working for a while now, never saw a need to fix it (now I do)
- Water pump is 3 months old

I don't have any experience with cooling systems, and I will be flatbedding the car tomorrow morning. Just trying to figure out what is going on.

[T.Dot E30]

Was the termostat done when u did all ur maintanence stuff ?

It could just be air in the system, but i doubt it. Its probably not fan/fan clutch related, since you were on the highway when this happened, if it was sitting in traffic then maybe.

Where is the car? You should have told me when u saw me today, I would have came and had a look.

[MattE30]

If the radiator tubes were all hot, then the t-stat is probably not at fault, since is letting coolant pass through.

When was the radiator last replaced?

[AdamF 88iS]

Don't rule out the gauge itself. Sometimes a odd connection gives a false reading. Give the cluster a knock or 2 and see if the gauge pops back down to normal. This has been known to happen on these cars. It's unusual for the car to just simply start overheating with full coolant and nothing had been touched or worked on.

[Mystikal]

Trev: I was actually thinking of calling you up, but I didn't want to take another one of your days off. ;)

Matt: You're right, that was my logic too. T-stat was my first thought, but yes, all hoses are hot, the system is open.

Adam: My second thought. I slapped the dash/cluster repeatedly to no avail. The only real reason I have to believe that it is actually overheating is that the air coming through the vents is scorching, seems much hotter than usual.

The only idea I'm left with is the rad has started to fall apart and isn't working up to spec. Two days ago it was running very warm but still just barely within range, and yesterday it went above that. Semi-gradual, I suppose.

[arsevader]

https://<br /> The only idea I'm lef...al, I suppose.

Overheating at highway speeds does seem to point to a problem with the radiator. Maybe also get your cooling system pressure tested.

James

[bddog]

If you did not replace the fan clutch when you replaced the water pump, do it now. Cheaper than fixing a head.

[Brew]

Its also possible that the thermostat is stuck completely open and flowing coolant through the radiator too quickly. I've never had the problem myself, but it is something I was taught in school. Its pretty easy to check the thermostat though; just feel the radiator hoses for coolant flow after a cold start- there shouldn't be any.

[Bryson]

it would be running too cold if that were the case (tsat stuck open), and if it was stuck half open then it would heat up at idle and not at speed

[Brew]

it would be running too cold if that were the case (tsat stuck open), and if it was stuck half open then it would heat up at idle and not at speed

I was taught that a thermostat stuck completely open would allow the coolant to flow too quickly through the radiator, especially at higher engine/ water pump rpms (highway). Since the coolant is flowing so quickly, it doesn't have a chance to release its heat through the radiator fins.

...At least thats what they taught me. If you've had different experiences, I'd be happy to hear them and learn.

[Mystikal]

Simple solution to a simple problem: It was the thermostat.

Looks like the times when I checked the heat of the hoses the entire engine bay had gotten hot enough to fool my hand. When it was nice and cold in the morning and I started it up and left the hood open, after 5 mins the temp swung above normal and the lower hose was ice cold.

OEM thermostat and it's all better. Also replaced the aux fan resistor, I know I had the fan itself replaced not too long ago, figured it was just the resistor. Sure enough, that got it spinning perfectly. Now I have that much more security if this whole ordeal happens again.

I love how simple our cars are.