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Old 04-27-2010, 01:33 PM   #1
Shandysplace
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Default A Lesson in Towing Capacity

We recently took our 1997 Suburban 1500 (110,000 miles) and our '08 3326 over the Grapevine into and out of LA to visit Custom RV in Anaheim for annual maintenance.

The Grapevine crosses the mountains north of Los Angeles with 5-6% grades both up and down.

We found that 3rd gear and about 2500 rpms would pull the rig up the steepest grades at not more than 45mph. On the steepest downgrades 3rd gear engine breaking at about the same rpms held the speed to between 55 and 60mph with only light occasional braking.

It's doubtful we could have made the same trip in very hot weather. With the AC off and at the steepest part of the climb our water temp topped out at 210 while 160 is the regular temp. Our Suburban is equipped with the factory towing package and a WDH.

Most posters here with far more knowledge on this subject than us have commented that it's not uncommon for tow vehicles to be underrated for the TM they're pulling. It's one thing to pull in the flat on I-5 and quite something else to go over the Grapevine.

Our 3326 fully loaded for the road weighs 5,000 lbs which is the factory rated maximum for our Suburban. We're grateful to those forum members for helping us properly outfit our rig for a trip like this.
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Old 04-27-2010, 04:30 PM   #2
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If you were towing in the summer, when the temperature is high and you are probably running the air conditioner, an old trick is to roll down the windows, turn off the a/c and put the heater on full blast.

Turning off the a/c decreases the load on the engine.

Turning on the heater helps cool the coolant.

Opening the windows is to try and keep you comfortable.

Not everyone knows this trick. My daughter has to do this in her Miata on the Grapevine in the summer, but she can put the top down instead of rolling the windows down.

I expect to never have this problem. I have a smaller TM and a bigger truck. I set cruise control for 55 and let the on-board computer take over.

But, your average mpg is probably better than the 11 that I get.
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Old 04-27-2010, 06:21 PM   #3
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You should check to make sure your coolant system is clean and the thermostat works properly. A chemical flush and replacement of the thermostat is a good idea in a 13 year old vehicle.

Also, you may want to try the water wetter chemicals auto stores sell to help your system cool more effectively. Make sure your fins are clean and not bent for proper airflow.
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Old 04-27-2010, 10:16 PM   #4
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We are always glad to have our Chevy 1500 when we go over the Grapevine. Usually when we go over it with the TM, there is snow on the side of the road or up on the hills, because we're headed down to Desert Hot Springs in January and we don't really have to worry about overheating.

We really appreciate the tow capacity when we're headed up to the Sierras or on the I-5 near Ashland, OR.

Wayne suggests doing what B always says...turn off the A/C when going up a steep hill. We even do that with our cars, it just puts less stress on the engine. That's also a good idea about turning on the heater, if you can stand it inside the car . Bryan and I were lamenting the demise of windwings driving somewhere last week, it could have been on the way home from the TM rally.
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Old 04-28-2010, 10:47 AM   #5
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Bryan and I were lamenting the demise of windwings driving somewhere last week, it could have been on the way home from the TM rally.
Wind wings disappeared about the time people stopped using desert bags on their bumpers and side mirrors.

fwiw, I get a radiator flush every 2 to 30 years in all of my vehicles. Be aware that you probably can not do this at home because the used coolant is a hazardous waste.
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Old 04-28-2010, 02:10 PM   #6
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Quote:
Originally Posted by Shandysplace View Post
With the AC off and at the steepest part of the climb our water temp topped out at 210 while 160 is the regular temp. Our Suburban is equipped with the factory towing package and a WDH.
I hope that you don't consider 210* to be extreme. Your engine is designed to run @ 210*. In fact, it came from the factory with a 210* thermostat installed and your engine should run ~200 minimum. You may be doing more harm by running @160 than running @ 210.

I wouldn't be conserned about the temp until it reaches >225-235 (considering that you have the proper concentration of coolant in your radiator). High water temp isn't the real issue. BOILING is what must be avoided. When the coolant boils, it will cause air pockets in the engine that may be super-heated to excess of 600* and stop the flow of coolant. That's when you have a real problem. A properly mixed coolant should have a boiling point of >280* minimum. Ethylene glycol has a boiling point of 370*.

Your engine is made up of a mixture of materials from cast iron block & heads to aluminum pistons and several other parts. All of these different metals have different expansion rates @ different temps. When they design a piston (for instance), they design it so that it is within tolerances @ a certain temp, in your case that is ~200*. When you run @ 160* the aluminum piston fits in the steel cylinder more loosely than it does @ 200*. The engine block has a lesser expansion than the pistons so the cylinders are not at the proper size @160* either. This farther exacerbates the problem.

Some mechanics think that they can resolve over-heating issues by installing a lower temp thermostat. This is not true. A lower temp thermo will merely not allow the engine to achieve it's normal operating temp when the air temp is cool. When it is hot out, either thermostat will be fully opened and allowing the same amount of coolant flow. This theory of a lower temp thermo is not only mis-guided, it is ultimately harmful. ALWAYS stick with the factory recommended thermostat. In some States, the practice of installing a 160* thermo is illegal. If you take your vehicle to have a "Smog Check" it probably won't pass if the engine is under 195* because most emission control devises are designed to operate >195* and the pistons do not seal properly until >195*.

As for shutting off the AC......... it does slightly lower the stress on the engine but far more importantly, it lowers the air temp of the air that passes through the AC condenser that is used for cooling the radiator. NEVER turn the AC "down", that does not help and could actually increase the temperature at the AC condenser, thereby super heating the air that reaches the radiator, after it passes through the AC condenser. I would consider shutting off the AC @ ~230*. If it doesn't reach 230-235....there is no reason to suffer. I wouldn't even consider turning on the heater unless the temp reaches 250-260 and I've pulled off the road (with engine running and my family out of the vehicle) to let it cool down for awhile. Running the heater is pretty uncomfortable and only mildly helpful if the real stress has been removed.

Modern day engines can reach temps of 300* without damage. Agian........BOILING is the enemy. It can help to have a spray bottle handy to spray water on the hot radiator to reduce the cooling time, with the engine running. NEVER remove a radiator cap on a hot radiator. If there is steam comming out, you have boiling. Shut the engine off, let it cool, then check the coolant level. Don't leave an engine running if it is steaming. You may have a vapor lock in the cooling system.
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Old 04-28-2010, 02:31 PM   #7
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I would have thought a Suburban would have a higher tow rating than 5000
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Old 04-28-2010, 02:57 PM   #8
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Default Many thanks

Many thanks to all who responded to this thread. It's been an education.
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Old 04-28-2010, 04:13 PM   #9
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Quote:
Originally Posted by PopBeavers View Post
Wind wings disappeared about the time people stopped using desert bags on their bumpers and side mirrors.

fwiw, I get a radiator flush every 2 to 30 years in all of my vehicles. Be aware that you probably can not do this at home because the used coolant is a hazardous waste.
30 years is a little long.......

Again.....be sure to use anti-freeze/coolant at the recommended rate. Some coolants are concentrated and must be mixed with a certain ratio of water. Some are pre-mixed and you just use it right out of the bottle (do not add water).

The key is keeping the coolant from boiling. Water will boil @ 180*. Weak coolant solution may boil @ 235*. A proper mixture should not boil below 280-370*. Just be careful not to get the concentration too high. That's the other evil. If the concentration is too high, the boiling point will be higher but the cooling capacity will be lower and thus it will reach boiling sooner. Nothing cools batter than straight water, however, straight water has too low of a boiling point......thus, the coolant. The coolant doesn't cool better, it just raises the boiling point.

For people in warmer climates, it's best to aim for protection @ ~280*. In cold climates, one must be careful to balance the protection from freezing to your particular area. In some cases, It could be wise to run a higher concentration in winter and a lower concentration in summer or on long trips that might encounter extreme temps.

No matter what.....I would change that 160* thermo to at least a 195*. Running the engine at lower temps will increase the wear and tear on the engine.
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Old 04-28-2010, 09:41 PM   #10
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Very well said Wayne, a lot of good information. The only thing I could add is if you change the coolant yourself and the cooling system uses a temperature activated switch in the cooling system to turn on the cooling fan is make sure you bleed the cooling system of air or an air bubble could prevent the cooling system sensor switch from turning on the cooling fan for the radiator. Some systems have a bleed valve in the system near the top of the cooling system to bleed air. Of course always follow the manufacturers instructions for correct procedures for changing coolant.

Making sure the clutch fan is working is also important. You should hear the fan moving lots of air when it is hot. It's very obvious in my Dodge when the clutch fan engages when it gets hot.

In my experiences the cooling system bypass hose is the first to leak. After ten years I changed all my hoses. The bypass hose looked the worst. Robert
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