Hello,

I have a 2007 Chevy Suburban 2500 with a 6.0 (I believe it is an LY6). I live in Phoenix, and we have hot summers. Ever since I got the truck it has run a little warm when idling in the summer with the AC on. I have done a lot to the truck to try and improve the cooling system, but the problem just seems to get worse over time. Here is what I have done so far, in order:
- installed lower temperature thermostat
- coolant flush
- installed new fan clutch
- installed auxiliary electric cooling fans to push air across the radiators
- installed hood louvers to let hot air out of engine bay
- replaced factory radiator with a large 3 row aluminum radiator
- replaced factory transmission fluid cooler with a large 40k style transmission oil cooler
- replaced mechanical fan with factory style electric fan setup, giving the truck electric fans in front of and behind the radiators
- replaced water pump with Melling water pump, installed new motorad thermostat

I have done all of these modifications over the course of about 3 years and 50k miles. I feel like I've done everything I can think of, and the truck still runs a bit warm in Phoenix temperatures when idling with the AC on. I have a set of OBD2 gauges to get precise coolant and trans temperatures since I don't trust the gauges in the truck. The OBD gauges say the truck gets around 230 when idling for a while if it is over 100 degrees outside. If I am pulling anything (which I do regularly with the truck) it will run around 230-250 going down the road at this point.

I would love any suggestions anyone has for this problem. I am willing to put work into the truck to keep it running well, but I don't know what else to do at this point...

Thanks for your help!

 

I'm also in Phoenix.

We've had a 1988 Suburban with 5.7 engine, 1994 Suburban with 5.7 engine, 2005 Yukon XL Denali with 6.0 engine, 2011 Yukon XL Denali with 6.2 engine, and now 2014 Yukon XL Denali with 6.2 engine. The Yukon Denali XLs were all-wheel drive.

NONE of these have run hot either while driving, when idling, or in city traffic, or even towing 2 horses up the mountains on Interstate 17. We've done NOTHING additional to the factory equipment. All five were used for towing horses, mid-summer, AC always on. By "not running hot" I mean according to the factory temperature gauge; are you actually into the red warning zone? Anywhere in the "OK" region of the gauge is OK; modern engines are designed to run hotter than engines of the past, to both reduce emissions and to boil off any moisture from the oil (one reasons engines last 300K miles these days).

DO you have all the factory fan shroud in place???

 

Hi Cusser!

Thanks for responding to my question. Sounds like you've had a wonderful fleet of suburbans over the years. On the factory gauge it has never hit the red, but it almost always runs past the middle, which is 210 degrees. It may very well have hit the red at times if I hadn't taken precautions like turning off the AC and pulling over to let it cool off before it got there. The cooling system simply doesn't seem to be working as effectively as it ought to. I have read on other forums that my specific generation of 2500 Suburban (which started in 2007) often has an issue with running warm when ambient temperatures hit 100 degrees. Do you think I should just be ok running at 250 degrees so long as it doesn't hit 260, which is the pegged, red area on my factory gauge?

In regards to the factory fan shroud, I had the factory shroud in place when I had the stock mechanical fan. Now that I have converted to the factory style electric fans, I have the factory shroud for those in place as well.

 

Weagle - we've never had to switch the AC off even in summer, even when going north on I-17 past Bumble Bee approaching Sunset Point, on any of those vehicles I listed. So I believe something is not right with your SUV.

I don't use mechanics very often, but I did use Blackwell Automotive at 40th Street and Greenway a couple of years ago for an involved problem on my 2004 Frontier, and I have had good success using Smart Automotive on Cave Creek south of Greenway several times over the years.

Mark Salem of Salem Boys Auto in Tempe is retired now, but his shop is run by his kids; he retired from the Saturday morning talk show a few weeks ago but says he'll still answer E-mail questions at mark@marksalem.com

Also see his FAQ #19 https://salemboysauto.com/marksalem/faqs/faq-19.htm

FAQ-19

Cooling systems, overheating, leaks
& electric cooling fans.

The coolant and water mix is pumped through the engine by the water pump. The job of the liquid is to pick up the heat and carry it to the radiator so it can be dissipated. The water pump can't pump foam, so they put anti-foaming agents in the coolant. We know that every car that overheats, does so because of the lack of coolant (because of a leak) or because of a restriction of the flow (closed thermostat, plugged radiator, or a water pump that's not pumping because of a drive belt that broke or an impeller that's come loose).

The thermostat's job is to open when the coolant gets too hot and let the coolant travel faster into the radiator. If it senses the coolant is too cold, it closes to slow down the flow to keep the coolant in the engine longer.

We all know that water boils at 212 degrees Fahrenheit. For every pound of pressure you put water under, it will raise the boiling point approximately 2 degrees. So a good 15 pound radiator cap will raise the water's boiling point 30 degrees from 212 to 242 degrees Fahrenheit. Add 50 % of coolant and the boiling point of the mixture is well over 265 degrees Fahrenheit.

We know that steam can't be pumped by the water pump, that's why we need the coolant to stay in a liquid form. It's important to know we want today's cars to operate at 220 degrees Fahrenheit . So if the coolant turns to steam too early because of a bad radiator cap or a weak mix of coolant and water, the car will overheat at 230 degrees or so, which leaves little room for an extended stop at a traffic light on a hot summer day.

Very few overheated cars are fixed with just a radiator cap and I've never seen a car fixed with a flush. Flushing a car to fix an overheat is like rinsing out your mouth with mouthwash to kill cavities. A flush is done after the repair, not as the repair.
When should I flush my car's cooling system?
Flush your cooling system once a year. The best time is at the beginning of the summer or the beginning of the winter. A good technician will flush the engine block and heater core. He will clean out the overflow bottle and test the radiator cap. He will fill the cooling system with a 50/50 mixture of coolant. He will pressure test the system at a few pounds over the normal operating pressure. If after a short time there is no pressure loss indicating a coolant leak and none of the hoses blow or swell up, then all is OK.

It's the anti foaming agents, the rust inhibitors, and the water pump lubricants that wear out. With the price of plastic tank radiators approaching $6-800 and damage related to the deterioration of aluminum timing covers costing $600 to $1,000 to repair, why not spend between $60 and $125 for a cooling system flush every 30k or so?
If a 50/50 mix of water and coolant is good,
how come 65/35 isn’t better?
Remember that antifreeze needs water to work. You should never use a mixture of more than 60% coolant or antifreeze. You see the ability of the coolant mix to carry heat away is reduced by an over concentration of coolant. So your protection against boil over or freezing actually goes down after 60% coolant, 40% water.
Overheating problems
Your engine will overheat for a few reasons:
1. Lack of coolant. This is created by a leak and the symptoms are typically the same each time it overheats. You fill up the radiator, everything is OK for awhile (20 miles maybe) then it overheats. It overheats because the leak creates a shortage of water or coolant.

The repair is to simply pressure test the cooling system and find and fix the leak. We have hand held pumps which we attached to the neck of the radiator after we remove the radiator cap. We look at the pressure limit of the cap. It might say 13 psi. We then pump air into the radiator and cooling system until the gauge reads 13+ psi. The newer the system, the higher over the cap pressure you can go. Likewise, if you have a 15 year old cooling system, you better not pump the system to 20 psi with a 12 pound cap or you will pop it like a balloon. This cooling system pressure test is typically $25-40 dollars.

2. Lack of circulation. This is caused by a closed thermostat, a plugged radiator or a bad waterpump belt or a bad waterpump.

If the engine seems to overheat more around town and seems to be fine on the highway, that is a clear indication that the air flow across the radiator has been effected. This typically means a bad fan clutch or a bad electric fan or relay or the sensor that is supposed to trigger the fan relay that turns the fan on.

If the engine seems to be fine while driven slowly (35-45 mph) and overheats quickly on the highway (55+) and takes forever to cool down, you should suspect a plugged radiator.

3. The engine is consuming the coolant. This is created by a bad head gasket or a broken engine block and has some very specific symptoms. And water in the oil is only one of the many symptoms we look for. For the record, a head gasket can be bad and we won’t find a drop of coolant in the oil ‘cause all the coolant that is leaking into the cylinder is being sent out the exhaust and is not going into the engine oil system.

The first thing you may notice is the engine misses when it is restarted after it has sat for between 15 minutes up to 3 or more hours. When the engine is shut off, coolant is forced by pressure into one of the cylinders and when the engine is restarted, the coolant causes a miss until all the coolant is forced out into the exhaust. You may or may not see steam come from the tailpipe. STEAM FROM THE TAILPIPE ALONE IS NEVER ENOUGH TO CONDEMN THE HEAD GASKET. All cars have to deal with moisture in the exhaust on a cold morning start up, so steam from the tailpipe is very normal as the catalytic converter heats up and boils the water sent to it by the cold engine.

There are three tests we use to find a bad head gasket or being more precise, a coolant leak into the combustion chamber.

1. We use a dye and suck the fumes out of the radiator and run them through this blue dye. If the dye turns yellow, that means the presence of exhaust gases in the cooling system.

I must tell you I don’t think much of this test. The positive results of this test mean nothing ALL BY THEMSELVES.

2. Apply pressure to the cooling system and watch the pressure gauge as you rev the engine. If the pressure rises quickly, that is a very good indication there is a combustion leak.

3. Fill the cooling system up with coolant, drive the engine till it gets good and warm. Park the car and shut off the engine. Make sure the upper hose is stiff and hard which indicates good cooling system pressure. Apply external pressure if needed via a cooling system pressure pump. After allowing the engine to cool for about 30 minutes, pull the plugs and crank the engine over. If any coolant comes blasting out of any cylinder spark plug hole, there is no doubt the engine has a combustion leak.
I make our techs perform all three tests and the car has to fail all three tests before we can say for sure this engine has an internal combustion leak, like a bad head gasket or broken or cracked head.
Electric Cooling Fans.
You have to understand how they work in order to fix problems in electric cooling fan circuits:

A/C OFF = A single wire temperature switch or sender is screwed into radiator or the engine, normally close to the t-stat housing. This switch or sender provides a ground to the cooling fan relay which passes battery power to the fan motor(s). To test this circuit, you simply remove the single wire from the switch or sender and ground it for no longer than the count of 1-2 and the radiator cooling fan should come on. If not, the fan relay is bad and/or the power from the battery through the relay to the fan is defective and/or the fan motor is bad. If you suspect the motor, hit it with the wooden handle of a hammer then ground the sending wire again and see if it tries to spin.

A/C ON = The fan may run all the time when the A/C is on or be triggered on by another pressure switch in the A/C system. This switch is often in the back of the A/C compressor or in an A/C line. Otherwise, if the high pressure side of the A/C system gets to 350 psi, the switch closes and grounds the relay which turns on the radiator cooling fan.
Next FAQ

Back to FAQs Index
Copyright ©1997-2023, Mark Salem, Salem Boys Auto, All Rights Reserved

 

Another way coolant can enter into the oil is through a leaky intake manifold gasket for the crossover between the heads. At least that's what happened on a couple of small block Chevy 350s that I worked on.

 

Thanks again for the info Cusser and 73shark! I don't seem to be losing coolant, and I don't have any signs of coolant in the oil, so I don't think that's the cause of the cooling system issue. One thing mentioned in the article you shared could be the issue though. The article mentioned that you need to use a 50/50 coolant/water mix in the cooling system. Three years ago when I had a mechanic do a coolant flush he replaced the coolant with pure antifreeze. He said having a 50/50 mix increases corrosion in the engine, so he prefers pure antifreeze. I didn't realize that pure antifreeze doesn't cool as well as a mix of antifreeze and water. I'll go get the system flushed again and refilled with a 50/50 mix and see if that helps. At least I have something I can try now!

 

50/50 and have them use distilled water, not tap water.

 

From what I've read over the years, pure antifreeze is not an effective coolant. Better stick with a 50/50 mix. And I second the use of distilled water.

 

I agree that 100% coolant should not be used. Definitely use 50/50.


Not uncommon for a mechanic to have his own views on such topics, but remember that the mechanic's knowledge of thermodynamics and heat transfer are likely non-existent.

You didn't mention 100% coolant in your earlier posts, or folks would've suggested then to switch over back then. Hope this works for you, temperature was only like 105F yesterday !! April W. on Channels 3 and 5 says no more 100F days !!!

 

Well, I flushed all the coolant out and replaced it with premixed 50/50 coolant. I also replaced my lower radiator hose while I was at it (I had replaced my upper hose not too long ago). I hooked up the suburban and tried towing some vehicles afterwards and it still ran warmer than it should have - at one point the engine coolant temp hit 241 degrees. That was with temperatures in the 90's in Phoenix and towing on nice flat freeways. It would certainly have overheated towing a trailer up a mountain in summer temperatures.

My neighbor suggested I should stop routing my transmission fluid through my radiator since I already have a large aftermarket trans cooler installed. I don't know if that will make much of a difference or not since my trans temps are always lower than my engine coolant temps, but at this point I'm running out of things to try...

Any thoughts?