Chevy 2500 HD 6.0 question

[jkilroy]

I’m towing a 7500 lb. Cougar 28SGS. The truck I have is a 03 Silverado 2500 HD 6.0 with 4.10 rear. This rig tows fine in cooler weather with no A/C and fairly flat to moderate hills. When I pull in decent mountains and it’s hot the trans temp climbs past 200, and coolant goes to 230 range. As soon as I turn off a/c everything is fine. Has plenty of power I must say. I usually set rpm to 3000 and let it run.

So question is can I do anything to truck to help the problems? Can I put a cooler thermostat in it? I’ve already added a second trans cooler. It helped a little. A diesel is in my future but I’d like to pay off camper first if possible. They are so expensive.

[jkilroy]

LIKE2BUILD wrote:

jkilroy wrote:
I’m towing a 7500 lb. Cougar 28SGS. The truck I have is a 03 Silverado 2500 HD 6.0 with 4.10 rear.

One more thing on this engine. When towing hard like you're doing, you will eventually snap exhaust manifold bolts. Usually it's not if, but when this finally happens. I don't know the reason why, but it's very common on the 5.3L and 6.0L engines when used for towing.

Most often it's the bolts on the front and rear cylinders on either side. It happened to mine and I decided to just let a shop do the work. I also bought stainless shorty headers to get a little better exhaust flow. The shop charged $350 to remove the old manifolds, extract the broken bolts, and install the new headers. This did not give me a boost in HP, but I did find the engine revved a little quicker. With the headers when I gave it throttle climbing a hill it seemed to jump into that 3500RPM and higher range a little earlier than with the manifolds which translated to a slightly easier climb.

KJ

I already replaced the broken manifold bolts. I have some shorty headers I need to install yet. Once I get the cooling problem fixed I will give the higher rpm a try. Just dosent seem right, but I’ve have enough input to trust to try it. Will save me from buying a diesel in the short term.

[BubbaChris]

Another vote for running the right RPMs for getting all the performance you can out of that engine.

Our home is at 2,300' and during the summer we're towing up to 7,000'-10,000' to escape the hat. I'm able to pull and accelerate at those high altitudes "IF" I'm in the right gear and the motor is in the sweet spot.

[LIKE2BUILD]

jkilroy wrote:
I’m towing a 7500 lb. Cougar 28SGS. The truck I have is a 03 Silverado 2500 HD 6.0 with 4.10 rear.

One more thing on this engine. When towing hard like you're doing, you will eventually snap exhaust manifold bolts. Usually it's not if, but when this finally happens. I don't know the reason why, but it's very common on the 5.3L and 6.0L engines when used for towing.

Most often it's the bolts on the front and rear cylinders on either side. It happened to mine and I decided to just let a shop do the work. I also bought stainless shorty headers to get a little better exhaust flow. The shop charged $350 to remove the old manifolds, extract the broken bolts, and install the new headers. This did not give me a boost in HP, but I did find the engine revved a little quicker. With the headers when I gave it throttle climbing a hill it seemed to jump into that 3500RPM and higher range a little earlier than with the manifolds which translated to a slightly easier climb.

KJ

[LIKE2BUILD]

Curly2001 wrote:
Let it run at 4,000 or above on the hills. It does it's best at higher RPM's than lugging it slower. Have had mine at 4,500 rpm going up some longer passes towards Flagstaff. It is made to do it's best at higher rpm.
Curly

True. My 6.0L would tow okay under 3,000RPM, but when I hit the hills it would lug a little, but then acted like it drank wake-up juice between 3500-4500RPM.

For some light reading, here's information on the GM LQ4 engine.
LQ4 engine specs

Just for reference, here is dyno test results showing the torque and HP curves of the engine. If you notice, peak torque is achieved at 4,000RPM with the meat of the band between 3500-4500 RPM. Max HP is achieved at 4,400RPM. So yes, if you keep the engine between 4,000-4,500 RPM you're in the range where absolute maximum power is being produced.

[LIKE2BUILD]

jkilroy wrote:

What’s the cooling stack?

And anyone know if you have to change the water pump with the clutch fan?

No, cooling fan is separate from the water pump. As mentioned, the stack is your radiator, A/C condenser, and tranny cooler.....everything that is sandwiched together that cools fluids.

Take a garden hose and spray through the stack with the engine not running. You will quite likely see bug carcasses, dirt, cotton wood fluff, and all kinds of other junk come through. All of these things blocking the passages between the cooling fins reduces cooling efficiency.

Just watching the fan spin doesn't tell you if the fan clutch is good or bad. It's a fluid coupling clutch so even if it's bad the blades will spin a little. When the clutch is working properly it fully engages and makes the blades spin 1:1 with the pulley. When this happens you'll know it because it is a VERY LOUD ROAR. When your truck hit 220*F the other day you should have heard that fan roaring like a firetruck siren. If you did not, that's a pretty good sign your fan clutch is failed and needs replaced. When I towed in the Appalachian's with my '04 Chevy 2500 6.0L we climbed a few good grades around Daniel Boone Nat'l Forest. My engine temps would climb to about 210*F and the fan clutch would kick in. When that happened my passengers started looking around to see if we had an ambulance coming up behind us. :E

Also, as I said before, if you have never flushed the cooling system it's extremely important that you do so. DexCool coolant works just fine, but it has a limited life. You're supposed to flush and change it every 5 years or 100,000 miles. Over time the organic acids in the coolant become oxidized and form sludge. Draining and flushing the system removes the degraded organic acids and prevents the sludge. These extended life coolants work fine, but they need to be serviced at the proper intervals.

One other possibility is your water pump is bad. It might not be leaking, but if you've had cavitation it can cause pitting on the impeller blades which reduces the efficiency. This leads to worsening cavitation and air bubbles which then reduces heat transfer in the engine.

KJ

[jkilroy]

Ok. Never heard it called that.

[Pure_Diesel]

This is your whole cooling system behind the grill. Your condenser is in front of your radiator. Over time stuff accumulates on the cooling fins and blocks the air flow from going through the radiator. If your separate the condenser from the radiator look in between them for stuff. If there is material or bugs you flush it out from inside the engine compartment out towards the front of the vehicle.

[jkilroy]

Pure Diesel wrote:
Check the cooling stack. Has it ever been cleaned out? Over time, miles, location, debris and bugs can block the air flow going through.

What’s the cooling stack?

And anyone know if you have to change the water pump with the clutch fan?

[JCK]

When you run a higher rpm your water pump turns faster pumping more water through your motor and helping with cooling. Other advantages your oil pressure is higher and that also helps to keep parts cool. Your motor is just a big air pump more air in more out also caries heat out through the exhaust system. Never lug a motor If you give it more gas and it doesn’t speed up your lugging it to hard down shift

[jkilroy]

Wow, 4500 rpm!

I checked clutch fan and it has a little resistance when I spin it. I need to check it against a new one at auto zone.

[Curly2001]

Let it run at 4,000 or above on the hills. It does it's best at higher RPM's than lugging it slower. Have had mine at 4,500 rpm going up some longer passes towards Flagstaff. It is made to do it's best at higher rpm.
Curly

[morphrider]

I make mine scream going up these Colorado mountains. She pulls well, don't get rpm's too crazy. You will find the sweet spot and enjoy it.

[jkilroy]

I’m good with 3000 rpm. 4000 rpm seems a bit high but I’ll give it a try. Didn’t know that.

[jkilroy]

Getting temp reading from factory gauge. Got to 220 today. Fan is working I saw it when I checked another issue. I think my trailer brake was bad. Made horrible noise.

I’m going to change thermostat and get radiator flushed and go from there.