Davpmars

Each time I drive my suburban up a mountain it seems to run hot. I've had plenty of other cars that cool the engine just fine while driving up the same mountain here in Utah.

The one thing that I seem to notice is that it cools better when I run at higher rpm up the mountain.

I don't think that this is related but every once in a while I have to put about a quart of water in the reservoir. I always make sure that the water is completely full whenever I am going to go up a steep hill. Why would my car cool better at higher RPM?

SWHouston

The forward motion of your vehicle, causes increased air flow through the radiator, thus better cooling ability.
You should first go to a Radiator Shop, and have them do a test on the Coolant. It sounds like you may have a hot gas leak into the cooling system (head gasket leak).
If they eliminate that as the cause, then we can discuss other causes for the overheat.

Get back to us when you get that done.

Scotiapilot

what are you considering hot and what grade are you driving up to what altitude.

Davpmars

Normally my suburban runs at the 1/2 way mark which I believe is 210°. When I go up hills it reaches the three-quarter mark.

If I punch the gas to get the RPMs to raise I can immediately watch the needle go down and the engine to start cooling even if my speed stays the same. I don't see how a blown head gasket applies in this situation. If the head gasket was blown wouldn't the temperature continue to rise with higher RPM given the engine is running faster and hotter?

AZSCTACO

Get the thermostat checked out.....or just put a new one in. They are cheap

SWHouston

You said that you had to add "water" to the reservoir occasionally.
If at all, one might normally add "Coolant" to his reservoir once a year, if that.
If you just add water, you reduce the efficiency of the Coolant to protect from freezing and additionally reduce the efficiency of cooling it's self. This is somewhat a separate problem, save that it lowers the efficiency of the coolant to cool.
Get the test done !

I don't know if your readout (temp reading) is right or not, but your temp should read normally at 185*. When you change to a lower gear (keeping the same speed) you increase the flow of coolant through the engine/radiator. This leads me to believe that you have a dirty/clogged cooling system.

Without more specific information, you should...

Thoroughly clean and Flush the cooling system
Replace the Thermostat and Radiator Cap.
inspect Hoses for interior deterioration, and replace as necessary.
View/check the Air Shroud (if OEM) for correct position, or the distance of the Fan from the Radiator. Should be about 2" if you don't have a Shroud.
Check for any debris lodged in the Radiator Fins, and clean* as necessary.
Check A/C Condenser for debris, and clean* as necessary.
Check the Air Dam (the space forward of the Radiator and Condenser) for blockage or other restrictions like aftermarket Grills, Running/Fog Lights or any non OEM equipment which may obstruct the air flow.

Now, assuming you've done the above, and the Coolant is a 50-50% mix (water/coolant), AND your Reservoir is filled with the same proportion, DON'T just add water to it. IF it gets low (and some do after a flush) have a gallon or so of properly mixed coolant to replenish it, or, you can buy Coolant that is pre-mixed to the proper proportion for topping off the reservoir.

*= Usually a strong blast of air from the engine side of the radiator/condenser forward, will blow any trash out of the fins.

Davpmars

I like your approach to fixing the problem. I first changed the thermostat and then I sprayed out the radiator with water from the engine inside. I did those two things months ago and they didn't fix it.

Last night I changed the lower radiator hose. I could tell it had just a little bit of gunk on the bottom side which leads me to believe that it had a very slow leak. I also changed the water pump.

There is no need to worry about the mixture of water and coolant as I am careful to add both. Previously I had to add about a quart every couple of months but now with the new lower radiator hose I hope that fixes that specific problem.

Can you tell me if air bubbles will simply work their way out? Or do I need to proactively try and purge air from the system after I drained all the court last night?

Rednucleus

A quart every couple months is too much consumption. Maybe a pressure test if the problem continues?

SWHouston

Umm, hard to say about captured air in your system. Some vehicles are VERY stubborn about burping it out. Most Radiator Shops and Dealers have a Vacuum Pump for those vehicles. I'd just run with it like you have it, watch how much Coolant you have to add (within a reasonable time) and if it's captured air which causes you to add, then you're eventually (like a couple Quarts or so) going to get it out of there. However, IF you continue to have to add, then...

You have a Head Gasket leak, or...
The Radiator Cap is bad, causing surges of Coolant that the Reservoir can't handle, and it's dumping your Coolant out, or...
You may have a Crack in the Reservoir or Tubing (near the top of the Reservoir) where when there is expansion (like when you stop at a stop light) it briefly lets some of the Coolant out.

I know one thing for sure, you're one stubborn a$$ed guy !
If you think a Radiator Shop is going to charge you for getting the Exhaust Gas Test done, then just buy a Tester and do it yourself. They're not all that expensive, and you won't have to get a second opinion, which I recommend for any issue where you would get a shop/dealer involved.

Scotiapilot

Does the 2007 have a mechanical fan? MY 02 denali had one and it would do the same. I swapped fan clutch and used RP ice and it substantially reduced operating temps driving over mountain to San Diego from AZ.