Hi,
I've always driven on city roads and pretty flat highways and have never had any issues with overheating, however a couple weekends ago I went driving up in some hills. I was going maybe 30 mph and it started getting really hot so I had to eventually pull over and let it cool off. Next day I went up a different hill and same thing happened. I've pressure tested the system and the cap to 18 psi and there's no leaks and it will works just fine with any city driving or highway driving still. Any ideas what I should be trying next? Car is a 2000 Camaro if that helps. Thanks!

 

When is the last time (or ever) that you cleaned the outside of the condensor...?

Are you sure BOTH fans are working in BOTH high and low settings....and always running together, not separately....?

Is your lower air dam in good condition.
No obstructions in front of the condensor.

Possibly a sticking tstat that is not opening FULLY.....just partially, and cannot keep up with the added heat of going up hill.

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I should of mentioned the AC has been deleted so no condenser present. The lower air dam is in good condition. I'm pretty sure both fans turn on and they stay on even when the car is off when it was overheating...I'll have to let it idle and make sure both of them turn on. Is there a way I can test the tstat to make sure it is opening fully?

 

I'm pretty sure the only way to test the thermostat is to remove it and place it in a pot of boiling water and record the temperature of the water with a cooking thermometer and see what temperature the thermostat opens and closes and how wide it opens.

 

You can watch the thermostat open by starting up your car with the radiator cap off. You will start to see flow on the top of the radiator once it opens. An inexpensive cooking thermometer will give you an accurate enough temp. It really doesn't matter so much as when the Tstat opens, only that it does. If it weren't opening at all you wouldn't get very far. Not sure how often they fail in mid-position but you would probably see those effects just in normal driving on level ground on hotter days.

Is your coolant of the proper mixture? For heat removal in hotter climates a 50-50 summer mix would probably hurt you. I had a Plymouth '68 GTX that ran hot no matter what I did. And over 3 years I did everything possible....short of a separate engine oil cooler. What did work a little bit was running 20-80 or 10-90 coolant/water mix in the summer + one bottle of Redline water wetter (good to around +20 to +30 deg F). Once October/November rolled around I'd increase the concentration back towards 50-50. Gained about -10 deg of temp with that set up on the hottest days. Water removes heat better than glycol. It's just that demin water has none of the beneficial chemicals that the anti-freeze does. A poor tune could also add heat from the engine. Running too thick of an oil could possibly do that too (40-50 wt). Anything that increases friction in the drive train from tires to rear end can add to the total heat removal load. The cooling fans not working properly could do it. You could tune them to come on earlier though on a sustained drive temperatures would still reach the same point - the same as if you got a lower rated T-stat. They only delay the onset of too much heat....not cures for it. If the engine is "built" that's more heat too for the stock cooling system.

To keep the floaters and bugs off the front of my condenser I installed some flexible screening material over the front of it. It's been on there for 3 years now and never came loose using only friction at the top and a pair of notebook spring clamps at the base. Been putting these on all my classic cars since 1993. Bought a small roll of the stuff for <$10 back then and I still have stuff left. Considering I've never used a screen on any daily drivers, it wouldn't appear there's much cooling loss from what little debris gets into your radiator...at least not up here in New England.

 

Do the boiling pot of water test....see if it opens fully. If it does.....check up into the air duct in front of the radiator....see if the front surface of your radiator is all jammed up with debris...rocks, sticks, grass, bird feathers, sometimes a friggin bird, etc.......

Also.....by removing the condensor, that can change the way the air travels through that duct system "shroud". It could be the reason you don't get sufficient airflow. It could be turbulent going through there.......usually it doesn't hurt to remove the condensor but its possible.

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Firebrian made some great points. Anything that adds friction can cause it. Your brakes could be dragging, making your engine heat up more. Happens more often than you would think

 

If this is a "A4" vehicle, both water and trans temperature will rise before the transmission achieves "lockup" (around 40-43mph).

 

I do not believe you stated the mileage on your car. I believe that your radiator has seen better days in that under load, it no longer has the needed flow to keep the temperature down. I had the very same issue on 2 vehicles. When I would drive normal city or freeway mileage with zero hills, everything was fine and gave zero indication of a problem. Being on the hills and.........